ASSESSING THE ROLE OF BENEFICIAL INVERTEBRATES IN CONVENTIONAL AND INTEGRATED FARMING SYSTEMS DURING AN OUTBREAK OF SITOBION-AVENAE

The impact of predatory invertebrates on Sitobion avenae was evaluated using exclusion barriers in integrated and conventionally farmed wint er wheat. The numbers of polyphagous predators was reduced considerabl y in the enclosed areas. There was no difference in the numbers of Car abidae, Staphylinidae and Linyphiidae between the integrated and conve ntionally 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 mal es than females contained aphid remains. The other main food items wer e other arthropods and an unidentifiable liquid. The populations of Si tobion avenae exceeded recommended spray thresholds but were not signi ficantly different between the control areas and where numbers of poly phagous predators had been experimentally reduced. There were 1.5 fewe r grain aphids per tiller in the plots managed using an integrated com pared with the conventional farming system, but the age population str ucture was similar. There was no difference in grain yield between con trol and exclusion areas. The study confirmed that polyphagous predato rs cannot prevent an aphid outbreak late in the season when population s increase rapidly.