Are arthropod communities in cotton really disrupted? An assessment of insecticide regimes and evaluation of the beneficial disruption index S. Mansfield a,b, * , M.L. Dillon a , M.E.A. Whitehouse a a CSIRO Entomology and the Australian Cotton Cooperative Research Centre, Australian Cotton Research Institute, Locked Bag 59, Narrabri, NSW 2390, Australia b Ensis—Forest Biosecurity and Protection, Private Bag 3020, Rotorua, New Zealand Received 29 June 2004; received in revised form 29 September 2005; accepted 24 October 2005 Available online 5 December 2005 Abstract Non-selective chemical control of crop pests disrupts beneficial insects and spiders. For Australian cotton crops, a beneficial disruption index (BDI) has been developed that ranks the impact of different insecticides on beneficial arthropods. To evaluate this index as a measure of natural enemy disruption, the abundance of beneficial arthropods was monitored in ten conventional and nine INGARD 1 Bt cotton fields on ten commercial farms during the 2001–2002 season. Beneficial insects were more abundant in those fields subjected to a more selective insecticide regime (low BDI) than in fields that received broad-spectrum insecticide treatments (high BDI). However spider abundance did not change in relation to insecticide regime. Family composition of spider communities was affected by BDI and crop type (Bt or conventional), whereas family composition of insect communities only showed a trend to be affected by BDI and crop type. This difference may indicate that insects are more uniformly affected by the BDI than spiders. The beneficial disruption index is an effective measure of insecticide impacts on beneficial insects in Australian cotton crops. # 2005 Elsevier B.V. All rights reserved. Keywords: Australia; Beneficial arthropods; BDI; Biological control; Cotton; Insecticide regime; IPM; Parasitoids; Predatory insects; Spiders 1. Introduction An important goal of integrated pest management (IPM) is to combine pest control methods in order to maintain the target pest populations below the threshold for economic damage to the crop. Furthermore, IPM aims to reduce dependence on broad spectrum chemical controls by employing non-chemical alternatives such as biological control agents, cultural controls or host plant resistance, in combination with selective insecticides (Naranjo et al., 2003). IPM requires extensive knowledge not only of the pest spectrum, but also their associated natural enemies and alternative control methods (Kogan, 1998). Translation of this knowledge into crop management strategies that are readily understood is requisite to the application of IPM by growers (Ooi, 1996). In Australia, cotton is a crop of major economic importance that requires significant inputs of fertilizer, water and insecticides (Peacock et al., 1996). On average 12 insecticide sprays are applied to conventional cotton fields per season in Australia (Doyle et al., 2002). Key issues are: (1) the high costs of chemical control (A$280 million for 2000–01, Doyle et al., 2002); (2) the disruptive impacts of insecticides on beneficial arthropods; (3) pest resurgence following insecticide application; (4) the development of insecticide resistance; (5) the increased concern about environmental impacts from insecticide use. These issues drive the development of practices that are more compatible with IPM in Australian cotton systems. Tactics for cotton IPM in Australia (reviewed by Fitt, 2000) include pest resistant plant varieties, regional insecticide resistance www.elsevier.com/locate/agee Agriculture, Ecosystems and Environment 113 (2006) 326–335 * Corresponding author. Tel.: +61 2 9716 9952. E-mail address: sarah_mansfield@yahoo.com (S. Mansfield). 0167-8809/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.agee.2005.10.012