ABSTRACT
Due to the contamination and biological toxicity of some fragrance compounds, the environmental and ecological problems of such compounds have attracted more and more attention. However, studies of the toxicity of fragrance compounds for insects have been limited. The toxicity of 48 fragrance compounds for the silkworm Bombyx mori were investigated in this study. All of the fragrance compounds examined had no acute toxicity for B. mori larvae, but eight of them (menthol, maltol, musk xylene, musk tibeten, dibutyl sulfide, nerolidol, ethyl vanillin, and α-amylcinnamaldehyde) exhibited chronic and lethal toxicity with LC50 values from 20 to 120 µM. In a long-term feeding study, musk tibeten, nerolidol, and musk xylene showed significant growth regulatory activity. They were also extremely harmful to the cocooning of B. mori, resulting in small, thin, and loose cocoons. Two important insect hormones, namely, juvenile hormone (JH) and 20-hydroxyecdysone (20-E), were quantified in hemolymph following chronic exposure to musk tibeten, nerolidol, and musk xylene, respectively. Musk tibeten significantly increased JH titer and decreased the 20-E titer in hemolymph, and musk xylene had a significant inhibitory effect on JH titer and increased 20-E titer. Although nerolidol had no effect on hormone levels, exogenous JH mimic nerolidol increased the physiological effects of JH and significantly slowed the growth rate of B. mori larvae. The results showed that these fragrance compounds could interfere with the insect endocrine system, leading to death and abnormal growth. The risk to insects of residual fragrance compounds in the environment is worthy of attention.
ABSTRACT
BACKGROUND: Discovery of novel insecticides and targets has received global attention in recent years. Ten genes coding for enzymes involved in the juvenile hormone biosynthetic pathway of Manduca sexta were studied as potential insecticide targets. RESULTS: We determined the expression of genes encoding some critical enzymes in the JH biosynthetic pathway. Farnesol dehydrogenase (FOLD), Juvenile hormone acid O-methyltransferase (JHAMT) and Juvenile hormone epoxidase (CYP15C1) were selected as the candidate targets based on gene expression results. RNAi silencing and enzyme inhibitor tests were performed to validate whether these candidate genes could be the potential insecticide targets. The down-regulation of FOLD, JHAMT and CYP15C1 resulted in a 68%, 82% and 79% reduction in the rates of JH biosynthesis in vitro, respectively. In addition, RNA interference and inhibitor studies of these enzymes following oral administration demonstrated the potential application in pest management, with respect to high mortality and effects on growth. CONCLUSION: Based on our study, FOLD, JHAMT and CYP15C1 could be potential targets for pest control as a consequence of their important roles in insect development. © 2019 Society of Chemical Industry.
