Effects of the cultivation of genetically modified Bt crops on nontarget soil organisms - Microbial Ecology in Sustainable Agroecosystems - page 201

toxic effects detected on the survival or reproduction of F. candida or X. griesea (Sims and
Martin, 1997) and no effects of purified Cry2A on P. saber (Sims, 1997).
Only in a few studies have negative effects of Bt proteins on microarthropods been
reported: Wandeler et al. (2002) found that P. scaber fed significantly less on Bt maize
expressing Cry1Ab than on non- Bt maize during a 20-day feeding trial in the labora-
tory in soil microcosms; Griffiths et al. (2006) reported lower collembolan abundance
and higher mite populations in soil cultivated with Bt maize expressing Cry1Ab than in
soil cultivated with non- Bt maize in the laboratory; and Bakonyi et al. (2006) found that
there were species-specific effects in feeding preference when the collembolans F. candida ,
Heteromurus nitidus, and Sinella coeca were fed dried leaves of Bt (Cry1Ab) or non- Bt maize
in laboratory feeding tests— F. candida preferred non- Bt maize as a food source over Bt
maize, but there was no difference in feeding preference for H. nitidus and S. coeca . Cortet
et al. (2007) detected a minor negative effect of Bt maize (Cry1Ab) cultivation on micro-
arthropod abundance (mites and collembolans) in high-clay soils in field trials; however,
agricultural practices had a comparable or greater effect on microarthropod abundance
than the Bt crop. Debeljak et al. (2007) also reported a lower abundance of collembolans
in field soil cultivated in Bt maize (Cry1Ab) but only at one site and only in early fall; no
difference in functional groups of Collembola was detected.

8.4.5.1 Research recommendations: Effects of the cultivation
of Bt crops on microarthropods
In general, cultivation of transgenic Bt crops, Bt plant biomass, or purified Bt proteins,
including Cry1Ab, Cry1Ac, and Cry3Bb1, has had little to no effect on most microarthro-
pods tested. When effects have been reported, they were minor, and the microarthropods
were often more affected by temporal differences in sampling time, agricultural practices,
plant varietal differences, or other biotic and abiotic factors not related to a particular Bt
protein. Although most studies have not shown a consistent pattern of Bt effects on micro-
arthropods, longer-term field experiments would improve the current understanding Bt
effects on the abundance and diversity of microarthropods in the soil environment (e.g.,
Theissen and Russell, 2009). Future research studies should focus on multitrophic-level
interactions and continue to evaluate the effects of new and different types of Bt crops on
nontarget microarthropods in the soil.

8.4.6 Effects of the cultivation of Bt crops on nontarget

Lepidopteran larvae and aquatic insects

Although most insects are not generally classified as soil organisms per se, many insect
orders (e.g., Lepidoptera, Coleoptera, and Hymenoptera) have a larval stage that lives in
or feeds in close proximity to Bt plant leaves and other residues, Bt pollen, or Cry proteins
in soil. Thus, it is possible for nontarget insects, including pollinators, prey and predator
species, and biocontrol agents, to be affected by the cultivation of Bt crops, even if they
do not feed on the GM crop directly. As the number of studies evaluating the effects of Bt
crops on nontarget insects are too numerous to review in this chapter, only the nontarget
effects of the cultivation of Bt crops on selected species of Lepidoptera and aquatic insects
are summarized here ( Table 8.9) . More information on the nontarget effects of the cultiva-
tion of Bt crops on a variety of insect species can be found in several reviews (including
those of Romeis et al., 2006; Marvier et al., 2007; Thies and Devare, 2007; Duan et al., 2008;