Host regulation by the aphid parasitoid Aphidius ervi: the role of teratocytes

The biochemical profile and metabolism of Acyrthosiphon pisum (Harris) (Hom optera, Aphididae) are markedly altered and redirected in response to paras itization by the endophagous braconid Aphidius ervi Haliday (Hymenoptera, B raconidae). In the present study, the role played in the host regulation pr ocess by teratocytes, cells deriving from the dissociation of the embryonic membrane of the parasitoid, is taken into consideration. The protein synth esis activity of these cells of embryonic origin is analysed in vitro and a n essential characterization of those proteins de novo synthesized and rele ased in the incubation medium is provided. Teratocytes, obtained by dissect ing parasitized host aphids, 3, 4 and 5 days after parasitoid oviposition, were incubated in vitro and, at the end of the incubation period, were sepa rated from the medium for SDS-PAGE analysis of both cellular and secreted p roteins. Various cellular proteins were more abundant as the time between p arasitization and teratocyte collection increased. Furthermore, two protein s, showing an approximate molecular mass of 15 kD (p15) and 45 kD (p45) res pectively, were abundantly secreted in the incubation medium by 5 day-old t eratocytes. Incubations in presence of S-35 radiolabelled amino acids indic ated that p15 and p45 are both synthesized by A. ervi teratocytes. The amin o acid composition of these two proteins was similar to that reported for o ther insect proteins with a demonstrated nutritional function. The p45 prot ein was found to be glycosylated. A tentative physiological model describin g the host regulation role played by different parasitoid-derived factors i s proposed.