Interaction of Bracon hebetor (Hymenoptera: Braconidae) and Trichogramma pretiosum (Hymenoptera: Trichogrammatidae) in Suppressing Stored-Product Moth Populations in Small Inshell{middle dot}Peanut Storages

Abstract

Biologicalcontrol tests in small inshell peanut storages indicated that the release of Bracon hebetor Say as a parasite of moth larvae and Trichogramma pretiosum Riley as a moth egg parasite have considerable potential for suppression of stored-product moth populations. Population suppression of the Indianmeal moth, Plodia interpunctella (Hiibner), but not of the almond moth, Cadra cautella (Walker), was dependent on the species of parasite released. Population suppression of Indianmeal moth over the storage season was 37.3% of the check treatment for T. pretiosum alone, 66.1% for B. hebe tor alone, but 84.3% when parasites were used in combination. For the much more abundant almond moth, reductions averaged 96.7, 97.3, and 98.0% for the three treatments, respectively. Larval feeding damage to peanut kernels was reduced to ~ 1.12% by all three parasite treatments as compared with 15.84% in the untreated checks. Thus, B. hebetor and Trichogramma spp. may be useful as parts of an integrated pest control program for lepidopteran pests of stored inshell peanuts. KEY WORDS Insecta, biological control, stored-product pests, parasite IN 1984, GEORGIA produced >2.1 billion pounds of peanuts, accounting for ~49% of total U.S. production (USDA 1985). Peanuts may be stored in-shell for up to 1 yr, and during the first 3-4 mo the Indianmeal moth, Plodia interpunctella (Hiib-ner), and the almond moth, Cadra cautella (Walk-er), are the predominant pests present (Womack 1984). Populations of these moths can increase very rapidly on peanuts (Hagstrum 1984) and feeding damage caused by moth larvae significantly decreases the quality and value of stored peanuts. Insecticides and fumigants have been used routinely by warehousemen for control of these two moth species. Furthermore, because of this long-term use, these two species have become very resistant to the commonly used insecticides (Zettler et al. 1973, Beeman & Schmidt 1982, Zettler 1982, Arthur et al. 1988). Thus, there is a critical need for the development of an integrated pest management approach for the control of pests in stored inshell peanuts. There is renewed interest in biological control research in general and new appreciation for the possibilities of using biological control for control of storage pests (Arbogast 1984). Several small scale biological control attempts aimed at suppression of either the Indianmeal moth or the almond moth have recently been completed. Press et al. (1982) showed that Bracon hebetor Say reduced by 97% the number of almond moth adults that emerged from food debris in a nearly empty room, and Cline et at. (1984) reported that B. hebetor greatly reduced the number of small commodity-filled bags infested by residual almond moth populations and also the number of moth larvae per bag. Keever et al. (1986) reported on a study where B. hebetor and the warehouse pirate bug, Xylocoris flavipes (Reuter), were released in a partially filled peanut warehouse to control stored-product moth populations. This combination treatment reduced moth populations 54-83%. Brower (1988) released Trich-ogramma pretiosum Riley into small inshell peanut storages and significantly reduced populations of the Indianmeal moth and the almond moth. T. pretiosum attacks eggs of stored-product moths (Brower 1983), but any eggs that escape parasitiza-tion may live to become reproducing adults, whereas B. hebetor attacks larvae of both moth species (Keever et al. 1985). Thus, we combined these two complementary parasites for the biological control of these moths, hoping to reduce moth populations faster and more significantly. Here we report the results of a small inshell peanut warehouse test to determine moth population suppression when either parasite was used alone or when the two were used in combination. Materials and Methods Small inshell peanut storages were established in four 25-m 3 empty metal buildings (2.5 m by 5 m