Effects Of Larval Diet On The Fitness And Insecticide Resistance Profile Of Anopheles Gambiae S.L. (Diptera: Culicidae) From Opeibea Area In The Greater Accra Region, Ghana.

Malaria is a life-threatening disease and is hyper-endemic in Ghana. The Anopheles gambiae complex is established to contain the main vectors that transmit malaria parasite, Plasmodium falciparum in Sub-Saharan Africa and it has been implicated as the main vector of malaria in Ghana. Vector control remains the most effective measure to prevent malaria transmission. This can largely be achieved by the use of insecticides. However, the effectiveness of insecticide-based vector control is threatened by the emergence of resistance in Anopheles mosquitoes to the insecticides used. Nutrition is an extrinsic and biotic factor that affects the growth, life cycle and other life history characteristics of the larva, which has a corresponding modulating effect on the fitness of the adult. Fitness is also known to affect the ability of insects to respond to stress. Hence, the aim of this study is to assess the effect of larval nutritional status on fitness and insecticide resistance status of Anopheles gambiae s.l. Mosquito larvae and pupae were collected from Opeibea area in the Greater Accra Region of Ghana using the dipping method and reared to the adult stage. Mosquitoes were further molecularly identified to sibling species of the Anopheles gambiae complex by polymerase chain reaction (PCR) assay following standard protocols. A total of 208 adult females were identified. An. gambiae s.s. was predominant (205) followed by Anopheles coluzzii, formerly M form (2) and hybrids of the two species (1) Eggs obtained from the established colony of wild population of the Opeibea strain and reference population of the Kisumu strain from the Laboratory were reared at two diet regimes, rabbit pellet and baking yeast. Insecticide susceptibility was carried out on the adult females using four different insecticides selected from different insecticide classes. The susceptibility test results showed that An. gambiae populations in Opeibea were resistant to all the four insecticides (0.05 % Deltamethrin, 4 % DDT, 5 % Malathion and 0.1 % Bendiocarb) tested. The mean adult body size (wing length) of the mosquitoes fed with baking yeast (2.89 ± 0.0072 mm) and (2.89 ± 0.0068 mm) for Kisumu and Opeibea strains respectively was significantly higher (p < 0.001) as compared with that of rabbit pellet (2.84 ± 0.0072 mm) and (2.81 ± 0.0076 mm) for Kisumu and Opeibea strains respectively. However, rabbit pellet had the highest positive impact on larval survivorship and higher pupal weight in a preliminary study, which was evident in the adult response to susceptibility assay. For both Kisumu and Opeibea strains, baking yeast had a non-significant (p > 0.05) lower KDT50 and KDT95 when compared to rabbit pellet for all the insecticides except for Malathion where the reverse was the case. However, for Kisumu, DDT and Deltamethrin there was significant (p < 0.001) difference in the KDT50 and KDT95 for both larval diets. The baking yeast for both Kisumu and Opeibea strains consistently required higher time than its rabbit pellet-fed counterpart in order to produce the same level of knockdown. Fitness and resistance in both Kisumu and Opeibea strains were positively correlated (correlation = 1 and p > 0.05). Rabbit pellets is highly recommended for use in therearing of Anopheles gambiae s.s. larvae in the insectary. The results from this study indicate the importance of larval diet in determining the insecticide resistance status of mosquito vectors. This is very useful in the formulation of future vector control strategies as well as getting a standard larval diet that gives the best fitness for routine monitoring of insecticides resistance.