The effects of the foliar fungicide pyrazophos on beneficial arthropods in barley fields.

The insecticidal properties of the foliar fungicide pyrazophos were investigated in autumn- and spring-sown barley crops using several methods to estimate the density of non-target arthropods and by using manipulative experiments. In autumn-sown crops, pyrazophos significantly reduced densities of cereal aphid natural enemies relative to pre-treatment levels compared to areas of crop that were left unsprayed. These significant differences persisted in most groups for over 45 days after treatment. Groups most affected were aphid-specific predators, polyphagous predators, (Carabidae, Staphylinidae but not Araneae) and parasitoids. Insects known to be preferred food items of wild gamebird chicks and other non-target groups such as the Collembola were also significantly reduced in density on plots sprayed with pyrazophos, the effects again persisting for over 45 days. Densities of beneficial and non-target insects were also reduced in plots of spring barley sprayed with pyrazophos. However, the experimental design meant that levels of reductions were not significant for most arthropod groups.

Removal of prey items (Drosophila pupae) placed in sprayed and unsprayed spring barley plots showed that the proportion predated was significantly lower on pyrazophos-treated plots compared to those remaining unsprayed, the difference persisting for at least 7 wk after treatment. Removal of cereal aphids from colonies introduced to sprayed and unsprayed plots was also significantly lower on plots treated with pyrazophos. Difficulties of data interpretation associated with experimental design are discussed together with the consequences of the use of broad-spectrum pesticides in I.P.M. programmes in cereals.