A comparison of the effectiveness of insecticides in constant and variable thermal conditions

ABSTRACT

The effectiveness of insecticides differs with changes in temperature, but insecticide toxicities are determined at constant temperatures. Constant thermal conditions do not occur in the field, where insects can change their behaviors to achieve a preferred temperature. The aim of this study was to assess whether the choice of ambient temperature affects the mortality rate of intoxicated firebugs and Colorado potato beetles. The insects’ mortality following insecticide exposure was monitored at constant temperatures (15, 25, and 35 °C) as well as in a thermal gradient system, where the insects could freely select their preferred ambient temperature. Firebugs treated with oxadiazine showed 58% higher mortality when held at a constant temperature post-treatment compared to mortality levels seen when able to choose a preferred temperature in a thermal gradient. Similar results were seen in Colorado potato beetles treated with oxadiazine (15%–33% higher mortality in constant vs. preferred temperature) or organophosphate (36% higher mortality in constant vs. preferred temperature). The insects’ ability to mitigate the impacts of pesticide exposure by selecting more beneficial thermal conditions is an important consideration for pest management. Therefore, the application rates of insecticides used under field conditions should be additionally analyzed to take this factor into account.

KEYWORDS:

• Colorado potato beetle
• constant vs. variable thermal conditions
• firebug
• insecticides
• mortality
• thermal choice

Acknowledgements

The Authors would like to express their gratitude to the Peer Reviewers for their helpful comments which helped to improve this manuscript.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

Nicolaus Copernicus University [grant number 182/2016/1146].