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Competency Area 4: Management of Arthropods

PO 29. Know the advantages and disadvantages of using pesticides to control arthropod crop pests.

The use of chemical pesticides has long been viewed as the “line of first attack” when the use of pesticides should be viewed as a “strategy of last defense”. The past widespread use of pesticides has created as many problems as it has solved. The development of insecticide resistance in insects, herbicide resistance in some weed species and fungicide resistance in an array of plant disease pathogens was predicted by scientists, ignored by the agribusiness industry and has created a number of difficult pest management problems. These situations have led to the development of “resistance management strategies”.

  • Resistance Management: Resistance management is the adoption of agricultural practices which delay, reduce or prevent the development of resistance to a specific pest management strategy.
    Initially, the genetics for resistance in a population is extremely rare and resistance only becomes a problem when the selection pressure on the population is intense enough that only the resistant individuals survive, interbreed and concentrate the genes for resistance in the population. An effective resistance management program utilizes a wide array of pest management practices which allows enough susceptible individuals to survive to interbreed with the resistant individuals to prevent the concentration of the genetic resistance in the majority of the population.

  •  Pesticides: Widespread use of insecticides since the 1940’s has promoted the development of insecticide resistance in numerous insect species. For a time, the insecticide industry could develop new insecticides as fast as insecticide resistance developed and the issue of resistance management was ignored. With the slowing of insecticide development in the late 1980’s, the issue of preserving the various insecticides by managing the exposure of the target insects to the insecticide and reducing the development of insecticide resistance became a key issue. Currently, the use of insecticides only when economic losses are expected and the rotation of different insecticide classes reduces the selection pressure on the insect population to develop insecticide resistance. An additional strategy which helps to prevent the rapid development of insecticide resistance is the deployment of refuges as described in the above described section.

  • GMO crops: Many GMO crops have an insect active toxin incorporated into the plant genome. The presence of this toxin in plant tissue has a significantly more potent genetic selection pressure on the insect to develop resistance than the use of a topically applied or systemic insecticide. The plant based toxin is present in the plant at all time where the external insecticide concentration degrades with time, allowing some insects to reduce exposure and survive without mechanisms of genetic resistance. Currently, the EPA requires the planting of GMO-toxin free refuges in coordination with the planting of the insect active GMO crops. For example, the planting of GMO Rootworm resistant corn varieties requires a 20% refuge plant within the field or immediately adjacent to the field with a corn variety of the same maturity rating where the plant incorporated toxin is absent in the plant. This allows rootworm larvae to survive, emerge as adults and mate with any potential resistant individuals that have successfully survived exposure to the plant based toxin.