Effect of Density and Instar of Heliothis zea1 on Parasitization by Hyposoter exiguae 2

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Abstract
The effects of age and density of larvae of Heliothis zea (Boddie) on parasitization by the endoparasitic ichneumonid, Hyposoter 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 ♀ wasp was: 2nd instar ≥ 3rd instar ≥ 1st instar > > 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 weight and longevity of the F 1 adults. Several explanations for the effects of host age on the developmental period of parasitic larvae and the longevity of adult wasps are offered.