To discover new potential pesticide candidates, recently, structural modification of natural bioactive products has received much attention. In this work, a series of new piperine-type ester derivatives were regio-and stereoselectively synthesized based on a natural alkaloid piperine isolated from Piper nigrum. Their structures were characterized by IR, mp, 1 H NMR ( 13 C NMR), and high-resolution mass spectrometry (HRMS). Against Tetranychus cinnabarinus Boisduval (Acari: Tetranychidae), compounds 4e, 4f, 4u, and 4v displayed the most significant acaricidal activity with LC 50 values of 0.155, 0.117, 0.177, and 0.164 mg/mL, respectively. Particularly, compound 4f showed >120-fold higher acaricidal activity than piperine (LC 50 : 14.198 mg/mL). Notably, the acaricidal activity of 4f was equivalent to that of the commercial acaricide spirodiclofen (LC 50 : 0.115 mg/mL). Additionally, against Eriosoma lanigerum Hausmann (Hemiptera: Aphididae), compounds 4w and 4b′ showed 1.8-fold aphicidal activity of piperine. Furthermore, via the scanning electron microscope (SEM) imaging method, the obvious destruction of the construction of the cuticle layer of 4f-treated T. cinnabarinus was observed. Compound 4f could be further studied as a lead acaricidal agent.

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 from Sophora flavescens is 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 of MT with another alkaloid oxymatrine (OMT) (isolated from S. 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. Against Plutella xylostella, when the mass ratio of MT and OMT was 8/2, good larvicidal activity was obtained; against Tetranychus urticae, when the mass ratio of MT and OMT was 3/7, good acaricidal activity was obtained. Especially when MT and OMT were combined with CN, the significant synergistic effects were observed: against P. xylostella, the co-toxicity coefficient (CTC) of MT/OMT (8/2)/CN was 213; against T. urticae, the CTC of MT/OMT (3/7)/CN was 252. Moreover, the activity changes over time of two detoxification enzymes, carboxylesterase (CarE) and glutathione S-transferase (GST) of P. xylostella treated with MT/OMT (8/2)/CN, were observed. In addition, by scanning electron microscope (SEM), the toxicological study suggested that the acaricidal activity of MT/OMT (3/7)/CN may be related to the damage of the cuticle layer crest of T. urticae.