Evaluation of nitrogen fertility and plant growth regulator impacts on annual bluegrass weevil (Listronotus maculicollis) oviposition and larval survivorship

Abstract

The annual bluegrass weevil (Listronotus maculicollis), is the most destructive insect pest of fine turf found on golf courses in eastern North America. Although considerable densities of adults may be found on putting greens in spring following emergence from overwintering, larval damage in these areas is rare. Annual bluegrass (Poa annua L.) putting surfaces are frequently treated with nitrogen and plant growth regulators during this time. We assessed whether these inputs alone and in combination influenced L. maculicollis oviposition site selection, larval fitness, or survival. Significantly more females were found in high-nitrogen (39 kg N ha -1 mo -1 ) treatments in laboratory preference assays, though significantly more eggs were found in the moderate concentration treatments (19.5 kg N ha -1 mo -1 ). Choice and no-choice assays demonstrated an ovipositional preference for the moderate nitrogen rate as well, though no fitness advantage was observed. Given that most P. annua greens management programs include plant growth regulation, field experiments were conducted to assess ovipositional preference in P annua treated with various nitrogen concentrations (4.88, 19.5 and 39 kg N ha -1 mo -1 ) in combination with a gibberellic acid inhibitor (trinexapac-ethyl) and/or a seedhead suppressor (ethephon). Significantly fewer larvae were found in trinexapac-ethyl treatments in two of the three years of study, with significantly higher counts in the other year. No differences were detected in larval survival or fitness related to nitrogen in any year. Taken together, these findings suggest that fertility regimes are not likely to influence L. maculicollis development, though further studies are needed to assess the effects of trinexapacethyl.