CPB undergo complete metamorphosis: adult, egg, larva, and pupa.
Adults are hard-shelled with a round, convex shape. Their forewings are yellow with a total of 10 black stripes running longitudinal. They are about a half an inch long. Adults eat foliage until they pupate.
Eggs are oval, yellow to bright orange. They are layed in clusters of 10 to 30 eggs on the underside of leaves.
Larvae are slug-like with a soft shell. They are red to orange to tan depending on age and they have two rows of black dots on each side. The body which is humped enlarges with time and grows in four size stages. Larvae eat foliage as they grow and this is the most destructive stage.
Pupae are small and are found in the soil .
Adults overwinter four to 12 inch deep in the ground of harvested potato fields and emerge in spring around May. Adults do not migrate but will fly for several miles to find its Solanaceous hosts. Besides potato, these include weeds such as nightshades and include garden crops such as tomato and pepper. Adults then mate and lay eggs on the host plants. Egg laying may last as long as a month and may be as many as 500 eggs on a single plant. After four to 10 days depending on temperature, eggs hatch. The cooler the air temperature the longer it will take for hatching. The hatchlings are tiny larva. The larva grow in four progressive stages (instars), eating the host foliage all the while. Depending on temperature, the larval stages will last two to five weeks or when about 400 degree days have accumulated. Then, the larva will go into the ground, three to six inch deep, and pupate. The Pupa last for five to 10 days after which new adults emerge. The emerged adult travels around, looks for mates, and after seven to 10 days begins to lay eggs. The full cycle takes five to eight weeks per generation. Usually, there are two generations per season in Nebraska, early to mid June and early to mid August. In cooler States, less than two generations may occur. At the end of the season, remaining larva move into the soil and overwinter as pupa.
CPB larvae are the most damaging form but adults also feed on the foliage. Due to feeding, leaflets have holes of varying sizes usually starting around the margins. The leaf blades are eaten often leaving a skeleton of veins and petioles behind. This results in defoliation. Defoliation threshold levels are reported as 25% before tuber bulking, 10% during the first half of bulking, four to six weeks and 25% after bulking. Vine damage results in yield loss due to loss of foliage to support tuber growth and mis-shaping of tubers is also possible. Severe damage may result in plant stunting as well.
Monitoring the edges of fields, nearby gardens and surrounding weeds especially nightshades will give warning when CPB are entering the field. Since they are poor fliers, CPB enter a field along the edge usually at a corner that is closest to the previos year’s crop. Economic threshold levels have been reported.
Crop Value Control Cost
Bechinski, E.J., Sandvol, L.E., and Stoltz, R.L. 1994. Integrated Pest Management Guide to Colorado Potato Beetles. Univ Idaho Coop Ext Circ #757.
The trench method is a semi-successful mechanical control of CPB mostly applicable to small acreage. In areas where close rotations are used or potatoes are grown adjacent to last years potato fields, this method may help to alleviate first generation CPB damage. A trench is plowed between overwintering sites and this year's potato field. The trench should be at least 12 inches deep with sides sloping 45 to 90o. Emerging beetles walk to find their early season hosts and become trapped in the trench. A fine coating of dirt on the plastic prevents the beetles from being able to get out of the trench. Note some CPB adults may fly over the trench; however, this method can be surprisingly effective at trapping beetles.
Using a flamer is another mechanical method for controlling CPB. Its best fit is also in areas where trap crops are used to congregate immigrating beetles for easier control. Flaming is used on plants that are up to 8 inches tall with little adverse effects on them. Larger plants will provide more protection for the beetles and effectiveness is reduced. Flaming involves using two propane-powered flame jets that are directed in an offset manner toward the row. A single unit can be bought for under $3,o00 or constructed. Propane usage is about 3½ to 5½ gallons per acre. Speed is also an advantage. As might be suspected, you don't want to go too slow with this type of machine. A speed of 4 to 6 mph is recommended. Control with the flamer should be done on a clear warm day so the beetles are up on the plants. Data for early-season control have been as high as 90% with this method.
Moyer, D.D. 1992. Fabrication and operation of a propane flamer for Colorado potato beetle control. Cornell Coop Ext Bull. pp. 7.
Olkowski, W., Saiki, N. and Daar, S. 1992. IPM options for Colorado potato beetle. The IPM Practitioner 14:1-21.
Several common beneficial insects, predators, are good agents for devouring CPB eggs and even attacking larva; see lady beetles and others. Since CPB overwinter in potato fields, rotating crops is key and the following season’s potato fields should be planted a few miles away from the previous season’s potato fields. Since CPB will develop on weeds in the same family as potato, controlling these especially the various night shades is an important part of the management program. Bt products such as Dipel have been used to kill young CPB larvae but timing is crucial for efficacy. In the 1990s, potato clones began to be engineered (GMO) with Bt genes to protect plants from CPB. This technology is very successful in doing that but due to uninformed political pressure this GMO technology has been slowed on potato although common in corn and soybean.
Most systemic insecticides applied at planting will kill the CPB's first generation. Most foliar insecticides will take care of later invasions by CPB. The key is not to let the population de-synchronize. If this happens, weekly applications of foliar insecticides could be needed. The best application stage is on the young larvae, first and second instar, because they have most of their eating ahead of them. Older larvae have less eating to do and also are less sensitive. Killing adults works but the result may be so/so because they may have already laid eggs and you may be killing their predators such as lady beetles as well. These predators would devour the CPB egg masses. Since CPB enter fields along the edges and gradually move inwardly, with good scouting, often only the field’s perimeter needs to be treated.
It is very important to note that the CPB is highly capable to develop resistance to insecticide products. On the East Coast and Great Lakes region, the CPB has developed resistance to combinations of products, multiple-resistance or “super” bugs. Therefore, management needs to be an integrated program of biological and chemical methods, at least until the consumer market allows resistant potato lines to return.
To control CPB in garden potatoes as well as peppers and tomatoes, apply carbaryl (Sevin) to plants when the adults or young larvae are present. But be aware not to treat around flower areas to avoid killing honey bees needed for pollination.
Adult - round with yellow and black stripping, 1/2 inch long
Larva - slug-like, pinkish with two rows of black dots on each side, four instars from 1/10 to 1/2 inch
Egg - small yellow to orange in masses under leaflets
Overwinters as an adult in soil of previous year’s crop
One to two generations which can de-synchronize easily
Can appear from April to September
Defoliation; tuber yield loss
Foliar Insecticides but beware of resistance
GMO potato engineered with Bt gene