Nature’s assassins can be cruel
We had a nest of Carolina wrens this spring outside our window. One morning, the chirping stopped. A snake was curled in the corner with three lumps in its belly. My daughter wanted to teach the snake a lesson. Predators, however, are essential to nature’s balance, and insects are no exception.
In August, tomato growers may find caterpillars as large their index finger with a red spike on the abdomen. The spike is harmless but tomato hornworms are hungry. Left unattended, they will eat every leaf. Occasionally, wasps will stop them.
Braconid wasps are parasitic wasps about the size of a gnat. Females will sting the hornworm with the ovipositor to lay eggs inside the caterpillar.
After hatching, larvae start eating the caterpillar and the caterpillar stops eating your tomato plant.
The braconid larvae eventually chew their way out to pupate. They attach cylindrical white cocoons to the caterpillar’s body. The hornworm, meanwhile, is still alive but still not eating your tomato plant. An adult braconid wasp will emerge to search out another hornworm.
Numerous beneficial insects sustain their populations on a steady diet of aphids. Lady beetles, mealybug destroyers, syrphid flies and assassin bugs frequently graze an aphid-infested host.
Aphids’ only defense is to reproduce faster than predators can eat.
One commonly seen beneficial aphid-feeder is the wheel bug. The wheel bug is an assassin bug with a half-disc of spikes on its back, reminiscent of what insects might have looked like during the Stone Age. These large, intimidating insects pick up aphids and pierce them with a long, straw-like mouthpart to suck out their insides, discarding the emptied exoskeleton when finished.
Braconid wasps also attack aphids. They’ll lay an egg in individual aphids with their stinging ovipositor.
Unlike the hornworm, the braconid wasp larva pupates inside the aphid. The parasitized aphid is easily identified among living aphids by the bronze exoskeleton and the exit hole where the braconid wasp emerged.
The red imported fire ant was introduced from South America around 1930. This ant species has become a problem because they lack natural predators in the United States. To curb their aggression, natural predators such as the phorid fly have been introduced.
Clemson first released the phorid fly in 1998 to reduce red imported fire ant aggression and subsequent releases have shown encouraging results. The tiny, hump-backed fly is also known as the ant-decapitating fly. Phorid flies stalk ant mounds and lay eggs in the thorax, or mid-section, of an emerging ant.
The larva migrates into the head where it consumes the brain. The mindless ant will wander around like a zombie until its head literally falls off. Eventually, an adult phorid fly will emerge.
These pests are the size of pollen and are frequently a problem in greenhouse production. Miticide-resistant spidermites frequently developed because spidermites complete generations, eggs to adults, in a few weeks.
However, predatory spidermites can be used to feed on some of the most troublesome spidermite infestations.
Jeremy Webber, a graduate of TTC horticulture, works for Koopert Biological Systems that releases spidermites for commercial greenhouse producers.
The approach has proven to be effective and economical. There is little chance of resistance and no pesticide residual.
Nematodes are microscopic roundworms that infect roots and sometimes foliage of crops, turf, and trees. There are parasitic nematodes, however, that seek out insect hosts such as caterpillars and white grubs.
Essentially, predatory nematodes use a host to farm bacteria. Once a predatory nematode penetrates the host, it releases lethal bacteria that the nematode will feed on.
Products such as Double Death contain two types of predatory nematodes and can be purchased by homeowners.
While many beneficial insects can be purchased and released, the outdoor effectiveness is not guaranteed.
Insects will often fly away. When purchasing products, always read the label. Using fewer pesticides and allowing feeder populations of insects, such as aphids, can increase the presence of beneficials.
Tony Bertauski is a horticulture instructor at Trident Technical College. To give feedback, e-mail him at tony. firstname.lastname@example.org.