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No evidence of an immune adjustment in response to a parasitoid threat in Lobesia botrana larvae

Vogelweith F, Moret Y, Thiéry D, Delbac L, Moreau J

Abtract

Immune function is a key determinant of an organism’s fitness, and natural insect populations are highly variable for this trait, mainly due to environmental heterogeneity and pathogen diversity. We previously reported a positive correlation between infection prevalence by parasitoids and host immunity in natural populations of the vineyard pest Lobesia botrana. Here, we tested whether this correlation reflects a plastic adjustment of host immunity in response to the local presence of parasites.

To this end, we measured immunity of non-parasitized L. botrana larvae exposed, respectively, to one of the two most common species of parasitoids in vineyards, over 6 days. Larvae were able to sense the parasitoid through visual, chemical, or mechanical cues, but contact larvae-parasitoid were excluded. Contrary to our hypothesis, we found that L. botrana larvae did not increase their immune defenses in the presence of parasitoids, despite their ability to sense a potential threat.

Our results therefore suggest that the positive correlation between infection prevalence by parasitoids and L. botrana immunity among natural populations may result from micro-evolutionary changes resulting from long-term local selection pressures imposed by parasitoids in wild populations rather than plastic adjustments of immunity.

Keywords

Campoplex capitator; Insect immunity; Grapevine moth; Phytomiptera nigrina; Plasticity; Prophylaxis

Journal of Insect Physiology 102, 7–11 doi.org/10.1016/j.jinsphys.2017.08.010