Submitted to: Journal of Entomological Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/6/2001
Publication Date: 8/1/2002
Citation: N/A Interpretive Summary: The fall armyworm (FAW) can be one of the most devastating pests of sweet corn and field corn (maize), forage crops and sod. Because of pesticide safety and control costs concerns, an integrated pest management (IPM) approach including use of natural enemies is under investigation. Natural levels of biological control do not keep FAW populations under economic levels, and efforts to augment, conserve and/or manipulate FAW natural enemies have not been adequate. By ensuring a supply of supplementary foods or alternative hosts, natural enemy populations may build up earlier in the season for availability when FAW populations increase. We observed that lambsquarters host a variety of larvae. Scientists at the Center for Medical, Agricultural and Veterinary Entomology, Gainesville, FL, investigated the species composition and abundance of noctuid larvae and their natural enemies on lambsquarters in a maize field to evaluate its potential as a nursery crop for enhancement of FAW biological control. Lambsquarters were sampled weekly for five weeks. In the laboratory, plants were inspected for larvae and beneficials. Noctuid larvae were dissected to determine levels of parasitism and species of parasitoid. High numbers of southern armyworm, a species which is not a serious pest of maize, were present in the lambsquarters, whereas very few FAW were found in these weeds. The beet armyworm and the cabbage looper also were found in moderate numbers. High levels of parasitism by generalist parasitoids occurred in all of the noctuids sampled, averaging between 35-40% for all species combined. These data indicate that lambsquarters in the maize agroecosystem may act as a refuge for parasitoids and predators, potentially providing a reservoir of natural enemies for enhanced biological control of FAW.
Technical Abstract: Lambsquarters (Chenopodium album) (L.) located along irrigation ditches in a north Florida maize field were sampled weekly for five weeks to determine the species composition and abundance of noctuid larvae and their natural enemies. High numbers of southern armyworm (Spodoptera eridania (Cramer)), a minor pest of maize, was present in lambsquarters (Chenopodium malbum)(L.), whereas few fall armyworms (Spodoptera frugiperda (J. E. Smith)), a serious pest of maize, were found in these weeds. Two other noctuids, the beet armyworm (Spodoptera exigua (Hubner)), and the cabbage looper (Trichoplusia ni (Hubner)) were present in moderate numbers. High levels of parasitism by generalist parasitoids, averaging between 35 - 40 % for all species combined, occurred in all of the noctuid larvae that were sampled in the first three weeks of the study while larval densities were high. The dominant parasitoid was Cotesia marginiventris (Cresson) (Hymenoptera: Braconidae). Other parasitoid species present in low number were Meteorus autographae Muesebeck and Chetogena scutellaris (Wulp). In addition, many predators (predominantly Orius insidiosus (Say)) were present on the lambsquarters throughout the sampling period. These data indicate that lambsquarters in the maize agroecosystem may act as a refuge for parasitoids and predators, potentially providing a reservoir of natural enemies for enhanced biological control of the fall armyworm.