Pulegone, a component of Schizonepeta tenuifolia volatiles can act as an effective fumigant of the rusty grain beetle Cryptolestes ferrugineus

Abstract

The utilization of new plant-based fumigants is one of the most important green control methods for safe storage and protection of grain. The rusty grain beetle, Cryptolestes ferrugineus (Stephens) (Coleoptera: Laemophloeidae), is a common stored grain pest that causes a great loss of stored grain every year. This study determined that, Schizonepeta tenuifolia Briq. spike (SS) powder had strong fumigant insecticidal effectiveness against C. ferrugineus. Moreover, the volatile eluates (VEs) of SS extracted with Porapak™ Q adsorbent at a flow rate of 600 mL/min exhibited higher insecticidal activity against C. ferrugineus adults than the larvae; the VEs LC50 of C. ferrugineus adults were 14.93%− 24.83% of those of C. ferrugineus larvae. The temperature, not the age of C. ferrugineus adults, significantly influenced the fumigation effect of SS VEs; at relatively low temperature (15 ℃) the SS VEs showed quicker and more efficient fumigant activity than at a high temperature (30–35 ℃). In addition, S. tenuifolia VEs showed better fumigation effects against Oryzaephilus surinamensis (Coleoptera: Silvanidae) and Sitophilus oryzae (Coleoptera: Curculionidae) compared to Tribolium castaneum (Coleoptera: Tenebrionidae). The four most abundant components of SS volatiles analyzed by GC-MS were pulegone (62.62%), isomenthone (18.34%), 2-isopropyl-2,5-dimethylcyclohexanone (2.45%), and isopulegone (1.32%), in order by their peak area ratio. Toxicity testing of the two compounds with the largest proportion indicated that only pulegone had insecticidal activity against C. ferrugineus adults with a LC50 (8.90 mL/L) at 72 h. Consistent with VEs, temperature also greatly affect the fumigant activity of pulegone and at low temperature (15 ℃) the pulegone showed more quick and effective insecticidal activity against C. ferrugineus adults. We further found that both VEs and pulegone can inhibit carboxylesterase (CarE), peroxidase (POD), and superoxide dismutase (SOD) in vivo and in vitro, especially the inhibition rate of carboxylesterase, which reached 84.87% and 63.82% at 24 h in vivo, which suggested that the fumigant insecticidal activity of SS VEs and pulegone may partly be mediated by affecting the detoxification and metabolism enzyme system of C. ferrugineus. Therefore, both S. tenuifolia and pulegone can be used as botanical fumigant to potentially control stored grain pests.