Non-target arthropods may be affected by toxins derived from Bacillus thuringiensis (Bt) expressed in transgenic maize. The objective of this study was to evaluate the possible impacts of Bt maize on the diversity and the composition of non-target arthropod species by analyzing one field cultivated with conventional maize (no expressing transgenic protein) and three fields cultivated with transgenic maize (expressing Bt proteins). In each field was sampled 50 entirely plants for the number of arthropod specimens and registred the degree of injury caused by the chewing insects. A total of 2.525 specimens of arthropods, comprising 29 species from 25 families, were recorded on 3.000 sampled plants. The most diverse family belonged to the order Hemiptera. Based on Shannon and Simpson indexes, the Bt-transgenic cultivar EXP3320YG had lower level of non-target arthropod diversity than other cultivars. From this study, it is clear that the diversity of non-target arthropods on maize crop is negatively affected by Cry1Ab protein, while the Cry1A105+Cry2Ab2+Cry1F proteins, and Cry1A105+Cry2Ab2+Cry3Bb1 proteins do not have any effect on arthropod species diversity and composition.
Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae) is an important natural egg parasitoids of pest insects in the agricultural environment, being used as a form of biological control, and it may be affected by the Bacillus thuringiensis (Bt) toxin present in transgenic plants widely used in Brazil. The aim of this study was to evaluate the effect of Bt maize pollen fed to adults of the parasitoid T. pretiosum Riley (Hymenoptera: Trichogrammatidae) reared in the eggs of the alternate host Ephestia kuehniella Zeller (Lepidoptera: Pyralidae). Three treatments (diets) were compared: pollen from Bt maize, pollen from non-Bt maize, and 10% honey solution (control). Each treatment consisted of 50 T. pretiosum females that were freshly emerged and mated (between 24 and 36 h old). Biological characteristics indicative of the efficiency of T. pretiosum as a biological control agent were evaluated for 4 generations. The results suggest that the consumption of pollen did not affect the evaluated biological characteristics, such as percentage of parasitism, sex ratio, and number of individuals reared per host egg, in any of 4 generations. Thus, we showed that Bt maize is compatible with the use of T. pretiosum for biological control.
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 of Cycloneda sanguinea (L.) (Coleoptera: Coccinelidae) in Bt and non-Bt maize. A sampling field of 2.500 m 2 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.
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