Non-target effects of insecticides, entomopathogenic fungi and nematodes applied against western corn rootworm larvae in maize

Field studies were conducted in southern Hungary over two field seasons to assess potential non-target effects of entomopathogenic nematodes (Heterorhabditis bacteriophora), entomopathogenic fungi (Metarhizium anisopliae), clothianidin-coated seeds and tefluthrin granules applied into the soil against larvae of the chrysomelid Diabrotica virgifera virgifera, one of the major North American and European maize pests. From field gauze cages set up over groups of maize plants, 1944 specimens of non-target ground-dwelling or emerging arthropods from 22 taxa were collected. The most abundant taxa belonged to the Diptera, Araneae and Hemiptera. Multivariate statistics revealed significant effects of soil conditions, year and treatments on non-target species composition. Soil parameters explained 10.5% of the overall variability in species composition. The application of biological control agents or insecticides for the control of Diabrotica larvae, together only slightly but significantly influenced non-target species composition, explaining 5.6% of the data variability. When pairwise comparisons were conducted, no significant effects on non-target compositions were detected for the entomopathogenic nematode, the entomopathogenic fungus, tefluthrin or clothianidin. However, clothianidin treatments tended to reduce densities of the beneficial arthropod taxa Coccinellidae, Hymenoptera, Araneae, and particularly Staphylinidae and Chrysopidae, whilst tefluthrin tended to reduce the Coleopteran families. No such trends were apparent for the two biological control agent treatments. Reasons for the small treatment effects on non-targets may be the generally poor arthropod diversity in soils of intensive field crops such as maize, as well as the application of all agents into relatively narrow soil areas close to maize plants.