Agriculture Reference
In-Depth Information
Acrobeloides
sp. and
Pratylenchus
sp. were significantly higher in soil under cultivation with
Bt
maize (Cry1Ab) than with non-
Bt
maize (Griffiths et al., 2006). However, in field trials,
Lang et al. (2006) found no effect of
Bt
maize (Cry1Ab) cultivation on
Pratylenchus
sp. When
nematode communities were evaluated in the field, cultivation of
Bt
maize expressing
Cry1Ab significantly reduced numbers of nematodes in the soil, although the effect was
small and within the normal variation observed in many agricultural systems (Griffiths
et al., 2005). Cultivation of
Bt
canola expressing Cry1Ac was associated with a shift in
nematode community structure when compared with community structure in soil culti-
vated with non-
Bt
canola (Manachini et al., 2004). Other studies have shown that
Bt
maize
expressing Cry1Ab has no negative effect on natural populations of nematodes in soil
microcosms (Saxena and Stotzky, 2001a) or in the field (Manachini and Lozzia, 2002), and
that
Bt
eggplant expressing Cry3Bb1 has no negative effect on nematode community struc-
ture in the field (Manachini et al., 2003).
of Bt crops on protozoa and nematodes
Because few studies have evaluated the effects of the cultivation of
Bt
crops on protozoa,
the results reported to date are difficult to assess. However, a review of the literature indi-
cates that there appear to be no consistent negative effects of purified
Bt
proteins (Cry1Ab
and Cry1Ac) or the cultivation of
Bt
maize (expressing Cry1Ab or Cry3Bb1) on protozoa
in greenhouse or in field studies. Future studies would benefit from evaluating a greater
variety of
Bt
crops for nontarget effects on protozoa in the soil and under a range of experi-
mental conditions. Moreover, data should be reported separately for the different classes
of protozoa (amoebae, flagellates, and ciliates) as each group may have a different response
to
Bt
proteins,
Bt
residue in the soil, or the cultivation of
Bt
crops.
Although nematode community structure, biodiversity, and number of individuals in
natural populations do not appear to be affected by cultivation of
Bt
crops, individual spe-
cies, such as
C. elegans
, appear to be sensitive to some Cry proteins, including the Cry1Ab
protein that is expressed in most lines of transgenic maize. As
Bt
maize is one of the
most commonly cultivated transgenic crops worldwide, and as nematodes are key indica-
tors of soil quality (Blair et al., 1996), more research on the impacts of Cry1Ab and other
Bt
proteins should be conducted to evaluate nontarget effects at both the individual and
population levels of nematodes. Insomuch as nematodes are one of the only groups of soil
organisms that have displayed direct toxicity of certain Cry proteins produced in trans-
genic
Bt
crops, they should be carefully evaluated for nontarget effects of
Bt
crop cultiva-
tion under a variety of environmental and experimental scenarios.
Earthworms are common soil invertebrates responsible for much of the degradation of
large pieces of plant material, incorporation of organic matter into lower strata of soil, and
increasing aeration of soil by creating large pores in soil as they burrow. Impacts of
Bt
plant
biomass,
Bt
proteins, and the cultivation of
Bt
crops on a variety of earthworm species have
been studied in numerous laboratory, greenhouse, and field experiments, and most stud-
reviewed by Stotzky, 2004; O'Callaghan et al., 2005; Birch et al., 2007; Icoz and Stotzky,
2008b). In laboratory studies, there was no negative effect of soil amended with biomass
of
Bt
maize expressing Cry1Ab on
Eisenia fetida
mortality and weight (Ahl Goy et al., 1995),
Search WWH ::
Custom Search