Colorado Potato Beetle
Colorado potato beetle (CPB) feeds exclusively on solanaceous crops and weeds, and can be a significant pest of potatoes, tomatoes and eggplant. Adult beetles have characteristic cream and black stripes across the back. Females deposit eggs in clusters on the underside of leaves. The eggs are orange and each mass will contain between 20-45 eggs. CPB larvae are crimson in the early instars with black legs and two rows of black spots on the sides of their body. Large larvae are orange and appear bloated and humpbacked. Pupae are located in the soil.
The beetle has 2 reproductive generations per growing season in Pennsylvania. The 1st comes from overwintering adults, and the second from in-field reproduction. Overwintering adults emerge in early May, locate a host and begin to feed and mate. Oviposition (egg-laying) occurs early to late June in central Pennsylvania, and earlier in warmer parts of the state. As with most insects, all forms of activity and development from one life stage to the next is temperature dependent. A female can produce up to 500 eggs in her lifetime. Eggs hatch in about a week depending on temperature. The larvae go through 4 instars (growth stages) in the span of about two weeks. Fourth instar larvae drop from the plant and burrow into the ground to pupation. The pupal stage lasts about a week, and marks the end of the first reproductive generation. Emergence of adults from these pupae - the "summer adults" - marks the beginning of the 2nd generation.
The behavior of these summer adults varies greatly based on photoperiod (day length), crop fed upon, and temperature. Adults emerging in late July and early August will generally mate and begin oviposition (starting another generation). Adults emerging after the middle of August usually feed for a few days, then burrow into the ground or fly to the edges of woodlots to enter diapause for the winter. The summer generation of adult beetles diapause within the crop field or fly to nearby trees or hedgerows before burrowing into the soil to diapause.
Crop rotation is an effective cultural practice to reduce CPB problems. Rotation prevents overwintering beetles emerging directly in the fields regardless of the distance that you rotate. The distance that you rotate influences the degree of reduction of immigrating adults. The further a field is located from the previous year's potato or tomato field, the longer overwintering adult CPB take to infest it. A field that is 1500 feet from previous year's potatoes can delay infestation about 7 days. Rotation by a .25 to .50 mile is best, if possible. Infestation can be further delayed by having winter wheat or hay between rotated fields. Another cultural practice is no-till, or using straw mulch. We are not sure why this works, but it has been effective in several studies with tomatoes, including observations in Lackawanna County. It is possible that the stubble or straw interferes with adults finding the fields, or the straw environment may harbor more predators.
Several predators are known to feed on CPB eggs, including one ladybird beetle (Coleomagilla maculata), and a predaceous stinkbug. Not all ladybird beetles feed on the eggs. In addition, the early hatching larvae feed on the eggs that have not yet hatched, reducing egg hatch by about 10%. One parasitoid, Endovum putlerri , has been very effective on CPB, but only on eggplant. In home gardens, hand-picking and row covers are effective.
We typically see much greater CPB pressure in eggplant and potatoes than tomatoes. In one recent study, a summer generation did not develop in tomatoes, but did develop in neighboring potatoes. By far, the greatest damage to plants is by the late instar larvae and adults. CPB affect potato yields more severally during tuber formation and less so during vegetative growth. Fortunately these growth phases are easy to determine. Tuberizaton is coincident with the flowering of potatoes; thus controlling pests during flowering is more essential than during other plant growth phases. For example, 4 big eaters (large larvae and adult CPB) per 10 plants requires treatment during flowering, whereas prior to or after the bloom period, a spray would not be needed until 15 big eaters were found per 10 plants. For established tomatoes, begin treatments (typically against overwintering adults) when densities exceed 15 adults per 10 plants. If chemicals are not needed for overwintering adults, wait for egg hatch, and direct sprays against densities exceeding 20 adults or larvae per 10 plants.
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