SUSCEPTIBILITY OF PREPUPAE OF THE COLORADO POTATO BEETLE (COLEOPTERA, CHRYSOMELIDAE) TO ENTOMOPATHOGENIC NEMATODES (RHABDITIDA, STEINERNEMATIDAE, HETERORHABDITIDAE)

This research investigated the ability of five species or strains of parasitic nematodes to control the Colorado potato beetle, Leptinotarsa decemlineata (Say), when beetle prepupae were released on potting soil containing the nematodes. The nematodes tested were: Steinernema carpocapsae Weiser (All strain); S. carpocapsae (Mexican strain); S. feltiae (= bibionis) (Filipjev) (strain #27); S. feltiae (strain #980) and Heterorhabditis bacteriophora Poinar. Six dosage levels ranging from 10.3 to 329.2 nematodes/cm2, in addition to the water-only controls, were used in these laboratory tests. Each dosage-strain combination was replicated four times with 20 prepupae exposed to each individual treatment. The five strains demonstrated 100% kill at 164.6 nematodes/cm2. Except for the Mexican strain of S. carpocapsae, every strain produced over 98% mortality at 82.3 nematodes/cm2. Dosage response regression equations were calculated for each strain. Although field applications probably would require higher rates to obtain the same mortality, the use of parasitic nematodes has potential for suppressing Colorado potato beetle populations. The cost or dosage rate of nematodes may have to be reduced before the control costs would be acceptable to a grower.