Immune response of Lymantria dispar to naturally occurring intracellular pathogens

Although insects lack the adaptive immune system of vertebrates, they do possess a complex innate defense system. Recognition of foreign microbes leads to a series of defense actions including signal proteins and antimicrobial peptides, as well proteins involved in the phenoloxidase cascade that defend against invading pathogens. Although ecologically and physiologically relevant routes of infection are primarily oral ingestion or entry through the tracheal system or cuticle, models of the humoral immune response in insects are typically produced by injection of facultative bacteria or foreign objects into the host. Immune responses are key factors determining the level of susceptibility of hosts to their natural enemies but comparative studies are rare, primarily because hosts or their natural pathogens are not easily available or produced. We chose the European gypsy moth, Lymantria dispar (L.) as our model species because its natural microbial enemies are well studied and available. We used a proteomic approach to study the induction of the immune response of gypsy moth larvae inoculated via oral ingestion to naturally occurring pathogens including the microsporidia Vairimorpha disparis and Endoreticulatus schubergi, nuclear polyhedrosis virus (LdMNPV), cytoplasmic polyhedrosis virus, and the microbial pesticide Bacillus thuringiensis kurstaki. Fourth instar larvae were inoculated and hemolymph was collected at 8, 18, and 36 hours post inoculation. Protein expression and abundance were quantified using 2-D gel electrophoresis with computer-assisted analysis of 2-DE patterns. We compared protein expression among treatments to determine if different pathogens with different host tissue targets induce differential expression of immune proteins.