Striped Cucumber Beetle Monitoring

Eric Burkness and Bill Hutchison, Department of Entomology, University of Minnesota

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Striped cucumber beetle (SCB), Acalymma vittatum, is a major pest of cucurbits in the Midwest. Besides causing direct feeding damage on foliage and fruit, SCB also vectors the bacterial wilt pathogen, Erwinia tracheiphila. Adult SCB has yellow wings with 3 longitudinal black stripes. Proper identification of SCB is important because they are easily confused with western corn rootworm adults, which are not an economic concern in cucurbits. An easy way to distinguish between the two is to check the legs of the beetles. SCB adults have faint yellowish bands on the legs whereas western corn rootworm adults have solid black legs. We also have the spotted cucumber beetle, which is not an economic concern.

SCB can overwinter as an adult under debris in wooded areas and along fence rows adjacent to cucurbit fields. We do not yet know whether SCB can overwinter in Minnesota, or migrate into the state each year. After emergence, the adults feed on the blossoms of many alternate hosts such as hawthorn, dandelions, and many other indigenous plant species. Once cucurbit plants emerge, the beetles are attracted to cucurbitacin, a plant kairamone, to locate cucurbit plants. In Minnesota, SCB will not take flight until mean daily temperatures reach 65°F. Feeding and mating begin shortly after colonization of a cucurbit field. After mating occurs females begin laying eggs in the soil at the base of cucurbit plants. Eggs hatch in about a week and larvae feed on the roots and underground portions of stems of the cucurbit plants. A second generation of adult SCB will emerge and begin to feed on foliage, flowers and fruit, if present. SCB hide in the soil around the plant, under clods of soil, or in cracks in the soil during the heat of the day.

Adult feeding is of particular concern when plants are in the cotyledon and 1-3 true-leaf stages. At this size, the plants are small enough that high populations of SCB can either defoliate the plants completely or girdle the stem. As plants grow beyond the 3 true-leaf stage, several cucurbits (cucumbers and pumpkins) can tolerate very high levels of defoliation. Once flowering occurs, SCB will usually move off the foliage and begin feeding on blossoms and pollen. This situation is more noticeable on the large flowering cucurbits like squash and pumpkin. Fruit or flower feeding does not usually become a yield concern. However, feeding on fruit may cause some cosmetic damage when high SCB populations are present in a field.

We recently developed a sequential sampling plan for rapid monitoring of beetle infestations requiring an average of 16 to 30 single plants per field. Once infestations have been detected and action threshold levels (0.5-1 beetle/plant) have been reached, there are several different insecticides that provide effective SCB control. Sevin continues to be an effective knockdown of SCB, Permethrin (Pounce or Ambush) and Asana also provide effective control of SCB. Other products labeled for SCB include: Thiodan, Capture, and Methoxychlor. Sabadilla is an organic-certified product. Excessive use of some materials that are toxic to pollinators may cause yield reductions. When flowers are present, every effort should be made to apply insecticides in the early morning (before 8 a.m.) or late evening (after 6 p.m.) to reduce contact with honeybees. A new product which is less hazardous to pollinators is Adios, a cucurbitacin bait that contains low levels of Sevin. The product contains Sevin encapsulated in a feeding stimulant, which induces SCB to feed on the Sevin but will not attract additional SCB into the field. The product is encapsulated and therefore is more difficult for pollinators to ingest while visiting flowers. Recent studies in Minnesota indicate Adios can be effective for low-moderate SCB infestations.

A new trap and lure have recently been developed by Trece, Inc., Salinas CA, for detection of SCB. The trap consists of a small plastic top that fits over a plastic cup. A “stun pill” is inside the trap and contains small amount of Carbaryl to kill SCB. On the outside of the trap is a lure that attracts SCB to the trap. Preliminary trials conducted in 1999 indicate that the traps are useful for early detection and may show promise as a control option for small acreage plantings (<1 acre) to trap out a signifacant portion of the population. These traps may be useful in organic production systems where few options are currently available for control of SCB. The trap study has been expanded for 2000.

For more information check out the VegEdge “Cukes” fact sheet at: http://www.vegedge.umn.edu/vegpest/cucs/cukes.htm

Co-Editors: Bill Hutchison, Department of Entomology, University of Minnesota, hutch002@tc.umn.edu
Jeanne Ciborowski, IPM Program, Minnesota Department of Agriculture, jeanne.ciborowski@state.mn.us
Cindy Tong, Department of Horticulture, University of Minnesota, ctong@extension.umn.edu
Production Editor: Suzanne Wold, Research Specialist, University of Minnesota, woldx018@tc.umn.edu

Disclaimer
Reference to products in this publication is not intended to be an endorsement to the exclusion of others which may have similar uses. Any person using products listed in this publication assumes full responsibility for their use in accordance with current directions of the manufacturer

Last Revised May 18, 2000.
The University, including the Minnesota Extension Service, is an equal opportunity educator and employer.©1999 Minnesota Extension Service, University of Minnesota. All rights reserved. Contact copyright@extension.umn.edu for information on reproduction or use of this material.