Abstract
Among the options to control Alabama argillacea (Hübner, 1818) and Heliothis virescens (Fabricius, 1781) on cotton, insecticide spraying and biological control have been extensively used. The GM'Bt' cotton has been introduced as an extremely viable alternative, but it is yet not known how transgenic plants affect populations of organisms that are interrelated in an agroecosystem. For this reason, it is important to know how the spatial arrangement of pests and beneficial insect are affected, which may call for changes in the methods used for sampling these species. This study was conducted with the goal to investigate the pattern of spatial distribution of eggs of A. argillacea and H. virescens in DeltaOpal™ (non-Bt) and DP90B™ Bt cotton cultivars. Data were collected during the agricultural year 2006/2007 in two areas of 5,000 m2, located in in the district of Nova América, Caarapó municipality. In each sampling area, comprising 100 plots of 50 m2, 15 evaluations were performed on two plants per plot. The sampling consisted in counting the eggs. The aggregation index (variance/mean ratio, Morisita index and exponent k of the negative binomial distribution) and chi-square fit of the observed and expected values to the theoretical frequency distribution (Poisson, Binomial and Negative Binomial Positive), showed that in both cultivars, the eggs of these species are distributed according to the aggregate distribution model, fitting the pattern of negative binomial distribution.
Highlights
Alabama argillacea (Hübner, 1818) and Heliothis virescens (Fabricius, 1781) (Lepidoptera, Noctuidae) are important pests of cotton that can cause considerable damage (Peres et al 2012)
A viable alternative to insecticides is the use of transgenic, as Bacillus thuringiensis Berliner Bt cotton varieties
Besides being effective in pest control, Bt- modified crops are an economically viable alternative toreduce the need for chemical insecticide applications (Baker et al 2008, Brookes and Barfoot 2007, Fitt 2008)
Summary
Alabama argillacea (Hübner, 1818) and Heliothis virescens (Fabricius, 1781) (Lepidoptera, Noctuidae) are important pests of cotton that can cause considerable damage (Peres et al 2012). Besides being effective in pest control, Bt- modified crops are an economically viable alternative toreduce the need for chemical insecticide applications (Baker et al 2008, Brookes and Barfoot 2007, Fitt 2008). For this reason, these GMOs are believed to be a more environmentally friendly alternative (Pray et al 2002, Qaim and Zilberman 2003) when compared with conventional pest control methods
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