Chitin is the main component of insect exoskeleton and midgut peritrophic membrane. Insect molting is the result of the balance and coordination of chitin synthesis and degradation in chitin metabolism under the action of hormones. In this study, a 678 bp dsRNA fragment was designed and synthesized according to the known CHI (Chitinase) sequence of Spodoptera frugiperda. It was injected into the larvae to observe the molting and development of S. frugiperda. At the same time, the activities of trehalase and chitinase, the contents of trehalose, chitin and other substances were detected, and the expression of related genes in the chitin synthesis pathway was determined. The results showed that CHI gene was highly expressed at the end of each instar, prepupa and pupal stage before molting; At 12 and 24 h after dsRNA injection of CHI gene of S. frugiperda, the expression of CHI gene decreased significantly, and the chitinase activity decreased significantly from 12 to 48 h. The expression of chitin synthase (CHSB) gene decreased significantly, and the chitin content increased significantly. Some larvae could not molt normally and complete development, leading to certain mortality. Secondly, after RNAi of CHI gene, the content of glucose and glycogen increased first and then decreased, while the content of trehalose decreased significantly or showed a downward trend. The activities of the two types of trehalase and the expression levels of trehalase genes decreased first and then increased, especially the trehalase activities increased significantly at 48 h after dsCHI injection. And trehalose-6-phosphate synthase (TPS), glutamine: fructose-6-phosphate amidotransferase (GFAT), UDP-N-acetylglucosamine pyrophosphorylases (UAP), hexokinase (HK), glucose-6-phosphate isomerase (G6PI) and phosphoacetylglucosamine mutase (PAGM) all decreased significantly at 24 h, and then increased or significantly increased at 48 h. These results indicated that when the expression of chitinase gene of S. frugiperda was inhibited, it affected the degradation of chitin in the old epidermis and the formation of new epidermis, and the content of chitin increased, which led to the failure of larvae to molt normally. Moreover, the chitin synthesis pathway and trehalose metabolism were also regulated. The relevant results provide a theoretical basis for screening target genes and developing green insecticides to control pests by using the chitin metabolism pathway.

Introduction:Spodoptera frugiperda is an omnivorous agricultural pest which is great dangerous for grain output.Methods: In order to investigate the effects of potential trehalase inhibitors, ZK-PI-5 and ZK-PI-9, on the growth and development of S. frugiperda, and to identify new avenues for S. frugiperda control, we measured the content of the trehalose, glucose, glycogen and chitin, enzyme activity, and gene expression levels in trehalose and chitin metabolism of S. frugiperda. Besides, their growth and development were also observed.Results: The results showed that ZK-PI-9 significantly reduced trehalase activity and ZK-PI-5 significantly reduced membraned-bound trehalase activity. Moreover, ZK-PI-5 inhibited the expression of SfTRE2, SfCHS2, and SfCHT, thus affecting the chitin metabolism. In addition, the mortality of S. frugiperda in pupal stage and eclosion stage increased significantly after treatment with ZK-PI-5 and ZK-PI-9, which affected their development stage and caused death phenotype (abnormal pupation and difficulty in breaking pupa).Discussion: These results have provided a theoretical basis for the application of trehalase inhibitors in the control of agricultural pests to promote future global grain yield.

Southern rice black-streaked dwarf virus (SRBSDV) caused serious rice losses. After the first outbreak in 2009 in northern Vietnam and southern China, the virus ravaged crops again on enormous scales in 2010, but infections have decreased sharply since 2011. We presumed that the sudden epidemics and fadeout of SRBSDV would be closely related to the migratory events of the insect vector, Sogatella furcifera. This study sought the source area of SRBSDV using the trajectory analysis method, and revealed the relationship between SRBSDV dynamics and migration of S. furcifera populations via an in-depth analysis of meteorological background of S. furcifera migration fields. The results showed that Northern Vietnam was the direct virus source area of the SRBSDV infection in China, and South Central Coast of Vietnam was the original source area of SRBSDV. Southwesterly winds were prevalent in spring of 2010 and carried large numbers of viruliferous S. furcifera to China from northern Vietnam. This infestation of S. furcifera was the direct cause of the SRBSDV outbreak in China in 2010. In 2011, the winter–spring temperatures were abnormally low and southeasterly and easterly winds dominated; therefore, the number of viruliferous S. furcifera that entered China was small, and consequently, the occurrence area of SRBSDV was rapidly reduced. The return of viruliferous S. furcifera to South Central Coast of Vietnam was an important factor that affected the occurrence scale of SRBSDV in the following year.

The Sogatella furcifera (Horváth) is an important migrating rice pest whose outbreak may be caused by large-scale congregated landings. Hitherto, the meteorological factors that influence congregated landings were thought to be rainfall and downdraft. However, for migratory insects on a plateau, low temperature may be another key factor leading to congregated landings. However, no reports have been published. Therefore, this paper evaluates the reason for a large-scale congregated landing in the mountainous area in Yuanjiang via light trap monitoring. The meteorological backgrounds during light catch peaks were analyzed using the numeric simulation method. The results were as follows: 1) from May 7th to May 9th, 2012, the congregated landing of S. furcifera was caused by precipitation; 2) the congregated landing of S. furcifera on May 10th, 2012, was a result of low temperatures in the mountainous region. The driving airflow of S. furcifera climbed along the mountain terrain, which led to a decrease in temperature with the rise of the mountain terrain. Low temperature created physiological changes in S. furcifera, forcing S. furcifera to a lower flight altitude and eventually to a congregated landing; and 3) in the statistical analysis on 39 peak periods from 2010 to 2016 in the early spring, 20 peaks were caused by precipitation, and 19 peaks were caused by a low temperature barrier. Therefore, this study provided evidence of a plateau-migrating S. furcifera population congregated landing caused by low temperature.

Trehalase inhibitors prevent trehalase from breaking down trehalose to provide energy. Chitinase inhibitors inhibit chitinase activity affecting insect growth and development. This is an important tool for the investigation of regulation of trehalose metabolism and chitin metabolism in insect reproduction. There are few studies on trehalase or chitinase inhibitors’ regulation of insect reproduction. In this study, ZK-PI-5 and ZK-PI-9 were shown to have a significant inhibitory effect on the trehalase, and ZK-PI-9 significantly inhibited chitinase activity in female pupae. We investigated the reproduction regulation of Spodoptera frugiperda using these new inhibitors and evaluated their potential as new insecticides. Compounds ZK-PI-5 and ZK-PI-9 were injected into the female pupae, and the control group was injected with solvent (2% DMSO). The results showed that the emergence failure rate for pupae treated with inhibitors increased dramatically and aberrant phenotypes such as difficulty in wings spreading occurred. The oviposition period and longevity of female adults in the treated group were significantly shorter than those in the control group, and the ovaries developed more slowly and shrank earlier. The egg hatching rate was significantly reduced by treatment with the inhibitor. These results showed that the two new compounds had a significant impact on the physiological indicators related to reproduction of S. frugiperda, and have pest control potential. This study investigated the effect of trehalase and chitin inhibitors on insect reproduction and should promote the development of green and efficient insecticides.

Spodoptera frugiperda is one of the world’s major agricultural pests and it occurs in many countries around the world. In Lepidoptera, the peritrophic membrane in the midgut protects the midgut epithelial cells and facilitates the digestion and absorption of food. Its main components are chitin and protein. Chitin synthase (CHS), as the last enzyme in the chitin biosynthesis pathway, is very important. Here, the expression of chitin synthase B (CHSB) gene identified from midgut was inhibited by RNA interference to explore its function in the metabolism of trehalose and chitin of S. frugiperda larvae. The results were as follows: SfCHSB was highly expressed in actively feeding larvae. Second, knockdown of SfCHSB resulted in decreased expression of most genes involved in chitin metabolism, including chitinase, and abnormal phenotypes of S. frugiperda were observed. In addition, membrane-bound trehalase activity and glucose content increased, and trehalose content decreased at 24 h after dsSfCHSB injection. Trehalase activities increased significantly and the glycogen content decreased at 48 h after dsSfCHSB injection. Finally, the activity of chitinase decreased and the content of chitin increased significantly. Our results indicate that SfCHSB expression is specific, SfCHSB has a large role in regulating chitin metabolism, and it has broad application prospects in the biocontrol of S. frugiperda.