Exploration of Synergistic Pesticidal Activities, Control Effects and Toxicology Study of a Monoterpene Essential Oil with Two Natural Alkaloids

With the increasing development of pest resistances, it is not easy to achieve satisfactory control effects by using only one agrochemical. Additionally, although the alkaloid matrine (MT) isolated fromSophora flavescensis now utilized as a botanical pesticide in China, in fact, its pesticidal activities are much lower in magnitude than those of commercially agrochemicals. To improve its pesticidal activities, here, the joint pesticidal effects ofMTwith another alkaloid oxymatrine (OMT) (isolated fromS. flavescens) and the monoterpene essential oil 1,8-cineole (CN) (isolated from the eucalyptus leaves) were investigated in the laboratory and greenhouse conditions. Moreover, their toxicological properties were also studied. AgainstPlutella xylostella,when the mass ratio ofMTandOMTwas 8/2, good larvicidal activity was obtained; againstTetranychus urticae,when the mass ratio ofMTandOMTwas 3/7, good acaricidal activity was obtained. Especially whenMTandOMTwere combined withCN, the significant synergistic effects were observed: againstP. xylostella,the co-toxicity coefficient (CTC) ofMT/OMT(8/2)/CNwas 213; againstT. urticae,the CTC ofMT/OMT(3/7)/CNwas 252. Moreover, the activity changes over time of two detoxification enzymes, carboxylesterase (CarE) and glutathioneS-transferase (GST) ofP. xylostellatreated withMT/OMT(8/2)/CN, were observed. In addition, by scanning electron microscope (SEM), the toxicological study suggested that the acaricidal activity ofMT/OMT(3/7)/CNmay be related to the damage of the cuticle layer crest ofT. urticae.Keywords:matrine;1,8-cineole;ternary complex;pesticidal activity;detoxification enzymes;SEMKey Contribution:Joint pesticidal activities ofMT–OMT–CNwere related to the mass ratio of ternary complex and controlling pests. These results will lay the foundation for the future study of different combinations ofMT–OMT–CNand the use ofCNas a synergist with other bioactive plant natural products as pesticidal agents in crop protection.