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Competency Area 4: Management of Arthropods

PO 33. Recognize the three major classes of beneficial organisms and know at least two examples of each (parasites, predators and pathogens).
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PO 34. For each example, be able to discuss its importance in pest population regulation. Examples include:
A. Spiders
B. Parasitic wasps
C. Parasitic flies
D. Predaceous insects
E. Damsel bug
F. Minute pirate bug
G. Lacewings
H. Big-eyed bug
I. Lady-bird beetle
J. Ground beetles
K. Predaceous mites
L. Entomopathogenic nematodes
M. Entomopathogenic fungi

All insects within their native homes are held in check with their own array of biological control organisms. These organisms include diseases, parasites and predators. In addition, adverse weather conditions also have a negative impact on insect populations. Insects (and other arthropods) become economic pests when conditions change which negatively impact the biological control organisms and allow the populations of the insect pest to increase to economically damaging levels. These changes can include the introduction of the insect to a new region without the introduction of the natural enemies/diseases or a change in the cropping system which inhibits the biological control activities of the natural enemies and encourages the population buildup of the crop pest. A large number of the current economically important crop pests in field crops are introduced insects into North America from other parts of the world. A couple of examples are European Corn Borer, Alfalfa Weevil, and Cereal Leaf Beetle. Alfalfa weevil and Cereal leaf beetle are generally not considered a widespread economic pest because of successful efforts to establish the biological control organisms from their native homeland which held them in check throughout their native range. Similar efforts for European Corn Borer have not been successful.

In contrast, Western and Northern Corn Rootworm are native to the US and have shifted from their native plants onto cultivated corn. The change of life style and habitat has released these insects from their natural enemies and the enhanced food source (cultivated corn) has allowed the insect to rise closer to their reproductive potential. As a result, corn rootworm is a very significant agricultural pest.

Types of Biological Organisms: Biological control organism fall into three different categories. There are insect diseases (viral, fungal, bacterial), internal parasites (parasitoids) and external predators.

  • Insect diseases (Insect pathology): Each insect species has an array of disease which keep the species in check within its native habitat. When an insect species is introduced into a new environment (usually through human assisted movement), the array of diseases are not usually moved with the insect and the insect population explodes in the new relatively disease free environment. The reintroduction of effective disease organisms into the new area and invasive population has been very effective in controlling invasive insects which become economically important in the new outbreak area. Examples of effective biological control with the use of insect disease organisms are Alfalfa Weevil and Gypsy Moth. Insect attacking nematodes (entomopathogenic) are also considered in the area of insect pathology. Entomopathogenic nematodes are most effective on soil insects.
  • Parasitoids (internal parasites): Whole groups of insects have adapted their lifestyles as internal parasites of other insect species. Insect parasitoids fall into two groups. The first group are parasitic wasps and the second group are parasitic flies. In both cases, eggs are either laid internally or externally on the insect host. The parasite egg hatches and feeds internally within the host insect. In the process of feeding, the host is killed. After development is completed, the parasitic insect pupates to an adult and emerges from the host insect cadaver. The newly emerged adult then searches for other suitable hosts in which to lay eggs (oviposit). The effectiveness of parasitoids as a biological control agent is determined by the adaptation of the parasitoid species to the new environment in which they are released and the matching of the parasitoid searching behavior to the new environment to which the host insect has adapted to. Examples of effective parasitoid based biological control are Alfalfa Blotch Leafminer, Cereal Leaf Beetle and Alfalfa Weevil (in some years).
  • Predators: There is a wide array of insect and mite species in numerous orders which have adapted to the role of insect predators. Insect predators search for, attack and consume other insects externally (as contrasted to internal parasitoids). Commonly recognized predators are the Lady-Bird beetle, Lacewings, Big-eyed Bug, and Damsel Bug. In addition, ground beetles and predaceous mites are also effective predators. Generally, predators are most effective when host insects are in high numbers. Examples of insects controlled by predators are aphids and plant feeding mites.