Varroa-Specific Hygienic Behaviour and Population Abundance of Varroa Destructor in Colonies of Apis Mellifera Scutellata in Karura Forest, Kenya
Cheruiyot, Sammy Kiprotich
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The ectoparasitic mite Varroa destructor is one of the parasite globally reported affecting honeybee health and causing high colony losses. Of notable importance is the association of the mite with viruses and their transmission to honeybees which causes great harm to bees. Kenyan beekeepers have reported that bee populations have been on decline in recent years and therefore the need for research to establish whether Varroa destructor is negatively affecting honeybee survival and development. The objectives of this study were to evaluate Varroa-specific hygienic behaviour of Apis mellifera scutellata, assess population abundance of V. destructor and determine the effects of V. destructor on local honeybee A. m. scutellata. The study was conducted at International Centre of Insect Physiology and Ecology (icipe) research apiaries located in Karura forest, Nairobi County. Thirty colonies were randomly selected and monitored from April to November 2016. Data collection on Varroa-specific hygienic behaviour was done from ten colonies and the response of A. m. scutellata to mite introduction were evaluated at intervals of 72 hours for a period of three months. The pre-pupae worker brood cells were uncapped and 10, 8 and 5 adult female phoretic mites were introduced repeatedly per colony and brood cells recapped. Assessing population abundance and the effects of V. destructor on colony size and productivity of Apis mellifera scutellata were done on twenty colonies. For each experimental colony, infestation of V. destructor on adult bees was measured twice a month using sugar shake method. Mite infestation in worker brood cells was assessed fortnightly by uncapping 200 purple eyed pupae and adult mites found were counted and recorded. Quantifying the amount of brood, adult bees and colony stores (pollen, nectar and honey) was done once every month. The data on Varroa-specific hygienic behaviour of Apis mellifera scutellata, population abundance of V. destructor and effects of V. destructor on Apis mellifera scutellata were analyzed using Generalized Linear Mixed Model and the means separated using Tukey’s HSD at P value = 0.05 (5% significance level). The mean percentage of untouched brood cells was significantly high in control experiments (80%, n = 579) compared to manipulated brood cells in which mites had been introduced (12.5%, n = 110) (P = <0.001). There were significant differences between the different densities of mites introduced and percentage response of Apis mellifera scutellata in untouched brood cells (UBC, P = <0.001) and where mites were removed and brood cells recapped (MRBR, P = <0.001). The population abundance of V. destructor varied within the months of study and was generally characterized by low mite infestation levels. The mites collected within the first four months of study (April, May, June and July) were significantly lower than those collected within the last four months (August, September, October and November) (P = <0.001). Colony stores also varied throughout the study period with the month of July recording the lowest mean numbers of nectar (38.8 ± 12.5 cm2), pollen (33.8 ± 8.8 cm2) and honey (45 ± 10.5 cm2). The number of adult bee population was positively correlated with overall V. destructor population with significant difference (P = 0.0014). The amount of honey was positively correlated with overall V. destructor population with significant difference (P = 0.03). In spite of the presence of the parasitic V. destructor in bee colonies, all the colonies appeared healthy. Therefore, control measures should be put in place by the government in order to curb any increase in infestation levels of V. destructor and maintain the apparent healthy status of honeybees in Kenya.
- MST-Zoological Sciences