Integrated Pest Management Guide

INSECT LIFE CYCLES

LEPIDOPTERA (BUTTERFLIES AND MOTHS)

All Lepidoptera undergo complete metamorphosis in which there are four life stages per generation: egg, larva (caterpillar), pupa, and adult. There may be one generation or multiple generations per year, depending on species, although some arctic species take up to 17 years to complete a single generation. The overwintering stage can be either egg, larva, pupa, or adult, again depending on the species.

Egg: Females lay eggs either by dropping them on the ground (e.g., girdler moths), or by laying them on or in specific host plants (e.g., blackheaded fireworm moths). The number of eggs varies from several to several hundred, depending on the species.

Larva: Larvae (plural of larva) are the destructive stage. Development is usually rapid as they are ravenous feeders. The larval skin does not stretch and is shed several times during the larva's life to allow for growth. The stage between each molt is called an instar. The newly hatched larva (or neonate) is called a first instar. After the first molt it's called a second instar and so on. There are commonly five to nine instars, depending on the species. Larvae have three pairs of thoracic legs near the front and two to five pairs of abdominal prolegs towards the back.

Pupa: The pupa is the resting stage during which the larva changes into a butterfly or a moth. When a larva is fully grown, it finds a concealed place to pupate. Butterflies typically hang upside down on a leaf or branch and shed their skin to form a chrysalis. Moths typically pupate within a cocoon constructed in a variety of ways. It may be made entirely of silk or, more frequently, a mixture of silk and foreign materials. It is usually hidden in the soil or under bark.

Adult: The adult's sole purpose is to mate and lay eggs. Female moths secrete pheromones that attract males for mating. Specialized cells on the male antennae are stimulated by the specific pheromone blend and the male flies upwind in a zig-zag pattern as it follows the pheromone plume to the female. Adults of some species feed on nectar or juices from rotting fruit but those of many species do not feed at all.

COLEOPTERA (BEETLES)

Like the Lepidoptera, beetles undergo a complete metamorphosis. There may be one to several generations per year, or larval development may take several years.

Egg: The number of eggs laid by the adult beetle varies among species. Eggs are usually laid in the habitat of the larvae and seldom diapause (enter a dormant stage for winter).

Larva: Beetle larvae are often called grubs. There are normally three to eight instars. Beetle larvae are varied in form but the head is well developed and sclerotized (hardened) in all species. Thoracic legs (near the front of the larva) are usually present but there are no abdominal prolegs (near the posterior end of the larva). The majority of the species are terrestrial but some species larvae and/or adults are aquatic.

Pupa: Like the Lepidoptera, the last instar larva sheds its skin to form a pupa. Pupation usually takes place in the soil or in the food plant. In some groups, a cocoon is spun.

Adult: Adults of some species live only a few days, while other species may live a year or more. Species of carabids (ground beetles) are carnivorous as larvae and adults and prey on pest species like weevil larvae. Other beetle groups, such as cucurlionids (weevils), are herbivorous and are often pests as adults and larvae.

DIPTERA (FLIES)

Like the Lepidoptera and Coleoptera, flies undergo complete metamorphosis; however, there is a major difference between these orders and the Diptera. The dipteran larva does not shed its skin during pupation - in most groups the larval skin hardens to form a shell. Because of this difference, the resting stage of Diptera is called a puparium. There may be one to several generations per year, depending on the species.

Egg: Mated female flies lay eggs directly on or near the food source. Egg development is normally rapid and larvae appear in a few days.

Larva: Fly larvae, more often called maggots, are soft-bodied. The larvae of most species of flies have a reduced head capsule. They do not have true legs and move by waves of muscular contraction through the body. They have an enormous variety of feeding habits, and individual species often have very precise requirements. Many consume decaying organic matter or are predacious. A large proportion are parasitic on other insects and other organisms. Larvae of most usually go through four instars but some species have as many as eight.

Pupa: Puparia (plural of puparium) may be naked or in a cocoon.

Adult: Adult flies have only one pair of functional wings, are mostly free-living and fly during the day. Some groups consume liquid food such as nectar (e.g., hover flies), others lap up juices from decomposing matter (e.g., blow flies), while many others are predacious (e.g., robber flies), or parasitic (e.g., black flies).

HOMOPTERA / HETEROPTERA (THE TRUE BUGS: SPITTLE BUGS, APHIDS, ETC.)

The true bugs have incomplete metamorphosis in which there are only three life stages per generation: egg, nymph and adult. There may be one generation or multiple generations per year, depending on the species. Species like cicadas may take many years to mature. Species such as aphids give birth to living young during spring and summer, but lay eggs in the autumn, that overwinter. Like in all insect orders, diversity is the rule.

Egg: Eggs are ovoid and simple. They are laid on or more often inserted into the foodplant.

Nymph: Depending on the species, there are usually three to seven instars. The nymphs resemble wingless, miniature versions of the adults. Froghopper nymphs, known as spittlebugs, produce a spittle-like mass that surrounds them for protection.

Adult: Most adults have two pairs of wings. The wings usually have a membranous texture and are held rooflike over the body. All species are terrestrial insects that feed on plant fluids. The damaging effect on plants may be direct or indirect. When the population of bugs is large the loss of sap results in poor yield and quality of plant. Indirectly, the weakened plant is more susceptible to attack by other pathogens, especially fungi and viruses. Many species of true bugs spread viruses from one plant to another. On the beneficial side, many homopterans play an important part in weed control. Some species prefer to feed on stems, others prefer the leaves, and some prefer the roots of plants. Several groups make galls on plants and feed within these growths.

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