PHD-Department of Zoologial Sciences

Permanent URI for this collection

https://repository.ku.ac.ke/handle/123456789/406

Browse

Now showing 1 - 20 of 103

Some Aspects of the Ecology, Behaviour and Vectorial Capacity of the Tsetse Fly Glossina Austeni Newstead.
(Kenyatta University, 1992) Owaga, Mary Ludvine Akoth
A study was undertaken in the south coast of Kenya, on the tsetse fly species, Glossina austeni Newstead. The objective was to investigate its population ecology, behaviour and vectorial capacity. The main aspects studied were: habitat requirements and density, responses to sampling devices and methods, such as traps and odours, activity pattern, and infection with trypanosome parasites. Some aspects of the study, such as sampling and activity experiments, evaluation of density, dispersal and habitat requirements, and trypanosome infection rates, were conducted in the field. Others, such as assessment of the effect of temperature and relative humidity on activity and response to odours, and evaluation of the efficiency ofG. austeni in picking up trypanosome parasites from infective blood meals, and in transmitting them to the next mammalian host, were conducted in the laboratory. I' Sampling was carried out using five trap-types, the biconical, the NG2B, the Lancia (original), Lancia (modified) and the 4t traps, to determine whether G. austeni could be trapped in sufficient numbers, and which trap might be most suitable for routine sampling. Similarly, five odour sources were tested as baits: buffalo urine, cow urine, acetone, urine derived phenols and dry ice. Period of activity, and activity pattern as related to feeding, were determined by continuous trapping, using traps and stationary vehicle, and by laboratory observation in a flight chamber, where only olfactory, but no visual stimulant, was presented to the flies. To study the density and dispersal ofG. austeni, the method of markrelease- recapture was used. By this method a sample of tsetse flies.....
The role of arthropod vectors in the transmission of lumpy skin disease in cattle
(2004) Misiani, Eunice Atieno Gai
Lumpy skin disease (LSD) is an economically crippling disease of cattle with epizootic occurrence particularly after the onset of the rainy season. Biting arthropods have been implicated as vectors of lumpy skin disease virus (LSDV) due to observations that there is no transmission of LSD when cattle are confined to insect-proof houses. Nevertheless, the method by which LSDV is transmitted under field conditions is not clear and no specific vector has been conclusively pinpointed. The main objectives of this study were to identify and incriminate biting insects as possible vectors of LSDV in outbreak areas and also determine the capacity of vectors thus implicated, in the transmission of LSDV, under laboratory conditions. Biting arthropods that are closely associated with livestock were trapped in three outbreak areas, namely Machakos, Kiambu and Kajiado Districts of Kenya. The insects were identified, dissected and inoculated onto prepubertal Lamb testis cell cultures to isolate virus from them. Blood meal analysis was carried out on engorged insects. LSD experimental transmission was done using Zebu cattle (80S indicus) and insects of the species Glossina morsitans morsitans, Glossina morsitans centralis, Stomoxys calcitrans, Phlebotomus dubosqui and Aedes aegypti. The Neethling strain of virus was used in challenging the animals, feeding the insects and in the virus neutralisation tests. Time series dissections were performed on the insects to isolate virus from various insect parts. Meteorological data from the study areas and other Kenyan districts were recorded. The distribution of biting arthropods in the study districts revealed a total of more than twentynine species of insects. Stomoxys niger species had the highest frequency of occurrence (18 %) while the tabanids species were the least frequent (0.2 %). The average number of females trapped at any given time was significantly greater than that of the male insects (27 compared to 18, P < 0.0001). The blood meal analysis showed that various insect species had , fed on human (14.9 %), bovine (20.7 %), goat (14.9 %), sheep (4.1 %), and lizard (33.6 %,) blood. A female field caught Prostomoxys species insect yielded a positive result for the presence of LSDV. There was a strong association between the insect species and insect parts from which virus was isolated (P = 0.000 Cramer's V = 0.5596). The largest proportion of the virus was recovered from the heads. The crops and hindgut pools had the smallest proportion of virus recovered from them. The source of virus had an effect on seroconversion of the animals (Pearson chi2 (3) = 8.6152, P < 0.035). There was a significant difference between the different species of insects as far as seroconversion of the animals they fed upon was concerned-P < .043. The association between days post virus feeding by the insects, and seroconversion was statistically not significant (P- value = 0.321). Climatic variables had different effects on LSD outbreaks in the areas studied (P < 0.05); however, relative humidity, maximum temperature and wind-speed had significant effects on occurrence of LSD in all the areas. Vaccination and quarantine significantly reduced LSD occurrence. The results showed that that several species of insects are able to transmit the LSD virus. Integrated vector management and application of meteorological information in planning LSD control programmes may have an effect on reduction of LSD outbreaks.
Breeding of the honey bee (apis mellifera l.) and its potential for royal jelly production in Kenya
(Kenyatta University, 2004-07) Maundu, Elliud M.; Mueke, Jone M.; Raina, Suresh K.
Royal jelly is a creamy, milky white, strongly acidic and highly nitrogenous substance secreted by the hypopharyngeal and mandibular glands of worker honey bees at the ages of 5 - 15 days of age. The jelly is fed to queens through out their life and also to drone and worker larvae of less than 3 days old. The principal constituents of royal jelly are water, protein, lipids, sugars and mineral salts. Due to differences in climate, Apis mellifera races have evolved in response to the local environmental conditions, with each race acquiring a different potential for production of honey and other hive products / and even pollination of crops. In Kenya, new generation commercial hive products like royal jelly, propolis and pollen are insignificantly produced or utilized due to lack of knowledge on production skills, awareness and undeveloped marketing systems and also due to the nature of hives used. The aim of this study was to develop a royal jelly production system and breed for high honey production and reduced defensiveness using the East African honey bees. Royal jelly production was done in queenright colonies following the procedure of Laidlaw and Eckert, (1962). Defensive behavior was evaluated following the procedure of Stort (1974) and Collins et al., (1984). The bred queens were mated by instrumental insemination and their honey production and defensive behavior compared to that of colonies headed by non-selected queens. There were no significant differences between Apis mellifera scutellata and Apis mellifera monticola in the cell reception rates and mean royal jelly yields. Grafting larvae at the age of 24 hours significantly increased queen cell reception and royal jelly yields compared to those of larvae grafted at the ages of 36; 48 and 60 hours. Supplementary feeding significantly increased colony cell reception, mean royal jelly yields per queen cell and colony royal jelly yields. Harvesting royal jelly 2 days after grafting resulted into a higher number of harvested cells compared to harvesting in a 3- day cycle. However, cells harvested 3 days after grafting yielded more royal jelly per queen cup compared to that produced by cells harvested 2 days after grafting. However, royal jelly yields were not significantly different in the 2 and 3-day cycle. The major components in the Kenyan royal jelly were found to be moisture, lipids, proteins, sugars and ash and their composition was comparable to that reported in literature. Colonies of Apis mellifera scutellata were found to have variations in both defensive behaviour and honey production. A negative and significant correlation for SN and Tl S was recorded. Variations were noted in honey production with annual honey yields of 27 - 48 kilograms per colony. There were no significant differences in sting number (SN), time to first sting (Tl S) and honey production between colonies headed by selected queens and those headed by unselected queens. Colonies headed by selected queens had significantly higher queen cup acceptance rates and royal jelly yields compared to those headed by unselected queens.
Assessment by performance attributes of indigenous egg parasitoids (hymenoptera: trichogrammatidae for biocontrol of african bollworm (helicoverpa armigera) in Kenya
(Kenyatta University, 2004-08) Kalyebi, A.
Trichogrammatid egg parasitoids are used extensively for the control of several lepidopteran pests in many areas of the world. They ar~he most promising biological control agents for inundative releases against the African bollworm Helicoverpa armigera, an injurious pest of several agricultural crops in Kenya and elsewhere in Africa. To enhance their potential impact in Kenya as well as eastern Africa, collections of indigenous species/strains (Trichogramma sp. nr. mwanzai and Trichogrammatoidea sp. nr. lutea from low altitude, Trichogramma sp. nr. mwanzai and Trichogrammatoidea sp. nr. lutea from medium altitude and Trichogramma bruni and Trichogrammatoidea sp. nr. lutea from high altitude) were made from different altitudes in Kenya and were evaluated following different criteria to select potential candidates for use against H. armigera. The major focus was their adaptation to a range of temperature and humidity \regimes. The criteria included functional response, lifetime parasitism and development and population growth characteristics at six temperatures (10, 15, 20, 25, 30 and 35°C) and two humidity regimes (40-50 and 70-80%). Preference of parasitoids for target pest and relative suitability for development among five lepidopteran hosts was also \ investigated, in addition to testing their capacity to attack H. armigera eggs occurring on two host plants (tomato and okra) in laboratory and field experiments. Functional response studies revealed that temperature affected parasitisation rates of the strains significantly, while relative humidity did not. Trichogrammatoidea sp.nr. lutea from high altitude, Trichogramma sp. nr. mwanzai from low altitude and T. sp. nr. mwanzai from medium altitude showed higher parasitism across the widest temperature range. There was no relationship between source altitude/climate and performance of the strains at the temperatures tested. Temperature and humidity interactions affected lifetime fecundity and progeny production. The highest parasitism at the two humidity levels was at 30°C for all the strains. The interaction of the two factors also affected adult longevity, which was longer at the lower than higher humidity. Survival followed a type l-survivorship curve at lower temperatures and a type III survivorship curve at the higher temperatures. These studies revealed that T sp. nr. mwanzai from both low and medium altitudes and T sp. nr. lutea from medium altitude appear as promising candidates for augmentative biocontrol of H. armigera. Temperature and humidity interactions also affected the population growth and development of parasitoids although temperature appeared to be more important. Developmental time was inversely related to temperature. The intrinsic rate of increase was found to increase with increasing temperature up to 30°C. The finite rate of increase also followed the same trend. The net reproduction rate also increased with increasing temperature up to a maximum at 30°C. Both net reproduction and intrinsic rate of increase were higher at the lower humidity. Temperature negatively affected generation time ofparasitoids regardless of the humidity level. Host acceptability studies showed that all the six species/strains did accept all the tested host species, although acceptance levels varied among strains and hosts. Most species/strains showed greater preference for noctuids over pyralids and yponomeutids. Suitability of hosts for progeny development varied from one species/strain to another. The different species/strains did not show significant differences in parasitising eggs of H. armigera when placed on two host plants, namely tomato and okra. From these studies, T. sp. nr. mwanzai CM), T. sp. nr. mwanzai CL) and T. sp. nr. lutea (M) offer great potential as candidates for augmentative biocontrol of H. armigera in Kenya.
Ecology and Biologically Based Management of Cereal Stemborers on Maize and Sorghum in the Amhara State of Ethiopia
(Kenyatta University, 2006) Ferede, Melaku Wale
Impact assessment of natural enemies on stem borer populations and maize yield in three Agro ecological Zones in Mozambique
(Kenyatta University, 2007-05) Domingos, Raquene Cugala
Lepidopteran stem borers are the major pests limiting the production of maize and grain sorghum under subsistence farming conditions of Southern Africa. Classical biological control has traditionally emphasized the control of introduced pests through the importation and/or introduction of coevolved natural enemies from the pest's native home. It is based on the assumption that coevolved natural enemies are best adapted to locating and successfully attacking the target host. On this basis, Cotesia flavipes Cameron (Hymenoptera: Braconidae) and Xanthopimpla stemmator (Thunberg) (Hymenoptera: Ichneumonidae) were introduced in Southern African countries for biological control of Chilo partellus Swinhoe (Lepidoptera: Crambidae) and Chilo sacchariphagus (Bojer) (Lepidoptera: Pyralidae). The current studies were conducted to evaluate the establishment and spread of C. flavipes and X stemmator in the release locations, assess the impact of natural enemies on the stem borer populations and maize yield, assess the effect of temperature on the development of X stemmator in three host species, and finally, to study population growth parameters of X stemmator and Dentichasmias busseolae (Heinrich) (Hymenoptera: Ichneumonidae). Several parasitoids including indigenous and the exotic species were recovered from egg, larval and pupal stem borer development stages. Egg parasitism of more than 80% due to Trichogramma bournieri (Hymenoptera: Trichagrammatidae) was reported on C. partellus eggs in the Southern region of Mozambique. C. flavipes was recovered at all release and other sampling sites. The highest percent parasitism (33.8%) due to C.flavipes was reported at Maracuene, one of the 1996 release sites. This introducrd exotic larval parasitoid was reported to increasingly becoming the more abundant in relation to C. sesamiae. The exotic pupal parasitoid X stemmator was recovered only from C. partellus pupae during the release season (2002/2003) and one year after its release, but it was not recovered in subsequent seasons. Results from field experiments indicated that damage levels due to stem borer attack varied from location to location. High damage levels were reported in the areas where C. partellus is dominant followed by the areas dominated by Busseolafusca Fuller (Lepidoptera: Noctuidae). However, stem borer density was higher at high elevation zones dominated by B. fusca compared to low and mid elevation zones. Yield losses varied from 28.8% to 34.5% across the regions. Yield losses were observed to increase (from 28.9 to 43.3, 34.5 to 40.8 and from 31.2 to 36.4% at low, mid and high elevation zones respectively) when natural enemies were excluded from the maize plots. The impact of natural enemies on maize yield increase was high at lowland zones (26.1 %) and lowest at high elevations (7.6%). Laboratory experiment indicated that while X stemmator successful developed in C. partellus, Bfusca and S. calamistis stem borer species, the more suitable host was C. partellus. The parasitoid developed faster at high temperatures and slowly at low temperatures. The lower temperature threshold for X stemmator reared on C. partellus was 9.76°C and the maximum threshold of 35°C. These results indicate that this exotic parasitoid could survive and remain active at low to mid elevations and could not survive at high elevations where temperatures during winter are usually below 9°C. However, in the areas where minimum temperatures are above 10°C, X stemmator could be an important agent of biological control against C. partellus in Mozambique.
Diversity, Ecology and population dynamics of Lepidopteran stem borers in Kenya
(Kenyatta University, 2009-07) Ong'amo, George Otieno; Kokwaro, Elizabeth D.; Silvan, Jean-Francois; Bruno, Le Ru
Stem borers are important field insect pests of maize [Zea mays L.] and sorghum [Sorghum bicolor (L.) Moench] in Africa. They account for more than 30% yield losses depending on fhe composition of the pest community. A total of 21 pest species have been reported in sub-Saharan Africa all of which are indigenous to the continent except for Chilo partellus (Swinhoe), which was accidentally introduced from Asia. Stem borers are susceptible to environmental fluctuations and the pest species are thought to have experienced changes in physiology and behaviour after close association with highly nutritive crops. Recent studies indicate that in addition to the pest species, there are noneconomic stem borer species among wild hosts in the uncultivated fragments. Owing to susceptibility of stem borer species, continued habitat fragmentation and degradation may ultimately result in host range expansion and eventual emergence of "new" pests. Unfortunately, previous studies have been geared towards reducing populations of pest species in the cultivated fields with few attempts to understand possible evolution of less known species to pest status. This research was therefore designed to gather information on stem borer species diversity, host range and ecology in selected agricultural landscapes in Kenya. Surveys were conducted during 2005/2007 growing seasons in and around selected cultivated fields in four localities, Muhaka, Mtito Andei, Kakamega and Suam, representing different altitudinal gradients across the country. A total of 29 stem borer species were identified from 9,771 larvae collected. The identified stem borer species were grouped into 10 different known genera (Acrapex, Busseola, Carelis, Manga, Poecopa, Sciomesa, Sesamia, Eldana, Chilo and Ematheudes) while the unknown species belonged to five different families (Crambidae, Peoriinae, Pyralidae, Schoenobiinae and Tortricidae). There was evidence of variation in both distribution and dominance among the surveyed localities with majority of the species belonging to the Noctuidae family found in Kakamega and Suam, while species belonging to Crambidae and Pyralidae were mainly found in Muhaka and Mtito Andei. The wild stem bore species were identified from 38 different plant species belonging to three different families (Cyperacea [27], Poaceae [10] and Typhaceae [1]), while pest species, Busseola fusca (Fuller), Sesamia calamistis Hampson, Chilo partellus Swinhoe, Chilo orichalcociliellus (Strand) and Eldana saccharina Walker were mainly found on maize and sorghum. Sesamia calamistis and B. phaia ssp. phaia occurred among both wild and cultivated hosts and provided good models for studying exchange of stem borer pest populations between the wild and cultivated habitats. Cytochrome b gene sequences, through the existence of strong genetic structuration, revealed evidence of limited exchange of S. calamistis populations between the habitats. However, genetic analyses of the same gene of Busseola phaia ssp. phaia Bowden populations revealed weak differentiation with respect to host use in different habitats (FsT = 0.016; P = 0.015). Observed variations in the distribution of pest and non-pest stem borer species coupled with differences in genetic structure among model species (S. calamistis and B. phaia ssp. phaia) suggest two things; i) no single management strategy would apply across different landscapes and ii) continued habitat fragmentation 1 degradation would affect ecosystem stability resulting in host range expansion or local species extinctions. Similar intensive studies need to be extended to other areas as it will form the basis upon which different integrated pest management (IPM) packages could be developed.
Host suitability and interspecific competition among the West African stemborer egg parasitoid Telenomus isis and other indigenous egg parasitoids in Kenya
(2011-07-11) Anani, Yaovi Bruce
In East and Southern Africa (ESA), the noctuid Busseola fusca and the exotic crambid Chilo partellus are among the most important lepidopteran stemborer pests of cereal crops. In western Africa, the scelionid egg parasitoids Telenomus busseolae and Telenomus isis are the most important biotic control agents of noctuid stemborers such as Sesamia calamistis and B. fusca. Telenomus isis had never been reported from ESA and was thus introduced into the International Centre of Insect Physiology and Ecology (ICIPE) laboratories in 2003 for possible release against B. fusca. This study aimed at assessing the potential of egg parasitoid, T Isis, as a biological control agent against B. fusca in ESA. Distribution and parasitism of noctuid stemborer eggs was assessed in some localities in Kenya. Busseolae fusca was the most prevalent species in high altitude areas (> 1500 m above sea level) but it co-existed with S. calamistis in mid altitude areas (500-1200 m above sea level). The highest egg parasitism rate (32.6%) was recorded in Kiboko with Telenomus busseolae dominated the egg parasitoid community followed by the trichogrammatid Trichogramma bournieri. Host acceptance and suitability were assessed using fifteen lepidopteran borer species. Only noctuid stemborers were successfully attacked by T. isis. Parasitism rate and developmental time significantly varied between the major borer species tested (S. calamistis, Sesamia botanephaga, and B. fusca) but no significant differences were observed in sex ratios (expressed as a proportion of female progeny). With increasing duration of host deprivation from 0 to 14 days, longevity for the three-stemborer species increased, whereas mean fecundity decreased, indicating resorption of eggs. The effects of temperature, humidity and host species on the bionomics of T. isis were studied. The lower and upper threshold for development were estimated at 10.6 to 36.5°C respectively, and the optimal temperature for development was between 30.5°C to 31.5°C for the three stemborer species and both two relative humidities. Furthermore, the effects of host species, host age and duration of host deprivation on the performance of Tr. bournieri, a polyphagous parasitoid of eggs of several cereal stemborer species in eastern Africa was evaluated as part of an interspecific competition study. The noctuids S. calamistis, S. nonagrioides and B. fusca, and the crambid Chilo partellus and pyralid Eldana saccharina were successfully parasitized by Tr. bournieri. Parasitism rate, number of progeny and developmental time of Tr. bournieri varied significantly among the host species. Sesamia calamistis and B. fusca eggs where the most suitable hosts, while E. saccharina was the least suitable host. While parasitism rate and the number of progeny tended to decrease with the age of host eggs, there were no significant differences in the sex ratio. Longevity of the parasitoid increased with increase in deprivation of hosts from 0 to 12 days. The mean lifetime fecundity per female decreased with increased of host deprivation increased, indicating resorption of eggs. In addition, oviposition behaviour of T. isis and two other indigenous parasitoids (T. busseolae and Tr. bournieri) were studied using S. calamistis, S. botanephaga and B. fusca as hosts to evaluate the degree of self-super, and superparasitism. Four distinct steps of behaviour were observed: foraging, palpitation with antennae on the eggs, insertion of ovipositor and egg marking. Walking and resting were observed less frequently than the other behaviours. On average, insertion of ovipositor took 2 to 3 minutes per female. Telenomus isis females responded pontualy to the calling virgin female moths indicating that the parasitoid uses pheromones to find the host eggs
Effect of ABO/Rhesus blood group phenotypes on immunosurveillance to plasmodium falciparum malaria in children in Kisumu town, Kenya
(2011-07-11) Ng,ong'a Gabriel Otieno; Margaret Oduor; John Vulule
Malaria is the world leading cause of deaths among the tropical infectious diseases particularly in children and pregnant women. A safe and effective vaccine would have been the easiest way to control this disease, but the development of vaccine has not been successful despite decades of research. The periodic mutation and production of parasite variants has not only posed a challenge to the vaccine production but also drug resistance. Also important is host-related factors that contribute to disease susceptibility and resistance. Although ABO Blood group phenotypes have been correlated with protection against malaria infection especially in Sir Lanka and Gabon, little study has been done in Africa and Kenya in particular. This study aimed at investigating the effect of ABO/Rh blood group phenotypes on immunosurveillance to P. falciparum infection in children 1-10 years in Kisumu town. The study design adopted was simple cross - sectional study, while population sampling technique used was probability proportion to size. The study was done with 78 malaria symptomatic children both males and females who presented at Nyanza Provincial General Hospital and living within Kisumu town. Children age between 110 years whose parents or guardians consented to the study were enrolled. The study population exhibited a predominance of group O+, in the order of O+ >A+ >B+ > AB+ and O-. Blood group O was negatively correlated with malaria infection. Parasitaemia levels were significantly higher in blood group A+ and B+ than in group O+. It was further established that blood group A+ registered the highest percentage malaria severity (45.8%) while group O+ recorded the least severity (8 .6%). Helper CD4+ and cytotoxic CD8+ subsets of T-lymphocytes cells were both inversely correlated with parasitaemia levels (r = -162, p = 0.04; r = -0.348, p = 0.002) respectively. Nevertheless, no significant association was observed between parasitaemia levels and differential leukocyte counts (P = 0.05). ANOVA revealed significant difference in malaria infection between and females with males having higher infection (p = 0.04). However age was inversely correlated with parasitaemia levels (r = -0.0278, p = 0.007) with younger children having higher parasitaemia levels than the older ones. Parasitaemia levels were significantly higher in males than female children, sex was positively correlated with malaria parasite infection (r = 0.199, p = 0.040). The results of this study therefore implicate blood group O in protection against malaria while group A and B are likely to predispose the victims to the infection. Since blood group A correlated with malaria infection and disease severity, its advisable that blood group A individuals traveling to malaria endemic areas be given prophylaxis. T-helper and cytotoxic T- lymphocyte cell levels decrease in severe malaria cases hence malaria infected individuals have reduced immunosurveillance. Since Helper T-cell (CD4+) and cytotoxic (CD8+) subsets of Tlymphocytes cells were reduced in malaria cases it is therefore imperative for the clinicians to monitor the levels of such cells in severe malaria cases and if possible immunopotentiaters be given since reduced levels of Helper T-cells and cytotoxic Tlymphocytes cells may subject the victim to prolonged healing and coinfections. Higher parasitaemia levels in males than in females living in the same malaria holoendemic areas are an indicator that males are more vulnerable to malaria infection than females.
Predicting productive larval habitats for anapheles gambiae in lowland Western Kenya
(2011-07-11) Mutuku, Francis M.; Mueke, J. M.; Kabiru, Ephantus W.; Bayoh, N. M.
Larval habitats of the anopheline vectors of human malaria form an integral part of transmission because they produce the adult female (i.e., vector) stage. In this study, conducted in a region holoendemic for Plasmodium falciparum malaria in lowland, western Kenya, location of aquatic habitats of larvae of various species of mosquitoes in the genus Anopheles were studied. The overall goal of the study was to predict location of productive An. gambiae s.l larval habitats in the Asembo study area. Two larval habitat surveys, one for wet and dry season each were carried out. Habitat characterization and the density of Anopheles larvae were determined during these surveys. A supervised land cover classification was developed from high resolution IKONOS satellite data and extensive ground sampling. The study area was divided into 4 x 4 meter cells, numbering 646,416. Cells with and without larval habitats were typified according to their land cover, Normalized difference vegetative index (NDVI) at radius of 60m, distance of the nearest stream, elevation and the interaction between land cover and distance of the nearest stream using logistic regression. A total of 1,198 habitats and 19,776 Anopheles larvae of 9 species were quantified in samples from a rainy season and 184 habitats and 582 larvae from a dry season. Anopheles gambiae s.l. was the dominant species. The results showed that anopheline larvae generally occurred most frequently in water pools that were shallow, unshaded with turbid (with suspended soil particles) water and with little or no aquatic vegetation and more often located close to streams on agricultural lands. Malaria vectors, An. gambiae s.1 larval habitats were significantly different from those of other non-vector anophelines. Larval habitats characteristics and spatial distribution of the sibling species in the An. gambiae complex were similar. Compared to An. gambiae s.l larval habitats, other anophelines larval habitats were deeper and closer to streams and with more aquatic vegetation. Agricultural land cover were positively associated with the presence of larval habitats, and were located relatively close to stream channels; whilst nonagricultural land cover were negatively associated with the presence of larval habitats and were more distant from stream channels. IKONOS imagery was not useful in direct detection of larval habitats (mostly because the habitats were small), but was useful in their localization through statistical association with land cover. The modelling outcomes demonstrated that areas that were close to streams, were at relatively low elevation and had agricultural land cover features had high probability of Anopheles mosquito larval habitats being located on them. In conclusions, more than a half of the anopheline larval mosquito population in Asembo study area comprised of An. gambiae s.l. It was clearly demonstrated that high resolution satellite images could be utilized in identifying high probability sites for the location of potential larval habitats such as those areas covered by maize fields and pasturelands, but may not be suited to directly detect specific water bodies which serve as potential larval habitats. The resulting continuous distribution maps from the modelling process showing the likely form of distribution of larval habitats in the Asembo study area can greatly compliment the existing larval ground surveys by helping direct vector control to areas that have high habitat suitability which comprise about '/3 of the total study area. The results of this study provide essential information for habitat-based control programs that aim at targeting productive malaria vector habitats
The ecology and economic potential of wild silkmoth Anaphe Panda (Boisduval) (Lepidoptera:Thaumetopoeidae) in the Kakamega forest
(2011-07-11) Norber, Mbahin
The superiority of silk as a textile fibre has been recognized from time immemorial, the luxurious look: sleek feel and lustre of silk fabric are unquestionably inimitable. The demand for silk is constantly increasing in the world market and this provides excellent opportunities for any producer country to diversify and optimize any source of production. African countries that enjoy congenital climate for rearing wild silkmoths have great scope and opportunity to promote sericulture. Studies were carried out during 2005-2007 on the ecology and economic potential of wild silkmoth Anaphe panda (Boisduval) which occurs in the Kakamega Forest. western Kenya. Silkworms feed on Bridelia micrantha (hochst). Egg clusters were present from mid-October to mid-May: silkworms appear from December to September: pupae are present from mid-April to January and adults occur from early October to April. Eggs hatch after 40 to 55 days depending of the temperature. Seven larval instars occur with a growth prodigious from 3 mg at 1 S` instar to more than 3.000 mg at the 7" ins=. The duration of larval development depends on temperature and ranged from 83 to 118 days. The duration of the pupal stage ranged from 107 to 178 days depending on the brood. Pupal and adult sex ratios are not even. A moth life span ranged from 4 to 7 days. The factor that contributes most to egg mortality appears to be egg parasitism. and in the Kakamega Forest. eggs were mainly parasitized by two chalcids: Telenomis gowaevi Grahan and Pleurotropis telenomis Lima. Eggs in the mixed indigenous forests (forest with indigenous and exotic species) seemed to be more affected than those of the indigenous forest (forest with indigenous species only), and the infection rate was also significantly different (P = 0.0025 < 0.05) between the mixed indigenous and indigenous forests. Higher mortality rate was observed from the Is' to 4`h instar. but a highly significant difference was observed between the unprotected and the protected silkworms. Nevertheless, the lowest mortality rate was observed from the 5 `h to 7t instars. High mortality rate of silkworms was observed in the mixed indigenous forest compared to the indigenous forest. The survival rate observed during the larval developmental period was significantly higher for the protected than for the unprotected silkworms. Protection with net sleeves seemed to minimize the instantaneous risk and effectively increased the survival of the silkworm. The tachinid fly Exorista cardinalis Fabr and the ichneumon wasp Cryptus leucopygus Granenhorst were found to be parasitoids at the larval stage. A. panda cocoon nests were found to be infested by various dipteran and hymenopteran parasitoids. Geographical information systems (GIS) and Poisson distribution revealed that distribution of the host plant B. micrantha: cocoon nests and egg-clusters were not uniformly distributed in the indigenous and mixed indigenous forests. A bamboo structure was found on A. panda fine structure filament. and this structure is characteristic and unique as compared with all other cocoon filaments of lepidopteran insects. By processing A. panda cocoon nests into silk shirts. the net income was multiplied twent\ four times. Therefore. wild silkmoth farming could be a supplementary activity carried out by farmers for income generation while at the same time conserving biodiversity.
Antiretroviral resistance and genetic diversity of human immunodeficiency virus among antenatal clinic respondents on nevirapine from North-Rift Kenya
(2011-07-11) Kiptoo, Michael Kibet
Mother-to-child transmission (MTCT) of HIV-1 is responsible for infection of hundreds of thousands of infants every year. It is estimated that 600,000 newborns are infected yearly worldwide, with MTCT accounting for 90% of these infections. Human immunodeficiency virus (HIV) can be transmitted from mother-to-child at various stages of pregnancy including in utero and intra partum. A number of feasible and effective interventions to reduce MTCT among women of child hearing age are available. These interventions include prevention of primary HIV infection, avoiding unwanted pregnancies among HIV positive women, reduction of transmission from infected mothers to infants during pregnancy, labour, delivery and breathfeeding through provision of voluntary counselling and testing (VCT) services, antiretroviral therapy (ART), safe delivery practices, and breast milk substitutes. However, these approaches are not always possible in resource-poor countries. The use of antiretroviral (ARV) drugs, in particular revirapine, zidovudine and zidovudine/lamivudine combination, has been studied in both developing and developed countries. Although these studies have shown reduction in transmission of HIV, concerns regarding the development of drug resistant strains have been raised. The Ministry of Health in Kenya has implement nevirapine regimen to reduce MTCT in the public health facilities. This study aimed to investigate drug resistance in an MTCT setting in Kenya. A total of 309 HIV seropositive pregnant women taking part in the prevention of mother of child transmission of HIV (PMTCT) programme in three hospitals, namely, South Nandi Hills, Kapsabet, and Kitale district hospitals were enrolled in this study. A structured questionnaire was used to collect demographic information. Venous blood was collected into vacutainer tubes containing EDTA as anticoagulant. The enumeration of T-lymphocytes was carried out by flow cytometry and viral load was determined by nucleic acid amplification. The proviral HIV DNA extracted from peripheral blood mononuclear cells (PBMCs) was sequenced to determine the drug resistance associated mutations and HIV-1subtypes. The significance of associations was investigated by chi-square test and odds ratios. The HIV prevalence among the pregnant women was 6.7% (309 of 4638). The majority (85%) of the women visiting the antenatal clinic were not aware of their HIV status. Sixty percent (60%) of pregnant women had a CD4 count of more than 350cells/mm3 . The HIV transmission rate was 6% (4 of 59 infants). Drug resistance associate mutations were detected as minor population except in one mother-child pair where major populations were found. Nevirapine drug resistance was detected in 19.4% (7 of 36) and 100% (3 of 3) of the women and infants tested respectively. Even though the women had not been exposed to nucleoside reversed transcriptase inhibitors (NRTIs), drug resistance associated mutations were detected in 8 mothers (22.2%) as minor populations. The major circulating HIV-1 subtype in North-Rift Kenya was identified as A1 (50% and 71.8%) based on the env (C2V3) and pol (RT) regions respectively. Human immunodeficiency virus type 1 subtypes D (12.8%), C (10.3%), A2 (2.6%) and G (2.6%) were also detected based on sequencing of the pol region. Drug resistance outcomes in mothers and infants should be considered as an important secondary end point in PMTCT assessment.
Spatial distribution and biology of Gonometa postica Walker (Lepidoptera: Lasiocampidae) with reference to its key parasitoids on Acacia species in Mwingi, Kenya
(2011-07-11) Fening, Ken Okwae
The African wild silkmoth, Gonometa postica Walker produces silk of high quality. A study on the spatial distribution and biological and biology of G. postica on host and non-host plants and the parasitism rates and reproductive strategy of its parasitoids was conducted during the long and short rainy seasons in 2006 and 2007. Three sites, each in the Imba and Mumoni forests of Mwingi eastern Kenya, were selected for sampling. One hundred trees of the host plants of G. postica were sampled at each site, in additional to the non-host plant species having G. postica pupae. In order of decreasing abundance, the host plants in Imba forest were Acacia tortilis, A. elatior and A. nilotica; and in the Mumoni forest, A. tortilis, A. nilotica, A. mellifera, and A. brevispica. Host plant species richness did not differ between the two forests but their evenness was significantly higher in Imba than in Mumoni. At Imba, the distribution of A. tortilis, A.nilotica and A.elaitor was clumped while the non-host plants were random. A. nilotica and A. brevispica were clumped in Mumoni, whereas A. tortilis, A. mellifera and the non-host plants were randomly distributed. The distribution of G. postica larvae was clumped on all host plants in Imba, except on the non-host plants, where they were randomly distributed. In Mumoni forest, larval distribution was clumped on A. tortilis but random on the other host plants. A. elatior had significantly more larvae than other host plants in Imba. In Mumoni, A. tortilis and A. mellifera had significantly more larvae, followed by nilotica and A. brevispica. The pupae of G. postica were randomly distributed on all host plants in Imba and Mumoni forests. Interestingly, the non-host plants harboured significantly more pupae than the host plants in both forests. Frequently, Imba had a significantly higher abundance of larvae and pupae than Mumoni. Generally, the female moth laid more eggs on the net sleeves, followed by the wooden board, plastic container and the twigs. The developmental periods for egg hatching, larva, pupa and the adult moth lifespan ranged between 11-12, 55-72, 101-126 and 3-10 days respectively. Larval developmental period and quality of cocoons differed according to the larval food plant, season and site, for those reared in semi-captivity. However, the quality of cocoons was similar on the different larval food plants from the wild habitat, though it varied according to season and site. Larvae reared on A. elaitor had the shortest developmental period and produced cocoons of the highest quality than those raised on A. tortilis and A. nilotica. Larval development was generally shorter in the sites and seasons where rainfall was high. Trapping of adult moths revealed that there were more males than females and that two districts peak periods occurred during a year. Six parasitoids, vis., four hymenopterans and two dipterans, were collected during the study. The most common parasitoids were Palexorista sp. (Diptera: Tachinidae) and Goryphus sp. (Hymenoptera: Ichneumonidae) with parasitism rate ranging from 1.8-32.7% and 2.2 - 7.5%, respectively. Parasitism rates on G. postica in relation to its host plants in the two forests of Mwingi. This information would be crucial in the monitoring, sustainable utilization and the conservation of this economically important silkmoth and its host plants species. The data on the bionomics and reproductive strategy of the key parasitoids will be a prerequisite in devising any management programme to boost cocoon production.
Bioecology of the new invasive fruit fly Bactrocera invadens (Diptera:Tephritidae) in Kenya and its interaction with indigenous mango-infesting fruit fly species
(2011-07-11) Ivan, Rwomushana
Bactrocera invadens Drew, Tsuruta & White (Diptera: Tephritidae), an alien invasive fruit fly species of Asian origin was first detected in Kenya in 2003. This pest has rapidly spread across sub-Saharan Africa and is currently reported from at least 24 countries. Because of its novelty status, there was no information on its biology and ecology that could aid development of management efforts. There was also evidence that B. invadens co-infested the same fruits with native fruit fly species and it was speculated that this could result in competitive displacement of native fruit flies. This study, therefore, was initiated to establish the bioecology of B. invadens in Kenya and its interaction with indigenous mango-infesting fruit fly species. The first step was to identify the most suitable temperature range for development and survival of immature stages of this pest. Studies were conducted in the laboratory at four constant temperatures of 15, 20, 25, 30 and 35°C. The longest development period occurred at 15°C (75.74 days) and was shortest at 30°C (17.76 days). The optimal temperature for survival was found to be 25°C while 35°C was the most lethal temperature. Countrywide surveys were then initiated to establish the host plants of this pest. The survey revealed that B. invadens infested fourteen plant species particularly Mangifera indica L., Musa sp. AAA and citrus [C. limon (L.) Burm. f., C. sinesis (L.) Osbeck and C. reticulata Blanco.] and the wild plants Sclerocarya birrea (A. Rich) Hochst. and Terminalia catappa L. In laboratory host preference studies, M. indica and Musa sp. were found to be the most preferred host plants among the nine cultivated plant species tested. The spatial and temporal population dynamics of this pest was also studied and revealed that three fruit fly species infested mango namely B. invadens, Ceratifs capitata (Wiedemann) and Ceraftis cosyra (Walker). The relative abundance index (RAI) of these pests in infested fruit was in the order B. invadens > C. cosyra > C capitata which was similar to the indices of adult population obtained by trapping. Percent fruit fly infestation and B. invadens fruit fly density was found to be always higher in mango on the ground than on the trees, demonstrating that mango fruits that fall to the ground serve as a major breeding site and may be a reservoir of non-immigrant B. invadens population in mango orchards in Kenya. The efficacy of the Easy, Multilure and Lynfield traps all baited with Nulure, Torula Yeast, Corn steepwater and a locally produced yeast product for trapping B. invadens was also evaluated. The multilure trap baited with torula yeast or nulure was the most attractive trap-bait combination and captured 19.7-30.3 B. invadensltrap/day and 10.54 -22.97 flies/trap/day respectively. In interspecific competition studies, there were significant differences in the larval developmental time, weight of puparia and number of adults that emerged of B. invadens, C. capitata and C. cosyra when the insects were soquentially co-infested on rearing medium at constant temperatures. When B. invadens was introduced into whole fruit before C. cosyra, the number of emergent adults of the IMa was greatly suppressed. Higher number of C. capitata adults was, however, recovered when in cross infestation with B. invadens particularly in the treatments where G capftata had a two or three days head start. This study demonstrated that the oedumisms contributing to the displacement of C. cosyra by B. invadens may be erodated with intricate interactions between resource pre-emption and fluctuations in temperature in mango agroecosystems
Characterisation of placental malaria in olive baboons (pappio anubis) infected with plasmodium knowlesi H strain
(2011-07-11) Mustafa, Barasa; Gicheru, M. M.; Hastings Ozwara
Pregnant women have increased susceptibility to malaria infection. In these women, malaria parasites are frequently found sequestered in the placental intervillous spaces, a condition referred to as placental malaria (PM). Placental malaria threatens the health of the mother and the child's life by causing intrauterine growth retardation, abortions, still births and reduction in gestational age. An estimated 24 million pregnant women in SubSaharan Africa are at risk. Mechanisms responsible for increased susceptibility in pregnant women are not fully understood. Baboons are susceptible to Plasmodium knowlesi and have similar host pathogen interactions and reproductive physiology similar to humans, making them attractive for the development as a model for studying mechanisms underlying development of placental malaria. This study exploited the susceptibility of baboons to Plasmodium knowlesi infection to develop a non-human primate (baboon) model for studying PM. The main objective of the study was to demonstrate PM and characterize immunological mechanisms underlying the pathogenesis of PM in baboons infected with Plasmodium knowlesi. The pregnancies of three time mated adult female baboons and their gestational levels (one in its second trimester and two in their third trimester) were confirmed by ultrasonography. On the 150th day of gestation, the pregnant baboons were infected with Plasmodium knowlesi H strain parasites together with four non pregnant controls. Peripheral parasitaemia development was monitored on a daily basis from two days post inoculation. Collection of sera, plasma, mononuclear cells and haematological samples was done on a weekly basis. Peripheral blood mononuclear cells (PBMC) were stimulated in culture with concanavalin A and P. knowlesi antigens and their proliferation quantified. Sera cytokine and immunoglobulin concentrations were measured by ELISA using respective enzyme conjugated antibodies. Two pregnant baboons aborted (one on day 6 and the other on day 7 post infection) and cesarean section was only done on one baboon. Smears prepared from placental blood demonstrated the presence Plasmodium knowlesi parasites in all the sampled placentas. On average, the pregnant baboons had more than 29 fold higher placental parasitaemia than simultaneous peripheral parasitaemia. This shows that Plasmodium knowlesi preferentially sequesters in the baboon placenta just like Plasmodium falciparum does in humans. Two baboons that had high placental parasitaemia experienced abortion, which is a sequele of human placental malaria. Results indicate that PM in this model is associated with significant (P < 0.05) suppression of immunoglobulin G, Interferon gamma, and interleukin 6 responses. Tumour necrosis factor alpha responses were significantly upregulated (P < 0.05) while immunoglobulin M, interleukin 10, interleukin 12, interleukin 4 and PBMC proliferation responses did not differ from controls (P > 0.05). These data are consistent with some findings from human studies, showing the feasibility of this model for studying mechanisms underlying placental malaria. The study has contributed valuable data to be used in further studies and the development of preventative, control and therapeutic measures against PM in women
Diversity and ecological preference of parasitoids associated with lepidopteran stem borers in Kenya
(2011-08-03) Mailafiya, D. M.; Kairu, E. W.; Bruno, Le Ru; Dupas, S.
Field surveys were carried out from 2005 to 2007 to assess parasitoid species diversity and stemborer parasitism in cultivated and natural habitats in four agroecological zones in Kenya. To increase the chances of collecting stemborer parasitoids, random sampling was employed in cultivated habitats, while both random and non-random samplings were applied in natural habitats. During this study, 7443 and 3676 stemborers were collected from cultivated and natural habitats, respectively. A total of 33 parasitoid species were recorded, of which 18 species were recovered from 6 stemborer species feeding on cereal crops, while 27 species were recovered from 21 stemborer species feeding on 19 wild host plant species. The most common parasitoid species in cultivated habitats were Cotesia flavipes (Hymenoptera: Braconidae), C. sesamiae (Hymenoptera: Braconidae), Pediobius furvus (Hymenoptera: Bethylidae) and Siphona sp. (Diptera: Tachinidae). In natural habitats, Siphona sp. was the most common. Parasitoid species diversity was significantly higher in natural than in cultivated habitats. Most of the parasitoid species recovered from cultivated habitats were also found in natural habitats. Natural habitats surrounding cereal crops appeared to serve as refugia for sustaining the diversity of stemborer parasitoids in adjacent cereal fields. Given that parasitoid diversity was higher in natural habitats with more diverse plant communities, but parasitoid abundance was higher in cultivated habitats, this study provided partial support for the `natural enemy' hypothesis. Across agroecological zones, stemborer parasitism was positively dependent on parasitoid species richness and abundance during different seasons in both cultivated and natural habitats. Rainfall had a significant negative effect on parasitoid abundance as well as stemborer parasitism in both cultivated and natural habitats. The negative relationship between parasitism and temperature in natural habitats only, suggested greater sensitivity of parasitoids to extreme temperatures in natural habitats. Across seasons, stemborer densities were generally higher on maize and sorghum in cultivated habitats than on wild host plants in . natural habitats. Stemborer parasitism rates were generally low (<15.00%) in both cultivated and natural habitats. Neither larval nor pupal parasitism differed significantly between seasons in natural habitats. Cotesia sesamiae was found in Kakamega and Suam in the Western and Rift Valley regions, respectively, where Busseola fusca (Lepidoptera: Noctuidae) predominates. By contrast, C. flavipes was found in Mtito Andei and Muhaka in the Eastern and Coastal regions, respectively, where Chilo partellus (Lepidoptera: Pyralidae) predominates. There was no indication of host plant and stemborer species specificity by C. sesamiae, as its host ranges varied with both habitat type and locality. Conversely, C. flavipes exhibited a high level of specificity to its target host C. partellus on maize and sorghum in cultivated habitats and on S. arundinaceum in natural habitats. Of the two Cotesia species, natural habitats served as a reservoir for C. flavipes only, because these habitats sustained some of the individuals on C. partellus during both rainy and dry seasons. This was however not applicable to C. sesamiae, as its cereal stemborer hosts B. fusca and Sesamia calamistis (Lepidoptera: Noctuidae) were scarce in wild host plants.
The distribution of stromal derived factor-1 mutation in Kenyan population
(2011-08-10) Ong'onda, Khamala John
Human immunodeficiency virus type-1 (HIV-1) appeared on the scene over twenty years ago and has since caused many deaths; left millions orphaned and created uncertainty in any families. The virus has also created a socio-economic burden to many countries. The entry into and tropism of the host immune cells by the HIV-1 depends on chemokine receptors and coreceptor interactions among other factors. Genetic polymorphism in chemokine receptors and coreceptor genes influences susceptibility to HIV-1 infection and disease progression. Polymorphisms in the stromal derived factor-1 (SDF-1) play an important role in the evolution of HIV-1 in patients. The mutant SDF-1 (stromal derived factor-1 3A'/3A') competes with the virus for the coreceptor site CXCR4 on the CD4+ Tcells therefore down-regulating evolution of non-syncytial to sync ytial induction during HIV-1 progression. The occurrence of SDF-1 3'A in populations varies between races, with blacks having 11% and whites having 37% in the USA. In India, SDF-1 mutations are rated between 25% and 38% while in East Asia they are rated between 3% and 67%. Caucasians have the highest frequency of the SDF-1 3'A/3'A mutations. South African Sotho and Xhosa tribes had 1% and 2.8% of this mutation respectively. In this study, a survey on the distribution of SDF-1 gene polymorphisms in the Kenyan provinces was conducted with a view of trying to check any genetic basis for variations in HIV and AIDS regional prevalence rates. Two hundred whole blood samples were collected from eight provinces of Kenya and analysed at the Kenya Medical Research Institute in Nairobi. Detection of SDF-1 gene polymorphisms was done by extraction of proviral DNA from whole blood and the SDF-1 target gene was amplified by polymerase chain reaction (PCR) using gene-specific primers. The different SDF-1 gene polymorphisms were detected by Restriction Fragment Length Polymorphism (RFLP) and gel electrophoresis. Two DNA bands were visualized at 202 and 100 base pairs for the homozygous dominant polymorphism (wild type), three bands of 302, 202 and 100 base pairs (heterozygous) and one band at 302 base pair for the mutant alleles. Chi-square test was used to compare the distributions of these mutations in the eight provinces as Pearson's moment of correlation coefficient was used to correlate the SDF-1 mutation with -HIV incidences in the eight provinces of Kenya. The data generated was used to calculate percentage distribution of the mutation per province. This study showed the presence of the stromal derived factor-1 polymorphism in Kenyan population with an average of 6.6% for the double mutant, 20.7% for heterozygous and 73.7% for the wild type. There was no correlation between the HIV prevalence and the SDF-1 distribution in Kenya; interestingly, Nyanza province recorded a high occurrence of the SDF-1 3'A/3'A (11.11%) double mutants but is also had the highest HIV prevalence (15.3%). The results obtained in this study will form a foundation for further research given that double mutants have been found to show some resistance to HIV infection. Since mutants show good response to anti-retroviral drugs, researchers can also incorporate genetics into the treatment of HIV.
Transmission dynamics and epidemiology of Rhodesian sleeping sickness in allopatric populations of glossina pallidipes of kenya
(2011-08-16) Okoth, Sylvance Okeyo
Trypanosoma brucei rhodesiense causes rhodesian sleeping sickness in humans. The disease is transmitted by tsetse flies and the distribution of the disease is highly localised to traditional foci. In Kenya, despite widespread distribution of Glossina pallidipes, rhodesian-sleeping sickness is only restricted to western parts of the country. Factors restricting disease distribution to traditional foci are not well understood. A comparative assessment of transmission dynamics and epidemiology of the disease was carried out in two G. pallidipes subpopulations of Kenya in an attempt to understand causes of the focalized distribution. Entomological, socio-economic, cultural and epidemiological risk indicators were studied. Results showed that tsetse flies from the Busia subpopulation had higher survival, longevity, susceptibility and transmission success than those from Nguruman subpopulation. Vector-host contact in both areas did not depend on prevailing weather conditions and, the influence of host movement on vector activity only became important at high host densities. Bovidae and suids were the most preferred hosts of G. pallidipes at Busia and Nguruman respectively. Livestock keeping was a higher risk activity than crop farming in both areas and, while women were more exposed by cultural activities at Busia, men were the most exposed by the same at Nguruman. Land use patterns showed that tsetse habitats have been significantly reduced by economic activities at Busia than Nguruman. Transmission risk at Nguruman was high during the dry season while that at Busia was high during the wet season. Although survival rates of the two subpopulations were similar, vector-host contact, teneral density and overall transmission risk were higher among the Busia subpopulation than the Nguruman subpopulation. Transmission risk projections showed that with increased contact, Nguruman subpopulation would pose significantly higher transmission risk than Busia subpopulation. The risk would however be reduced slightly by suppressed fly density but significantly by low teneral density. Results of this study therefore indicated significant differences in human-fly contact and in vectorial capacity of the two subpopulations. The differences sufficiently explain current epidemiological variations in disease occurrence in the two areas. Management of transmission risk would therefore require sustained suppression of vector population and avoidance of vector-host contact through strategic livestock grazing patterns that is out-of-phase with peak vector activity periods within respective seasons.
Impact assessment of natural enemies on stem borer populations and maize yield in three agroecological zones in Mozambique
(2011-11-04) Cugala, Domingos Raquene
Lepidopteran stem borers are the major pests limiting the production of maize and grain sorghum under subsistence farming conditions of Southern Africa. Classical biological control has traditionally emphasized the control of introduced pests through the importation and/or introduction of coevolved natural enemies from the pest's native home. It is based on the assumption that coevolved natural enemies are best adapted to locating and successfully attacking the target host. On this basis, Cotesia flavipes Cameron (Hymenoptera: Braconidae) and Xanthopimpla stemmator (Thunberg) (Hymenoptera: Ichneumonidae) were introduced in Southern African countries for biological control of Chilo partellus Swinhoe (Lepidoptera: Crambidae) and Chilo sacchariphagus (Bojer) (Lepidoptera: Pyralidae). The current studies were conducted to evaluate the establishment and spread of C. flavipes and X. stemmator in the release locations, assess the impact of natural enemies on the stem borer populations and maize yield, assess the effect of temperature on the development of X. stemmator in three host species, and finally, to study population growth parameters of X. stemmator and Dentichasmias busseolae (Heinrich) (Hymenoptera: Ichneumonidae). Several parasitoids including indigenous and the exotic species were recovered from egg, larval and pupal stem borer development stages. Egg parasitism of more than 80% due to Trichogramma bournieri (Hymenoptera: Trichagrammatidae) was reported on C. partellus eggs in the Southern region of Mozambique. C. flavipes was recovered at all release and other sampling sites. The highest percent parasitism (33.8%) due to C. flavipes was reported at Maracuene, one of the 1996 release sites. This introduced exotic larval parasitoid was reported to increasingly becoming the more abundant in relation to C. sesamiae. The exotic pupal parasitoid X. stemmator was recovered only from C. partellus pupae during the release season (2002/2003) and one year after its release, but it was not recovered in subsequent seasons. Results from field experiments indicated that damage levels due to stem borer attack varied from location to location. High damage levels were reported in the areas where C. partellus is dominant followed by the areas dominated by Busseola fusca Fuller (Lepidoptera: Noctuidae). However, stem borer density was higher at high elevation zones dominated by B. fusca compared to low and mid elevation zones. Yield losses varied from 28.8% to 34.5% across the regions. Yield losses were observed to increase (from 28.9 to 43.3, 34.5 to 40.8 and from 31.2 to 36.4% at low, mid and high elevation zones respectively) when natural enemies were excluded from the maize plots. The impact of natural enemies on maize yield increase was high at lowland zones (26.1%) and lowest at high elevations (7.6%). Laboratory experiment indicated that while X. stemmator successful developed in C. partellus, B fusca and S. calamistis stem borer species, the more suitable host was C. partellus. The parasitoid developed faster at high temperatures and slowly at low temperatures. The lower temperature threshold for X. stemmator reared on C. partellus was 9.76°C and the maximum threshold of 35°C. These results indicate that this exotic parasitoid could survive and remain active at low to mid elevations and could not survive at high elevations where temperatures during winter are usually below 9°C. However, in the a
Anopheles larval productivity and diversity in Mwea irrigation scheme, Kirinyaga district, Kenya
(2011-11-08) Mwangangi, Joseph Mumo
The use of irrigation to flood agricultural land during rice cultivation has over the years been associated with an increase in the number of disease vectors and corresponding increase in health burden due to malaria and other vector and waterborne diseases. In this study, field and laboratory studies were used to examine the primary factors responsible for regulating the aquatic stages of malaria vectors in a rice agro-ecosystem prior to implementation of a larval control programme. The objective of this study was to determine the environmental and agricultural factors that regulate malaria vector productivity and diversity in Mwea Irrigation Scheme, Kirinyaga district, Kenya. The study was conducted in 3 villages representing planned (Mbui Njeru), and unplanned rice cultivation with varying amount of land under rice (Kiamachiri and Murinduko). The physico-chemical variables were measured using different field based hand held equipments or visual assessment. Experimental plots were used to closely monitor the factors associated with Anopheles larval densities in the rice fields. A total of 29,252 immature stages of anopheline mosquitoes were collected in the three villages comprising of'78.23% (n = 22,885) early instars, 10.91% (n = 3,192) late instars and 10.85 % (n = 3,173) pupae. Anopheles gambiae s.l. was the most abundant and was found in all habitats that were positive for late anopheline instars in the 3 villages. Larval abundance was significantly higher in Murinduko compared to the other villages (F(2, 182) = 38.685, p< 0.01). Rainfall was positively associated with Anopheles gambiae s. l. larval abundance in Kiamachiri (r = 0.759) and Mbui Njeru (r = 0.602) but negatively associated in Murinduko (r = - 0.267). Multiple logistic regressions showed Anopheles larval density to be significantly associated with many interrelated biotic and abiotic variables including presence of other invertebrates, percentage Azolla cover, distance to nearest homestead, water turbidity, water temperature, conductivity, pH, and water depth. Anopheles productivity from different habitat types showed that paddies had most emergent mosquitoes (n = 143) followed by marshes (n = 65). Succession of Anopheles species was evident with An. gambiae colonizing the paddies throughout the rice growth cycle with peaks during the early stage of rice growth while An. rufipes and An. coustani occurred during the late vegetative stages. Larval densities were significantly higher at the centre of the paddy compared to the periphery during the transplanting period (F (1,166) = 4.809, P = 0.030) but the difference was not significant during the tillering period (F (1,362) = 0.037, P = 0.848). The survivorship of immatures in the paddies showed that there was 98.26% mortality of larvae. In conclusion, rice paddies and associated canals are the most productive habitats types throughout the year while peridomestic habitats are important during the long and short rains. The results further indicate that several biotic and abiotic factors interact to regulate Anopheles larval densities in aquatic habitats. These findings demonstrate the need to target larvicidal application in the entire paddy between transplanting and tillering stages in order to achieve effective larval control.

Browse

Browsing PHD-Department of Zoologial Sciences by Issue Date

Results Per Page

Sort Options