Are Insecticides Killing Beneficial Insects?

Types of Beneficial Insects

• Three basic categories of beneficial insects occur within your garden: pollinators, predators and parasites. The pollinators include honeybees, butterflies, some wasps and some moths. For many plants, pollinators are the key aspect in reproduction, meaning the plants can't produce fruit or flowers without them. The predators include ladybugs, lacewings, some wasps and the noninsect spiders, and certain moths. Parasitic wasps are the major players in the parasite category; these guys often lay their eggs on or in caterpillars and other pests and then slowly kill them before they can do too much damage or reach adulthood.

Broad-Spectrum Insecticides

• As the term "broad-spectrum" implies, these insecticides kill a wide range of insects, including the good guys. While at first it may seem like the ideal product, because it kills a variety of pests at one time, the bad far outweighs the good. Many of the beneficial insects in your garden may be visitors to your neighbors' gardens, with ranges that could reach several miles. When you kill them, you're effectively taking away an integral part of your neighbors' beneficial insects as well as your own. Examples of active ingredients in broad-spectrum insecticides or those that are most toxic to all insects include carbaryl, chlorpyrifos, acetamiprid, dimethoate, fenpropathrin, pyrethrins and sodium tetrathiocarbonate.

Studies on Honeybee Decline

• When the words "beneficial insects" come to mind, the honeybee is often one of the first thought of, and for good reason. These powerful little pollinators are vital players in the pollination of wildflowers and several crops. Purdue University scientists have been studying the honeybee decline and have found high levels of neonicotinoid insecticides. This type of insecticide is related to nicotine and works by damaging the nervous system; the insect's nerves become excited, and paralysis sets in that results in death. These insecticides coat corn and soybean seeds prior to planting and are mixed with talc to more efficiently coat the seeds and prevent sticking; the residual talc is then expelled by farm machinery upon planting. Because the talc product is so highly concentrated, even a small amount landing on a flower can prove fatal for foraging bees or, worse, the entire hive. Clothianidin and thiamethoxam, two other insecticides toxic to bees, were found in the soil up to two years after application.

Less Toxic Choices

• In general, it's best to resort to insecticides only when the pest populations are so great that other methods don't work. Several types of insecticides are less toxic to beneficial insects and include insecticidal soaps, botanical insecticides, Bacillus thuringiensis (Bt) and horticultural oils. Most of these are more environmentally friendly, as well. Bt works on caterpillars, while insecticidal soaps and horticultural oils work on soft-bodied insects. A few beneficial insects are also soft-bodied, but on the whole these insecticides will not affect most predators.