Rice volatile compound (E)-ß-caryophyllene induced by rice dwarf virus (RDV) attracts the natural enemy Cyrtorhinus lividipennis to prey on RDV insect vectors.

BACKGROUND: Rice dwarf virus (RDV)-induced rice plant volatiles (E)-ß-caryophyllene and 2-heptanol modulate the olfactory behavior of RDV insect vectors that promote viral acquisition and transmission. However, it remains elusive whether these two volatiles could influence the behaviors of the natural enemies of RDV insect vectors. Herein, we determined the effects of these two volatiles on the olfactory and predatory behaviors of Cyrtorhinus lividipennis (Hemiptera: Miridae), an important predator of RDV insect vectors in rice paddies. RESULTS: The results showed that C. lividipennis preferred RDV-infected rice plant odors over RDV-free rice plant odors. C. lividipennis was attracted by (E)-ß-caryophyllene, but showed no behavioral responses to 2-heptanol. The attraction of (E)-ß-caryophyllene towards C. lividipennis was further confirmed using oscas1 rice plants, which do not release (E)-ß-caryophyllene in response to RDV infection, through a series of complementary assays. The oviposition preference of the RDV vector insect Nephotettix cincticeps (Hemiptera: Cicadellidae) showed no significant difference between RDV-infected and RDV-free wild-type plants, nor between oscas1-RDV and oscas1 plants. However, the predation rate of C. lividipennis for N. cincticeps eggs on RDV-infected plants was higher than that on RDV-free plants, whereas there was no significant difference between oscas1-RDV and oscas1 plants. CONCLUSION: (E)-ß-caryophyllene induced by RDV attracted more C. lividipennis to prey on N. cincticeps eggs and played a crucial role in plant-virus-vector-enemy interactions. These novel findings will promote the design of new strategies for disease control by controlling the populations of insect vectors, for example recruiting more natural enemies by virus-induced plant volatiles. © 2023 Society of Chemical Industry.

Olfactory behavioral responses of two Drosophila species and their pupal parasitoid to volatiles from bananas.

BACKGROUND: Behavior-based manipulation is an essential part of Drosophila integrated pest management (IPM). Effective compounds are useful for improving the efficiency of baits and the development of attract-and-kill or push-pull strategies to manage Drosophila populations. Here, we investigated the olfactory behavior of two Drosophila species, as well as their pupal parasitoid, to volatiles from bananas, for the identification of effective compounds to control fly populations. RESULTS: The results showed that overripe bananas were most attractive to both flies, with a higher attraction index (AI) in Drosophila melanogaster than in Drosophila suzukii. The profiles of volatile organic compounds (VOCs) from bananas with three different ripening stages were compared, and six VOCs were selected for behavioral tests. D. suzukii showed significantly different responses to isoamyl alcohol with D. melanogaster. The effects of ethyl butyrate and ethyl isovalerate on the two flies were dose-dependent, with lower concentrations acting as repellent and higher concentrations acting as attractant. Isoamyl acetate, isoamyl butyrate and isoamyl isovalerate (0.005-0.05% v/v) were attractive to both flies. The parasitoid wasp Pachycrepoidus vindemmiae was repelled by isoamyl alcohol and ethyl butyrate, and attracted by ethyl isovalerate, but showed no significant response to isoamyl acetate, isoamyl butyrate and isoamyl isovalerate at the tested concentration. CONCLUSION: This study indicated that the behavioral response of Drosophila to the odor of chemical compounds is dose-dependent. Isoamyl alcohol and isoamyl acetate at certain concentrations could be used as repellents, whereas ethyl isovalerate as an attractant in control strategy design for D. suzukii. © 2023 Society of Chemical Industry.

Identification and Expression Analysis of Odorant-Binding and Chemosensory Protein Genes in Virus Vector Nephotettix cincticeps.

The insect odorant binding proteins (OBPs) and chemosensory proteins (CSPs) are involved in the perception and discrimination of insects to host odor cues. Nephotettix cincticeps, one of the destructive pests of rice plants, not only directly damages hosts by sucking, but also indirectly transmits plant viruses in the field. Previous study found that two rice volatiles ((E)-ß-caryophyllene and 2-heptanol) induced by rice dwarf virus (RDV) mediated the olfactory behavior of N. cincticeps, which may promote virus dispersal. However, the OBPs and CSPs in N. cincticeps are still unknown. In this study, to identify the OBP and CSP genes in N. cincticeps, transcriptomic analyses were performed. In total, 46,623 unigenes were obtained. Twenty putative OBP and 13 CSP genes were discovered and identified. Phylogenetic analyses revealed that five putative OBPs belonged to the plus-C OBP family, and the other classic OBPs and CSPs were distributed among other orthologous groups. A total of 12 OBP and 10 CSP genes were detected, and nine OBP and three CSP genes were highly expressed in N. cincticeps antennae compared with other tissues. This study, for the first time, provides a valuable resource to well understand the molecular mechanism of N. cincticeps in the perception and discrimination of the two volatiles induced by RDV infection.