I try very hard in this blog to say something positive about every bug, but I can’t think of one good thing to say about the Western Spotted Cucumber Beetle other than it’s a pretty shade of green. This bug is a poster child for the lesson that not every native creature is beneficial. It’s a North American native and a North American major pest. Its larvae resemble little worms in the soil and are hellish devourers of young plant roots. The grownups can fly and they have a voracious appetite for flowers, leaves, stems and fruits of many crops, including squash, cucumbers, cantaloupe, soybeans, cotton, beans, peas, lettuce, spinach, and corn. Worse, they transmit bacteria wilt diseases and mosaic viruses.
The literature about these bugs consists almost entirely of methods for getting rid of them. Plants of the cucumber family (Cucurbitaceae) exude the chemical cucurbitacin to repel most herbivores; it gives the plant a bitter taste. But the cucumber beetle loves cucurbitacin and uses it to make itself taste nasty to predators. Its spots also send the message that it might be poisonous, making birds think twice. However, there are some beetles, flies, and nematodes that don’t mind the taste and are somewhat useful as biological control agents against cucumber beetles. There are also some plants that exude a smell that cucumber beetles don’t like, such as radish, tansy, and nasturtium; planting those next to beetle target crops reduces beetle invasions. In commercial agriculture, the preferred control method remains pesticides.
We have no agricultural crops in the park, so the threat from these no-good beetles can be safely ignored. It’s useful to know, though, that they are present. If you should happen to step on one, forgive yourself.