Effect of three novel compounds on trehalose and chitin metabolism and development of Spodoptera frugiperda.
Objective: Chitin is the main component of insect exoskeleton and peritrophic membrane. Its synthesis begins with trehalase and ends with chitin synthase. The process of molting and epidermal remodeling needs to be completed by chitinase. In this study, three novel compounds were injected to detect the activities of trehalase and chitinase, the expression levels of related genes in Spodoptera frugiperda, and their growth and development were also observed. This study aims to verify the inhibitory effects of novel compounds on trehalase and chitinase, screen the compounds with obvious effects, and to explore the mechanism of their regulation on the growth and development of S. frugiperda. Method: Microinjection method was used to inject butenolactone analogues ZK-I-21, ZK-I-23 and piperine analogue ZK-PI-4 into the 3rd instar larvae of S. frugiperda. The changes of trehalase activity, chitinase activity and related sugar content were detected 48 h after injection, and the relative expression levels of SfTRE1, SfTRE2, SfCHS2 and SfCHT were measured at the molecular level by quantitative real-time PCR (qRT-PCR). The phenotypic changes of S. frugiperda were observed during the process from larvae to adults after injection. Besides, the mortality and deformities during developmental period were recorded. Result: Compared with the control group, the membrane-bound trehalase activity of S. frugiperda decreased significantly after ZK-I-21 (P < 0.01) and ZK-PI-4 (P < 0.05) injection. The expression level of SfTRE1 was significantly increased and SfCHT was significantly decreased after ZK-I-21 injection. After ZK-I-23 injection, the expression level of SfTRE1 was significantly decreased, and the expression level of SfCHT was significantly increased. The expression level of SfCHT was significantly decreased after ZK-PI-4 injection. The observation results of developmental duration showed that ZK-I-21 significantly prolonged the developmental period of 6th instar larvae of S. frugiperda, and at the same time, the pupa weight became lighter and the pupa length became shorter. In addition, ZK-I-23 significantly shortened the length of 5th and 6th instar larvae, and ZK-PI-4 caused a significant reduction in adult emergence rate. All the three inhibitors could disrupt trehalose metabolism of S. frugiperda and then disrupt chitin metabolism, resulting in difficulties in molting and even death. Conclusion: ZK-I-21 and ZK-PI-4 are membrane-bound trehalase inhibitor compounds, and ZK-I-23 can inhibit the expression of soluble trehalase gene. The three compounds all lead to the disturbances of chitin metabolism by affecting the process of trehalose metabolism, which results in difficulties in molting, deformities, and impaired growth and development of insects. The above results can provide a theoretical basis for the future use of novel inhibitors to regulate the growth of pests and thus control them, and support to promote the development of green and efficient pesticides.