Individual and combined effects of contact insecticides and high temperatures on Mediterranean flour moth,Ephestia kuehniellaZeller (Lepidoptera: Pyralidae)

Abstract

Mediterranean flour moth or mill moth Ephestia kuehniella Zeller (Lepidoptera: Pyralidae) is a common pest of cereals and flour throughout the world. In this study, eggs, third instar larvae, pupae and adults of E. kuehniella were exposed to five elevated temperatures at a range of 45 to 65 °C for 5, 8, 10, 14, 18, 23 and 30 min. The effect of cypermethrin and dichlorvos was assessed on third instar larvae. The larvae were exposed to the insecticides on glass and concrete arenas and their mortality was recorded 24 h after treatment. To determine combination effects, the third instar larvae were transferred into the Petri dishes treated with LC25 (lethal concentration that kills 25%) of each insecticide and exposed to high temperatures for the period of time equal to LTi25 values (time needed for killing 25% of tested insects). Exposing the eggs, third instar larvae and adults of E. kuehniella to 55 °C for 30, 18 and 30 min respectively, resulted in 100% mortality. In the pupa, exposure to 65 °C caused 100% mortality after 23 min. Based on the LTe50 values (temperature needed to cause 50% mortality in the tested population), pupa was the most tolerant life stage to the temperatures tested. The LC50 values of cypermethrin and dichlorvos were 423.1 and 2608.5mg active ingredient (a.i.) L-l on glass, and 2525.0 and 13502.8mg a.i. L-l on concrete, respectively. The effect of cypermethrin was synergized by high temperatures. High temperatures, cypermethrin and dichlorvos were effective against E. kuehniella. Exposure to combination of lower doses of cypermethrin and high temperatures at short time intervals may have potential in managing this pest. © 2021 Society of Chemical Industry.