Cotton cultivation practices with special reference to the effect of Bt-cotton on Arthropoda populations

Cotton is internationally regarded as an important crop. Organically grown cotton, the use of integrated pest management methods and the use of Bt-cotton are thee types of cotton cultivation practices that receive interest worldwide. A review providing a synopsis of recent literature on insect pest management strategies for the organic cultivation of cotton, including cultural methods, transgenic cotton, resistant cultivars, sterile insects, biological control, biopesticides and mating disruption techniques are presented. Pesticides are extensively sprayed on cotton crops to control pests. Fifteen insecticides, five herbicides and two nematicides, commonly used during cotton crop protection in South Africa, are discussed. An environmental impact assessment was conducted and no direct adverse effects on the environment because of pesticide usage on the farm under investigation were found. Bt-cotton, i.e. cotton containingCrygenes from Bacillus thuringiensis Berliner, is lepidopteran specific. Although no direct adverse effects on non-target arthropods are expected, the effect on non-target species and groups should be investigated. The efficacy of Bt-cotton against Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae), a major pest of cotton crops, and the effect on non-target arthropods, Arthropoda guilds, predator-prey interaction and spiders were determined during a two-year study at a cotton farm near Marble Hall, South-Africa. Scouting and pitfall trapping were conducted once a week. A sprayed non-Bt cotton field was included as a reference during the second season. Helicoverpa armigera larvae were effectively controlled by Bt-cotton and endosulfan applications. Moth numbers, H. armigera oviposition and parasitoid emergence from bollworm eggs were not influenced by Bt-cotton. Bt-cotton and endosulfan applications had no apparent effect on total arthropod abundance, Coleoptera, Collembola, Dermaptera, Diptera, Heteroptera, Hymenoptera, Isoptera, Orthoptera, Psocoptera, Acari and Chilopoda numbers; or on predator, parasitoid, herbivore, pollinator or decomposer Arthropoda guilds; or on aphid, whitefly, chrysopid and coccinellid abundance and their predator-prey interactions; or on spider populations occurring in cotton fields. More studies, however, are needed to determine if Bt-cotton poses possible long-term adverse effects on Arthropoda populations that are not evident with a two-year study.