Distribution. This insect apparently is native to North America. It is restricted primarily to the southeastern states, from Virginia to Florida in the East, and west to Texas and Oklahoma. Occasionally it is reported in more northern states, but causes no damage there. It also is reported to occur in Central and South America.
Host Plants. Cowpea curculio feeds principally on legumes, but other plants are sometimes consumed. Cowpea, snap bean, lima bean, and pea are the vegetables injured, but cowpea is the preferred host. Other crops attacked are cotton, soybean, and strawberry. Among weed-host plants are cutleaf evening primrose, Oenothera laciniata; moss verbena, Verbena tenuisecta; wild bean, Strophostyles umbellata and S. helvola; purple cudweed, Gnaphalium purpureum; heartwing sorrel, Rumex hastatulus; sheep sorrel, Rumex acetocella; and spring vetch, Vicia sativa. Weeds and cotton are primarily attacked early in the year, before cowpea is available, but sicklepod, Senna obtusi-folia is a host during the cowpea-cropping season. Sudbrink et al. (1998) provided data on the sequence of hosts in Alabama.
Natural Enemies. Several natural enemies have been reported, but most authors suggested that a fungus, Beauveria sp., is an important factor in overwintering survival of adults. The bacterium Serratia marcescens was observed to cause high mortality among larvae in South Carolina (Bell and Hamalle, 1971). Among parasitoids associated with cowpea curculio, only Myiophasia globosa (Townsend) (Diptera: Tachinidae) is consistently reported to be abundant. Arant (1938) also noted that unspecified ant species (Hymenoptera: Formicidae) and hot, dry weather affected larval survival. Russell (1981) observed that red imported fire ant, Solenopsis invicta Buren (Hyme-noptera: Formicidae), significantly reduced the rate of successful pupation by cowpea curculio.
Life Cycle and Description. This insect overwinters in the adult stage, emerging in April or May to begin feeding. Oviposition usually does not occur until cowpea is available, which is often June or July. There appear to be two generations annually in Alabama, but only one in Virginia. However, the adults are long-lived, often surviving for several months, so the generations are indistinct. About 30-40 days are required for a complete generation.
A good summary of cowpea curculio biology was given by Arant (1938). Additional useful observations were provided by Hetrick (1947).
Legumes are damaged by both adult and larval stages, both of which feed on seeds within the pods.
Small cavities and shallow furrows are typical forms of injury. In the spring, before pods are available, adults will feed on the lower epidermis of foliage, but this damage is insignificant.
Insecticides. Insecticides are commonly applied to cowpea by conventional spraying or ultra low volume techniques to protect against injury by curcu-lio (Dupree, 1970; Chalfant and Young, 1988), and adults are the usual target. Usually, one or more applications are made before pod development, followed by insecticide treatments at about 3-5 day intervals during pod growth. Insecticides directed to the soil beneath cowpea plants also are beneficial, because adults often aggregate during the heat of the day (Chalfant, 1973b). Treatment of mature pods is not necessarily beneficial (Chalfant et al., 1982). Insecticide resistance has become a problem for some classes of insecticides (N'Guessan and Chalfant, 1990).
Cultural Practices. As the adult rarely flies, but reaches its host plant principally by walking, crop rotation is beneficial. Also, tillage and destruction of alternate crop and weed hosts, and crop residue, will destroy overwintering beetles.
Host-Plant Resistance. Considerable effort has been devoted to the identification of resistance among cowpea varieties to cowpea curculio. Pod wall (hull) thickness has been identified as a key factor in conferring resistance, and several commercially available varieties possess this desirable trait (Chalfant et al., 1972; Cuthbert and Davis, 1972). However, when confronted with high curculio densities, these varieties do not impart complete protection, so they are best considered as part of a damage reduction program.
Biological Control. Entomopathogenic fungi have been evaluated for suppression of cowpea curculio. Strains of both Metarhizium anisopliae and Beauveria bassiana are effective under experimental conditions (Bell and Hamalle, 1971; Daoust and Pereira, 1986), but commercial products are not yet available.
Was this article helpful?