Occurrence of the Carabid Beetle, Pterostichus melanarius (Illiger), in Potato Ecosystems of Idaho and its Predatory Potential on the Colorado Potato Beetle and Aphids

Potato pest management in Idaho is primarily through insecticide applications. With the advent of newer and softer insecticides in recent years, it might be logical to explore other management options such as biological control. In this paper, we examined the prevalence and the predatory potential of a ground beetle (Carabidae) on important potato pests. An introduced generalist, Pterostichus melanarius (Illiger), is common in Idaho’s potato ecosystems. Pit fall sampling for two consecutive years in commercial potato fields indicated that P. melanarius was abundant in potato fields. However, P. melanarius was less abundant in preplant insecticide (aldicarb) treated fields when compared with untreated fields. Preference and functional response studies were conducted to evaluate the predatory potential of P. melanarius on Colorado potato beetle (CPB), Leptinotarsa decemlineata (Say), larvae and eggs, and Macrosiphum euphorbiae (Thomas). The preference study indicated that P. melanarius contacted and/or attacked aphids only after CPB larvae and eggs. When different densities of CPB eggs, larvae, and aphids were presented, one P. melanarius adult consumed up to 61 eggs in 24 h and ate as many as 24 CPB larvae in 24 h. Also, one P. melanarius adult consumed up to 55 aphids in 24 h. Vine-climbing experiment revealed that P. melanarius climbed potato vines and actively consumed CPB eggs. However, the predation rates were approximately four times greater on eggs at lower vine portions than at upper portions. These studies indicated that P. melanarius could be a valuable biocontrol agent in potato ecosystems