Larvicidal activity and microencapsulation of tobacco (Nicotiana tabacum) extract on Malacosoma neustria testacea larvae

Abstract

To understand and improve the stability of the insecticidal activity of tobacco extract, the 3rd instar larvae of Malacosoma neustria testacea was determined by the leaf film method. Spectrophotometry identified extract effects on activities of several enzymes. In addition, to improve the stability of the extract, microcapsules were prepared by complex coacervation and phase separation with the extract as core material, and gelatin and gum arabic as wall material. With the embedding rate as the evaluation index, the response surface method was used to optimize the preparation process of the microcapsules. The results show that the extract had a strong insecticidal activity on the larvae, with inhibitory effects on several enzymes examined of carboxylesterase, acetylcholinesterase, glutathione-S transferase, catalase, and superoxide dismutase. The inhibition rate increased with time. The best preparation process of tobacco extract microcapsules was 25% mass fraction of emulsifier, 2.05% mass fraction of gelatin, 3% mass fraction of gum arabic, 1.34 wall core ratio, 36 min of complex coacervation time. The embedding rate was 58.4% which is approximately the theoretical embedding rate (58.9%). The microcapsules prepared by this method have a smooth surface, good combining form and particle size distribution, and a median diameter of 8.6 μm. Infrared characteristic peaks of the extracts were preserved at 877.55 cm‒1 and 2922.13 cm‒1. Microencapsulation can improve the thermal stability of the tobacco extract. Indoor toxicity tests showed that LC50 of extract microcapsules was 20.2 mg·mL‒1, equivalent to the toxicity level of the tobacco extract itself, indicating that microencapsulation did not reduce extract insecticidal effects. This research may provide a reference for the optimization of the tobacco extract microcapsule preparation process.