Entomopathogenic Nematodes and Fungi Virulence to Cowpea Curculio (Coleoptera: Curculionidae) Larvae1
2018
Schmidt, Jason M. | Shapiro-Ilan, David I. | Graham, Casey | Barwick, Sydni | Sparks, Alton | Riley, David
Cowpea curculio, Chalcodermus aeneus (Boheman), is the major pest of southern peas or cowpea, Vigna unguiculata (L.). Throughout the southeastern United States, current management recommendations for cowpea curculio rely on insecticide applications; however, resistance has been observed. Entomopathogenic biocontrol agents, specifically nematodes in the genera Steinernema and Heterorhabditis and fungi in the genera Beauveria and Metarhizium, have shown efficacy with other curculio pests. We conducted laboratory bioassays to assess the virulence of entomopathogenic agents as a first step to provide alternative control strategies against cowpea curculio. Using controlled environmental conditions, we tested the effects of nematodes (Steinernema carpocapsae Weiser, Steinernema feltiae Filipjev, Heterorhabditis bacteriophora Poinar, and Heterorhabditis indica Poinar) and two fungi (Beauveria bassiana Balsamo and Metarhizium brunneum Petch) on survival and infectivity of cowpea curculio. Heterorhabditis indica had the greatest effect on cowpea curculio larvae, resulting in less than 20% survival and greater than a 65% infection rate. Conversely, cowpea curculio larvae exposed to fungal pathogens had similar survival to larvae exposed to water and less than 20% infection rates. For fungal pathogens, applying the pathogen to the soil surface prior to introduction of cowpea curculio larvae led to infection of the larvae. Our results suggest nematodes and fungal pathogens are capable of infecting cowpea curculio. Our data provide the basis for further tests examining the timing and application rates in field situations.
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