This study provides a promising controlled release form of nuclear polyhedrosis virus (NPV) for targeted control of lepidopteran pests. However, the application of NPV is limited due to its sensitivity to UV inactivation. This study investigated the anti-UV properties of microcapsules of SeMNPV occlusion bodies (OBs) encapsulated by calcium alginate (CA), and also the influence of the modification of CA by chitosan (CS), whey protein (WP), and polydopamine (PDA). These capsules were used to deliver, in a controlled release manner virions under alkaline pH conditions. Characterization of the structure, morphology, particle size, encapsulation efficiency, contact angle, insecticidal activity, UV resistance and in vitro release of the microcapsules was conducted. The modified microcapsules had better sphericity, and were devoid of SeMNPV OBs on the surface. The encapsulation rate was 84.76 ± 0.59%. PDA@CA-NPV had the highest wettability and the contact angle was 74.51 ± 0.53°. The 50% lethal concentration values (LC50) of CA-NPV, CS@CA-NPV, WP@CA-NPV and PDA@CA-NPV were 11.5, 10.7, 10.5 and 1.2 times that of SeMNPV OBs alone. The modified microcapsules all improved the anti-UV performance of the virus, and PDA@CA-NPV was the most UV-resistant. Using qPCR, it was observed that under alkaline conditions, a large number of virions were released from PDA@CA-NPV, CA-NPV and SeMNPV OBs. Microencapsulated virus under alkaline conditions did not change the release pattern of virions.
Background Biological pesticides, especially baculovirus, often lose their activity under the influence of external light, temperature, and other changes. This limited the application of them. The present study was aimed to prolong the biological activity and ensure the efficacy of a biological pesticide using microencapsulation technology. Results In this study, gelatin/carboxymethylcellulose (CMC)-Spodoptera litura nucleopolyhedrovirus microcapsules were prepared. The morphological characteristics, apparent morphology, embedding rate, virus loading, particle size, laboratory virulence, and UV resistance of the microencapsulated virus, were tested. The best conditions for preparing gelatin /CMC-S. litura nucleopolyhedrovirus microcapsules include the gelatin/CMC ratio of 9:1, wall material concentration of 1%, core material/wall ration ratio of 1:2, re-condensation pH of 4.67, and curing time of 1 h. The prepared microcapsules of S. litura nucleopolyhedrovirus exhibited a good external appearance and spherical shapes with an average particle size of 13 μm, an embedding rate of 62.53%, and a drug loading of 43.87%. The virulence test showed that the microencapsulated virus lost by 2.21 times of its initial activity than the untreated virus. After being treated with field exposure, the gelatin/CMC shell of the microcapsule can better protect the virus in the wild environment. Conclusion Microencapsulation improves the tolerance of S. litura nuclear polyhedrosis virus to ultraviolet radiation. These results will provide ideas for the research of stable and efficient baculovirus preparations and further promote the application and promotion of environmental friendly biological pesticides.
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