Finetti, L. | Search bioRxiv

bioRxiv2020

Tyramine receptor drives olfactory response to (E)2-decenal in the stink bug Halyomorpha halys

In insects, the tyramine receptor 1 (TAR1) has been shown to control several physiological functions, including olfaction. We investigated the molecular and functional profile of the Halyomorpha halys type 1 tyramine receptor gene (HhTAR1) and its role in olfactory functions of this pest. Molecular and pharmacological analyses confirmed that the HhTAR1 gene codes for a true TAR1. The RT-qPCR analysis revealed that HhTAR1 is expressed mostly in adult brain and antennae as well as in early development stages (eggs, 1st and 2nd instar nymphs). In particular, among the antennomeres that compose a typical H. halys antenna, HhTAR1 was more expressed in flagellomeres. Scanning electron microscopy (SEM) investigation revealed the type and distribution of sensilla on adult H. halys antennae: both flagellomeres appear rich in trichoid and grooved sensilla, known to be associated with olfactory functions. Through a RNAi approach, topically delivered HhTAR1 dsRNA induced a 50 % gene downregulation after 24 h in H. halys 2nd instar nymphs. An innovative behavioral assay revealed that HhTAR1 RNAi-silenced 2nd instar nymphs were less susceptible to the alarm pheromone component (E)-2 decenal as compared to control. These results provide critical information concerning the TAR1 role in olfaction regulation, especially alarm pheromone reception, in H. halys. Furthermore, considering the emerging role of TAR1 as target of biopesticides, this work paves the way for further investigation on innovative methods for controlling H. halys.

animal behavior and cognition↗

bioRxiv2020

Monoterpenes alter TAR1-driven physiology in Drosophila species

Monoterpenes are molecules with insecticide properties whose mechanism of action is however not completely elucidated. Furthermore, they seem to be able to modulate the monoaminergic system and several behavioural aspects in insects. In particular, tyramine (TA) and octopamine (OA) and their associated receptors orchestrate physiological processes such as feeding, locomotion and metabolism. Here we show that monoterpenes not only act as biopesticides in Drosophila species but can cause complex behavioural alterations that require a functional type 1 tyramine receptors (TAR1s). Variations in metabolic traits as well as locomotory activity were evaluated in both Drosophila suzukii and Drosophila melanogaster after treatment with three monoterpenes. A TAR1-/- D. melanogaster strain was used to better understand the relationships between the receptor and monoterpenes-related behavioural changes. Immunohistochemistry analysis revealed that, in the D. melanogaster brain, TAR1 appeared to be expressed in areas controlling metabolism. In comparison to the D. melanogaster wild type, the TAR-/- flies showed a phenotype characterized by higher triglyceride levels and food intake as well as lower locomotory activity. The monoterpenes, tested at sublethal concentrations, were able to induce a downregulation of the TAR1 coding gene in both Drosophila species. Furthermore, monoterpenes also altered the behaviour in D. suzukii and D. melanogaster wild types 24 h after a continuous monoterpene exposure. Interestingly, they were ineffective in modifying the physiological performances of TAR1-/- flies. In conclusion, it appears that monoterpenes not only act as biopesticides for Drosophila but they can also interfere with its behaviour and metabolism in a TAR1-dependent fashion.

animal behavior and cognition↗