Guild structure and seasonal distribution of insects associated with Amaranthus Hybridus under diverse cultivation practices in the Central Free State

[摘要] English: Biodiversity is a non-detachable part of the concept of sustainable agriculture. Thereliance on only a few crop species in the agricultural landscape poses specialproblems and risks due to biotic hazards. To enhance diversity, agriculture mustdiversify crop production and exploit under-utilized and new crops. Amaranthushybridus is such a crop and has great potential due to its hardiness and high nutritionalvalue. Acceptable crop yield depends on the influence of insects. Some sort of pestmanagement thus forms an integral part of agriculture. Due to detrimental effects onthe environment and the high cost of pesticides, farmers are looking for alternativelow cost methods, which will provide a long-term solution for pest problems.Cultivation practices are one such method, which aim to enhance natural enemyperformance. This study was conducted near the Tempe airport, 20 km northwest ofBloemfontein (SE 2926Aa) in the Free State. A monoculture trial was run in 1997and 1998, a mixed crop setup in 1998 and a staggered planting date culture in 1999.Monoculture, the most widely used method of farming in the Free State, reduces acomplex natural ecosystem to a single plant species environment, resulting in morevisual and chemical stimuli for flying phytophagous species, prompting them to landmore readily than in a more diverse plant environment. Thus, large populations ofphytophages occur in the mono culture, some of which, due to favourablemicroelimate could develop to pest status. Mixed cropping is a more diverse plantsystem, thus presenting a greater diversity of niches and consequently a higherdiversity of arboreal phytophages and natural enemies. Adjusting planting andharvesting time, such as staggered planting dates, can be used to escape pest damageand keep it below economic levels. By planting early sure pests population peaks canbe avoided. The terrestrial insect community is also of major importance, since manypredators are groundliving. Terrestrial insects are influenced by the microelimate andshelter provided by plants and preferred stands in which these factors are at anoptimum. In this study it was found that predators are most effective in large, sparsestands. To conserve natural enemies it is important to incorporate permanent habitatslike border areas where they can overwinter, build up population numbers and fromwhich they can disperse to newly planted crops. This study promotes conservationbiological control, which aims at using and enhancing beneficiais, which are alreadypresent, by using different cultivation practices. Farmers often lack the biological andecological information necessary to develop better pest management. This study wasaimed at providing that information to obtain maximum yield in the long term withlower production costs.

[发布机构] University of the Free State