BIOLOGICAL CONTROLÑMICROBIALS Survey of Entomopathogenic Nematodes and Fungi Endemic to Pecan Orchards of the Southeastern United States and Their Virulence to the Pecan Weevil (Coleoptera: Curculionidae) DAVID I. SHAPIRO-ILAN, 1 WAYNE A. GARDNER, 2 JAMES R. FUXA, 3 BRUCE W. WOOD, 1 KHUONG B. NGUYEN, 4 BYRON J. ADAMS, 4 RICHARD A. HUMBER, 5 AND MICHAEL J. HALL 6 Environ. Entomol. 32(1): 187Ð195 (2003) ABSTRACT The pecan weevil, Curculio caryae (Horn), is a major pest of pecans in the Southeastern United States. Entomopathogenic nematodes and fungi are potential alternatives to chemical insec- ticides for C. caryae control. Our objective was to survey pecan orchards in the southeastern United States for entomopathogenic nematodes and fungi and determine the virulence of the new isolates to C. caryae larvae. Soil was collected from 105 sites in 21 orchards in Arkansas, Georgia, Louisiana, and Mississippi. Entomopathogens were isolated by exposing soil to C. caryae and greater wax moth larvae, Galleria mellonella, (L.). We isolated entomopathogenic fungi and nematodes from 16 and 6 of the 21 orchards surveyed, respectively. The entomopathogenic fungi included Beauveria bassiana (Balsamo) Vuillemin and Metarhizium anisopliae (Metschnikoff) Sorokin, and nematodes included Heterorhabditis bacteriophora Poinar, Steinernema carpocapsae (Weiser), Steinernema glaseri (Steiner), and Steinernema rarum (Doucet). This is the Þrst report of Steinernema rarum in the United States. Soil characteristics in orchards were analyzed for pH, organic matter, and nutrients; we detected a negative relationship between fungal occurrence and manganese levels in soil and a positive relationship between M. anisopliae occurrence and calcium or magnesium levels. In laboratory assays, virulence of 15 nematode and 22 fungal isolates to C. caryae larvae was tested in small plastic cups containing soil. Results indicated poor susceptibility of the C. caryae larvae to entomopathogenic nematodes. Several fungal isolates that caused signiÞcantly higher mortality in C. caryae larvae than other strains (including a commercial strain of B. bassiana) should be investigated further as potential control agents of C. caryae. KEY WORDS Beauveria bassiana, Curculio caryae, Heterorhabditis, Metarhizium anisopliae, pecan, Steinernema THE PECAN WEEVIL, Curculio caryae (Horn) is a major pest of pecans throughout the southeastern United States (Mizell 1985). The insects have a 2 or 3 yr life-cycle (Harris 1985). Adults emerge from soil in late JulyÐAugust, and then feed on and oviposit in the nuts (Harris 1985). Larvae develop within the nut and fourth instars drop to the soil where they burrow to a depth of 8 Ð25 cm. The following year 90% of the larvae pupate and spend the next 9 mo in the soil as adults (Harris 1985). The remaining 10% of the pop- ulation spend 2 yr in the soil as larvae emerging as adults in the third year (Harris 1985). Control recommendations for the pecan weevil cur- rently consist solely of applications of chemical insec- ticides (e.g., carbaryl) to the canopy to suppress adults (Ellis et al. 2000). Late season applications of carbaryl, however, can result in resurgence of damaging aphid populations, because carbaryl suppresses certain aphid predators (e.g., coccinellids) but does not sup- press the pecan aphid complex (Dutcher and Payne 1985). As a result of the problems associated with aphid resurgence, as well as other environmental and regulatory concerns, research on developing alterna- tive control strategies is warranted. Microbial control (use of entomopathogenic virus, bacteria, protozoa, fungi, or nematodes) is one of the potential alterna- tives to chemical insecticides. Among entomopathogens of C. caryae studied thus far, nematodes (genera Heterorhabditis and Stein- ernema) and certain hyphomycete fungi i.e., Beauveria bassiana (Balsamo) Vuillemin and Metarhizium aniso- This article reports the results of research only. Mention of a proprietary product name does not imply USDAÕs approval of the product to the exclusion of others that may be suitable. 1 USDA-ARS, Southeastern Fruit and Nut Research Laboratory, 21 Dunbar Road, Byron, GA 31008. 2 Department of Entomology, University of Georgia, GrifÞn, GA 30223. 3 Department of Entomology, Louisiana Agricultural Experiment Station, Louisiana State University Agricultural Center, Baton Rouge, LA 70803. 4 Department of Entomology and Nematology, University of Flor- ida, Gainesville, FL 32611. 5 USDAÐARS, US Plant, Soil and Nutrition Laboratory, Ithaca, NY 14853. 6 LSU Agricultural Center, Shreveport, LA 71135.