Impact of Neem Seed Extract on Mortality, Esterase and Glutathione-S-Transferase Activities in Thai Polyvoltine Hybrid Silkworm, Bombyx mori L.

Simple Summary: Thailand's polyvoltine hybrid silkworm, Dok Bua, is 30% more productive than indigenous breeds and is robust and well-suited to the local environment, making it a preferred choice in Thai sericulture. However, synthetic insecticides used on mulberry pests pose risks to silkworms. Neem extract tends to be a safer alternative. The potential toxicity of Thai neem seed extract on this silkworm and their enzymatic detoxification capability could substantially affect their growth and productivity. To explore this, we carried out toxicological and biochemical assessments. The results indicated that the extract had a significant toxicity across all larval stages. Younger larvae were notably more susceptible. We proceeded to examine the activity of the key enzymes implicated in xenobiotic metabolism. The finding that the detoxification enzyme had a low level of activity in the early instar larvae aligned with the larvae mortality. Neem extract suppressed esterase activity but induced glutathione S-transferases (GST) activity, remarkably, in the whole body. Despite its toxicity, GST metabolism could mitigate the effects, indicating the detoxification capabilities of silkworms. These novel findings suggest that neem extract is toxic to all larvae, with GST playing a critical role in detoxification, highlighting the need for careful consideration in sustainable sericulture safety practices. Neem, a biopesticide, offers a safer alternative to the synthetic insecticides commonly used in mulberry cultivation, which can harm silkworms. This study aimed to investigate the effects of Thai neem seed extract on all instar larvae of the Thai polyvoltine hybrid silkworm, Bombyx mori L., Dok Bua strains, focusing on the mortality rate and the activities of esterase (EST) and glutathione S-transferases (GST) enzymes. Acute toxicity was assessed using the leaf-dipping method. Results showed that the mortality rate tended to be higher in younger instars than in older ones. The first instar larvae exhibited the highest mortality rate at 94%, whereas the LC50 was highest in the third instar at 5.23 mg L−1 at 72 h. This trend aligns with the activities of EST and GST, which were evaluated in the whole bodies of the first instar larvae and the midgut tissue of fifth instar larvae. As the extract concentration increased, EST activity decreased while GST activity increased in both the first and fifth instar larvae. These findings highlight that neem extract is toxic to all instar larvae, with GST playing a crucial role in detoxification, particularly in the whole body of the Thai polyvoltine hybrid silkworm. [ABSTRACT FROM AUTHOR]