Effect of Methamidophos Residue on the Pentatomid Egg Parasitoids Trissolcus basalis and T. utahensis (Hymenoptera: Scelionidae) JANET M. SMILANICK,FRANK G. ZALOM, AND L. E. EHLER Department of Entomology, University of California, Davis, California 95616 Received October 19, 1994; accepted August 15, 1995 Effects of methamidophos residue on adults and immatures of the pentatomid egg parasitoids Trissol- cus basalis (Wollaston) and T. utahensis (Ashmead) were assessed in the field and laboratory. Survival of adult females of both species exposed to field-treated tomato foliage was significantly reduced (ca. 50%) in the presence of 2- and 4-day old residues. Residues of as much as 16 days significantly reduced survival in T. basalis but not in T. utahensis. Emergence of T. basalis from egg masses of Nezara viridula (L.) exposed to the same field treatment was not significantly reduced, but survival of emergent adults was significantly reduced. Adult emergence of either T. basalis or T. utahensis from eggs of Euschistus conspersus Uhler and treated as pupae was not significantly affected, but survival of emergent females and males was significantly reduced for both species. When the parasitoids were treated as larvae, emergence rate was significantly reduced for T. basalis but not for T. utahensis, and survival of emer- gent males and females was significantly reduced for both species. Reproductive capacity of emergent fe- males was not significantly reduced in either species, but sex ratio of the progeny was male-biased for each species. Because postemergence survival of adults was greatly reduced by methamidophos treatment, percent- age emergence of parasitoids from treated eggs is not an adequate measure of ecological selectivity of this insecticide. r 1996 Academic Press, Inc. KEY WORDS: parasitoids, methamidophos; tomato; stink bug; Scelionidae; Trissolcus basalis; Trissolcus utahensis; Euschistus conspersus; Nezara viridula. INTRODUCTION The integration of chemical and biological control is often critical to the success of an integrated pest management (IPM) program for arthropod pests. Thus, over the past 25 years or so, there has been consider- able effort devoted to testing the effects of various chemical insecticides on natural enemies (Jepson, 1989; Croft, 1990; Brown et al., 1992). As part of our efforts to develop an IPM program for both processing and fresh-market tomatoes ( Lycopersicon esculentum Miller) in California, we have been especially concerned with integrating biological and chemical control of stink bugs (Hemiptera: Pentatomidae) because neither tactic is consistently satisfactory when utilized alone. Stink bug feeding causes a discoloration of the fruit upon ripening that renders the fruit unmarketable for either the fresh market or whole-peel processing, and they occasionally transmit Nematospora, a pathogenic yeast that can result in rejection of fruit as ‘‘mold’’ (University of California, 1989). The native stink bug species commonly associated with tomato production in California are consperse stink bug, Euschistus consper- sus Uhler, red-shouldered stink bug, Thyanta pallidovi- rens (Sta ¨ l), and Uhler’s stink bug, Chlorochroa uhleri (Sta ¨ l) (University of California, 1989). Consperse stink bug is the most common species statewide and is of particular importance in the Sacramento Valley, where about one-half of California’s processing tomatoes are grown. Red-shouldered stink bug is found throughout the Central Valley, though seldom in abundance. Uhler’s stink bug is prevalent in the San Joaquin Valley, where about 30% of U.S. fresh market tomatoes and about one-half of California’s processing tomatoes are grown. The exotic southern green stink bug Nezara viridula (L.) was first detected in California in 1986 and occurs in Sacramento Valley tomato fields (Hoffmann et al., 1987a). The importation and release of its egg parasite, Trissolcus basalis (Wollaston), which was initiated in 1986 (Hoffmann et al., 1991), may be an important factor associated with the low population levels of this pest currently observed. This parasitoid had previously been successfully introduced into Australia, New Zea- land, and Hawaii for control of N. viridula (Caltagi- rone, 1981). N. viridula is evidently native to Africa (Hokkanen, 1986), and systematic evidence suggests that T. basalis is also of African origin (Johnson, 1985). We began evaluating egg parasitoids for control of the native stink bugs species in 1991. This involved the mass rearing and release of T. basalis and indigenous parasitoids including Trissolcus utahensis (Ashmead), a scelionid of the western Nearctic region, where its BIOLOGICAL CONTROL 6, 193–201 (1996) ARTICLE NO. 0024 193 1049-9644/96 $18.00 Copyright r 1996 by Academic Press, Inc. All rights of reproduction in any form reserved.