Importance of arthropod pests and their natural enemies - HGCA

Skylark plots were found to support few extra invertebrates compared to the adjacent crop (Smith & Jones,2007). No information regarding the invertebrate fauna of fallow plots was found although speciescomposition is most likely to depend on the composition and abundance of weeds.Potential for biocontrolOwing to the relatively small area occupied by these two options, they would not be expected to have anyvalue for biocontrol.5.8 Reduced or no herbicide inputs (EF9-10, EF11; HF14, HF15, HF18, HF19, HG7)Within the crop modern herbicide regimes prevent the survival of all but the hardiest or herbicide resistantweeds. Unsprayed headlands were originally conceived as a means of protecting the native arable flora fromherbicides (Schumacher, 1987). They were trialled and adopted as Conservation Headlands in the UK asmeans to increasing food resources for gamebirds because many of the key chick food insects weredependent on weeds (Sotherton, 1991). More latterly in the UK they have been promoted as a method topreserve and encourage rare arable plants and farmland birds per se and the approach can be alsoimplemented within fields in some ES options. Their use by predatory arthropods has also been widelyexamined, because besides creating a suitable habitat the enriched invertebrate community should be asource of alternative food for polyphagous species. In addition, the flowers of arable plants can provide somepollen and nectar while the seeds are also consumed by polyphagous predators.Whether unsprayed crop headlands enhanced non-target arthropods within arable fields was reviewed byFrampton (2003) for Defra (PN0939). In total, 31 research studies were reviewed and of the 25 frequentlymonitored groups of arthropods, 19 exhibited significantly higher abundance and/or species number in theunsprayed edges and only three were significantly lower. Phytophagous invertebrates benefitted most,utilising the higher weed levels found within Conservation Headlands. It was concluded that there would beno increase in invertebrates within the adjacent sprayed crop. Of the predatory arthropods, there was nobenefit for Carabidae as also found in the Arable Stewardship Pilot Scheme ecological evaluation (Gardneret al., 1999). Carabid beetles were, however, shown to be better fecund more fecund in conservationheadlands compared to conventional cereals (Chiverton, 1984). Overall, only a marginal increase was foundfor Coccinellidae, Syrphidae and Araneae although in the Netherlands 3-4 times more invertebrates werecollected from the upper canopy of unsprayed winter wheat margins compared to conventionally sprayed(De Snoo, 1999). The increase was attributed to higher numbers of flower visiting species (Syrphidae) andaphid predators (Coccinellidae). Syrphidae, especially Episyrphus balteatus were shown to utilise the floralresources provided by the arable weeds in Conservation Headlands (Cowgill et al., 1993; De Snoo, 1999).Aphids were only significantly more abundant in the unsprayed margins (Cowgill et al., 1993) but they didnot spread into the adjacent crop (De Snoo & De Leeuw, 1996).58