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1 October 2005 Canopy- and Ground-Dwelling Predatory Arthropods in Commercial Bt and non-Bt Cotton Fields: Patterns and Mechanisms
Jorge B. Torres, John R. Ruberson, John R. Ruberson
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Abundance of canopy- and ground-dwelling predators was monitored in three pairs of commercial Bt and non-Bt cotton fields (5–15 ha) during three successive seasons using three sampling methods: bagged whole plants, drop cloth samples, and pitfall traps. Samples were taken throughout each growing season. Insecticides were applied to manage pests when economic thresholds were exceeded in both cotton types. Of 1,518 possible date-by-date orthogonal contrasts used to evaluate abundance of predators in all sampling methods, analysis of variance generated 23 contrasts with greater abundance in non-Bt and 20 with greater abundance in Bt cotton, comprising nine taxa. When data from all three seasons were pooled for each sampling method, only six contrasts comprising five taxa were significant, with two favoring Bt (Nabis spp. in whole plant inspections and spiders in drop cloths) and four favoring non-Bt cotton [Hippodamia convergens Guérin-Méneville in drop cloths and whole plant inspections and lady beetle eggs and Geocoris uliginosus (Say) in whole plant inspections]. The shift in abundance of canopy-dwelling taxa—especially coccinellids—between Bt and non-Bt cotton fields was likely associated with insecticide use. Analyses of predator community dynamics using principal response curves showed that the abundance of ground-dwelling predators was not affected by cotton type, whereas abundance of canopy predators varied across seasons with no particular trend for either cotton type. The abundance of predators across 3 yr in cotton fields with standard grower practices failed to exhibit any negative impact of Bt cotton on predator populations.

Jorge B. Torres, John R. Ruberson, and John R. Ruberson "Canopy- and Ground-Dwelling Predatory Arthropods in Commercial Bt and non-Bt Cotton Fields: Patterns and Mechanisms," Environmental Entomology 34(5), 1242-1256, (1 October 2005).[1242:CAGPAI]2.0.CO;2
Received: 22 March 2005; Accepted: 13 July 2005; Published: 1 October 2005

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