Biological Control 35 (2005) 163–171 www.elsevier.com/locate/ybcon 1049-9644/$ - see front matter  2005 Elsevier Inc. All rights reserved. doi:10.1016/j.biocontrol.2005.06.011 Evaluation of novel fungal and nematode isolates for control of Conotrachelus nenuphar (Coleoptera: Curculionidae) larvae Diane G. Alston a,¤ , Drauzio E.N. Rangel a , Lawrence A. Lacey b , Hernani G. Golez a,c , Jeong Jun Kim a,d , Donald W. Roberts a a Department of Biology, Utah State University, Logan, UT 84322-5305, USA b Yakima Agricultural Research Laboratory, USDA-ARS, Wapato,WA 98951, USA c Bureau of Plant Industry, National Mango Research and Development Center, Jordan, Guimaras 5045, Philippines d National Institute of Agricultural Science and Technology, RDA, Suwon 441-707, Republic of Korea Received 23 March 2005; accepted 26 June 2005 Available online 22 August 2005 Abstract The primary objective was to identify potential nematode and fungus pathogens for control of plum curculio (Conotrachelus nenuphar) larvae. Initial bioassays were conducted in the laboratory. Seventeen isolates (13 wild-types and four color mutants) of the entomopathogenic fungus Metarhizium anisopliae var. anisopliae were screened. Seven of the isolates were highly virulent for plum curculio larvae (LT 50 D 4.0–5.4 days at a concentration of 10 7 conidia ml ¡1 ). Of these isolates, four were color mutants induced by UV-B irradiation exposure (DWR 180, 145, 142, and 62), and three of these showed signiWcantly higher virulence than their parental wild-types (ARSEF 2575 and 23). The most virulent wild-type was the isolate ARSEF 1187. Surprisingly, higher virulence was not correlated with higher conidial adhesion to the cuticle of plum curculio larvae. A Utah-collected isolate of Heterorhabditis bacterio- phora was as eVective as a commercial strain of Steinernema feltiae in killing plum curculio larvae in laboratory bioassays. Larval mortality ranged from 21 to 89% at inoculum concentrations of 0.125 to 4.0 £ 10 6 infective juveniles (IJs) per m ¡2 . A diapausing (northern) population of plum curculio was less susceptible to S. feltiae (LC 50 D 8.6 £ 10 5 IJs m ¡2 ) than a non-diapausing (southern) population (LC 50 D 3.6 £ 10 5 IJs m ¡2 ). A time delay in adding plum curculio larvae to sterilized soil treated with S. feltiae signiWcantly reduced insect mortality after 2 days and reduced mortality below 50% after a delay of 7 days. In Weld tests, S. feltiae killed 22–39% of northern plum curculio larvae at concentrations of 0.5–2.0 £ 10 6 IJs m ¡2 .  2005 Elsevier Inc. All rights reserved. Keywords: Biological control; Entomopathogens; Heterorhabditis bacteriophora; Irradiation; Metarhizium anisopliae; Mutation; Plum curculio; Steinernema feltiae; Virulence 1. Introduction The plum curculio, Conotrachelus nenuphar (Herbst), is a native pest of rosaceous fruits in eastern North America (Armstrong, 1958). Since about 1980, an iso- lated population has been conWrmed in Box Elder County in northern Utah, USA (D.G.A., unpublished data). The primary infested sites are fruit trees in home yards and wild plum thickets. Development of eYca- cious biological controls is a priority for suppressing plum curculio densities in non-orchard sites, where con- ventional orchard practices [e.g., chemicals, crop habitat manipulations (Racette et al., 1992)] are prohibitive or impractical. During summer, fourth-instar larvae are vulnerable to entomopathogens as they exit fruit and burrow into the soil; adults are susceptible upon emer- gence from pupae in the soil (Armstrong, 1958). In the spring, adults may be exposed to entomopathogens in the soil as they walk to host trees from over wintering * Corresponding author. Fax: +1 435 797 1575. E-mail address: dianea@biology.usu.edu (D.G. Alston).