Managing Vineyard Insect and Mite Pests
Biology of Insects
Insect Growth and Development
Most insects start life in an egg stage. The act of egg laying is called oviposition. The reproductive adult females of many species lay their eggs specifically in the area where the offspring will feed. A few insects, such as aphids, give birth to live young. The two major categories of growth and development are simple and complete metamorphosis. Simple metamorphosis (sometimes called incomplete metamorphosis) occurs in those insect species in which the young usually look very similar to the adults, except that wings are absent and they are not reproductively mature.
The Egg Stage
Most insects begin their lives as eggs, although there are some exceptions, such as aphids, which are born alive. They might be deposited on or in the ground, the roots, the stems, the leaves, or the flowers. Eggs may hatch soon after they are laid, or they may have a long incubation period. In other cases, they have mechanisms that allow them to survive between seasons or during unfavorable seasonal periods.
Larva
The larva seldom looks like the adult it will become. Some common larval forms are the maggot, grub worm, inchworm, and caterpillar. As the larva grows, it must shed its old skin from time to time. This is called molting. The distinct immature stages between successive molts are called instars. The first instar hatches from the egg, the second instar is after the first molt, and so on. Many natural enemies, especially parasitic wasps, attack only certain instars of the target pest.
Pupa
The pupa is the life stage between larva and adult. Unless the larva is in a stem or root tunnel, it will usually construct shelter to pupate in. This cocoon might be made from soil particles, silk, chewed seeds, chewed plant material, ground litter, or combinations. Inside the cocoon/shelter/chamber/capsule/case the pupa is gradually transformed into an adult. In this stage, the insect does not feed and can be considered motionless. But inside the cocoon, the insect undergoes metamorphosis (MET-ahMORF-oh-sis).
Adult
After the metamorphosis is complete, the pupa hatches as an adult. The adult insect has wings, six legs, and reproductive maturity. Adult insects will find mates, and the females will lay eggs. Sometimes, this is all the adults do.
Nymphs
Nymphs are the young of an insect that undergoes incomplete metamorphosis or no metamorphosis. The nymph eats, grows, and molts, going through several different nymphal stages called instars. With each successive molt, the nymph grows larger and begins to develop wings. Nymphs (e.g., whiteflies) look similar to adults in appearance, with the exception that they do not have fully developed wings. Slowly, the nymph transforms into an adult.
Insect Feeding
Insects with simple metamorphosis often feed as both nymphs and adults in the same location and on the same food. This is true of aphids, mites, mealybugs, scales, and thrips. The larvae of insects with complete metamorphosis often feed in a different location and on a different food than the adults. For example, black vine weevil larvae feed on roots, but the adults feed on foliage. Some insects, especially those with complete metamorphosis, feed primarily in the immature stages, and adult feeding may be insignificant. For example, leafminer maggots feed by chewing on plant tissue in their mines, while the adult flies feed by sucking plant juices from holes made in the leaves.
Injury by Chewing Insects
Chewing insect pests cause damage by consuming plant parts such as leaves and stems or burrowing in plant tissues, which damages the host plant. Symptoms of chewing insect pests include holes in leaves, silvering of leaf tissue, complete removal of leaf tissues and burrowing in or around plant stems, branches or trunks.
Injury by Piercing-Sucking Insects
Another important method which insects use to feed on plants is piercing the epidermis (skin) and sucking sap from cells. In this case, only the internal and liquid portions of the plant are swallowed, while the insect feeds externally on the plant.
Feeding Habits
Insects with simple metamorphosis often feed as both nymphs and adults in the same location and on the same food. This is true of aphids, mites, mealybugs, scales, and thrips. The larvae of insects with complete metamorphosis often feed in a different location and on a different food than the adults..
Mites
Mites are not actually insects, but belong to the related class Arachnida, which also includes spiders, scorpions, and ticks. The major morphological differences between mites and insects are found in the number of major body parts and the number of legs. The head, thorax, and abdomen, which are separate for insects, are fused into a single continuous body region for mites and, except for the initial mite developmental stage mites have eight legs, whereas insects have six.
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