Effect of insect cadaver desiccation and soil water potential during rehydration on entomopathogenic nematode (Rhabditida: Steinernematidae and Heterorhabditidae) production and virulence K.O. Spence ⇑ , G.N. Stevens 1 , H. Arimoto, J. Ruiz-Vega 2 , H.K. Kaya, E.E. Lewis Department of Nematology, University of California, Davis, CA 95616, United States article info Article history: Received 29 June 2010 Accepted 27 October 2010 Available online 1 November 2010 Keywords: Heterorhabditis Steinernema Soil insects Cadaver Anhydrobiosis Biological control abstract We examined the influence of insect cadaver desiccation on the virulence and production of entomopath- ogenic nematodes (EPNs), common natural enemies of many soil-dwelling insects. EPNs are often used in biological control, and we investigated the feasibility of applying EPNs within desiccated insect cadavers. Desiccation studies were conducted using the factitious host, Galleria mellonella (Lepidoptera: Pyralidae, wax moth larvae) and three EPN species (Heterorhabditis bacteriophora ‘HB1’, Steinernema carpocapsae ‘All’, and Steinernema riobrave). Weights of individual insect cadavers were tracked daily during the des- iccation process, and cohorts were placed into emergence traps when average mass losses reached 50%, 60%, and 70% levels. We tracked the proportion of insect cadavers producing infective juveniles (IJs), the number and virulence of IJs produced from desiccated insect cadavers, and the influence of soil water potentials on IJ production of desiccated insect cadavers. We observed apparent differences in the desic- cation rate of the insect cadavers among the three species, as well as apparent differences among the three species in both the proportion of insect cadavers producing IJs and IJ production per insect cadaver. Exposure of desiccated insect cadavers to water potentials greater than À2.75 kPa stimulated IJ emer- gence. Among the nematode species examined, H. bacteriophora exhibited lower proportions of desic- cated insect cadavers producing IJs than the other two species. Desiccation significantly reduced the number of IJs produced from insect cadavers. At the 60% mass loss level, however, desiccated insect cadavers from each of the three species successfully produced IJs when exposed to moist sand, suggesting that insect cadaver desiccation may be a useful approach for biological control of soil insect pests. Ó 2010 Elsevier Inc. All rights reserved. 1. Introduction Entomopathogenic nematodes (EPNs) (Rhabditida: Steinerne- matidae and Heterorhabditidae) in the genera Steinernema and Heterorhabditis are obligate insect pathogens. They occur globally in natural soil systems and several species have been successfully commercialized for soil pest control in managed systems. The free-living infective stage juvenile nematode (IJ) is the only life stage that exists outside the insect host. Once the IJ finds and en- ters a suitable insect host (Lewis et al., 2006), it releases tens to hundreds of cells of its symbiotic bacterium. The bacterial cells reproduce within the insect host, kill it through septicemia, and serve as a food source for the developing nematodes (Poinar, 1990). The nematodes reproduce for usually 2–3 generations with- in the insect cadaver. Then, in response to declining nutritional quality of the cadaver, second-stage juvenile nematodes develop into specialized third-stage IJs, which leave the insect cadaver to search for a new host. Almost all commercial formulations of EPNs currently available are based on the free-living IJs which are applied in aqueous sus- pension. However, an increasing body of research demonstrates multiple potential benefits of using formulations involving the in- sect cadaver. First, the insect cadaver represents a shelter from environmental extremes. Nematodes within the cadaver are more protected from freezing (Lewis and Shapiro-Ilan, 2002) and desic- cation (Koppenhöfer et al., 1997) than free-living IJs. In addition, IJs that emerge from the insect cadaver directly into soil are more infectious (Shapiro-Ilan et al., 2003), more motile (Shapiro and Glazer, 1996) and survive desiccation better (Perez et al., 2003) than IJs that have been collected and stored in water. These studies and others have stimulated research into the application of insect cadavers containing nematodes for biological control programs. Despite these potentially attractive benefits of cadaver-associ- ated EPNs, handling and application of these insect cadavers are 0022-2011/$ - see front matter Ó 2010 Elsevier Inc. All rights reserved. doi:10.1016/j.jip.2010.10.009 ⇑ Corresponding author. Address: Department of Nematology, University of California, 1 Shields Ave., Davis, CA 95616, United States. Fax: +1 530 752 5674. E-mail address: kospence@ucdavis.edu (K.O. Spence). 1 Present address: College of Natural Sciences and Mathematics, Ferrum College, Ferrum, VA 24088, United States. 2 Present address: CIIDIR, IPN Unidad Oaxaca, Santa Cruz Xoxocotlán, Oax., México 71230, Mexico. Journal of Invertebrate Pathology 106 (2011) 268–273 Contents lists available at ScienceDirect Journal of Invertebrate Pathology journal homepage: www.elsevier.com/locate/jip