Distribution. This native insect is found widely in North America, east of the Rocky Mountains, though it is relatively infrequent in the western Great Plains. It also occurs spradically in the western states, as it also is reported from Arizona and Oregon.
Host Plants. The grape colaspis is known to feed on numerous plants, in both the larval and adult stage, though rarely does it cause much damage. The preferred hosts seem to be legumes, but it can be quite common in legume-grass mixtures. The adults have been observed to feed on such vegetables as bean, beet, cantaloupe, corn, cowpea, and potato. Other crops serving as hosts for adults include alfalfa, apple, bean, buckwheat, clover, grape, okra, pear, pecan, soybean, strawberry, sugar beet, trefoil, timothy, and watermelon. The larvae were successfully cultured on alfalfa, alsike clover, lespedeza, potato, red clover, rice, soybean, strawberry, timothy, and white clover. Suitable weed hosts include smartweed, Polygonum sp.; cinquefoil, Potentilla sp.; dock, Rumex crispus; and the grasses Poa compressa, Paspalum sp., and Muhlenbergia sp.
Natural Enemies. Few natural enemies of grape colaspis are documented. Elsey (1979) indicated that the nematodes Howardula colaspidis (Nematoda: Allan-tonematidae) and Mikoletzyka sp. (Nematoda: Diplo-gasteridae) are found in association with grape colaspis in North Carolina. Although up to 13% of the larvae were parasitized by Howardula and 39% by Mikoletzyka during certain periods of the year, there seems a little or no effect on the host. Diplogasterids typically have few effects, but Howardula normally affects ovarian development of female chrysomelids, reducing fecundity or inducing sterility.
Life Cycle and Description. The grape colaspis overwinters as partly grown larvae, and pupates in May and June. New adults and eggs are present beginning in June, and larvae are found throughout the summer and into the following spring. A single generation per year is reported from Iowa. In Arkansas, however, some of the new larvae do not overwinter, but go on to form adults and a second brood of larvae. The adults from the overwintering beetles disappear by mid-July, about the time the adults from the second brood begin to appear. Thus, there is a peak of adult activity in the spring, followed by another in the late summer, with larvae from both groups of adults overwintering.
Elements of grape colaspis biology were given by Forbes (1903), Bigger (1928), and Rolston and Rouse (1965). However, the most complete treatment of grape colaspis biology was the dissertation of Lindsay
(1943). Grape colaspis was included in the key to eastern beetles by Downie and Arnett (1966).
Damage usually occurs when susceptible crops are planted following grass-legume mixtures, weedy ields, and occasionally legume crops such as clover and lespedeza. Plant stand density may be reduced owing to feeding by larvae on germinating seeds. Young plants may have the roots pruned, resulting in stunting, desiccation, and even death. One common symptom of infestation in corn is foliage discoloration. The leaves turn purple due to inadequate phosphorus uptake. The adults chew small holes in the foliage, and when they are abundant, may skeletonize leaves.
Tillage in the spring can be detrimental to the overwintering larvae, but this is not an entirely reliable method for larval suppression. Larvae can be controlled by application of insecticide to seed. Seed treatment is advisable if susceptible crops follow legumes or grass-legume mixtures, particularly if there is evidence of infestation during the previous year. Larvae do not tolerate dry soil very well, so frequent irrigation should be avoided.
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