ASSESSING COMPENSATION FOR INSECT DAMAGE IN MIXED PLANTINGS OF RESISTANT AND SUSCEPTIBLE POTATOES

Plant mixtures have been proposed for pesticidal transgenic potatoes a s a means to reduce selection intensity favoring resistant insect geno types. Colorado potato beetle, Leptinotarsa decemlineata (Say), defoli ation was simulated in mixed plantings of susceptible and resistant po tato ''mimics'' to evaluate yield compensation. Various mixtures of su sceptible and resistant potato were planted at two densities and two l ocations in eastern North Carolina. Resistant plants were undamaged th roughout the season whereas susceptible plants were completely defolia ted by hand either during early or late bloom. The ability of non-defo liated plants to compensate for neighboring defoliated plants was inve stigated through single-plant and small-plot field experiments for 2 y ears. Yield compensation for defoliated plants by neighboring non-defo liated plants was not evident in our studies. Yield of two potato plan ts, positioned on either side of a defoliated plant, was not different from yield of two potato plants positioned on either side of a non-de foliated potato plant. Compensation in mixtures of resistant and susce ptible potato was not evident using several non-linear regression anal yses. A negative linear relationship existed between yield and an incr easing percent of susceptible plants in the mixture for all planting d ensities, at each location, every year.