Selectivity of plnat protection products used in wheat in summer on the major cereal aphid natural enemies

The effects of a range of insecticides and fungicides commonly used in wheat in Belgium were assessed on the three major group of aphid natural enemies: parasitic hymenoptera, aphid-specific predators and entomopathogenic fungi. Insecticides used to control cereal aphids were highly toxic in the laboratory on glass plate and leaf tests for adult parasitic hymenoptera Aphidius rhopalosiphi, but the last larval and the nymphal growth stage of the parasite were protected from insecticides inside the mummified aphid. Results of field studies showed that the insecticides tested had no effects or time-limited effects on Aphidiidae populations. Fungicides were in general less toxic than insecticides for A. rhopalosiphi in glass plate tests but many compounds commonly used were still harmful. The toxicity of these fungicides was reduced when they were tested on wheat plants, but some of them exhibited a marked repellent effect, so that the wasps spent less time on the plants and fewer aphids were parasitised. A field study showed that the parasitism rate of aphids in the field can be reduced by some fungicides, but the effect was short-lived and without consequence on the development of aphid populations. Twenty fungicides were also tested at their maximum field rate on the entomopathogenic fungi Erynia neoaphidis. Most of the products reduced the infectivity of conidia of this fungi, sometimes greatly. The effects of insecticides on aphid specific predators were assessed in the laboratory (syrphids) and on winter wheat in the field (syrphids, ladybirds and lacewings). Some products were harmless or slightly harmful for syrphids in the laboratory, but the majority of them were toxic. These results were confirmed by field-testing. None of the products can be considered as safe for both syrphids and ladybirds in the field. Lacewings were unaffected by the insecticides tested. Overall analysis of the results obtained since 1993 show that all insecticides currently used on wheat in Belgium will affect the major aphid natural enemies to a greater or lesser degree. Tests on parasitic hymenoptera and entomopathogenic fungi also indicate that the selection of fungicides used to protect wheat against diseases should be based not only on their efficacy and cost but also on their possible side-effects on aphid natural enemies.