The Nematode Neoaplectana carpocapsae Weiser 1 and its Effect on Selected Ichneumonid and Braconid Parasites 3

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Abstract
The exposure of larvae of the armyworm, Pseudaletia unipuncta (Haworth), containing the ichneumonid parasites, Hyposoter exiguae (Viereck), to the nematode, Neoaplectana carpocapsae Weiser, adversely affected the parasites. When armyworms containing 8-day-old H. exiguae fed on alfalfa leaves treated until runoff with a suspension of 500 or 1000 nematodes/ml, the majority of the parasites which farmed cocoons were infected with the nematode. Only 34 and 14%, respectively, of these cocoons yielded adult parasites in contrast to 93% of the cocoons in the control. Pupae of H. exiguae, Apanteles medicaginis Muesebeck and Chelonus sp. in intact cocoons were resistant to infection by N. carpocapsae while parasite pupae in intentionally punctured cocoons had infection rates between 56 and 100%. Scanning electron microscope observations on cocoon structure indicated that the resistance of these parasites to infection in intact cocoons was due to the presence of a pore-free layer of silk within the cocoon which acted as a mechanical barrier to the nematode. The impact of other microbial agents and N. carpocapsae on insect parasites is discussed.