Species

Western spotted cucumber beetle (Diabrotica undecimpunctata)

Related species

There are several other types of cucumber beetles, including the banded cucumber beetle and striped cucumber beetle, but the western spotted cucumber beetle can be recognized by its distinct yellow coloration and black spots.

Host/site

Western spotted cucumber beetles can be found in Arizona, California, Colorado, Oregon, and Washington. They attack a wide variety of plants, and are serious pests of smooth-skinned cucurbits such as melons. Typically the damage is caused to the leaves. Most adult plants can withstand damage from cucumber beetles, but younger plants may be more vulnerable, show substantial damage, and lead to death of the plant.

Identification

Appearance

• Adult beetles are about 0.25 inch long and have shiny yellow bodies with black spots, black heads, and long antennae.
• Larvae are whitish and slim with three pairs of short legs and a dark abdomen.

Indicators

• Adults generally feed on soft-skinned cucurbits such as melons and cucumbers, but attack other plants as well, such as hibiscus, dahlias, and peonies.
• Damaged plants have holes in leaves and scar runners on young fruits.
• The beetles can also spread cucumber mosaic virus, in which the leaves curl and become warty or misshapen.

Life cycle

• Adult beetles spend the winter in weedy areas and move to gardens when plants start to come up in early Spring.
• Their yellow-orange eggs can be found as groups at the base of plants or in soil cracks.
• Hatching larvae burrow into the ground and feed for 2 to 6 weeks, pupate and emerge as adult beetles, which then attack the plant.

Natural Enemies

The parasitic tachnid fly, Celatoria diabroticae, can be an effective predator of cucumber beetles when they are in small to moderate numbers. However, if cucumber beetles are in large numbers, natural enemies are rarely an effective solution.

Monitoring

Larvae do not generally damage garden plants and adult beetles are rarely in such large numbers that they must be controlled. In addition, mature plants should be able to withstand minor damage from cucumber beetles. However, protective measures may be required for young plants until they are old enough to withstand beetle damage. Begin monitoring for adults in mid to late Spring.

Action Thresholds

Leaf damage usually only happens when the pest is present in large numbers. Treatment of adults may be necessary if plants are in the seedling-to-4-inch-tall stage and there is an average of one beetle per plant.

Cultural and Physical Controls

*One of the best solutions for a cucumber beetle infestation is to apply protective cloth between the rows of young plants, and remove it when the plants are old enough to tolerate leaf damage.

• Locating and removing the pests by hand or with a vacuum is another possible solution.

Highly vulnerable varieties

Some cucurbit varieties are highly preferred by cucumber beetles and should be avoided. Alternatively, they can be planted to attract the pests away from the gardener's preferred species. These varieties are:
Black Jack zucchini
Big Max pumpkin
Cocozelle summer squash
Green Eclipse zucchini
Seneca zucchini
Senator zucchini
Baby Boo pumpkin
Super Select zucchini
Ambercup buttercup squash
Dark Green zucchini
Embassy Dark Green zucchini
Caserta summer squash
Classic melon

Biological Controls

The introduction of natural predators such as Celatoria diabroticae (tachnid fly) as well as various general predators can be used to control cucumber beetles, but this method is rarely effective when beetle populations are in large numbers.

Chemical Controls

• The chemical insecticides sabadilla, rotenone, or pyrethrum are moderately effective in combating cucumber beetles, but should not be used, due to their harmful effects on bees and other beneficial insect species. Therefore, chemical sprays should be a last resort and must be aimed directly at adult beetles.
• Organic alternatives such as a combination of azadarachtin (an extract from the neem tree) and karanja oil (from the tree Pongamia glabra) are sometimes effective.

References

Diver, Steve. "Cucumber Beetles: Organic and Biorational Integrated Pest Management. National Sustainable Agriculture Information Service. 2008. <http://attra.ncat.org/attra-pub/cucumberbeetle.html>.
Godfrey, L.D. "UC IPM: UC Management Guidelines for Cucumber Beetles on Corn." University of California IPM Program. Jan 2006. <http://www.ipm.ucdavis.edu/PMG/r113301011.html>.
"How to Manage Pests in Gardens: Vegetables: Invertebrates: Lifecycle—Cucumber beetle life cycle." University of California IPM Program. 17 August 2009. <http://www.ipm.ucdavis.edu/PMG/GARDEN/VEGES/PESTS/LIFECYCLE/lccubeetle.html>.
"Managing Pests in Gardens: Vegetables: Invertebrates—Cucumber Beetles" Aug 17 2009. University of California IPM Program. <http://www.ipm.ucdavis.edu/PMG/GARDEN/VEGES/PESTS/cucumberbeet.html>.
Natwick, E.T. UC IPM: UC Management Guidelines for Cucumber Beetles on Cucurbits" University of California IPM Program. Dec 2009. <http://www.ipm.ucdavis.edu/PMG/r116300511.html>.
Rosetta, Robin. "Western Spotted Cucumber Beetle." Oregon State University Department of Horticulture. 5 June 2009. <http://oregonstate.edu/dept/nurspest/western_spotted_cucumber_beetle.htm>.