Abstract
Cultivation of Bt crops is an important tactic in integrated pest management. The effect of Bt maize on arthropod predators needs to be investigated because of the important role of these natural enemies in the absence of target pests. The objective of the present study was to generate information on the distribution model ofCycloneda sanguinea (L.) (Coleoptera: Coccinelidae) in Bt and non-Bt maize. A sampling field of 2.500 m2 area, divided into 100 plots, was used in this study. Five plants per plot, totaling 500 plants in each field, were studied. We counted the total number of adults every week, totaling six samples for each field (Bt and non-Bt). 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) revealed that, in both cultivars, the adults of C. sanguinea were distributed according to the random distribution model, which fits the pattern of Poisson distribution. Key words: Spatial distribution, natural enemy, lady beetle, Poisson.
Highlights
The aggregation index and Chi-square fit of the observed and expected values to the theoretical frequency distribution (Poisson, binomial, and negative binomial positive) revealed that, in both cultivars, the adults of C. sanguinea were distributed according to the random distribution model, which fits the pattern of Poisson distribution
Since its commercial release in 2008, the use of Bt crops containing Bacillus thuringiensis (Berliner) genes for insect resistance is being increasingly adopted by Brazilian farmers (James, 2011), especially as it decreases the need of insecticide application for targeted pest such as Spodoptera frugiperda (Brookes and Barfoot, 2008; Mendes et al, 2011)
Coccinellid species are important polyphagous predators within agroecosystems, as Cycloneda sanguinea (L.) is a voracious predator of pests such as aphids, mealybugs, and eggs of Lepidoptera (Bruck and Lewis, 1998; Smith et al, 2004). These natural enemies are reported to be affected by the toxins of Bt cotton, for example, Funichello et al (2012) reported changes in the biological parameters of aphids when fed from Bt cotton
Summary
Since its commercial release in 2008, the use of Bt crops containing Bacillus thuringiensis (Berliner) genes for insect resistance is being increasingly adopted by Brazilian farmers (James, 2011), especially as it decreases the need of insecticide application for targeted pest such as Spodoptera frugiperda (Brookes and Barfoot, 2008; Mendes et al, 2011). Bt crops may have indirect effects because of possible changes in the behavioral aspects of natural enemies of pests in insufficient target technology (Zwahlen et al, 2000; Stephens et al, 2012). Coccinellid species are important polyphagous predators within agroecosystems, as Cycloneda sanguinea (L.) is a voracious predator of pests such as aphids, mealybugs, and eggs of Lepidoptera (Bruck and Lewis, 1998; Smith et al, 2004). These natural enemies are reported to be affected by the toxins of Bt cotton, for example, Funichello et al (2012) reported changes in the biological parameters of aphids when fed from Bt cotton
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