Understanding the ability of parasitoid insects to succeed in new host populations is a relevant question for biological control and adaptive mechanisms. Cotesia typhae is an African parasitoid specialized on the moth Sesamiae nonagrioides, also called the Mediterranean corn borer. Two Kenyan strains of C. typhae differ in their virulence against a new host population from France. We explored behavioral and physiological hypotheses about this differentiation. Cotesia genus belongs to a group of Hymenoptera in which females inject a domesticated virus in their host to overcome its resistance. Since viral particles are injected along with eggs and since the strain with the higher virulence injects more eggs, we hypothesized that virulence could be explained by the quantity 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 quantities of eggs or viral segments, indicating that virulence differentiation is explained by other causes. The virulence against the respective natural hosts of the two C. typhae strains was also measured, and results suggest that local adaptation to a more resistant natural host may explain the pre-adaptation of one strain to the new host population. We also identified a differentiation of oviposition strategy and subsequent offspring number between the parasitoid strains, which is important in a biocontrol perspective.

中文翻译：

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产卵行为，毒力和局部适应在寄生虫在新宿主中繁殖的机会中的作用。

了解寄生虫昆虫在新的宿主种群中成功的能力是生物学控制和适应机制的一个相关问题。斑疹伤寒（Cotesia typhae）是一种非洲寄生虫，专门用于蛾芝麻（Sesamiae nonagrioides），也被称为地中海玉米bore。肯尼亚的两种伤寒梭菌菌株对来自法国的新寄主种群的毒力不同。我们探讨了有关这种分化的行为和生理假设。Cotesia属属于膜翅目，其中雌性向宿主注射驯养的病毒以克服其抗性。由于病毒颗粒是与卵一起注射的，并且由于毒力较高的菌株注射了更多的卵，因此我们假设毒力可以通过注射的病毒数量来解释。为了检验这个假设，我们测量了几个寄生虫卵中每个寄生虫菌株的卵和病毒颗粒（通过病毒DNA片段估计）的注射量，以改变这些量。出乎意料的是，结果表明，针对法国寄主的毒力与卵或病毒片段的注射量无关，这表明毒力分化是由其他原因引起的。还测量了针对两种伤寒梭菌菌株各自天然宿主的毒力，结果表明，对更具抵抗力的天然宿主的局部适应性可能解释了一种菌株对新宿主种群的预先适应。我们还确定了产卵策略与后代寄生虫菌株之间的后代数量的差异，这在生物防治方面很重要。