Invertebrate responses to the management of genetically modified herbicide–tolerant and conventional spring crops. II. Within-field epigeal and aerial arthropods

Abstract

The effects of the management of genetically modified herbicide-tolerant (GMHT) crops on the abundances of aerial and epigeal arthropods were assessed in 66 beet, 68 maize and 67 spring oilseed rape sites as part of the Farm Scale Evaluations of GMHT crops. Most higher taxa were insensitive to differences between GMHT and conventional weed management, but significant effects were found on the abundance of at least one group within each taxon studied. Numbers of butterflies in beet and spring oilseed rape and of Heteroptera and bees in beet were smaller under the relevant GMHT crop management, whereas the abundance of Collembola was consistently greater in all GMHT crops. Generally, these effects were specific to each crop type, reflected the phenology and ecology of the arthropod taxa, were indirect and related to herbicide management. These results apply generally to agriculture across Britain, and could be used in mathematical models to predict the possible long-term effects of the widespread adoption of GMHT technology. The results for bees and butterflies relate to foraging preferences and might or might not translate into effects on population densities, depending on whether adoption leads to forage reductions over large areas. These species, and the detritivore Collembola, may be useful indicator species for future studies of GMHT management.

Responses of plants and invertebrate trophic groups to contrasting herbicide regimes in the Farm Scale Evaluations of genetically modified herbicide–tolerant crops

“…Sampling methods are described in detail in Brooks et al (2003), Haughton et al (2003) and Heard et al (2003a).…”

“…Among crop species and treatments, mean weed biomass ranged from 4 g m 22 (geometric mean) in the GMHT treatment in beet to 41 g m 22 in the conventional treatment in spring oilseed rape (Heard et al 2003a). The invertebrate taxa differed less, and less systematically, between treatments than the weeds (Brooks et al 2003;Haughton et al 2003). Examples of taxa showing consistent effects included Collembola (mainly detritus feeders), which were greater in GMHT treatments, bees and butterflies, which were lower in beet and spring oilseed rape GMHT treatments, and Heteroptera, which also occurred at lower densities in GMHT half-fields towards the end of the growing season (Brooks et al 2003;Haughton et al 2003).…”

“…The invertebrate taxa differed less, and less systematically, between treatments than the weeds (Brooks et al 2003;Haughton et al 2003). Examples of taxa showing consistent effects included Collembola (mainly detritus feeders), which were greater in GMHT treatments, bees and butterflies, which were lower in beet and spring oilseed rape GMHT treatments, and Heteroptera, which also occurred at lower densities in GMHT half-fields towards the end of the growing season (Brooks et al 2003;Haughton et al 2003). Species of carabid beetle showed a mixture of both positive and negative responses to GMHT management (Brooks et al 2003).…”

On the rationale and interpretation of the Farm Scale Evaluations of genetically modified herbicide-tolerant crops

“…Other organisms were either less coupled or less sensitive because of their wider foraging range (e.g. carabid beetles, bees, butterflies), but selected groups were studied for comparison (Brooks et al 2003;Heard et al 2003a,b;Haughton et al 2003;Firbank et al 2003). Most soil-dwelling organisms were considered to be too loosely coupled to weed management during a season.…”

“…Within each split-field, the study would concentrate on the plants and more-or-less sedentary herbivores and detritivores that react rapidly to any major change in field management (figure 3a). Protocols for measuring these organisms at defined sample points in each half-field were devised (Heard et al 2003a;Haughton et al 2003;Brooks et al 2003;Roy et al 2003). The split-field arrangement had to be repeated over a large number of sites-between 60 and 75 for each crop type-both to gain the statistical power to detect differences of ca.…”