Abstract
The dynamics of release and degradation of the microencapsulation formulation containing spinosad (SP) and emamectin benzoate (EM) were evaluated in the present study. SP and EM were microencapsulated using biodegradable poly-lactic acid (PLA) as the wall material. Their release from and degradation within the prepared SP and EM microspheres (SP-EM-microspheres) were studied. It was found that the encapsulation significantly prolonged the insecticide release. The release could be further extended if the external aqueous phase was pre-saturated with the insecticides and the microspheres were additionally coated with gelatin. On the other hand, increasing the water content of the emulsion or the hydrophilic polycaprolactone (PCL) content in the PLA/PCL mixture accelerated the release. Due to the photolysis and hydrolysis of SP and EM by sunlight, the toxicity of the non-encapsulated insecticides in water declined continuously from 0 through the 9th day (d), and dissipated in 13 d. In contrast, an aqueous suspension containing 5% SP-EM-microspheres maintained a mostly constant toxicity to Plutella xylostella for 17 d. The biodegradable SP-EM-microspheres showed significantly higher long-term toxicity to P. xylostella due to lower release, reduced photolysis and hydrolysis of the encapsulated insecticides, which were affected by the varied preparation conditions.
Highlights
Both spinosad (SP) and emamectin benzoate (EM) were biological insecticides highly effective against a wide range of insects
There were no significant differences in the rates determined by either high-performance liquid chromatography (HPLC) or spectrophotometer (t-tests, P ≤ 0.05)
The results indicated that spectrophotometer could be used to determine the release rate of the two insecticides in the release medium (Table 1)
Summary
Both spinosad (SP) and emamectin benzoate (EM) were biological insecticides highly effective against a wide range of insects. A microsphere is when a solid core material is enclosed in a polymeric network, while a microcapsule is a liquid/ or solid core surrounded by a polymeric wall[11, 12] The latter is formed using a non-biodegradable material, such as polyurea[13] or polyurethane[14] as the wall material, as widely found in formulating controlled-release www.nature.com/scientificreports/. The effects of preparation conditions on the physicochemical characteristics, insecticide release and degradation of the SP-EM-microspheres are presented. Both short- and long-term toxicities of the microspheres on Plutella xylostella, one of the most devastating pests in the vegetable fields worldwide, were evaluated under sunlight exposure
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