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

## TL;DR

Researchers tested if natural enemies used to control western flower thrips can also control onion thrips in greenhouses, finding they are equally effective in the lab.

## Contribution

The study provides the first direct comparison of biocontrol efficacy against two thrips species in controlled laboratory settings.

## Key findings

- Natural enemies like Amblyseius swirskii and Orius insidiosus consumed more onion thrips than western flower thrips in laboratory trials.
- Steinernema feltiae caused higher mortality in onion thrips compared to western flower thrips.
- Biocontrol agents showed no significant difference in effectiveness against the two thrips species in most cases.

## Abstract

Thrips are among the most damaging insect pests affecting greenhouse horticulture crops. Research on biological control of these pests has focused on the dominant species, western flower thrips (WFT). However, a second species, onion thrips (OT), has become more prevalent in greenhouse ornamentals in Ontario, and biocontrol strategies for WFT do not control OT sufficiently to prevent crop losses. Although thrips’ natural enemies have been tested against OT alone, there are few studies examining how effective they are for OT compared to WFT. We conducted several laboratory trials examining the relative efficacy of several natural enemies typically used in thrips biocontrol, including predators, parasitic nematodes, and a fungal-based biopesticide. All of the natural enemies tested were at least as effective at killing OT as they were for WFT in the laboratory, indicating that they all have the potential to manage both species equally well. Possible explanations why this potential is not realized in commercial greenhouse operations are explored.

Thrips biocontrol research in greenhouse crops has focused primarily on western flower thrips (WFT; Frankliniella occidentalis). However, recent outbreaks of onion thrips (OT; Thrips tabaci) 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 (Amblyseius swirskii, Neoseiulus cucumeris, Amblydromalus limonicus, Iphiseius degenerans), a large generalist predator (Orius insidiosus), an entomopathogenic fungus (Beauveria bassiana strain GHA), and entomopathogenic nematodes (Steinernema feltiae, S. carpocapsae, Heterorhabditis bacteriophora). In no-choice trials, A. swirskii and O. insidiosus consumed more OT than WFT (first instars and adults, respectively). In choice trials, A. swirskii, N. cucumeris, and O. insidiosus consumed more OT than WFT. Steinernema feltiae 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.