Established populations of Aphthona flea beetles on leafy spurge may be in jeopardy in areas of western rangelands where damaging populations of grasshoppers require insecticide treatments. To determine the impacts of actions to manage grasshoppers on flea beetles, the following questions were studied.
Do treatments applied for controlling grasshoppers on rangeland infested with leafy spurge cause mortality to adult flea beetle biological control agents? Which treatments if any, do not cause mortality? Of those that do, what is the immediate mortality level? What level of suppression on the population of biological control agents results after one year? How long is required for the effected population to return to pretreatment population levels?
Laboratory bioassays and field evaluations were conducted to determine the impacts of grasshopper control treatments. In laboratory bioassays, diflubenzuron spray produced no significant mortality. Malathion spray produced moderate (25%-41%) mortality while carbaryl spray produced high (86%-96%) mortality. No differences in mortality in direct impingement studies were detected between A. nigriscutus and A. lascertosa with malathion, carbaryl or in untreated populations. However, on treated vegetation A. nigriscutus was observed higher on the plants and demonstrated higher mortality than A. lascertosa. In the season of treatment, field evaluations showed that diffubenzuron resulted in 18% and 0% mortality at 1 and 2 weeks post treatment respectively. Carbaryl bait resulted in low (17%) mortality while malathion spray resulted in moderate (21%-44%) mortality and carbaryl spray resulted in high (60%-82%) mortality.
At one year after treatment adult Aphthona populations in 23 of the 24 study plots had surpassed peak pretreatment levels. Treatments had occurred when grasshoppers averaged third instar stage. Adult Aphthona populations were near their seasonal peak at treatment.
Species 1: Coleoptera Chrysomelidae Aphthona nigriscutis
Species 2: Coleoptera Chrysomelidae Aphthona lacertosa
Keywords: Leafy Spurge, Grasshopper treatments
The ESA 2001 Annual Meeting - 2001: An Entomological Odyssey of ESA