Proceedings of the 1997 Colorado Potato Beetle IPM Forum

Managing the Colorado Potato Beetle:

Insecticide Resistance is a Reality

David N. Ferro
Department of Entomology
University of Massachusetts
Amherst, Massachusetts

The Colorado potato beetle is the major insect pest of potato in North America. Potato growers in many locations have mismanaged the beetle by becoming dependent on multiple applications of broad-spectrum, synthetic insecticides to control it. The beetle has developed resistance to all categories of insecticides currently registered for its control. Resistance is now documented from Virginia and North Carolina in the south and Massachusetts and New York and New Brunswick in the north and as far west as Michigan. Because of widespread resistance by the beetle to a widerange of insecticides, it has become very costly for growers to control this pest. This situation was the impetus for a bevy of research activity to develop innovative approaches to managing the beetle.

Although larval feeding accounts for most of the plant damage, the density of the colonizing adults will determine the density of larvae and subsequent feeding damage. The development of new tactics for managing the beetle are based on a new understanding of its biology, in particular tactics that disrupt the colonization process. The beetle overwinters as adults within the field of origin, and within uncultivated habitats adjacent to the field, such as woody borders and drainage ditches. As spring soil temperatures exceed the 10EC threshold, beetles begin to regenerate their flight muscles and reproductive system. If beetles do not find any host plants within 4-5 days, they engage in migratory flights in search of hosts. The closer a field is located to the overwintering sites the greater the probability that it will be colonized by migrating beetles. Fields located more than a few hundred meters from overwintering sites are colonized 1-3 weeks later in the season than nonrotated fields, and because of the diffusion of migrating beetles these fields will be colonized by fewer beetles. This is why rotating fields that were previously planted to another crop into potatoes reduces insecticide applications by 50 per cent.

There are situations where growers are unable or unwilling to rotate their potato fields. These fields are colonized by resident beetles within the field and by beetles that overwintered outside of the field. In one study, we estimated that 56-85 per cent of the colonizing population came from woody borders around the fields, where densities of up to 800 beetles/m² were found. We found colonization by overwintered beetles to occur over a 3-4 week period and the onset of colonization in nonrotated fields to vary only a few days for the 1992-1995 seasons.

The most effective control strategy is to integrate crop rotation with judicious use of insecticides. Other control tactics that can and have been integrated are delaying the planting date, perimeter treatment of field with imidacloprid (Admire), plastic-lined trenches, and natural enemies.

For further information, contact your GO representative.