The ecology of Glossina fuscipes fuscipes (Diptera: Glossinidae) and its responses to 4-Methylguaiacol and specific compounds in waterbuck odour

Abstract

Tsetse flies (Glossinidae) are important biological vectors of trypanosomes, the protozoan parasites that cause Nagana and sleeping sickness. They are distinguished into three taxonomic groups; morsitans, palpalis and fusca. Morsitans and palpalis group tsetse species are the most important vectors of both nagana and sleeping sickness. Control methods of nagana and sleeping sickness that target the vector all exploit particular aspects of tsetse biology. So far none of the methods can be considered as a silver bullet as they are usually used in a variety of complementary combinations; allowing for development of other methods to complement the already existing ones. Use of repellents is one such method that has been developed and shown to reduce levels of nagana in cattle, transmitted by tsetse from the morsitans group. However, these repellents had not been evaluated against tsetse species from the palpalis group, hence the need to also evaluate these repellents against tsetse from the palpalis group. Herein, studies were carried out in western Kenya on four islands (Big and Small Chamaunga, Manga and Rusinga) of Lake Victoria which harbour Glossina fuscipes fuscipes an important vector from the palpalis group in order to understand the ecology of this vector and its responses to known synthetic and natural repellents. On two of the islands (Big Chamaunga and Manga), an intervention previously undertaken between 2011 and 2013 reduced fly densities from over 3 flies per trap per day to less than 1 fly per trap per day. Thus, the recovery of fly densities and the population structure of G. f. fuscipes on the islands were first assessed. Since tsetse species in the palpalis group usually occur at lower densities compared to those from the morsitans group, apart from the standard biconical trap, a more efficient sampling tool is required in order to capture any effect on the fly catches due to the candidate repellent. The small targets previously shown to attract and kill more tsetse was modified and its efficiency compared to those of biconical traps. Furthermore, the responses of G. f. fuscipes to the known repellents (4-methylguaiacol and specific compounds from waterbuck odour) were assessed in biconical traps and sticky small target for their use as baits.A before and after intervention study was undertaken to assess the recovery of fly densities and the populations structure of G. f. fuscipes on the islands while randomised block design experiments were used to evaluate sampling tools and responses of G. f. fuscipes to 4-methylguaiacol and specific compounds in waterbuck odour. Using wing geometric morphometric analyses the population structure of G. f. fuscipes was determined. Whilst the effects of trapping devices and responses of flies to repellents were evaluated using generalised linear models. Results indicates that tsetse population densities on the islands had recovered to preintervention levels and the flies that recovered were smaller in size indicating that vector control does have an effect on fly size. Sticky small targets caught seven times more G. f. fuscipes than biconical traps. Furthermore, when4-methylguaiacol or specific compounds in waterbuck odour were dispensed from trapping devices, catches of both sexes of G. f. fuscipes was significantly reduced by between 17 – 29% overall (P<0.05). Thus, indicating their efficacies as potent repellents. Following these findings, there are needs for studies to understand the mechanism behind the effect of vector control on fly size as it may guide future control strategies. Sticky small targets should also be evaluated for their cost effectiveness as alternative sampling tools to biconical traps. Further studies to assess the potential of 4-methylguiacol and specific compounds in waterbuck odour dispensed near hosts to protect from bites of G. f. fuscipes are also required.