Innate immunity: Eggs of Manduca sexta are able to respond to parasitism by Trichogramma evanescens

Abstract

So far, it was unknown whether immune responses of insect eggs are inducible or suppressed by parasitism. We investigated whether transcription of immune related genes in eggs of Manduca sexta changed in response to parasitism by Trichogramma evanescens. First, using DDRT-PCR, several cDNA elements known to represent immune related M. sexta genes inducible by bacterial challenge were isolated from eggs. In addition, two novel cDNAs were found: (a) immulectin-V ( IML-V) suggested to be involved in recognition of foreign bodies, and (b) a new like-moricin protein with possible antimicrobial effects ( L-Mor). Quantitative real time RT-PCR analyses revealed enhanced transcription in parasitized eggs compared to unparasitized ones for IML-V, prophenoloxidase ( ProPO), prophenoloxidase activating protease I ( PAP I), and proparalytic peptide ( ProPP). No significant differences between parasitized and unparasitized eggs were detected for sequences encoding the antimicrobial peptides L-Mor, leureptin Leu, and attacin II Att II. Transcript levels of other antibacterial peptides were suppressed after parasitization for 3 d (cecropin 6, Cec 6) and 2 d (gloverin, Glov). While nearly 100% of the Manduca eggs contained Trichogramma specimens 1 d after exposure to parasitoids, only 64% of the host eggs harbored parasitoid larvae 4 d after parasitization. Our data demonstrate that the immune system of Manduca eggs shows differentiated responses to parasitization and suggest that insect eggs can defend against parasitization.