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BIOLOGICAL CONTROL

Biological control is the use of living creatures such as predators, parasites and diseases to control pest insects.

Predators are organisms that kill and feed on their prey outright. They are generally larger than their prey and must consume numerous prey in order to complete development. Parasites, on the other hand, are usually smaller and often weaker than their prey. They lay eggs on or within a host insect and the immature(s) use the host for food over time. Individual parasites utilize only one or a few insects for food.

Predators and parasites account for much of the reduction of pest insect populations in nature. However, in agricultural and sometimes garden situations, their effects are often not dramatic enough to satisfy a farmer or homeowner. There are, of course, exceptions.

PREDATORS
(Organisms that require several prey to complete development.)

Insects

Ladybeetles
These rounded beetles come in many sizes and colors. The most common species found in Arizona is the convergent ladybeetle, named for the two converging white stripes on the back of its thorax. The beetles are brightly colored with red front wings speckled with black markings. The adults lay orange eggs in clusters on plants near groups of aphids. The eggs hatch into tiny black and orange larvae which feed on aphids in great numbers. As the larvae grow, they resemble tiny beaded dragons. Once they reach maturity, they form a rounded black and orange-marked pupa attached to the plant. The pupae may be mistaken for bird droppings.

Much has been made of the fact that wild-caught ladybeetles sold in garden stores are in diapause (a hibernating state where they do not feed or reproduce) and will fly away as soon as they are released. However, most reputable stores now feed the beetles before shipment so they are ready to settle down and lay eggs as soon as they arrive. Of course, they should be released near the aphids you are trying to control. In most areas of Arizona, ladybeetles arrive naturally when aphids appear. Thus, it is better to encourage their survival by not applying insecticides, than to purchase them.

Less common species of ladybeetles are smaller (about 1/4 inch long), with shiny black front wings. Some may have two or more brownish-orange patches on either side. Often their head is hidden from above. They may feed on other insects, such as mealy bugs, cottony cushion scales, California red scales or spider mites.

Green Lacewings
Adult green lacewings are delicate, pale green insects from 1/2 to 3/4 inch long. Their wings have many veins, which gives them the net-like or "lace" appearance. They are attracted to lights at night and may be mistaken for moths except they have a characteristic fluttering flight when disturbed. Lacewings lay their pale green eggs on the tips of threadlike stalks on the underside of leaves. The immature lacewings hatch within a few days. They are no longer than 1/8 inch, alligator-shaped with large, sickle-shaped mandibles and light brown or grayish in color. They are ferocious feeders, and consume large numbers of aphids and other insect pests, for example moth eggs. When the larvae mature they form a yellow silken cocoon in which to pupate.

There are two species of lacewings that are brown as adults. They also feed on small insects and insect eggs as immatures.

Praying Mantises
The praying mantis is among the best known of the generalist predators. It sits and waits on plants until another insect crosses its path, and then it captures its victim with its spiny front legs. Female praying mantises lay their eggs in one to two inch long "cases" made of a dark brownish-gray papery material with numerous compartments. The egg cases are glued to twigs or branches, and are commonly found attached to the underside of boards. Praying mantis immatures emerge from the cases in the spring. They look like miniature adults.

Despite stories to the contrary, the female praying mantis does not bite off the male’s head during mating. That behavior was only observed when starving bugs were placed together under artificial conditions in the laboratory. A well-fed praying mantis in nature does not eat her mate.

Assassin Bugs
These brown insects are about 1/2 inch long, and often have spines on their legs. They are members of the "true bugs" and have sucking mouthparts, as do all the following bugs. Assassin bugs tend to creep over plants in search of caterpillars and other insects. They use their sharp "beak" to pierce their prey, and suck out the juices. The nymphs resemble the adults, except they lack wings.

Ambush Bugs
These insects are often brightly colored and sit and wait on flowers for other insects to visit. When an unsuspecting fly or wasp stops by the flower for nectar or pollen, it is "ambushed." They are known for their thickened forelegs, and the immatures resemble the adults.

Damsel Bugs
Nabids or damsel bugs are pale tan to gray insects about 3/8 inch long. They are elongate, and resemble assassin bugs, except they lack spines on their legs. Damsel bugs are common predators and are found in crops, grasses and weeds.

Big-eyed Bugs
These true bugs are about 1/8 inch long as adults, and are named for their strongly protruding eyes. The immatures resemble the adults, except are light-colored and lack wings. Big-eyed bugs are known to feed on caterpillars and whiteflies.

Minute Pirate Bugs
These smaller relatives of big-eyed bugs are important predators of spider mites, insect eggs and many other small insects. Both the immatures and adults are effective predators. They are often found in flowers where they feed on thrips. When prey is not abundant, some species may survive and reproduce by feeding on pollen.

Spined Soldier Bugs
Most members of the family known as "stink bugs" feed on plants, but the spined soldier bug is an exception. It feeds on the eggs, immatures and adults of a number of different insects, particularly moths.

Syrphid Flies or Flower Flies
We usually associate fly larvae with decaying garbage or manure, but the larvae of these flies are ferocious predators of aphids. The larvae are soft-bodied, tapering in shape and spend their lives on plants. The mature larva is about 1/2 inch long and most are translucent green in color. The adult flies are black with yellow markings, and may resemble bees, except they have two wings rather than four. The adults are excellent pollinators and are seen in hovering flight around flowers.

Wasps
Wasps are generally known for their ability to sting, but they are also beneficial because they are predators of other arthropods. The adult mud dauber wasp captures prey such as an armyworm caterpillar. If the caterpillar is too large to carry back to her mud nest, she may tear off a bite size piece and return several times, until the caterpillar is consumed. She feeds the caterpillar bits to her larvae in much the same way a female bird feeds worms to her babies.

Dragonflies and Damselflies
These aquatic insects are great aerial acrobats. They catch small winged insects such as mosquitoes, flies or moths on the wing.

Spiders

All spiders are predators. They feed on a wide variety of insects and other invertebrates. All spiders spin silk, but not all spiders make a web to trap their prey. Some spiders are active hunters, such as wolf spiders, jumping spiders or crab spiders. Crab spiders have their legs directed forwards, so they resemble crabs. They are often brightly colored, and sit and wait on flowers for unsuspecting insects to visit.

Other arthropods are also predators of insects, including sun spiders, scorpions, whip scorpions, centipedes, and predatory mites. The importance of these creatures in controlling pest insects is often ignored.

Other Creatures Which Use Insects for Food Are:

• Fish - In fact, certain species of fish may be added to ponds used in landscapes to feed on the larvae of mosquitoes. Every fisherman knows to use flies to catch a trout. The best "fly" to use is the one that resembles the aquatic insect which the trout is currently using for food.
• Amphibians - Frogs feed on a number of insects.
• Reptiles - Snakes, some turtles, and lizards all feed on insects and other arthropods.
• Birds - Many different kinds of birds are insectivores, including owls.
• Mammals - Bats, shrews, moles, etc. all feed on insects. Many other types of mammals supplement their diet with insects, including humans.