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Biological Controls: Insects
Methods of controlling insects biologically

The Natural life cycles of insects

One method of preventing bug problems is to take advantage of their natural cycles. If you have gardened for a few seasons you no doubt have noticed that insects usually appear at about the same time every year.

They live their short active lives and disappear until the next year or until a second generation is spawned. In many cases, this leaves plenty of time to sneak in a crop, either before or after the bugs go through their hunger stage. Although seed planting and transplanting seedlings is very dependent on the vicissitudes of local weather, a couple of examples should be instructive.

Cabbage may escape the ravages of the cabbage worm, looper and aphid if planted as early as possible. Near New York City, snap beans planted early in June should miss the Mexican bean beetle.

This season, log the kinds of pests that cause trouble, when they appear, and when they disappear. Your garden records should suggest several possibilities for timed planting.

Biological Controls

If a crop is endangered despite your precautions, you should first consider biological controls. While most gardeners are familiar with the predaceous ladybug and praying mantis, many lesser known beneficial insects and even pathogens deserve recognition as effective natural organic insect controls.

Insect predators

The parasitic tachinid flies resemble ordinary houseflies and as maggots they feed on caterpillars. Ambush, assassin and damsel bugs are fierce predators of many insects, including various caterpillars and grubs. There are also many helpful beetles, including large, dark ground beetles, checkered beetles, soldier beetles, and the larvae of lightning bugs. Several species of lacewings eat significant numbers of mealybugs and aphids. Braconid and chalcid wasps parasitize mealybugs, aphids, scale, and the larvae of many beetles and moths. One egg parasite, known as trichogramma, is commercially available.


In addition to these insect predators, there are several types of pathogens at work in the garden: bacteria, viruses, fungi, rickettsia, nematodes, and protozoans. The bacterial diseases are most numerous; they usually work by entering insects through the mouth and then multiplying in the bloodstream. Two such diseases are available commercially.

Bacillus thuringiensis and Bacillus popilliae

Bacillus thuringiensis is effective against an impressive number of common pests, most of which are moth and butterfly larvae. Bacillus popilliae is used to combat the grubs of the Japanese beetle. The spores that form within infected grubs lend a whitish cast to the victims, explaining the pathogen's common name, milky spore or milky disease.

Toxic chemicals

All of these controls work in the home garden, but there are several things you can do to increase their populations and effectiveness. Most important is excluding toxic chemicals. Because beneficial insects are often more susceptible than pests to chemicals, spraying and dusting often allow the target insect to come back stronger than ever. Another malfunction of the unnatural clockwork caused by toxins is the outbreak of secondary pests that were innocuous and went unnoticed until doses of pesticide killed off the beneficials that had been keeping them at bay.

Pesticide resistance

Another problem spawned by pesticide interference with biological control is pesticide resistance. Because of their greater reproductive powers and better chances for adaptation, plant-eating bugs are able to build up resistance faster than their natural enemies, and successively larger doses only serve to set back these enemies. Well over 200 pests are known to be resistant to one or more pesicides.

Encourage beneficial insects

You can encourage beneficial insects by companion planting with the favorite crops of those species you wish to attract.

For instance, the adult forms of some beneficial species are not carnivorous and rely on high-protein foods such as nectar and pollen to sustain themselves.

Some ladybugs will turn to pollen if the aphid population drops off, and this suggests the importance of companion planting for insects by growing pollen-producing plants near crops of trees vulnerable to aphids.

Spring Gardening
Copyright© 2016 Gene DeFazzio
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