  Cotesia typhae is an eastern African endoparasitoid braconid wasp that
targets the larval stage of the lepidopteran stem borer, Sesamia nonagrioides,
a maize crop pest in Europe. The French host population is partially resistant
to the Makindu strain of the wasp, allowing its development in only 40% of the
cases. Resistant larvae can encapsulate the parasitoid and survive the
infection. This interaction provides a very interesting frame for investigating
the impact of parasitism on host cellular resistance. We characterized the
parasitoid ovolarval development in a permissive host and studied the
encapsulation process in a resistant host by dissection and histological
sectioning compared to that of inert chromatography beads. We measured the
total hemocyte count in parasitized and bead-injected larvae over time to
monitor the magnitude of the immune reaction. Our results show that parasitism
of resistant hosts delayed encapsulation but did not affect immune abilities
towards inert beads. Moreover, while bead injection increased total hemocyte
count, it remained constant in resistant and permissive larvae. We conclude
that while Cotesia spp virulence factors are known to impair the host immune
system, our results suggest that passive evasion could also occur.
