Interactions of a Parasite, Bracon hebetor (Hymenoptera: Braconidae), and a Predator, Xylocoris flavipes Hemiptera: Anthocoridae), with Populations of Tribolium castaneum and Plodia interpunctella

Abstract

A stored-product insect community including a parasite and a predator was evaluated to determine interactions that might exist and the degree of biological control achieved. The insect community was composed of the Indian meal moth Plodia interpunctella (Hubner); the red flour beetle Tribolium castaneum (Herbst); Bracon hebetor, a parasite; and Xylocorisflavipes, a predator, on a substrate of shelled corn. Bracon hebetor was an ineffective parasite of the Indian meal moth. The red flour beetle was opportunistic and increased its population numbers by feeding on parasitized and dead and moribund Indian meal moths. Because of the strong interaction between the Indian meal moth and the red flour beetle, the interactions of the parasite and predator with the hosts were obscured. INTRODUCTION Recently, two insect species with potential as biological control agents have come to the attention of researchers working with postharvest insect pests. The predaceous bug, Xylocorisflavipes (Reuter), preys on most immature stages of many species of postharvest Coleoptera and Lepidoptera (Jay et al., 1968; Press et al., 1975; Arbogast, 1976; LeCato et al., 1977). The parasitic wasp, Bracon hebetor Say, is a natural enemy of the migrating larvae of postharvest pyralid moths (Morrill, 1942). Press et al. (1974a and 1974b) attempted to use X. flavipes and B. hebetor simultaneously to enhance the management of Cadra cautella (Walker) the almond moth, and Plodia interpunctella (Hubner) the Indian meal moth. These studies indicated that X. flavipes fed on the immature siages of the parasite as well as on moth eggs and larvae. Other studies have shown that X. flavipes is effective as a predator of the exposed larvae of stored-product pests, preferring the larger larvae of smaller species and the smaller larvae of larger species and that its predaceous activities are influenced by the size of the interstitial spaces allowing for freedom of movement in the food (habitat of the prey) (LeCato and Davis, 1973; Press et al., 1973; LeCato, 1975; and Press et al., 1978). Thus as postharvest moths are largely surface dwellers and postharvest beetles tend to disperse throughout the depth of a raw agricultural commodity, it may be the predator occupies space other than that of the parasite. The purpose of our study was to determine if these natural enemies of postharvest pests occupy different niches in the presence of their preferred hosts and if they interact. MATERIALS AND METHODS Xylocorisflavipes, Bracon hebetor and Tribolium castaneum (Herbst) the red flour beetle, the host for X. flavipes in this study, were obtained from stock colonies maintained at the Stored-Product Insects Research and Development Laboratory, Savannah, Georgia. Bracon hebetor and X. flavipes were reared on the last instar larvae and eggs of the Indian 1Present address: Agricultural University of Warsaw, 02-776 Warsaw, 02-766 Warsaw wl. Nowoursynowska 166, Poland. 2Research entomologist.