One of the most common garden insect questions I get asked is “what are those little black, spotted beetles that are in my sweet corn, tomatoes, raspberries and perhaps worst of all, in your beer! These little nuisances are called picnic or sap beetles. They are attracted to ripe or damaged fruit and vegetables. I was harvesting some sweet corn that had some bird feeding damage at the tips of the ears. When I cut the tips off, a couple dozen of the little beetles came crawling out. Yuck! Needless to say they found their way to the compost bucket in a hurry! The ears of corn that did not show any damage at the tips were just fine.
Once people find out what they are, they want to know how to get rid of them. That is a more difficult question to answer. These little guys are actually rather difficult to control. First, they are not that easily killed by insecticides. Secondly, just when you want to control them, that is the time that you are harvesting the produce too. Thirdly, if the beetles are feeding down inside an ear of corn or in an overripe tomato, it will be difficult to get the insecticide where it will kill the beetles. Sap beetles are also pretty good flyers and also seem to have a good sense of smell to be able to find you beer, just a few minutes after you have opened it. Most garden insecticides have a pre-harvest interval, during which you are not supposed to harvest and eat the produce.
So, what can you do? The best thing to do is keep up with harvesting so that you don’t allow fruit to get over-ripe or remain on the plant after it has been damaged in some way. The sap beetles will be attracted to any waste fruit or vegetables too, so if you can keep waste materials away from your yard, that will help to reduce problems in the future. The adults will lay eggs near decomposing fruits and vegetables, so reducing waste piles will also help for next year. Some people take advantage of the beetle’s affinity to muskmelon (their favorite food) by using it as bait that they treat with an insecticide. As the beetles are attracted to the melons or rinds, they will be killed by the insecticide, preventing them from laying eggs in the fall.
