Abstract
The current difficulty facing risk evaluations of Bacillus thuringiensis (Bt) crops on nontarget arthropods (NTAs) is the lack of criteria for determining what represents unacceptable risk. In this study, we investigated the biological parameters in the laboratory and field population abundance of Nilaparvata lugens (Hemiptera: Delphacidae) on two Bt rice lines and the non-Bt parent, together with 14 other conventional rice cultivars. Significant difference were found in nymphal duration and fecundity of N. lugens fed on Bt rice KMD2, as well as field population density on 12 October, compared with non-Bt parent. However, compared with the variation among conventional rice cultivars, the variation of each parameter between Bt rice and the non-Bt parent was much smaller, which can be easily seen from low-high bar graphs and also the coefficient of variation value (C.V). The variation among conventional cultivars is proposed to be used as a criterion for the safety assessment of Bt rice on NTAs, particularly when statistically significant differences in several parameters are found between Bt rice and its non-Bt parent. Coefficient of variation is suggested as a promising parameter for ecological risk judgement of IRGM rice on NTAs.
Highlights
Substantial equivalence[8,11]
The potential risk of insect-resistant GM (IRGM) crops on natural enemies has been debated in reviews and results differ primarily because of different analysis method with one method not accounting for prey quality[28,48]
Reduced reproduction was found in the springtail, Folsomia candida (Collembola: Isotomidae) when it was fed on Bacillus thuringiensis (Bt) rice plant tissue[50]
Summary
Substantial equivalence[8,11]. The compositional equivalence between GM crops and their counterparts was confirmed over the course of 20 years of testing[12]. In the case of Bt rice, compositional comparison assessments suggested that Bt rice products are substantially equivalent to their non-transgenic counterparts[13,14,15]. Since Bt rice lines were developed, numerous laboratory and field tests have been conducted on the potential risk of these lines on the environment, focusing on nontarget arthropods (NTAs), soil ecosystems and gene flow. The assessment of GM crops on NTAs typically starts with laboratory experiments under worst-case scenarios following a tiered framework conceptually similar to that used for conventional pesticides[32,33]. Most of these tier-1 studies have indicated that Cry proteins have no direct toxicity on NTAs34,35. Biological parameters of N. lugens, including nymphal development duration, suvival rate, honeydew weight and fecundity under laboratory conditions, and field abundance were used to estimate the variation range
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