Managing Beneficial Insects in Commercial Cotton Fields
Cotton crops in Australia are visited by a wide range of beneficial insects. These include generalist predators and specialist parasitoids which attack key pests. The potential value of these beneficial insects has not been widely exploited in cotton pest management due to lack of understanding of their impact on pests, lack of techniques to maximise their abundance and effectiveness and indiscriminate use of broad-spectrum insecticides on cotton crops against major pests. The adoption of within field monocultures in the cotton production system in Australia also discriminate against and reduce the activity of beneficial insects because they lack ecological diversity (Hagen and Hale, 1974). In such agroecosystems, pest populations increase, minor pests become major pests and non-pests become pests. This is because the food, hosts, prey, and hibernating or over wintering sites of the natural enemies are reduced thus affecting biological control (DeLoach 1971; Mensah, 1997; 1999). Natural enemies of cotton pests usually have different food requirements in the larval and adult stages to develop and survive through the season. In contrast, adult pests particularly Helicoverpa spp. can nominally lay their eggs without any feeding, relying only on food reserves transferred from their larval stage (Beirne 1967). Helicoverpa spp. are highly migratory and can rapidly infest cotton crops and lay their eggs. Unless natural enemies are present and well established in high numbers before the pest arrive, they cannot respond rapidly enough to control these pests (Fitt, 1989; Mensah, 1997, 1999).