Interference of Steinernema carpocapsae (Nematoda : Steinernematidae) withCardiochiles diaphaniae (Hymenoptera : Braconidae), a parasitoid of melonworm and picklewormm (Lepidoptera : Pyralidae)

Entomopathogenic nematodes are generally considered beneficial organisms. H owever, they can affect beneficial insects such as parasitoids. The infecti vity of Steinernema carpocapsae (Mexican strain) to Cardiochiles diaphaniae Marsh, a solitary internal wasp parasitoid of melonworm, Diaphania hyalina ta (L.). and pickleworm, D. nitidalis (Stoll), was determined under laborat ory conditions. S. carpocapsae induced 100% infection in melonworm hosts du ring exposure periods of 6, 24, 36, and 48 h. The number of nematodes penet rating the host was proportional to the length of exposure period, and the emergence rate of wasp parasitoids was inversely proportional to exposure t ime. Though only 0-10% of immature C. diaphaniae were parasitized by nemato des within hosts, newly emerged and, to a lesser degree, cocoon-spinning wa sp larvae were readily infected by nematodes. In contrast, pupae of C. diap ahaniae in completely formed cocoons were resistant to infection, S. carpoc apsae adversely affected C. diaphaniae developing in melonworm principally by causing the premature death of the host before the wasp could complete i ts development. If the wasp larvae were 6 or 7 d old when the melonworm hos t was parasitized by nematodes, then all the wasp larvae died. However, if the wasp larvae were 8 d old when nematodes parasitized the melonworm, then 39-92% of the melonworms successfully produced wasp parasitoids. Many wasp larvae that emerged from nematode-parasitized melonworms did not form coco ons, and died within 24 h of emergence. However, only a small proportion of the larvae contained nematodes as determined by dissection. The percentage of infected parasitoids and the proportion of emerged parasitoid larvae dy ing increased as the exposure time to nematodes increased. Overall, S. carp ocapsae nematodes are somewhat compatible with parasitoids because they do not kill all parasitoids, and the pupal stage is resistant to infection. Ho wever, the direct and indirect mortality of wasps caused by nematodes could result in some interference with biological suppression.