   Understanding Insects - May 12, 1999 Jeff Schalau, County Director, Agent, Agriculture & Natural Resources Arizona Cooperative Extension, Yavapai County Insects are probably the toughest part of my job as Yavapai County Agriculture and Natural Resources Agent. In college, I took only one course that discussed insects: Forest Protection. This course lumped insects with fire, fungal pathogens, and parasitic seed plants (things like mistletoe). The instructor was a borderline pyromaniac; so guess how we spent most of our lab time? Adult insects have three distinct body regions: head, thorax, and abdomen. Their jointed legs are attached to the thorax. Insects are invertebrates (lacking backbones) and have a hardened exoskeleton made of chitin (pronounced kitten with a long "I"). Insects range in size from wasps less than a millimeter long to long-horned beetles that reach up to sex inches in length. To date, approximately one million insects have been identified and it is likely that a total of 1.3 million exist. All insects change shape and size during their life cycle. These are tow of the main reasons why insects are so difficult to identify and study. To really understand an insect, one must follow it through its life cycle. There are two distinct types of insect life cycles or metamorphoses. More primitive insects go through a simple metamorphosis. Here the egg hatches and as the insect grows, it molts passing through several nymph stages. The nymphs resemble the adult insect and generally feed on similar hosts to the adult stage. The adult is the sexually mature stage. Grasshoppers, crickets, cicadas, earwigs, termites, cockroaches, aphids, and true bugs have simple metamorphosis (also known as nonmetamorphosis). More highly developed insects go through complex metamorphosis. Here the egg hatches into a larval stage that goes through several molts until it pupates (forms a resting body). The pupa stage does not feed. In the pupal case, the insect literally rearranges itself at the molecular level. When the process is complete, the adult insect emerges to find a mate and procreate. Butterflies are the classic Example of this but flies, bees, wasps, and beetles also have complex metamorphosis. Remember the movie "Invasion of the Body Snatchers?" It was based on complex metamorphosis. The most critical insect features to the backyard gardener are insect mouthparts. Sucking and chewing mouthparts are often used to consume our crops and ornamentals. Cicadas, aphids, true bugs, thrips, and whiteflies have sucking mouthparts that drain the cell sap and transmit plant diseases. Grasshoppers, crickets, caterpillars, beetles, and borers have chewing mouthparts that remove large areas of plant tissue. These clues lead to proper identification of pests and sound decisions about what action to take if any. Before taking any action, the insect must be identified. The most common question I am asked in the Cooperative Extension office is "how do I kill this @#$%&* insect?" Most often the insect in question is either benign or beneficial. Sometimes the client has applied a chemical insecticide to an identified "pest" such as an aphid. This approach will also kill beneficial predators and pollinators that visit the area. What is it about insects that inspires human beings to kill them without knowing whether or not they are causing any serious damage? Of course, insecticides are wonderful tools that have increased our ability to produce food and fiber. They have a place in our world and much research is being done to make them safer in the environment. Insect growth regulators (IGRs) are an excellent example. I've used a IGR on fleas that prevents a flea from molting to the next nymph stage yet it has no harmful effects on human metabolic systems. The more you learn about insects, the more respect you have for them and Arizona is an excellent place to learn to appreciate them. For some reason we are innately afraid of insects and stomp, swat, or spray them before we think. One of my theories is that some home gardeners kill insects because they can. The 1950's movie "Them" probably started our hate for insects and we've been building on it from there. "Them" was the movie were ants were exposed to radiation and they grew to the size of B52s. Thank goodness we overcame them with machine guns and hand grenades. The University of Arizona Cooperative Extension has publications and information on insects: harmful and beneficial. If you have other gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113 or E-mail us at mgardener@kachina.net and be sure to include your address and phone number. |