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

Author
item REED, DARCEY - U OF WASH, PULLMAN, WA
item LOEB, MARCIA
item BECKAGE, NANCY - U OF CALIFORNIA, RIVERSID

Submitted to: BARC Poster Day
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: In this work we investigated the effects of wasp parasites and parasite products in causing degeneration of the gonads of their caterpillar hosts. Insect parasites can kill their hosts and thus aid in decreasing the population of feeding insects, but also can castrate their hosts by causing the gonads to atrophy. Here we showed that the degeneration of testes of tobacco hornworm caterpillars was due to loss of sperm, and also to death of the hormone-producing tissue of the testes. Although minor testicular damage could be inflicted by injecting large quantities of the insect hormones which circulate during parasitization, it was not nearly as severe as the effect of the parasites or the viruses and venom deposited when the wasp lays its eggs in the caterpillar. This information can be used by scientists in studies of the effects of parasitism, and may lead to development of products which chemically castrate insect populations, based on the materials released by the parasites and their virus riders. These substances might be useful to decrease populations of insect pests which reproduce several times in each season.

Technical Abstract: Cotesia congregata is a gregarious larval endoparasitoid of the tobacco hornworm, Manduca sexta. Parasitized larvae cause developmental arrest, characterized by the absence of wandering behavior and suppression of pupation. Arrest appears attributable to maintenance of an elevated titer of juvenile hormone and reduced levels of hemolymph juvenile hormone esterase activity. Injection of the wasp's polydnavirus into nonparasitized larvae also causes developmental arrest. Parasitism also inhibits normal development and differentiation of testes in male host larvae, causing atrophy. Parasitism causes a severe reduction in testicular volume, attributable to a reduction in the number of developing germ cells. The sheaths surrounding the testicular follicles also was disrupted; the tissues appeared grossly abnormal compared to those of nonparasitiized larvae. Intrahemocoelic injection of purified C. congregata polydnavirus, in combination with venom, into nonparasitized fourth instar larvae, or topical application of methoprene to fourth instar larvae, also altered sheath integrity and reduced the numbers of developing germ cells, but not to the same degree as observed in parasitized hosts. The alterations in testicular integrity were accompanied by the appearance of characteristic novel testicular and hemolymph proteins; some endogenous proteins normally found in developing nonparasitized larvae were absent from tissues of parasitized larvae. The occurrence of onset of cell death in the male gonad was documented using the vital dyes acridine orange and ethidium bromide.