Sublethal Effects of Insecticides on Feeding Behaviour of Testse Flies Glossina Pallidipes Austen and Glossina Morsitans Morsitans (Westwood) (Diptera: Glossinidae)

Esther Kibuka-Sebitosi

University of South Africa, Institute for African Renaissance Studies, 287 Skinner Street, P.O. Box 392, UNISA 0003, Pretoria South Africa.

ABSTRACT: The feeding behaviour of wild caught G. pallidipes and laboratory reared G. m. morsitans was investigated following topical application of deltamethrin and natural pyrethrum extract in acetone. Flies were weighed before and after every blood meal (on rabbits) and maintained at 250C and 65-70% relative humidity. Females with a 3rd instar larva were separated, observed until larviposition and larvae watched for pupation, until death. Results showed that both G. m. morsitans and G. pallidipes were more susceptible to deltamethrin compared to pyrethrum extract. Flied fed in groups showed varied feeding behaviour while those feed individually revealed a 4-day feeding cycle. The treated females demonstrated a 7-day feeding cycle that was characterized by frequent but small blood meals. Female. G. Pallidipes treated with 0.0001-0.01ng deltamethrin showed a peak of 35 mg blood meal. These results showed that insecticides disrupted feeding cycles of treated flies. Failure of flies to feed means a reduction in the reserves and a reduction in the survival with implications on transmission of trypanosomes. Flies that recovered were probably due to abortions; inert storage of insecticides in the fat body; and partitioning of the insecticides into the uterine milk gland during pregnancy. It appears that sublethal doses of insecticides have a role to play in the feeding behaviour, subsequent pupal weights, progeny and tsetse fly population and should be taken into consideration when designing control strategies. All these factors are discussed in relation to the tsetse fly population dynamics; control and transmission challenges. The potential threat to other insects that occupy similar ecosystems with tsetse flies is highlighted calling for more sustainable and environmentally friendly control methods.

KEYWORDS: Tsetse flies; insecticides; Deltamethrin; Pyrethrum extract; Feeding behaviour

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