Since the commercial cultivation of genetically modified (GM) crops began in the late 1990s, the planting area for such crops has markedly increased, especially in the USA, Canada, Argentina and China. The current predominant GM crops are both herbicide-tolerant and insecticidal (Bt) crops, the latter accounting for about 25% of the total area worldwide. Some researchers have suggested that transgenic insecticidal crops may have negative effects on non-target insects such as the monarch butterfly, green lacewing and ladybird beetle. However, subsequent studies have shown that these negative effects occur only in the laboratory under non-choice conditions, and that non-target insects are scarcely affected under field conditions. When considering the environmental effects of GM crops, it is important to well understand the above facts. This review summarizes research reports on the effects of transgenic insecticidal crops on non-target natural enemies and soil microfauna. To date, none of the reports have described deleterious effects on non-target arthropods in the field or under field-cage conditions. GM crops expressing new types of insecticidal proteins such as lectins, protease inhibitors and vegetative insecticidal proteins are scheduled for commercial cultivation, and these crops will need to be evaluated cautiously for their ecological safety prior to field cultivation. As secondary insect pests that GM crops cannot control may become important pests, it will be necessary to study the complex interaction of transgenic crops, insect pests and their natural enemies in agro-ecosystems. Studies on soil microfauna have a number of methodological problems, such as which species or groups should be monitored, and how long the census period should continue. Most studies on the ecological impact of GM crops have been published by scientists who have created the crops themselves. In future, therefore, more reports by independent ecological researchers will be needed in order to provide more reliable data for citizens who are concerned about the safety of GM crops.
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