Field Crops News

Ground Beetles: Our Friends in Soybeans

Adults of many carabid beetles are predaceous on plant feeding insects and considered beneficial in field crop production systems. To evaluate the importance of ground beetles in soybean fields in Ohio, researchers at the Ohio State University examined the activities of carabids and their potential role in biological control in soybean ecosystems.

A total of approximately 3,000 ground beetles representing 45 species were collected in a soybean field during a two-year study. Five species (Anisodactylus sanctaecrucis, Pterostichus chalcites, P. stygicus, Scarites substriatus, and Agonum punctiforme) were the dominant species comprising 75% of total pitfall trap catch. All the dominant species of ground beetles exhibit clear seasonal patterns. P. chalcites, S. substriatus and A. sanctaecrucis were abundant in the early growing season, while P. stygicus and A. punctiforme were only abundant in the late season. Early season species, such as P. chalcites, A. sanctaecrucis, and S. substriatus, have been reported from many crops in most parts of the U.S. They generally overwinter as adults and become active again in the spring when they breed. These early-season species feed on insect prey or plant hosts. These species coincide with the occurrence of the early-season prey or hosts as environmental conditions are favorable.

In contrast, the late-season species or autumn breeders, such as P. stygicus, and A. punctiforme, prefer warmer weather for their development and reproductive activities and coincide with the occurrence of late-season prey or plant hosts. The simultaneous occurrence of predaceous carabid beetles with immature insect pest suggests that these beetles have potential as natural pest-control agents. P. chalcites and S. substriatus have been shown to be potential natural control agents for soil-inhabiting pests, such as black cutworm, corn rootworm, and armyworm. P. stygicus feeds on plant seeds as well as on dead invertebrates, and can feed on eggs of cabbage maggots, and attack larvae of European corn borer. P. stygicus could reduce weed populations though has little potential as a natural control of insects.

The spring breeders coincide with the immature stage of the first generation of bean leaf beetles and Mexican bean beetle, while the late seasonal species coincide with the immature stages of the second generation of bean leaf beetles in soybean fields. This suggests the potential for predation of these pests, however, the species composition and seasonal abundance of ground beetles may change from year to year influencing the level of control they may offer.

- Source: Z. Chen and H. R. Willson.1996. Species composition and seasonal distribution of carabids in an Ohio soybean field. J. Kansas Entomol. Soc. 69(4):310-316.

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