RELATIONSHIP BETWEEN CROP-ROTATION DISTANCE FROM PREVIOUS POTATOES AND COLONIZATION AND POPULATION-DENSITY OF COLORADO POTATO BEETLE

Populations of adult Colorado potato beetle, Leptinotarsa decemlineata (Say), were significantly lower in fields located 0.4 to 0.7 km or >1 .25 km away from the previous year's nearest potato planting compared with fields adjacent to the previous year's potatoes. However, site-sp ecific factors other than distance allowed high populations of Colorad o potato beetle to develop at three of the farthest sites. Regression analyses inferred no significant linear correlation between distance t o the previous year's potato field and early-season immigration or fie ld populations: fields separated by 0.4-0.7 km benefited as much by di stance rotation as fields separated by 1.3-3.1 km from the previous ye ar's potatoes. A significant linear correlation was observed between n umbers of adult beetles caught in pitfall traps placed at the edges of fields and in-field adult beetle populations early in the season, and between adult populations and egg mass densities at the different sit es. In areas where potato production is concentrated in a small geogra phic region, crop rotation helps to reduce populations of Colorado pot ato beetle but seldom eliminates the need for other methods of control .