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Natural Enemy Abundance in Commercial Bollgard® and Conventional Cotton Fields

Graham Head, Barry Freeman, William Moar, John Ruberso and Sam Turnipseed


 
ABSTRACT

A set of large scale, long-term field studies were initiated in 2000 to evaluate the relative impact of transgenic Bollgard ® cotton and conventional varieties treated with insecticides varieties on natural enemy abundance. Three or four pairs of Bollgard ® and conventional cotton fields were monitored in each of northern Alabama, southern Alabama, Georgia and South Carolina. Pairs of fields were chosen to be as similar as possible in location, variety, tillage practices, and border vegetation. Fields were at least 10 acres in size, and as large as 50 acres. Arthropod populations were sampled approximately weekly throughout the course of the season using a combination of whole plant samples, beat buckets and beat sheets. In the 2000 season, environmental conditions and Heliothine pest pressure were highly variable among the different regions. Of the four regions where paired sites were initiated, the only area with substantial Heliothine pressure was South Carolina. At the South Carolina sites, specific insecticide use for lepidopteran pests was necessary on the conventional cotton fields, and this led to significantly reduced numbers of various arthropod natural enemies relative to the Bollgard ® fields. Populations of predatory bugs including Orius and Geocoris species, spiders, and ants were all significantly decreased by conventional insecticide use relative to the Bollgard ® fields. These differences were clearly associated (in time) with the insecticide applications and presumably reflect direct toxic effects of these insecticides on non-target species. At the same time, aphid populations increased in the conventional cotton fields, as did ladybird beetle numbers. The impact on aphids is likely to be an indirect effect caused by reduced biological control. The ladybird beetles then appear to be immigrating into these fields to feed on the aphids. In the other regions where Heliothine pressure was lighter, conventional insecticide use was no different between the Bollgard ® and conventional cotton fields, and no significant differences were seen in the arthropod natural enemy populations in these fields. These preliminary results suggest that Bollgard ® preserves natural enemy populations more effectively than broad spectrum conventional insecticides. This can lead to better secondary pest control in Bollgard ® fields and indicates that Bollgard ® can be an important tool for integrated pest management in cotton.





Reprinted from Proceedings of the 2001 Beltwide Cotton Conferences pp. 796 - 798
©National Cotton Council, Memphis TN

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Document last modified XXXXXX, XXX XX 2001