Relative toxicity of three wheat herbicides to two species of Coccinellidae

  On the High Plains of the USA, herbicides specific for broad‐leaf weeds are regularly applied to winter wheat in the early spring, sometimes late enough to coincide with the colonization of fields by cereal aphids and their natural enemies. We tested the toxicity of three such herbicides, Ally (Dupont), Rave (Syngenta) and 2,4‐D ester (generic), to neonate larvae of two coccinellid species important in cereal aphid biocontrol, Coleomegilla maculata DeGeer and Hippodamia convergens Guérin‐Méneville. Topical treatment of larvae with 2,4‐D resulted in 25% and 60% mortality in the two species, respectively, with surviving C. maculata larvae experiencing a 5% increase in developmental time. No significant effects were noted for the other two materials, save for a 2.5% increase in developmental time for C. maculata larvae exposed to Rave. No material caused significant mortality in either species when larvae were fed on prey ( Schizaphis graminum Rondani) treated with herbicide 24 h earlier, although 2,4‐D reduced developmental time slightly in C. maculata . When herbicide applications are delayed enough in spring to coincide with aphid activity in wheat, farmers can reduce the risk of disrupting biological control by selecting an alternative to 2,4‐D.