INHIBITORY EFFECTS OF PARASITISM BY THE GREGARIOUS ENDOPARASITOID COTESIA-CONGREGATA ON HOST TESTICULAR DEVELOPMENT

Cotesia congregata is a gregarious larval endoparasitoid of the tobacc o hornworm, Manduca sexta. Parasitized larvae exhibit a variety of phy siological and developmental aberrations, the most obvious of which is the induction of developmental arrest characterized by the absence of wandering behavior and suppression of pupation. This arrest appears a ttributable to continued maintenance of an elevated titer of juvenile hormone and reduced levels of hemolymph juvenile hormone esterase acti vity. Injection of the wasp's polydnavirus into nonparasitized larvae also causes arrest and the larvae eventually form larval-pupal interme diates instead of normal pupae, indicating the virus may be partially responsible. Aside from causing arrested host development, parasitism also inhibits the normal development and differentiation of testes in male host larvae, so that the testes atrophy instead of growing synchr onously with other larval tissues. Here we report that parasitism has pronounced disruptive cytological effects on the developing reproducti ve organs of male hosts, in addition to causing them to atrophy. Paras itism results in a reduction in testicular volume attributable to a re duction in the number of developing germ cells. Microscopy revealed th at the structural integrity of the sheaths surrounding the testicular follicles also is disrupted, so that the tissues appear grossly abnorm al compared to those of nonparasitized larvae. Intrahemocoelic injecti on of purified C. congregata polydnavirus in combination with venom in to nonparasitized fourth instar larvae, or topical application of 100 mu g of methoprene to fourth instar larvae, also alters sheath integri ty and reduces the numbers of developing germ cells, but not to the sa me degree as the pattern observed in truly parasitized hosts. The occu rrence of cell death in the male gonad was documented using the vital dyes acridine orange and ethidium bromide. (C) 1997 Wiley-Liss, Inc.