Possible role of teratocytes of the gregarious parasitoid, Cotesia ( = Apanteles) glomerata in the suppression of phenoloxidase activity in the larval host, Pieris rapae crucivora

Abstract

AbstractA number of theories have been proposed concerning the means of avoiding host's encapsulation by parasitoid larvae. Our available data, however, are still not sufficient to explain the encapsulation–inhibiting effects of the gregarious endoparasitoid Cotesia ( = Apanteles) glomerata on its larval host, Pieris rapae crucivora. This study was prompted initially by the observation that the hemolymph obtained from parasitized fifth instar larvae failed to melanize. Phenoloxidase (PO) activity in the hemolymph of parasitized and nonparasitized Pieris larvae was determined spectrophotometrically by measuring the degree of dopachrome formation in diluted hemolymph with Ca2+‐free saline. PO activity was inhibited in host hemolymph containing young‐phase teratocytes, 1.5‐day‐old cells 40–45 μm in diameter, but not in that containing old‐phase teratocytes, 7‐day‐old cells 90–100 μm in diameter. Similar results with young‐phase teratocytes were obtained in vitro. Our data suggest that young teratocytes may suppress PO activity in the host hemolymph and interfere with encapsulation of C. glomerata larvae by the host. However, the mechanism of PO suppression remains to be determined.