Greenhouse Insect and Mite Pest Management
Biology of Insects
Knowledge of the biology of insect and mite pests and their natural enemies is a prerequisite for manging insect and mite pests. A successful management plan requires information about a species biology including its diet and lifecycle, how it interacts with the environment and with other species as well as species behavior and how the behavior of both pest and beneficial insects can be manipulated to prevent or reduce yield losses.
Insect Growth and Development
A life cycle is the series of changes an animal goes through during its life. Some insects have a four-stage life cycle. The insect lives as an egg, larva (LARvuh), pupa (PYOO-puh), and an adult. Others have a three-stage life cycle. The insect is born as an egg, hatches as a nymph (NIMF), and changes into an adult. In greenhouse systems, it is important to be able to recognize both the adult and immature life stages of insects to be able to make appropriate management decisions.
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
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 is undergoing 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.
Nymph
In the three-stage life cycle, eggs do not hatch as larvae. They hatch as nymphs, which look like small adults. Some nymphs do not have full wings. Others, such as the dragonfly nymph, may live underwater. As the nymph grows, it slowly matures into an adult with fully formed wings and reproductive organs.
Insect Feeding
Insect mouthparts are of two main types: chewing and piercing-sucking. Some insects have modifications of these two basic types. Mouthparts determine how an insect feeds and therefore play a role in the type of insect control that is most effective. Insects feed on leaves, buds, stems, roots, fruits and seeds, as well as on plant tissue at various stages of decay.
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 internal and liquid portions of the plant are swallowed, while the insect feeds externally on the plant. These insects have a slender and sharp pointed part of the mouthpart which is thrust into the plant and through which sap is sucked.
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. For example, black vine weevil larvae feed on roots, but the adults feed on foliage.
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.
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