Regional Gardening Reports :: National Gardening Association

In the Garden:
Southwestern Deserts
October, 2010
Regional Report

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This beneficial spider awaits prey by camouflaging itself with colors of the flower it hides in.

Integrated Pest Management Part 4: Biological Control Methods

Integrated Pest Management (IPM) combines diverse methods to control pest or disease problems and grow healthy plants, with chemical controls used as a last resort. My favorite IPM topic? Biological controls: living organisms (including predators, parasites and pathogens) that provide pest control while I sit in a chair with a cool beverage. The nifty thing about most biological controls is that they will appear in the garden on their own schedule, when conditions provide them with something to consume or a host in which to deposit their eggs.

Predator insects voraciously munch up other living insects and insect eggs. They move around a plant, or from plant to plant, hunting for their next meal. Some have developed strong jaws to hold and chew their prey. Others use sharp mouthparts to pierce the victim and suck out its juices. As a bonus, predators are some of the prettiest (green lacewing, ladybeetle) and most intriguing (praying mantid) insects to grace your garden.

There are many effective predators that are not as showy or well known who work equally hard to rid the landscape of aphids, leafhoppers, mites, thrips, whiteflies and insect eggs. Some species of biological predator is probably at work in your garden right now, if you take the time to peer closely. Look for assassin bugs, big-eyed bugs, damsel bugs, green lacewing larvae, ladybeetles and larvae, minute pirate bugs, predatory ground beetles, predatory mites, spined soldier bugs and syrphid fly larvae.

And don't forget spiders! Although eight-legged spiders are classified as arachnids, not insects, but they are equally capable predators. They control a wide variety of insects, including annoying household pests such as cockroaches. Some spiders take on the coloration of the flowers they visit, camouflaging themselves as they wait for prey.

Parasites lay eggs on or within another living organism, known as the "host." When the eggs hatch, the larvae feed on the host, who eventually dies. There are many species of parasitic wasps and flies, and most are particular about which insect species they attack as hosts. These wasps are tiny and do not sting humans or pets. Common parasites are braconid wasps, trichogramma wasps and tachinid flies.

Braconid wasps deposit a single egg within an aphid body. The hatching larva devours the aphid from the inside out. The wasp eventually pupates and cuts a hole in the aphid's now-lifeless body to emerge in its adult form. Left behind is a brown, dry shell called an "aphid mummy."

Trichogramma wasps are often active in the garden, going unnoticed because of their tiny size (1/100 to 1/25 inch). Wasps lay their eggs on the eggs of caterpillar species, including such troublemakers as cabbage loopers, codling moths, corn earworms, and tomato hornworms.

Tachinid flies parasitize cucumber beetles, caterpillars, cutworms, grasshoppers and sawflies.

Certain disease organisms, such as bacteria, fungi and viruses, cause disease in other living things. Bacillus thuringiensis (Bt) is a bacterium that is probably the most commonly applied pathogen in the garden. It works only on caterpillars, destroying their digestive system. Susceptible plants are treated with Bt, caterpillars feed on the foliage and eventually die. Over 30 types of Bt target different species of butterfly and moth larvae. Bt israelensis controls mosquito larvae.

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