Chalcodermus aeneus Boheman Coleoptera Curculionidae

Natural History

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.

  1. The egg is oval, and white. It measures about 0.9 mm long and 0.6 mm wide. Eggs are deposited in the pod, or within the seed in the pod. The female deposits her eggs in feeding sites, with only a single egg deposited in each feeding puncture. Each female deposits, on average, about 112 eggs (range 30-280) during an oviposition period of about 45 days. Duration of the egg stage is about four (range 3-6) days.
  2. The larva is pale yellow, though the head and prothoracic plate are yellowish brown. The larva lacks legs, but bears deep furrows around its body. The body is thickest about one-third the distance between the head and anus, tapering gradually to a fairly pointed posterior end. The body bears stiff bristles. The larva attains a length of about 7 mm at maturity. There are four instars. Duration of the larval stage was reported to require about 9.4 days in Alabama, but only about 6-7 days in Virginia. In the latter study, development times of the four instars averaged about 1,1,1, and 3.2 days, respectively.
  3. At completion of the larval stage the insect drops to the soil and burrows to a depth of about 2.5-7.5 cm. During a prepupal period of about six (range 3-14) days, the larva creates a pupal cell and molts to the pupal stage. The pupa greatly resembles the adult in shape and size, but is yellowish white. Duration of the pupal stage is about 10 (range 5-19) days. After transformation into the adult, the beetle remains in the pupal cell for 2-3 days while it hardens, and then digs to the surface to emerge.
  4. The adult is oval and robust in appearance. It is black, with a faint bronze tint. The mouthparts are elongate, being slightly longer than the thorax, and only slightly curved. The thorax and elytra are marked with coarse punctures. The beetle measures 4.8-5.5 mm long. The adults are most active during the morning and early evening, and seek shade during the heat of the day. They feign death and drop to the soil when disturbed. Beetles rarely fly. Adults overwinter in the soil, under leaves, and other organic debris.

A good summary of cowpea curculio biology was given by Arant (1938). Additional useful observations were provided by Hetrick (1947).

Damage

Legumes are damaged by both adult and larval stages, both of which feed on seeds within the pods.

Chalcodermus Aeneus Larvae
Adult cowpea curculio.

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.

Management

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.

0 0

Responses

  • Futsum
    How to kill long beetle type bug in houseplant soil?
    8 years ago
  • LORI
    How to kill Cowpea Curculio?
    6 years ago
  • marian
    How to grow your own Metarhizium anisopliae Strain F52?
    3 years ago

Post a comment