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BACKGROUND Pyrethrum from dry flowers of Chrysanthemum is a well‐known botanical insecticide and repellent. Its insecticidal activity attributes to its six insecticidal esters, collectively known as pyrethrins. Pyrethrins and its synthetic analogs pyrethroids exert their toxic action by modifying the function of voltage‐gated sodium channels. Aside from insecticidal activity, pyrethrum has also been used to repel mosquitoes for centuries. Today, pyrethrum continues to be used as an active ingredient in mosquito coils and other mosquito‐repellent devices globally. However, the mechanism of pyrethrum repellency remains largely unknown. RESULTS Here we report that pyrethrum vapor induced spatial (non‐contact) repellency in Aedes albopictus, a major vector of dengue and West Nile viruses. Using electroantennogram (EAG) recordings from adult antennae, we found that pyrethrum elicited EAG response in a dose‐dependent manner. We then isolated the six insecticidal esters, pyrethrins I and II, cinerins I and II, jasmolins I and II from pyrethrum extract and discovered that five of the six esters, except jasmolin I, all elicited EAG responses. Furthermore, pyrethrins I and II, cinerin II and jasmolin II induced repellency, whereas cinerin I and jasmolin I did not. CONCLUSION Of the six pyrethrins, four of them, pyrethrins I and II, cinerin II and jasmolin II, activate olfactory‐receptor neurons and elicit spatial repellency in Ae. albopictus. Our study provided a foundation for future structure–function studies of pyrethrins, their cognate olfactory receptors and efficacies of repellency and for the development of new and more effective mosquito repellents for controlling vector‐borne human diseases. © 2021 Society of Chemical Industry.

Background The Asian tiger mosquito Aedes albopictus is a competent vector of several viral arboviruses including yellow fever, dengue fever, and chikungunya. Several vital mosquito behaviors (e.g., feeding, host-seeking, mating, and oviposition) are primarily dependent on the olfactory system for semiochemicals detection and discrimination. However, the limited number of studies hampers our understanding of the relationships between the Ae. albopictus olfactory system and the complex chemical world. Methods We performed RT-qPCR assay on antennae of Ae. albopictus mosquitoes of different sexes, ages and physiological states, and found odorant receptor 11 (AalbOr11) enriched in non-blood-fed female mosquitoes. Then, we examined the odorant preference with a panel of physiologically and behaviorally relevant odorants in Xenopus oocytes. Results The results indicated that AalbOr11 could be activated by ten aromatics, seven terpenes, six heterocyclics, and three alcohols. Furthermore, using post-RNA interference (RNAi) hand-in-cage assay, we found that reducing the transcript level of AalbOr11 affected the repellency activity mediated by (+)-fenchone at a lower concentration (0.01% v/v). Conclusions Using in vitro functional characterization, we found that AalbOr11 was a broadly tuned receptor. Moreover, we found that AalbOr11 shared a conserved odorant reception profile with homologous Anopheles gambiae Or11. In addition, RNAi and bioassay suggested that AablOr11 might be one of the receptors mediating (+)-fenchone repellency activity. Our study attempted to link odor-induced behaviors to odorant reception and may lay the foundation for identifying active semiochemicals for monitoring or controlling mosquito populations. Graphical Abstract

The striped flea beetle, Phyllotreta striolata, is one of the most destructive pests of Cruciferae crops worldwide. RNA interference (RNAi) is a promising alternative strategy for pest biological control, which overcomes the weakness of synthetic insecticides, such as pest resistance, food safety problems and toxicity to non-target insects. The homolog of Spt16/FACT, dre4 plays a critical role in the process of gene transcription, DNA repair, and DNA replication; however, the effects of dre4 silencing in P. striolata remain elusive. In this study, we cloned and characterized the full-length dre4 from P. striolata and silenced Psdre4 through microinjection and oral delivery; it was found that the silencing of dre4 contributed to the high mortality of P. striolata in both bioassays. Moreover, 1166 differentially regulated genes were identified after Psdre4 interference by RNA-seq analysis, which might have been responsible for the lethality. The GO analysis indicated that the differentially regulated genes were classified into three GO functional categories, including biological process, cellular component, and molecular function. The KEGG analysis revealed that these differentially regulated genes are related to apoptosis, autophagy, steroid hormone biosynthesis, cytochrome P450 and other signaling pathways. Our results suggest that Psdre4 is a fatal RNAi target and has significant potential for the development of RNA pesticides for P. striolata management.

RNA interference is an efficient approach for gene function identification and a potential novel strategy for selectively controlling pests. The red flour beetle, Tribolium castaneum (Coleoptera: Tenebrionidae), is a major global storage pest, which causes great economic loss. Juvenile hormone esterase (JHE), a carboxylesterase, is responsible for the degradation of juvenile hormone. However, the knockdown effect of jhe on metamorphosis of pupae or adult in T. castaneum is unknown. In this study, we analyzed the expression profiles of Tcjhe in the larval stage, we found that Tcjhe was expressed throughout the whole larval instars and the expression levels were relatively high right after molting. Furthermore, we knocked down the expression of Tcjhe by injecting dsTcjhe, which significantly increased the mortality of adults and decreased the eclosion rate. In addition, abnormal developmental phenotypes, including wing deformitity, pupal–adult monsters and shrunken adults, were observed. Our finding indicates that JHE plays an important role in the metamorphosis and development in T. castaneum, suggesting that Tcjhe could be used as a potential target for the development of RNAi‐based control strategies in T. castaneum.