While going through my garden this week, I noticed some strange activity on some of my nearly ripe tomatoes. Upon closer inspection, I realized that some of the tomatoes had damage that pierced the skin, and that there were small black beetles present in the wounds (Figure 1). These beetles are commonly referred to as sap or picnic beetles and they can become a pest from now until the first hard frost in gardens and orchards.
Picnic beetle adults are attracted to ripe or decaying plant matter, which they will feed on and lay eggs within. These beetles are normally an indicator of previous damage to the plants, but will also assist with the breakdown of the plant material. In some cases, they can be a pest if they increase the size of the damaged area on fruits and vegetables such as apples (Figure 2), strawberries, raspberries, sweet corn and tomatoes, or if they begin feeding on undamaged fruit. Picnic beetle feeding is usually associated with deep cavities in the fruit. Their feeding can also introduce fungal spores that will lead to additional breakdown of the fruit.
Figure 1. Picnic beetle adults feeding on a damaged tomato. Courtesy: Adam Varenhorst
Figure 2. Picnic beetles and sap beetles feeding on a damaged apple. Courtesy: Adam Varenhorst
Sap beetles are about ¼ inch long, brown in color and do not have any spots. Picnic beetles are slightly larger than the sap beetles and are black in color. Picnic beetles also have four yellow to orange colored spots on their abdomens.
Protecting Your Garden Produce
The first thing to do to reduce picnic or sap beetle problems is to maintain a clean garden or orchard. Remove any overripe, damaged, or diseased fruit and vegetables regularly. Simply throwing them into a compost pile won’t be enough as these beetles are mobile. The best strategy is to bury the infested fruits or destroy them using other means. This will remove the beetles’ food sources and reduce the attractiveness of the garden or orchard.
If picnic or sap beetles are already present, bait traps can be used to attract and remove the beetles from the area. These bait traps can be made using a bucket baited with ripening fruit, bread dough, stale beer, or vinegar. When using a liquid bait, add a drop or two of liquid dish soap to break the surface tension of the liquid so the beetles will sink. These traps should be placed outside of the area that you are trying to remove the beetles from, and the contents need to be discarded every 2-3 days to prevent infestations from becoming worse. Once the contents are discarded, the traps should be rebaited and replaced until all produce can be harvested.