Striped cucumber beetles often fly from their hibernating sites early in the season, even before plants emerge. As soon as the cucumber, squash, pumpkin, melons and related seedlings push up through the soil, beetles can eat off the stems and cotyledons, frequently killing them. Adults later feed on the leaves, vines and fruits of plants that survive. Sometimes, deep pits are gnawed into the rind, making the produce unfit for consumption or market.
Damage is also caused by the larvae feeding on the roots of host plants, which weakens the plant and makes it susceptible to other problems. Adults also feed on beans, peas, corn and blossoms of other plants.
Most important, these beetles are vectors of a serious cucurbit disease known as bacterial wilt. Plants infected with the disease wilt quickly with leaves drying out prior to plant death. The causative bacteria, Erwinia tracheiphilia (E.F. Smith), overwinters in the bodies of hibernating beetles. These beetles introduce the bacteria into the plants through the fecal contamination of feeding wounds. This is the only natural method of infection known. Beetles also spread squash mosaic virus.
An adult striped cucumber beetle is oblong, yellowish-green in color, about 1/4 inch long, and marked by three slate-black stripes. The head and antennae are dark colored. Wings are covered with very small punctures clearly seen under magnification.
Eggs are light yellow or orange colored, and round to oval shaped. Larvae are worm-like and about 3/8 inch long when full grown. Larvae are white with a dark head and have three pairs of legs on the thorax. Pupae are whitish-yellow and about 1/4 inch long.
Life Cycle and Habits
Adult beetles overwinter and leave Their hibernating quarters in the spring when temperatures reach 65 degrees F or more. When cultivated cucurbit plants begin to emerge through the soil surface, large numbers of beetles may suddenly appear and feed on the seedlings or crawl into soil cracks in reach of sprouting seed. Beetles soon mate and continue feeding throughout the season. Eggs are laid 8-25 days after mating. Females deposit 225-800 in small clusters or singly into soil cracks at the base of cucurbit plants.
Eggs hatch 5-8 days later, with larvae spending about 15 days feeding on the roots and stems of fruit that is in contact with the soil. The pupal period is 6-7 days. The time from egg to adult for The first generation of beetles requires about 1 month and slightly longer for succeeding generations.
After cucurbit plants mature and cool autumn weather approaches, beetles migrate to wooded, bushy areas, crawling under litter to overwinter. Some may overwinter a mile from the hatching site. In Ohio, only 1 generation occurs while 2 or more generations may be produced in the Gulf states.
It is important to inspect newly planted cucurbit plants frequently for the presence of any adult striped cucumber beetles. Unfortunately, there is no control for The bacterial disease once tile infection has been introduced into the plants.
Inspect plants frequency for beetle infestations. Row covers can provide protection, but during blossoming time, tile covers must be removed for several hours each day, to allow pollination. Plant wilt-resistant varieties and use trap crops, if appropriate.
Although There are several insecticides that control the beetle, only a few chemicals can be used on cucurbit plants because of their sensitivity to chemical injury. Application of an insecticide is usually recommended as soon as the plants begin to emerge through the soil. For prevention of bacterial wilt, it is often advisable to spray at 5-day intervals, beginning when seedlings emerge or after transplanting and continuing spray schedule until vines run. If rain occurs within the 5-day period, repeat the treatment promptly and then return to the regular 5-day treatment interval.
Sprays prepared from wettable powders are less phytotoxic than sprays prepared from emulsifiable concentrates. Dusts are likewise effective if plants are Thoroughly covered. Rotenone 1% dust gives good beede control. Malathion may cause injury to plants if applied before they start to vine. Malathion may cause some foliar burning and should not be applied when plants are wet. Do not combine Malathion and Sevin for application to cucumbers due to possible phytotoxicity.
Recommended chemicals include rotenone, methoxychlor, malathion and carbaryl (Sevin) applied according to label directions and safety precautions.
Predators and Parasites
Natural predators include soldier beetles, tachinid flies, braconid wasps and certain nematodes.