USE OF IMIDACLOPRID-TREATED ROW MIXTURES FOR COLORADO POTATO BEETLE (COLEOPTERA, CHRYSOMELIDAE) MANAGEMENT

The ''high dose'' strategy of applying imidacloprid as an ''at-plantin g'' soil treatment uniformly throughout a potato held may result in ra pid pest adaptation, as it has for other systemic insecticides. Altern atively, treated and untreated plants in a field provide a refuge to p ests so that some portion of the population is not subjected to select ion. In 1993- and 1994-field experiments involving potato cultivars wi th contrasting maturity periods, plots of mixtures of imidacloprid-tre ated and untreated rows were compared with plots of untreated and 100% , treated rows to determine their effects on the Colorado potato beetl e, Leptinotarsa decemlineata (Say). First-generation populations and f eeding injury were significantly reduced by mixtures of imidacloprid t reated rows, when post-diapause adults were released along the edge of plots to simulate a typical colonization pattern. Densities of life s tages and percentage defoliation decreased as the proportion of imidac loprid-treated rows increased. The effectiveness of imidacloprid was g reater than the additive effect based on the proportional contribution of the treated rows. Beetle populations decreased as the distance inc reased inward from the outer rows, because invading beetles were incre asingly suppressed as they encountered rows of imidacloprid-treated pl ants. This suggests that the treated row at the edge of the field in a row mixture acted as a toxic barrier to colonizing beetles. Even when colonizing adults were introduced uniformly in row mixture plots, the treated rows trapped many dispersing adults and suppressed feeding in jury on adjacent untreated rows. Mixtures of treated and untreated row s deployed alone or in combination with a perimeter treatment are disc ussed as ways to reduce the amount and cost of insecticide used create refuges to minimize resistance development, and reduce environmental risks.