Influence of temperature on the toxicity of fipronil to Spodoptera littoralis (Boisd.) (Lepidoptera: Noctuidae)

An effective pest management necessitates the use of insecticides throughout the entire season under a wide range of temperatures. Fipronil is a broad-spectrum insecticide that can be used indoors and outdoors throughout the year to control various pests. Using a leaf-dipping bioassay technique, the effect of different temperatures (range, 15°C–35 °C) on the toxicity of fipronil against the fourth instar larvae of Spodoptera littoralis (Boisd.) was assessed. The temperature coefficient was calculated, and the toxicity of fipronil showed a positive correlation with temperature within the range of 20 °C−25 °C (3.78-fold). Meanwhile, fipronil exhibited a negative correlation over the 15 °C−20 °C temperature range (−6.55-fold). The most intriguing finding was that when the temperature rose from 20 °C to 35 °C, the toxic effect of fipronil improved by 14.5-fold. The fourth instar larvae were treated with an estimated LC 50 value of each fipronil thermal condition (15 °C, 20 °C, 25 °C, and 35 °C), and the protein hemolymphs of the treated larvae were analyzed using sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The highly effective tested treatment, the 35 °C fipronil-maintained group (LC 50 of 2.79 ppm), and its control group displayed the lowest number of protein bands (seven bands). The effect of fipronil under the different thermal conditions on amylase, total lipids, aspartate aminotransferase, alanine aminotransferase, acid phosphatase, and alkaline phosphatase of S. littoralis larvae was also evaluated. Treatments showed varied effects on the biochemical parameters measured. This study emphasizes the benefits of using fipronil under specific thermal conditions to achieve the highest efficiency in combating target pests with the fewest concentrations.