Determining Field Insecticide Efficacy on Whiteflies with Maximum Dose Bioassays

Area of Science:

• Agricultural Entomology
• Pest Management
• Insecticide Resistance

Background:

• The sweetpotato whitefly (Bemisia tabaci) is a significant pest in cucurbit crops, causing substantial economic losses.
• Effective insecticide management is crucial, but requires accurate methods to assess efficacy and monitor resistance.
• Rapid bioassays offer a potential tool for timely decision-making before field applications.

Purpose of the Study:

• To evaluate the accuracy of a 24-hour laboratory bioassay for predicting field efficacy of insecticides against adult Bemisia tabaci.
• To assess insecticide tolerance and potential shifts in susceptibility in Bemisia tabaci populations.
• To correlate laboratory bioassay results with field performance of ten insecticides in squash and cucumber.

Main Methods:

• Leaf-dip bioassays were conducted using the maximum labeled field rate of ten insecticides.
• A reduced concentration (1/10 rate) of four specific insecticides was used to assess population tolerance.
• Bioassay results (adult survival) were compared with field efficacy data (adult counts) 24 hours post-treatment across two field seasons in Georgia, USA.

Main Results:

• A significant positive correlation was found between laboratory bioassay results and field efficacy, explaining 50-91% of the variation.
• The low-dose assay helped identify populations with a loss of susceptibility between 2021 and 2022.
• A rate response in the low-dose assay indicated a decrease in insecticide susceptibility over time.

Conclusions:

• The 24-hour laboratory bioassay is a reliable tool for predicting field insecticide efficacy against Bemisia tabaci.
• This rapid method can aid in making informed insecticide application decisions and monitoring resistance.
• Monitoring insecticide susceptibility using both maximum and reduced rates is essential for sustainable pest management.