Diet‐mediated immune response to parasitoid attacks on a caterpillar with a broad diet breadth

• Published in: Ecological entomology Vol. 47; no. 4; pp. 636 - 644
• Main Authors: Vyas, Dhaval K., Murphy, Shannon M.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.08.2022; Wiley Subscription Services, Inc
• Subjects: Developmental stages; Diet; dietary generalism; ecoimmunology; fall webworm (Hyphantria cunea); Fitness; Flowers & plants; haemocyte; Herbivores; Hyphantria cunea; Immune response; Immune response (cell-mediated); Immune system; Insects; Larvae; Larval development; Leukocytes (granulocytic); natural enemy; Parasitoids; Plant species; plant–insect interactions; Species; Trophic factors
• ISSN: 0307-6946; 1365-2311
• DOI: 10.1111/een.13148

Bottom‐up (plant) and top‐down (natural enemy) trophic factors can interact to have significant influence on the diet breadth of herbivores. For herbivorous insects that are victim to parasitoid attacks, diet composition can modulate insect immune responses against the parasitoid. However, immune responses are costly and insect herbivores experience a trade‐off between investment in immune defences and other physiological processes. We used a split‐brood laboratory experiment to explore how the diet of the fall webworm (Hyphantria cunea), a species that eats over 400 plant species, affects larval growth and fitness and cellular immune response to attacks from a parasitic wasp. We reared larvae on four different plant diets (apple, alder, chokecherry, cottonwood) and then exposed them to an immune challenge from a parasitoid attack. We found that diet influenced larval development as well as parameters indicative of immune response. Larvae reared on the plant that led to the poorest development also had the fewest granulocytes and the highest odds of containing a parasitoid larva. However, larval growth was not a predictor of immune response. Overall, we show that the bottom‐up effect of diet variability has significant impacts on insect immune response such that larval fitness varies considerably when fed different dietary plant species. Broad diet ranges may offer herbivorous insects the opportunity to exploit a different set of resources depending on the severity of top‐down pressures. Here, we show that this variability in plant quality also has significant impacts on larval immune response. Therion sassacus attacking a fall webworm (Hyphantria cunea) caterpillar. Diet influenced the growth patterns of fall webworm caterpillars as indicated by differential head capsule widths across diets. The occurrence of the parasitic wasp Therion sassacus was greatest in fall webworm caterpillars fed a diet that reduced the caterpillar's granulocytes. We showed diet variability impacted fall webworm immune response against parasitoid attacks.