A Study of the predators of the tsetse fly Glossina austeni Newstead (Diptera glossinidae )at Muhaka forest, south coast Kenya.
Wanyiri, Jane Wangui
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Glossina austeni Newstead is one of the eight tsetse species that occur in Kenya. It is confined to the humid and subhumid coastal zone in Eastern Africa. Some attempts have been made in the past to control G.austeni using cultural, chemical and sterile male control methods, but with little success. The application of insecticides has proved to be quite expensive, in addition to being hazardous to the environment and harmful to non-target organisms. Therefore efforts should be directed towards developing compatible management strategies and methods for an integrated approach to tsetse control. One such strategy is the manipulation of biological control organisms. However, little has be been attempted to date by way of bio control technique. As part of an effort to explore environmentally safe management strategies for tsetse, a one-year research programme was carried out at Muhaka forest at the south coast of Kenya to study the predators of both puparia and adult of G. austeni. The inveterbrates found in the larviposition sites, and /or captured in pitfall and water traps and tested in the laboratory as predators of puparia comprised of members of coleoptera, Formicidae, Gryllidae and Gryllotalpidae. Those which attacked adult tsetse in the laboratory cage tests and which, therefore, were suspected to prey on them either in the larviposition sites or in the general habitat included Araneae, Mantidae, Tettigonidae, Asilidae, hymenoptera, anisoptera and zygoptera. Laboratory experiments to determine whether the potential predators could feed on the tsetse adult and puparia, revealed that adult and puparia of G. austeni are palatable to a wide range of predators with the highest percentage predation (65.65) on puparia being recorded in Liogryllus sp. (Orthoptera: Gryllidae). Adults were most palatable to Gonypetera sp. (Mantidae) with a percent predation of 90.7%. In the preference studies, none of the predators was observed to be specific for G. austeni. However, a preference was apparent in all cases. In the presence of G. pallidipes and G. brevipalpis, the two species of tsetse that co-exist with G. austeni in Muhaka forest, the Promachus sp. (Diptera:Asilidae) had the highest preference (75%) for G. austeni adult. Other predators with high preference for G. austeni were Amaurobius sp. (Araneae: Amaurobidae) and Gryllacris sp. (Orthoptera: Gryllidae) 66.7% and 60% respectively. The puparia predator Odontomachus sp. had 85% preference for G. austeni. In the presence of other arthropods, Promachus sp. has the highest percentage preference (50%) for G. austeni among the predators of adult G. austeni while among the predators of puparia Odontomachus sp. showed the highest percent preference (58.8%). Handling time experiments revealed that predators with extero-digesting feeding patterns had longer handling times than those that chewed their prey. For instance, Promachus sp. (Asilidae) which exhibited the former feeding pattern had a handling time of 1.450.2hrs while Liogryllus sp. (Gryllidae) which exhibited the latter, had a handling time of 2.90.1min. Laboratory studies on the interactions of predators and tsetse adult and puparia (prey) showed that an increase in prey density reduced searching efficiency. This was probably due to prey interferance. However, the number of tsetse killed per predator increased as prey density and duration of exposure to the predator increased. Nevertheless, different predators showed different functional responses. The spiders, Amaurobius sp. and Dysdera sp., the asilids, Promachus sp. and Formicidae, Odontomachus sp. showed density dependent sigmoid or Holling's Type III relationship to adult and puparia of the tsetse. The Alcimus sp. (Asilidae), Platythrea sp. (Formicidae), Gryllacris sp. and Liogryllus sp. (Gryllidae) showed curvilinear density dependent relationships similar to Holling's Type II functinal response while the spider Salticus sp. and mantid Gonypetera sp. (adult) showed a type V response. There was no significant relationship between the predators apparent densities and climatic factors tested except in Mantidae which showed a significant positive relationship with the rainfall (Reg. Coeff. =0.09839 t=3.29 P<0.05). Significant relationships between most of the predators and tsetse numbers were not established except in Mantidae (r=0.849 p<0.05). This Study revealed that there are a number of predators, which showed preference for G. austeni to other arthropod prey, which if properly studied may be useful in biological control programmes of integrated management.
- MST-Zoological Sciences