Role of egg-laying behavior, virulence and local adaptation in a parasitoid’s chances of reproducing in a new host

Understanding the ability of parasitoid insects to succeed in new host populations is a relevant question forbiological control and adaptive mechanisms.Cotesia typhaeis an African parasitoid specialized on the mothSesamiae nonagrioides, also called the Mediterranean corn borer. Two Kenyan strains ofC. typhaediffer in theirvirulence against a new host population from France. We explored behavioral and physiological hypothesesabout this differentiation.Cotesiagenus belongs to a group of Hymenoptera in which females inject a domes-ticated virus in their host to overcome its resistance. Since viral particles are injected along with eggs and sincethe strain with the higher virulence injects more eggs, we hypothesized that virulence could be explained by thequantity of virus injected. To test this assumption, we measured the injected quantities of eggs and viral particles(estimated by viral DNA segments) of each parasitoid strain along several ovipositions, to vary these quantities.Unexpectedly, results showed that virulence against the French host was not correlated to the injected quantitiesof eggs or viral segments, indicating that virulence differentiation is explained by other causes. The virulenceagainst the respective natural hosts of the twoC. typhaestrains was also measured, and results suggest that localadaptation to a more resistant natural host may explain the pre-adaptation of one strain to the new host po-pulation. We also identified a differentiation of oviposition strategy and subsequent offspring number betweenthe parasitoid strains, which is important in a biocontrol perspective.