Comparative effects of pesticides, fenitrothion and fipronil, applied as ultra-low volume formulations for locust control, on non-target invertebrate assemblages in Mitchell grass plains of south-west Queensland, Australia

he effect of an aerial application of two broad-spectrum insecticides, the organophosphorus compound, fenitrothion, and the phenyl pyrazole pesticide, fipronil, on non-target invertebrates was investigated during Australian plague locust (Chortoicetes terminifera, (Walker, 1870)) control operations on a Mitchell grass (Astrebla spp.) plain in south-western Queensland, Australia, between 2002 and 2004. The invertebrate assemblages were monitored using yellow pan and Malaise traps to target flying invertebrates and pitfall traps to target ground-dwelling invertebrates, sampled immediately before spraying and then at 3, 7, 39, 79, 189 and 414 days after spraying. Both pesticides caused significant changes to invertebrate community composition immediately after spraying, largely due to changes in the abundance of Orthoptera, Collembola and Formicidae. The richness and abundance of invertebrates in Malaise and yellow pan traps did not differ significantly with pesticide application although significant changes in assemblage composition persisted for up to 79 days. Although not statistically significant, the richness and abundance of invertebrates in pitfall traps declined at sprayed sites after treatment, relative to controls. Assemblage composition in pitfall traps at sprayed sites was significantly different from that in the control sites and these differences persisted for up to 189 days post-spray. Prolonged drought across the study site is likely to have affected the recovery of invertebrate populations and a return to pre-spray abundances did not occur until after heavy rain fell approximately one year after the commencement of the study. The controlling influence of climatic conditions on recovery of non-target arthropod populations after exposure to pesticides therefore has implications for risk assessments for the use of pesticides in arid environments.