Laboratory Investigations on the Potential Efficacy of Biological Control Agents on Two Thrips Species, Onion Thrips ( Lindeman) and Western Flower Thrips ( (Pergande)).

Thrips biocontrol research in greenhouse crops has focused primarily on western flower thrips (WFT; ). However, recent outbreaks of onion thrips (OT; ) in Ontario, Canada, demonstrate that biocontrol-based IPM programs for WFT do not control OT sufficiently to prevent crop losses. A lack of comparative studies makes it difficult to determine which program components for WFT are failing for OT. We conducted several laboratory trials examining the extent to which commercial biocontrol products kill OT compared to WFT. These included phytoseiid mites (, , , ), a large generalist predator (), an entomopathogenic fungus strain GHA), and entomopathogenic nematodes (, , ). In no-choice trials, and consumed more OT than WFT (first instars and adults, respectively). In choice trials, , , and consumed more OT than WFT. caused higher mortality in OT than WFT. There was no difference in mortality between thrips species exposed to other biocontrol agents. This suggests available tools have the potential to manage OT as well as WFT. Possible explanations why this potential is not realized in commercial settings are explored.