318 Gill & Raupp: Entomopathogenic Nematodes USING ENTOMOPATHOGENIC NEMATODES AND CONVENTIONAL AND BIORATIONAL PESTICIDES FOR CONTROLLING BAGWORM by Stanton A. Gill and Michael J. Raupp Abstract. Formulated microbial biological control agents such as entomopathogenic nematodes and Bacillus thuringiensis have potential as alternatives to conventional control pesticides for arborists offering IPM and Plant Health Care services. However, few data compare the efficacy of these materials with other pesticides under field conditions. This study demonstrates that in some cases microbial biological control agents are effective in controlling bagworms on ever- greens. Bagworm, Thyridopteryxephemeraeformis, an indigenous, defoliator damage a wide range of evergreen and deciduous plants. Bagworm feeds on over 128 species of plants (2), but does the most serious damage to evergreens such as arborvitae, Leyland cypress, spruce, pines, and junipers. Even relatively small amounts of defo- liation cause nurserymen severe economic loss. Sadof and Raupp (11) reported that as little as 4% defoliation by bagworms significantly reduced the value of arborvitae in retail nurseries. Control of bagworms is most effective when synthetic or bacterial insecticides are applied to young larvae (7,8). Improved timing of insecticide applications can be obtained using heat accu- mulation models to predict emergence of bagworm (9). Unfortunately, arborists and nurserymen of- ten overlook small, early instar bagworms and pesticide applications are made to late instar larvae. Late season control using recommended dosages of synthetic carbamate and organo- phosphate insecticides produced mortality per- centages of less than 28 percent (8). Public concern about adverse effects of chemical insecticides has created an environ- ment in which biological, botanical, less acutely toxic insecticides are regarded as promising al- ternatives to some older material with higher toxicities. The purpose of this study was to field test several biological, botanical, and newer syn- thetic insecticides for efficacious control of middle and late instar bagworms. A major group of biological agents that we were interested in evaluating were entomopathogenic nematodes. The entomo- pathogenic nematode, Steinernema carpocapsae, has been reported to infect several Lepidopterous larvae including spruce budmoth, Zeiraphera canadensis(4), Mexican rice borer, Eoreumaloftini (10), peachtree borer, Synanthedon exitiosa (5), and dogwood borer, Synanthedon scitula (3). In a petri dish bioassay, steinernematid and heterorhabditid nematodes gave high mortality, over 80%, to caterpillars of the giant looper, Boarmia selenaria (6). Based on these previous studies we included entomopathogenic nematodes of Steinernema species in our field trials. We were particularly interested in the effectiveness of several tactics to control mid- season to late season bagworm larvae since there are relatively few effective biological or biorational control op- tions for these stages. Bacillus thuringiensis strains are effective in controlling early instars of lepidopterous larvae but have generally not performed as well on later instar stages (1). In the second year of this study we evaluated a wettable powder formulation of Bacillus thuringiensis var. kurstaki. Materials and Methods The first field trial was conducted in the summer of 1992. Forty four Arborvitae 'Emerald Green', grown in 1 gallon containers and irrigated with a trickle system, were infested with 10 bagworm larvae. Larvae were allowed to feed for 7 days before pesticides were applied. Larval densities were adjusted to 10 per plant before the treatments were started. The field trial was a complete, ran-