Like it or not, insects play an important role in gardening and landscaping. Often, insects such as lady beetles, lacewings, ground beetles, bees and others are beneficial. On the other hand, pest insects such as aphids, leafhoppers, cutworms and ants can either damage plants or drive us crazy. In order to know how to manage pests and do as little damage as possible to the “good guys,” it helps to have an understanding of insect characteristics and their life cycles. Timing a pesticide application to the correct stage of insect development can make a big difference in reducing pest populations while minimizing harm to beneficials.
Insects are part of a large group called arthropods. They have segmented bodies with a head, thorax and abdomen, an exterior skeleton (exoskeleton) and six legs. How arthropods feed, with either sucking (aphids) or chewing (beetles) mouthparts, determines what kind of plant damage they might do. Most insects start as eggs, although aphids have live births. After hatching, they usually go through a series of immature stages before becoming adults. Because their exoskeleton expands very little as they develop, it is necessary for them to molt, shedding the confining skin and growing a larger one. Some insecticides, called insect growth regulators, disrupt normal growth and development by interfering with the hormones that trigger molting.
Insects change from egg to juvenile to adult through a process called metamorphosis. Simple metamorphosis means immature insects (nymphs) look similar to the adults as they go through various growth stages. They usually feed on the same plants as the adults. Aphids and leafhoppers go through simple metamorphosis. On the other hand, many insects are quite different in appearance in their immature stages to the adult stage. They go through complete metamorphosis. The young in this type of metamorphosis are called larvae. They usually have chewing mouthparts, while the adults often have sucking mouthparts, and each stage eats different things. Butterflies are a good example of complete metamorphosis, going from the caterpillar stage to the cocoon (pupa) and finally to the adult winged stage. Flies and beetles are other examples.
Coordinating control tactics with the appropriate life stage can increase the effectiveness of the control and reduce costs and effort. For example, horticulture oils are most effective against exposed eggs, immature stages and soft-bodied adult insects such as scales, aphids, whiteflies and leafhoppers. Before applying a pesticide, whether organic or inorganic, identify the insect and its life stage to maximize results.
JoAnne Skelly is the Carson City/Storey County Extension educator for University of Nevada Cooperative Extension and may be reached at skellyj@unce.unr.edu or 887-2252.
