Immune assay data for Lycaeides melissa larvae reared on different host plants and with/without egg microbes

1.     Maternally transmitted
microbes are ubiquitous. In insects, maternal microbes can play a role in
mediating the insect immune response. Less is known about how
ecological factors, such as resource use, interact with maternal microbes
to affect immunity. 
2.     In the context of a
recent colonization of a novel host plant by the Melissa blue butterfly
(Lycaeides melissa), we investigated the interaction between host plant
use and vertically transmitted, extracellular egg-associated microbes in
determining the strength of the insect immune response. 
3.     We reared larvae on
two different host plant species: a native host Astragalus
canadensis and a novel host Medicago sativa.
Egg-associated microbes were removed through a series of antimicrobial egg
washes prior to hatching. Immune response was measured through three
assays: standing phenoloxidase (PO), total PO, and melanization. 
4.     We detected strong
effects of microbial removal. Egg washing resulted in larvae with an
increased immune response as measured by total PO- contrary to reports
from other taxa. The effect of washing was especially strong for larvae
consuming the native host plant.   
5.     This result may
explain why consumption of the egg casing is not a universal behaviour in
insects, due to negative effects on larval immunity.