Impact of Agricultural Insecticides in the Vertical Transmission of the Tolerance among Anopheles gambiae s.s over Several Generations in Laboratory Conditions

Abstract

Background: The present work aimed to highlight process of transmission of tolerance to insecticides in An. gambiae population over several generations. Methodology: The experiment was carried out at the laboratory with the strain of An. gambiae that was continuously raised under laboratory conditions for more than five years. The insecticides used during this study belong to three families: methyl-parathion (carbamates), dimethoate (organophosphate), and cypermethrin (pyrethroids). For each insecticide we chose the concentration of insecticide able to exert a selective pressure on An. gambiae without inducing a total mortality. The experiment was done through 12 consecutive generations of An. gambiae s.s. the Endpoints measured: the duration of larval development, larval mortality, and the size of adults. Results: For cypermethrin (pyrethroid) and methyl-parathion (carbamates), the development duration of the larval phase as well as larval mortality decreases significantly from the 7th generation onwards. In the other hand, the size of the adults increases significantly as early as the 5th generation for females especially for cypermethrin and the 7th generation for males. However, with dimethoate, the duration of the larval phase did not vary significantly over the generations. A decrease in larval mortality was noted from the 8th generation but it remained too high. Adult size also increased significantly from the 8th generation onward in both the two genera. This work showed the improvement over generations of certain biological indicators of the resistance. Thus, Conclusion: we can state that resistance appears fairly early in An. gambiae s.s., especially for insecticides that are effective at low doses, such as cypermethrin and methyl-parathion