The Colorado potato beetle adult is about 10 mm long and 7 mm wide, and somewhat rounded. Its head and pronotum are brown-orange to yellow and covered with variously shaped black markings. Ten black lines run the length of the wing covers (elytra), which otherwise are yellow. Females can be recognized by their greatly distended abdomen and the absence of a depression in the last abdominal segment when viewed from below. The eggs are elongate, and yellow to orange. They are usually laid on the underside of leaves of the host plant in clusters of about 30. The larva is humpbacked, and red-orange with two rows of black spots along the sides of the body.
The Colorado potato beetle cannot be confused with any other beetle in Canada.
The adult overwinters in the soil of the previous year's potato fields and adjacent hedges. As the temperature increases in the spring, the beetles start to move upward in the soil. They first appear in the last week of May or early June, and immediately seek host plants. They feed for a few days, after which mating and egg laying occur. Individual females lay 300 to 500 eggs from June to late July. During this period they may move from older to younger plants. The extended egg laying period means that larvae may be present in the field for three to five weeks, although larval development from hatch to pupation requires only two to three weeks. Pupation occurs in the soil and new adults appear after a further one to two weeks.
The poor food quality of the host plant, diminishing daylength and relatively low temperatures during the emergence period prevent the new adults from mating. Instead, they feed and prepare for an overwintering diapause. Thus, there is only one generation of the beetle. Occasionally in New Brunswick, Nova Scotia and Prince Edward Island, some of the new adults emerge early enough to mate and lay some eggs, creating a partial second generation. However, these mated adults soon stop producing eggs and start preparing for overwintering. The partial second generation usually develops too late in the season to have a significant impact on potato yield in these provinces.
The adult and all larval stages feed mostly on foliage, chewing irregular holes in and along leaf margins, but they may also attack stems. High populations can completely defoliate plants throughout large portions of a field. Extensive feeding at any time during the season, especially when the crop is in bloom, can reduce yield. Generally, a reduction in leaf surface decreases the ability of potato plants to produce nutrients for storage in the tubers.
Monitoring - the density of egg, larval and adult stages can be estimated by visual counts on a fixed number of whole plants or plant stems chosen randomly from different parts of the field. Currently, there are no specific economic thresholds. Recommendations to commence control are based solely on empirical observations: an average of two larvae per plant in 12 m of row in Atlantic Canada. There is on-going research in New Brunswick, Manitoba and Quebec to establish economic thresholds. Present information suggests that only very low levels of Colorado potato beetle do not justify control and that the economic threshold is affected by the intensity of other factors stressing the crop.
Cultural Practices - Apart from the use of insecticides, crop rotation is one of the few control techniques currently available to potato growers. Rotation can significantly reduce beetle numbers. It also concentrates the beetles at the periphery of the field where insecticides can then be applied as a spot treatment. Not all growers will be able to avail themselves of this strategy because they may not have the land needed for rotation and alternate crops tend to be less profitable than potato. In these cases, it is best to avoid planting in fields where high numbers of adult beetles were present at the end of the last growing season.
Biological Control - Populations of native predators, which include the ground beetles Lebia and Pterostichus spp., the two-spotted stink bug Perillus bioculatus (Fabricius) and the spotted lady beetle Coleomegilla maculata (DeGeer) and the parasite Myiopharus doryphorae (Riley) [syn. Doryphorophaga doryphorae (Riley)] rarely have a significant impact on the abundance of the Colorado potato beetle. Toxins from strains of the bacterium Bacillus thuringiensis (Berliner) have been registered for commercial use and have good potential for utilization because of their specificity to Colorado potato beetle.
Chemical Control - An array of systemic and foliar chemical insecticides is available. Growers are encouraged to spray only when necessary and to alternate their choice of insecticides from among the different chemicals available.
In New Brunswick, the genetic potential for resistance is present in many locations, and is expressing itself in more and more populations. The level of insecticide resistance in beetle populations from the other provinces is unknown. Spot treatments with foliar insecticides should be applied against adults early in the season where numbers warrant. Insecticides for control of the larval stages should be applied particularly during bloom where numbers warrant and at the end of the season for control of adults when unusually high numbers are present. The bacterial insecticide must be applied early, and regularly, once egg hatch is in progress, until no more small larvae are present.