NATURAL ENEMIES IN STRAW-MULCH REDUCE COLORADO POTATO BEETLE POPULATIONS AND DAMAGE IN POTATO

The effects of mulching on Colorado potato beetle (Leptinotarsa decemlineata) populations and damage to potato are reported. Potato plots were established in 1991 and wheat straw was placed in half the treatments after potato emergence. Quadrat samples were taken of soil predators and plants were visually searched for all Colorado potato beetle stages and foliar predators. In both 1991 and 1992, mark-release-recapture experiments were conducted on adult populations of the Colorado potato beetle. Mulching had no significant effect on beetle migration. The number of second, third, and fourth instars of first-generation Colorado potato beetle and all instars of second-generation Colorado potato beetle was significantly lower in mulch than in nonmulch plots. A significant increase in number of soil predators began in mulch plots approximately 2-3 weeks after straw was placed in the field. Many of the soil predators climbed potato plants and fed on second and third instars of the Colorado potato beetle. Eggs and first and second instars of the Colorado potato beetle were heavily fed on by coccinelids and chrysopids. Significantly more Colorado potato beetle eggs and larvae experienced mortality in mulch plots than nonmulch plots. Nonmulch plots suffered 2.5 times more defoliation than mulch plots. Tuber yields were 35 and 32% greater in mulch plots than in non-mulch plots in 1992 and 1992, respectively. Higher populations of natural enemies in mulch plots than in nonmulch plots probably accounted for the increase in yield by reducing Colorado potato beetle foliage feeding. (C) 1994 Academic Press, Inc.