Chilli thrips, Scirtothrips dorsalis. Photo credit: Lance Osborne, UF/IFAS

Insecticides are often the most effective and rapid method for reducing damaging insect pests. This is particularly true for many invasive pests who have escaped their natural predators and parasitoids. Several of the most commonly used insecticides, like pyrethroids, provide broad-spectrum control of insects within a relatively short period of time. This means that homeowners can rapidly reduce pests to protect their favorite rose cultivars or pest control professionals can provide speedy relief of pests for their clientele. Unfortunately, these broad-spectrum insecticides are frequently associated with non-target effects like killing off predatory or parasitic insects, which leads to additional pest problems and plant damage.

Other more selective insecticides, like neonicotinoids, can provide longer-term control of insect pests by penetrating plant vascular tissue and persisting within plant content for several weeks. These products are safer for non-target organisms like the predatory mites or parasitoid wasps because they become concentrated within plant tissue where these biological control organisms are rarely feeding. However, they also have limitations because of known threats to non-target organisms like pollinators or predatory insects.

Fortunately, increasingly more synthetic insecticides classified as reduced risk pesticides are becoming commercially available. The U.S. Environmental Protection Agency (EPA) classifies pesticides as reduced risk based on five primary criteria:
1. Low non-target toxicity to people and wildlife
2. Low potential for groundwater contamination
3. Low use rates
4. Low likelihood of pests developing resistance
5. General compatibility with IPM programs

A recent study led by UF/IFAS Entomology & Nematology MS graduate student and Doctor of Plant Medicine student, Matt Borden, investigated the potential of new reduced risk insecticides for their control of an important exotic pest of ornamental plants. Specifically, he tested a relatively new chemistry available to the turf and ornamental industry, cyantraniliprole (trade name: Mainspring), for its control of Chilli thrips (Scirtothrips dorsalis), which is a damaging and difficult to control insect pest of over 100 plant species (most commonly Indian hawthorn and roses in Florida landscapes). These insects feed on newly expanding leaves and cause severe scarring, leaf distortion, and defoliation (see below).

Damage to rose. Credit: Lyle Buss

Damage to Indian hawthorn. Credit: Lyle Buss

Matt tested two reduced risk insecticides, spinosad (trade name: Conserve) and cyantraniliprole (trade name: Mainspring), against a product containing pyrethroids and a neonicotinoid to measure their effect on chilli thrips and one of their primary predators, Orius insidiosus.

In line with our expectations of reduced risk insecticides, Matt found that both spinosad and cyantraniliprole had minimal effects on the predatory insect. Importantly, Matt also found that both reduced risk products have benefits in terms of chilli thrips control. Spinosad provides rapid control of active chilli thrips populations, but not long term plant protection. Cyantraniliprole provided six weeks of plant protection from chilli thrips damage to Indian hawthorn shrubs, but did not cause rapid toxicity to chilli thrips in laboratory experiments.

Therefore, these results suggest that spinosad provides a safe, rapid reduction in chilli thrips, which can be followed up with a cyantraniliprole application to protect plants from chilli thrips that try to re-establish and cause damage.

To learn more, read the full article here: http://www.bioone.org/doi/pdf/10.1653/024.101.0213