Pakistan J. Zool., vol. 48(3), pp. 703-711, 2016. Evaluating Insecticide Spray Regimes to Manage Cotton Leafhopper, Amrasca devastans (Distant): Their Impact on Natural Enemies, Yield and Fiber Characteristics of Transgenic Bt Cotton Rabia Saeed, 1 Muhammad Razaq, 2 * Muhammad Rafiq 1 and Muhammad Naveed 1 1 Entomology Section, Central Cotton Research Institute, Multan, Pakistan 2 Department of Entomology, Faculty of Agricultural Sciences and Technology, Bahauddin Zakariya University, Multan A B S T R A C T Cotton leafhopper Amrasca devastans (Dist.) is a major sucking insect pest of cotton and unfortunately natural enemies are not effective for its control. Insecticides are the only option for the management of this pest in Pakistan. On the introduction of transgenic cotton, insecticides are applied to manage sucking insect pests only. In the present study, nine combinations of conventional and new insecticides were evaluated against A. devastans and natural enemies for two years in transgenic cotton field. In every spray regime three insecticides were applied after an interval of 15 days. Spray regime of dimethoate, chlorfenapyr and acephate was the best in reducing A. devastans populations. However, the efficacy of insecticides against A. devastans was reduced when insecticides having same mode of action were applied in a spray regime. All the regimes proved toxic to varying degree to generalist predators like Orius spp., Geocoris spp., Chrysoperla carnea (Stephen), Coccinellids spp. and spiders. Spray regimes differed in their impact on growth and reproductive parameters of Bt cotton, which was directly related to A. devastans infestation. Overall higher root length (cm), shoot length (cm), number of leaves, yield (kg ha -1 ), ginning out turn (GOT %), micronare (µg inch -1 ), staple length (mm) and fiber strength were found in plants treated with spray regime. These results will help to manage A. devastans on transgenic cotton and will ultimately reduce the yield and fiber quality losses. INTRODUCTION Adoption and cultivation of genetically modified crops has become a normal practice worldwide including Pakistan. More than half of the cotton grown area is occupied by cotton containing Bacillus thuringiensis genes in the world (known as Bt cotton) (Ali et al., 2010; Naranjo, 2011). In 2005, Bt cotton was introduced in Pakistan to control insecticide resistance strains of lepidopteron pests with expected results of reduction in insecticide use (Sabir et al., 2011). Due to reduced use of insecticides against cotton bollworms, the populations of sucking insect pests increased that might had been suppressed by insecticidal applications (Williams, 2006; Naranjo, 2011). In addition, transgenic Bt cotton attracts or enhances the growth of some sucking pest populations resulting in more insecticidal applications. Introducing transgenic varieties led to alteration in insecticidal regimes to manage non-target pests. These alterations in pesticide application regimes might affect the pest and natural enemy populations (Men et al., 2004; Arshad et ___________________________________ * Corresponding author: muhammadrazaq@bzu.edu.pk 0030-9923/2016/0003-0703 $ 8.00/0 Copyright 2016 Zoological Society of Pakistan al., 2009). Cotton leafhopper, Amrasca devastans (Dist.) is a principal insect pest of cotton causing more than 37% seed cotton losses. It also reduces photosynthesis activity in its hosts (Razaq et al., 2014). Farmers rely solely on pesticides to manage this pest (Saeed et al., 2015a), which are applied on cotton without any gap since long. Pesticides are highly effective, rapid in action, convenient to apply, usually economical and most powerful tools in pest management. However, indiscriminate, inadequate and improper use of pesticides has led to severe problems such as development of pesticide resistance, resurgence of target species, outbreaks of secondary pests, destruction of beneficial insects, as well as health hazards and environmental pollution (Yadav, 1989). In Pakistan, resistance to pyrethroids, neonicotinoids and insect growth regulators (IGRs) has been reported in sucking insect pests of cotton such as Bemisia tabaci (Gennadius), A. devastans and Aphis gossypii Glover (Ahmad et al., 1999; Basit et al., 2011). Organophosphates like chlorpyrifos and fenitrothion have been reported to be toxic for vespidae predators of coffee leaf miner, Leucoptera coffeella Guérin-Méneville (Gusmão et al., 2000; Galvan et al., 2002; Fernandes et al., 2010). Due to continuous insecticidal applications, some natural enemies had developed resistance and Article Information Received 22 May 2015 Revised 18 October 2015 Accepted 25 October 2015 Available online 14 March 2016 Authors’ Contributions RS conducted the study and collected data. RS and M Razaq analyzed the data and wrote the article. M Razaq, M Rafiq and MN supervised the work. Key words Chemical control, toxicity, insecticide rotation, organophosphates, predators, transgenic, Bt cotton, cotton leaf hopper, fibre characteristics of cotton spray regimes.