EFFECT OF DENSITY AND INSTAR OF HELIOTHIS-ZEA (LEPIDOPTERA, NOCTUIDAE) ON PARASITIZATION BY HYPOSOTER-EXIGUAE (HYMENOPTERA, ICHNEUMONIDAE)

The effects of age and density of larvae of H. zea (Boddie) on parasitization by the endoparasitic ichneumonid, H. exiguae, (Viereck) were assessed in the laboratory. The instar-ranking of % parasitization of H. zea (highest to lowest) after a 24 h exposure to one .female. wasp was: 2nd instar .gtoreq. 3rd instar .gtoreq. 1st instar .mchgt. 4th instar. Fifth-instar H. zea were not parasitized. For 3rd and 4th instar H. zea % parasitization declined as density of hosts increased. The % parasitization of either 1st- or 2nd-instar hosts was not affected by increases in density of the host (up to 50 larvae/wasp). Parasitization of older hosts resulted in a shorter larval period of the parasite and an increase in wt and longevity of the F1 adults. Explantations for the effects of host age on the developmental period of parasitic larvae and the longevity of adult wasps are offered.