4 Spot Sap Beetle

By Kathleen Cue, Nebraska Extension Horticulture Educator

Picnic beetles are small black insects with yellowish spots on their wing covers. This nuisance insect feeds on over-ripe and decaying fruits and vegetables. Its common name comes from its annoying habit of showing up in your potato salad at outdoor events. While it can damage fruits and vegetables, picnic beetles take advantage of over-ripe produce, often eating their way through and enlarging the amount of damage. Their saliva and fecal material introduce an abundance of bacteria and fungi into wounds, hastening the decay process.

The picnic beetle’s other common name is the sap beetle, referring to its propensity for feeding on sap oozing from fresh pruning cuts on trees. This insect is the vector for oak wilt, carrying the causal fungal pathogen in its gut. Oak wilt is spread primarily from the beetle’s habit of regurgitating before feeding on sap. This pre-digestive step helps to dissolve their food and further complicates things by inoculating oaks with the oak wilt pathogen. To interfere with the spread of oak wilt, oaks should never be pruned March through October, when the picnic/sap beetle is still flying.

• Minnesota has several species of the sap or often called picnic beetles. They range in size from 1/8-inch to 1/4-inch. Depending on the species, they are mottled brown to black with one species having four distinct rust-orange spots on its wing covers. Another key identifying characteristic is the “knob” at the end of the antennae.
• Quadrisignatus is 5- 6 mm (1/4 inch) long, dark brown to black with two pale yellow spots on each wing cover. Carpophilus spp. Are usually elongate, flat, oval beetles that vary from 2- 4 mm (1/8 inch) in size. Most species are pale to dark brown-black. The pale yellow spots may be present depending on species. Often Confused With N/A.
• Sap beetle description Sap beetles are tiny (0.1 to 0.2 inches long), flat, and usually brown or black. They are active and move quickly. There may be spots on short wings and the antenna are clubbed. Larvae are white with a tan head, 3 pairs of legs and 2 horn-shaped structures on their back end.

Four-spot Sap Beetle Pictures Below are images of the Four-spot Sap Beetle. Click on the thumbnails to enlarge the images or return to the article.

There is no simple answer to managing picnic beetles on produce. Insecticides aren’t necessarily good choices because produce is close to harvest. Any insecticide sprayed on fruits and vegetables requires a period of time to elapse before harvest takes place. Called a pre-harvest interval (PHI), a PHI allows for the degradation of insecticides from wind, rain and sunlight. When choosing to use an insecticide, be sure to harvest first and then use an insecticide with a short PHI, such as Sevin, Neem oil or insecticidal soap.

Further complicating things, the picnic beetle is often inside the fruit or vegetable, making it tough to reach them with an insecticide. The best option for picnic beetle management is to harvest regularly and keep the garden clear of over-ripe and rotting produce. This insect lays eggs in rotting materials, so make sure your compost pile is situated a good distance from your orchard and vegetable garden. More information about the picnic/sap beetle is found here: https://hortnews.extension.iastate.edu/sap-beetles .

4 Spot Sap Beetle

Photo Below: Picnic Beetle on Under Ripe Tomatoe

Interested in finding out more about the Nebraska Extension Master Gardener program’s 2019 classes? Plan to attend one of two informational meetings in November:

November 15, 5:30 pm, Nebraska Extension in Dodge County, 1206 West 23^rd Street in Fremont

OR

4 Spot Sap Beetle Larvae

November 16, 1:30 pm, Nebraska Extension in Washington County, 597 Grant Street in Blair.

Go to Dodge County Horticulture Web Page for more gardening information.