Vegetation diversity and insect pest outbreaks

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Abstract
The development of most insect pest complexes have been associated with the expansion of crop monocultures at the expense of weeds, hedgerows and other natural vegetation, thereby decreasing local habitat diversity. This simplification can seriously affect the abundance and efficiency of natural enemies, which depend on habitat complexity for sources of alternate prey/hosts, pollen and nectar, shelter, nesting and overwintering sites. Plant diversification of agroecosystems can result in increased environmental opportunities for natural enemies, and consequently improved biological pest control. Agronomically, there are two ways to design plant diverse cropping systems. One way is by manipulating the vegetation of field margins, and this can imply the management of the species composition and density of plants in ditchbanks, hedgerows, windbreaks and other types of shelterbelts. Within‐field plant diversity can be manipulated by designing polycultures of various temporal and spatial crop arrangements. The effects of some of these systems on the dynamics of insect populations will be discussed as it pertains to corn, beans, and cole crops. In addition, the effects of cover crop management on codling moth in apple orchards will be discussed. Another way to enrich the vegetational structure of cropping systems is through weed management. The impact of weed diversity in the form of weed borders, alternate rows, or by providing weeds in certain periods of the crop growth on insect dynamics will be presented.