Advancing ecologically based management for Acalymma vittatum, a key pest of cucurbits

Open Access
Author:
Lewis, Margaret Theresa
Graduate Program:
Entomology
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
March 03, 2015
Committee Members:
  • Shelby Jay Fleischer, Thesis Advisor
  • John Frazier Tooker, Thesis Advisor
  • Elsa Selina Sanchez, Thesis Advisor
Keywords:
  • cucurbits
  • Acalymma vittatum
  • reduced tillage
  • Carabidae
  • biological control
  • spinosad
  • cucurbitacin
Abstract:
Striped cucumber beetle, Acalymma vittatum (Coleoptera: Chrysomelidae), is a key pest of cucurbit crops in the northeastern United States. Systemic and foliar insecticides provide consistent control of the adult beetles and are the primary management tool available to growers. However, many of these chemicals are excluded from use in organic production systems. Additionally, there are concerns about the potential for development of insecticide resistant populations of A. vittatum and the non-target effects on beneficial insects within cucurbit cropping systems. In this thesis, I explore alternative management options for A. vittatum, considering both efficacy and the potential for integration into an ecologically based pest management system. I first take a systems based approach to A. vittatum management, considering how horticultural production practices shape pest and beneficial insect communities in cucurbit systems. In a two year field experiment, I measured how soil production systems and row cover use influence ground beetle (Coleoptera: Carabidae) activity density. The presence or absence of a row cover had no significant effect. However, soil production system did significantly influence the overall carabid community. Certain species, particularly Cicindela punctulata, had significantly higher activity density in a reduced tillage system relative to a conventional till/plasticulture system. Overall, a reduced tillage system also seemed to support greater species richness. These results suggest that horticultural production practices play an important role in shaping the natural enemy community within cucurbit cropping systems. I also monitored parasitism of A. vittatum at two field sites in central PA between June and October 2014. Two parasitoid species were found: a tachinid fly, Celatoria setosa, and a braconid wasp, Centistes diabroticae. Though their presence had been confirmed outside of Pennsylvania, this is the first record of parasitoid activity within the state. Parasitism rates were surprisingly high, reaching up to 56% for C. setosa and up to 17% for C. diabroticae. Based on the results of this initial survey, both species seem to be strong candidates for a conservation biocontrol program. Finally, I integrated two plant and microbial metabolites into a biorational insecticide for A. vittatum: spinosad, a broad spectrum, oral insecticide derived from the soil bacterium Saccharopolyspora spinosa, and cucurbitacin, a secondary plant metabolite that induces a compulsive feeding response in A. vittatum. I attempted to increase spinosad’s efficacy as a control for A. vittatum by mixing in a cucurbitacin feeding stimulant, which presumable increases beetle ingestion of insecticide droplets. In laboratory bioassays, the addition of cucurbitacin significantly reduced the LC-50 of spinosad, though bioassay data also suggested that male beetles are more responsive to cucurbitacin compared to female beetles. Field trials in 2014 evaluated the efficacy of three different rates of spinosad/cucurbitacin. There was a dose dependent response to the insecticide, with higher rates of spinosad and cucurbitacin providing the best suppression of A. vittatum compared to an untreated control. These results suggest that integrating spinosad with cucurbitacin has the potential to suppress A. vittatum. In the final chapter, I summarize the results of this thesis and suggest future directions for this work. The management practices detailed in this thesis are not intended to be stand-alone tactics. However, with further refinement, each practice has the potential to play a key role in developing an ecologically based management program for A. vittatum.