Assessing the role of beneficial invertebrates in conventional and integrated farming systems during an outbreak of Sitobion avenae.

Abstract

The impact of predatory invertebrates on Sitobion avenae was evaluated using exclusion barriers in integrated and conventionally farmed winter wheat. The numbers of polyphagous predators was reduced considerably in the enclosed areas. There was no difference in the numbers of Carabidae. Staphylinidae and Linyphiidae between the integrated and conventionally farmed systems, but the total number of predators was higher in the integrated system. Gut dissections of Pterostichus spp. showed that up to 34% contained aphid remains and a greater proportion of males than females contained aphid remains. The other main food items were other arthropods and an unidentifiable liquid. The populations of Sitobion avenae exceeded recommended spray thresholds but were not significantly different between the control areas and where numbers of polyphagous predators had been experimentally reduced. There were 1.5 fewer grain aphids per tiller in the plots managed using an integrated compared with the conventional farming system, but the age population structure was similar. There was no difference in grain yield between control and exclusion areas. The study confirmed that polyphagous predators cannot prevent an aphid outbreak late in the season when populations increase rapidly.