title: The response of natural enemies to selective insecticides applied to soybean.
abstract: Natural enemies of the invasive pest Aphis glycines Matsumura can prevent its establishment and population growth. However, current A. glycines management practices include the application of broad-spectrum insecticides that affect pests and natural enemies that are present  in the field at the time of application. An alternative is the use of selective insecticides that affect the targeted pest species, although having a reduced impact on the natural enemies. We tested the effects of esfenvalerate, spirotetramat, imidacloprid, and a combination of spirotetramat  and imidacloprid on the natural enemies in soybean during the 2009 and 2010 field season. The natural enemy community that was tested differed significantly between 2009 and 2010 (F = 87.41; df = 1, 598; P < 0.0001). The most abundant natural enemy in 2009 was Harmonia  axyridis (Pallas) (56.0%) and in 2010 was Orius insidiosus (Say) (41.0%). During 2009, the abundance of natural enemies did not vary between the broad-spectrum and selective insecticides; however, the abundance of natural enemies was reduced by all insecticide treatments when compared  with the untreated control. In 2010, the selective insecticide imidacloprid had more natural enemies than the broad-spectrum insecticide. Although we did not observe a difference in the abundance of the total natural enemy community in 2009, we did observe more H. axyridis in plots  treated with spirotetramat. In 2010, we observed more O. insidiosus in plots treated with imidacloprid. We suggest a couple of mechanisms to explain how the varying insecticides have different impacts on separate components of the natural enemy community.
authors: Department of Entomology, Iowa State University, Ames, IA 50011, USA. ajv@iastate.edu
authors: A J
authors: AJ
authors: Varenhorst
authors: M E
authors: ME
authors: O'Neal
mesh_terms: D000818:Animals; D001042:Aphids; D001372:Aza Compounds / Q000633:toxicity*; D001517:Coleoptera / Q000187:drug effects*; D020062:Heteroptera / Q000187:drug effects*; D007093:Imidazoles / Q000633:toxicity*; D007306:Insecticides / Q000633:toxicity*; D007484:Iowa; D000073943:Neonicotinoids; D009570:Nitriles / Q000633:toxicity*; D009574:Nitro Compounds / Q000633:toxicity*; D010572:Pest Control, Biological / Q000379:methods; D011156:Population Density; D011157:Population Dynamics; D011722:Pyrethrins / Q000633:toxicity*; D013025:Glycine max; D013141:Spiro Compounds / Q000633:toxicity*
chemical_list: D001372:Aza Compounds; D007093:Imidazoles; D007306:Insecticides; D000073943:Neonicotinoids; D009570:Nitriles; D009574:Nitro Compounds; D011722:Pyrethrins; D013141:Spiro Compounds; C082359:imidacloprid; C570705:spirotetramat; C017690:fenvalerate