The Colorado potato beetle has been shown to be susceptible to steinernematid nematodes in several previous studies. In field tests in Washington State, 1.5-3.1 million nematodes/yd2 caused 59-71% mortality of late instar beetles, while lower rates were more variable in studies at other sites. Prepupae were susceptible too, with adult emergence rates reduced 66-77% when Steinernema carpocapsae was applied at up to 1.5 million/yd2 on Long Island.
S. carpocapsae was tested for its ability to kill fourth-instar larvae, pupae and adult Colorado potato beetle held in small containers filled with a layer of soil. Nematode applications at a rate of 500,000/yd2 resulted in 100% mortality in all groups.
The potential of this nematode for management of late-season adults was then examined in field trials in northeastern Canada. Nematodes were applied to plots in New Brunswick and Prince Edward Island at rates of 760,000/yd2 in 1992 and 640,000/yd2 in 1993. Water was applied both before and after the nematodes were sprayed on the plots in mid July. Only the highest rate of nematodes reduced populations of summer adults at one location, but only by 31%. Results were variable at the other location, probably because life expectancy of the nematodes is much shorter in the field than under laboratory conditions.
The rates used in these trials were selected to be reasonably cost-effective. Higher rates that might have been more effective could be too expensive for most growers to afford. Repeated applications, higher rates of nematodes, different nematode species, or improvements in the application technology would probably be necessary to obtain consistent control. Until further investigations show otherwise, the use of nematodes for adult Colorado potato beetle control cannot be recommended.
Stewart, J. G., G. Boiteau, and J. Kimpinski. 1998. Management of late-season adults of the Colorado potato beetle with entomopathogenic nematodes. Can. Entomol. 130(4): 509-514.
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