STORED-PRODUCT Mortality of Life Stages of Cowpea Weevil (Coleoptera: Bruchidae) Exposed to Low Pressure at Different Temperatures GEORGE N. MBATA, 1 MARIO JOHNSON, THOMAS W. PHILLIPS, 2 AND MARK PAYTON 3 Department of Biology, Fort Valley State University, 1005 University Dr., Fort Valley, GA 31030 J. Econ. Entomol. 98(3): 1070Ð1075 (2005) ABSTRACT Previous studies have shown that low pressure creates a low oxygen controlled atmo- sphere that can kill stored-product insects. The current study was conducted to determine the mortality of life stages of the cowpea weevil, Callosbruchus maculatus (F.) (Coleoptera: Bruchidae), exposed to different low pressures and temperatures for various exposure periods. The adults were the most susceptible life stage to low pressure; 99% mortality was achieved within 0.8 h at 32.5 mmHg, 30°C. The pupae were the most tolerant life stage to low pressure, requiring exposure periods between 28.98 and 153.20 h at temperatures of 20 Ð35°C to achieve 99% mortality. Mortality increased with exposure time and also with increasing temperature in all life stages. Early stage eggs (3 h old) and late stage eggs (48 h old) experienced higher mortality (values for LT 99 of 42.331 and 46.652 h, respectively) compared with intermediate aged eggs (24 h old; LT 99 of 74.735 h) under the same conditions of low pressure and temperature. Dried beans, including cowpea, Vigna unguiculata (Walp.), are currently protected with fumigants. Application of low pressure as a pest management tool represents a potential nonchemical alternative to fumigants such as methyl bromide and phos- phine for controlling the cowpea weevil and related bruchids. KEY WORDS pest management, dried beans, vacuum, methyl bromide alternative, controlled atmospheres THE COWPEA WEEVIL, Callosbruchus maculatus (F.) (Co- leoptera: Bruchidae), is a worldwide pest of cowpea, Vigna unguiculata (Walp.). Infestation of cowpea by this bruchid commences in the Þeld before mature seeds are harvested (Huignard et al. 1985). Infestation level of cowpea is very low at harvest and may some- times be undetectable (Hagstrum 1985, Huignard et al. 1985). The cowpea weevil multiplies very fast in storage, giving rise to a new generation every month, and losses up to 30% in 3 mo (Ouedraogo et al. 1996, Sanon et al. 1998). Barring containment of the pest, complete loss of cowpea could occur within 6 mo of storage (Caswell 1961). The most effective pest man- agement tool used in the de-infestation of commercial quantities of cowpea is fumigation with synthetic in- secticides such as methyl bromide or phosphine gas (Mbata 2004). Use and production of the fumigant methyl bromide was scheduled to end in developed countries by January 2005 and worldwide by 2020 under the terms of the Montreal Protocol (United Nations Environment Programme 1998). Uses of other insecticides in stored products are facing restriction, and pest populations are evolving resistance to chem- ical insecticides (Hagstrum et al. 1999, Phillips et al. 2000). Several traditional measures for protecting har- vested cowpea are in use in subsistence agriculture, but their efÞcacy is often unveriÞed (Alebeek 1996). Physical methods, such as controlled atmospheres (Mbata et al. 1994), are effective in controlling bruchid pests of cowpea because they do not leave chemical residues on products, but many are expen- sive or impractical. Low-oxygen atmospheres derived from the appli- cation of vacuum to achieve low pressure have been demonstrated to be effective in the control of post- harvest insect pests (Bare 1948, El Nahal 1953, Cal- deron and Navarro 1968, Calderon and Leesch 1983, Navarro and Donahaye 1987, Locatelli and Daolio 1993, Mbata and Phillips 2001). Insect mortality under low pressure is predominantly a result of the low oxygen concentration affecting cell physiological pro- cesses such as glycolysis, and not physical effects of pressure or dehydration from lowered water concen- trations under vacuum (Navarro and Calderon 1979, Freidlander and Navarro 1983). Most of the earlier studies concentrated on the activity of vacuum alone (Back and Cotton 1925, Bare 1948, Calderon et al. 1966, Calderon and Navarro 1968), but the effects of temperature, life stage, and pressure level have been investigated recently for Cadra cautella (Walker), Plo- dia interpunctella (Hu ¨ bner), Tribolium castaneum 1 E-mail: mbatag@fvsu.edu. 2 Department of Entomology and Plant Pathology, 127/110 Noble Research Center, Oklahoma State University, Stillwater, OK 74078. 3 Department of Statistics, Oklahoma State University, Stillwater, OK 74078. 0022-0493/05/1070Ð1075$04.00/0  2005 Entomological Society of America