Insecticide activity of botanical compounds against Spodoptera frugiperda and selectivity to the predatory bug Podisus nigrispinus

Abstract

Pest control based exclusively on the use of organosynthetic insecticides can cause several problems including the reduction of populations of natural enemies. Thus, the use of selective insecticides is essential for efficient pest control. In this study, we evaluated the lethal effects of the essential oil of Lippia sidoides and its major compound thymol on the fall armyworm, Spodoptera frugiperda, as well as the selectivity and behavioral effects of these compounds on Podisus nigrispinus, an important predator of defoliating caterpillars. The botanical compounds were more selective to the predator than the insecticide deltamethrin, which was about 2.7 times more toxic to P. nigrispinus than to S. frugiperda. The insecticide deltamethrin caused rapid mortality to nymphs of P. nigrispinus with LT50 = 0.36 h. Additionally, the mortality of individuals exposed to this treatment reached 100% in less than 3 h. The essential oil (LT50 = 119 h) and the thymol (LT50 = 93 h) acted more slowly on the predator. On the contrary, for the pest, the botanical compounds acted faster than the synthetic insecticide. Nymphs exposed to deltamethrin and thymol showed behavioral changes, as there was an increase and decrease in speed and distance covered, respectively. All insects stayed longer on the untreated side of the arenas. The present study reveals the potential of the essential oil and thymol for the control of the S. frugiperda pest and, at the same time, the selectivity of these compounds over P. nigrispinus.