Evaluation of a Spinosad Controlled-Release Formulation Based on Chitosan Carrier: Insecticidal Activity against Plutella xylostella (L.) Larvae and Dissipation Behavior in Soil

Abstract

Controlled-release pesticide formulations using natural polymers as carriers are highly desirable owing to their good biocompatibility, biodegradability, and improved pesticide utilization. In this study, the application potential of our previously prepared spinosad/chitosan controlled-release suspension (SCCS) was evaluated through both toxicity and dissipation tests. A comparison with the spinosad suspension concentrate and the commercial spinosad emulsion in water showed that the insecticidal activity of SCCS against Plutella xylostella larvae displayed the best quick-acting performance as well as long-term efficacy of more than 20 days. The 48 h LC50 for a 20-day efficacy was calculated to be 29.36 mg/L. The dissipation behavior of spinosad in the spinosad/chitosan microparticles in soil was found to follow the first-order kinetics, with a relatively shorter half-life (2.1 days) than that observed for the unformulated spinosad (3.1 days). This work showed the positive effect of chitosan on spinosad in improving insecticidal activity and reducing environmental risks in soil, which provided useful information on the application potential of pesticide–carrier systems based on natural polymer materials in crop protection and food safety.

Coprecipitation‐based synchronous chlorantraniliprole encapsulation with chitosan: carrier–pesticide interactions and release behavior

“…Taking the nontreated larvae as control, the corrected mortality rate (CMR) of larvae after 48 h of feeding was calculated as follows: where M a and M b stand for the mortality rate of larvae treated with and without pesticides, respectively. The median lethal concentration (LC 50 ) of the formulation to P. xylostella larvae also was calculated based on the statistical analysis of these CMR data according to the regression equation described in our previous work 30 …”

“…As an exploration of this scientific hypothesis, a controlled-release formulation of the biological insecticide spinosad has been prepared successfully in our previous work, which displayed high cumulative pesticide release, excellent anti-ultraviolet ability and outstanding insecticidal activity, as well as good dissipation behavior in soil. 29,30 In particular, an obvious synergistic effect of CTS on the toxicity of spinosad has been observed. Despite these satisfactory results, some issues related to this scientific hypothesis still need to be understood, including: (i) Is this coprecipitationbased synchronous encapsulation technique suitable for the fabrication of other types of insecticides, especially the chemical synthesized ones?…”

“…The median lethal concentration (LC 50 ) of the formulation to P. xylostella larvae also was calculated based on the statistical analysis of these CMR data according to the regression equation described in our previous work. 30 3 RESULTS AND DISCUSSION…”

“…Taking commercial suspension concentrate as the control, the improvement in insecticidal activity of CCF against P. xylostella was significantly less than the enhanced efficacy in the spinosad controlled-release formulation in our previous work. 30 Unlike spinosad featuring structural similarity of its rhamnose/forosamine sugars to the glucose units in chitosan, the chemical CAP molecule shows significant structural difference to the natural polymer CTS. Thus, it is considered that the carrier CTS only plays a positive role in the sustained-release property of CCF, and does not show a synergistic effect on the insecticidal activity of CAP.…”

“…Based on the dissolution of CTS in acidic conditions as well as its good swelling abilities, an innovative easy‐to‐prepare approach for pesticide encapsulation is proposed by our group to co‐precipitate the CTS and pesticides under alkaline conditions. As an exploration of this scientific hypothesis, a controlled‐release formulation of the biological insecticide spinosad has been prepared successfully in our previous work, which displayed high cumulative pesticide release, excellent anti‐ultraviolet ability and outstanding insecticidal activity, as well as good dissipation behavior in soil 29,30 . In particular, an obvious synergistic effect of CTS on the toxicity of spinosad has been observed.…”