Insecticidal efficacy of α-pinene and limonene against Spodoptera frugiperda (Lepidoptera: Noctuidae)

The fall armyworm, Spodoptera frugiperda (J.E. Smith, 1797) (Lepidoptera: Noctuidae), is a major polyphagous lepidopteran pest. Currently, the use of chemical insecticides for the management of this pest is strictly controlled because of their possible negative effects. This scenario has led to an increased focus on investigating alternative pest management strategies, particularly the use of bioinsecticides, emphasizing the role of monoterpenes. Therefore, this research aimed to evaluate the insecticidal properties of α-pinene and limonene, both alone and in combination, to investigate the potential synergistic interactions against S. frugiperda. The results displayed that the larvicidal activity of α-pinene (lethal dose [LD50] = 9.52 μg/larva) was more effective than limonene (LD50 = 12.69 μg/larva) against S. frugiperda. All combinations of α-pinene and limonene in a ratio ranging from 9:1 to 1:9 (v:v) demonstrated synergistic insecticidal effects against S. frugiperda, with the 7:3 ratio showing the highest insecticidal efficacy (LD50 = 3.66 μg/larva). In addition, the combined use of α-pinene and limonene affected certain growth and developmental abnormalities in S. frugiperda. Furthermore, S. frugiperda larvae treated with limonene alone, as well as those treated with a combination of α-pinene and limonene, revealed a decrease in acetylcholinesterase activity. Moreover, the carboxylesterase and glutathione-S-transferase activities of S. frugiperda larvae were decreased after treatment with α-pinene and limonene in combination. In conclusion, our research indicated that α-pinene and limonene alone and in combination may serve as effective alternatives for the control of the agricultural pest S. frugiperda.