Beneficial Insects: Not All Bugs are Bad
(Page 5 of 8)
April/May 1995
By John Vivian
Japanese Beetles
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Popillia japonica arrived in North America in 1916 on shipments of Japanese iris, and has spread from Maine to the Carolinas. An example of an uninvited immigrant with no species-specific local predator, these aggressive, iridescent, halfinch-long scarab beetles can aggregate on orchard fruit and garden plants and chew them to shreds. I have known so many to gather on my pole beans and tall sunflowers their weight makes the plants droop. When you approach, they stick their spiky hind legs up, then buzz off before you can knock them into a can of water.
Milky spore disease is an effective bacterial killer of the underground larvae of Japanese beetles. You can purchase the dormant spore material and scatter it on the lawn, where it attacks the beetle grubs as they develop from eggs laid in the sod. In time, the disease will spread and exert a degree of control on the pests. Trouble is, the adults can fly long distances. You might enlist your neighbors and inoculate a large area of lawn.
A pair of unrelated insects that feed on nectar as adults, tachinid flies and the oneand-a-quarter-inch five-banded tiphiid wasp, evolved to locate native may beetle (june Bug) larvae underground and dig down to lay their parasitic eggs on or near them. They are becoming effective predators of Japanese beetles as well. You could mistake many species of tachinids for houseflies and the tiphiid wasp for a stinging pest and swat either of them. Don't.
And finally, please don't kill the moles that tunnel around in the lawn. They live on beetle grubs and will clean up the Japanese beetle larvae missed by milky spore and the parasitic insects.
Caterpillars
Moths and butterflies are pretty to look at, but their larvae are a major nuisance of garden and orchard. And, some of the most effective predators of caterpillars are the most likely to get swatted. The giant ichneumon (three inches long) wasp is really fearsome looking. It has a long, sticklike abdomen ending in a bulb, and in addition, the females have a long ovipositor (egg layer) at the tip. Legs dangle as they fly, and when they light on a leaf, they coil the long tail under them in a menacing fashion. But, they are a menace only to garden pest-insects. Along with the much smaller chalcid, braconid, and smaller ichneumon wasp species, they lay their parasitic eggs on all kinds of caterpillars.
Typically, a parasitic wasp lays one egg at a time on dozens of caterpillars.
Some female wasps will sting, but most live on nectar and won't bother anything but caterpillars unless you hassle them. Some are tiny and go after small larvae. Others specialize in large and voracious caterpillars such as tomato hornworm: the larvae of Manduca quinquemaculata, a big but seldom-seen night-flying moth. The huge caterpillars feed at night on foliage of green pepper plants, eggplant, tomato, potato, tobacco, and wild nightshades. If you see a big caterpillar (up to four inches long, tomato-green with a black, rear-facing curved spine at the back) with 1-50 little white eggs like rice grains along its back, let it be. The wasp larvae will hatch and tunnel inside the body, and in time the worm will die "giving birth" to a new generation of predatory wasps. By the way, the tomato hornworm's "horn" is not poisonous as often represented. If you see a hornworm without parasites, pick it. The spines of some other caterpillars can pierce your skin, break off, and cause a minor irritation—but not so much that you should resist knocking them off your plants.
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