Assessment of the developmental success of Anopheles coluzzii larvae under different nutrient regimes: effects of diet quality, food amount and larval density

In a context of increasing resistance of both vectors toward main classes of insecticides used in public health and parasites toward anti-malarial drugs, development of new and complementary molecules or control approaches is fundamental to achieve the objective of controlling or even eliminating malaria. Concerning vector control, the sterile insect technique and other genetic control approaches are among promising complementary tools in an integrated management strategy for malaria control. These approaches rely not only on a good understanding of vector biology (especially during larval stages), but also on the availability of adequate supplies and protocols for efficient mosquito rearing. The aim of this study was to assess the factors impacting the life history of Anopheles coluzzii mosquitoes at the larval stage, in the context of genetic and sterile insect approaches to control malaria vectors. The effect of different larval diets and larval rearing densities on the development of An. coluzzii were evaluated in the laboratory. Emergence rate (ER), pre-imaginal developmental time (DT) and adult wing length (WL) were measured under different food regimes. Four diets were tested among which three were provided by the Insect Pest Control Laboratory (IPCL) of the FAO/IAEA Joint division. Data showed significant differences in the quality of the different diets and suggested a negative density dependence in all three life history parameters measured under tested rearing conditions. ER and WL increased with food availability, but decreased with increasing larval density. Conversely DT was shortened with increasing food availability but increased with larval density. These data demonstrates intraspecific larval competition modulated by food amount and space availability. Of the four diets tested, the one made of a mix of tuna meal, bovine liver powder, brewer's yeast, squid liver powder and vitamin mix (diet 2) yielded the best results as it produced a good balance between ER, DT and WL. Food availability for optimal development (highest survival at shortest time) was in the range of 180-400 µg/larvae/day for the three diets provided by the IPCL. There is an interaction between diet type, diet concentration and larval density. Best results in terms of optimal larvae development parameters happen when moderately high values of those three variables are observed.