Discovering the Scent Sensor for Camphor in a Moth Species

Greg Howard
25th January, 2024

Discovering the Scent Sensor for Camphor in a Moth Species

According to the study, Orthaga achatina (pictured) is attracted to Camphor.

Photo adapted from: りなべる / CC BY (Source)
Camphor trees ( Cinnamomum camphora ) produce a strong-smelling chemical called camphor, historically used to protect stored foods from insect damage. However, a moth called Orthaga achatina has uniquely adapted to not only tolerate camphor but to actively feed on camphor trees. This presents a puzzle: how can a pest thrive on a plant defended by a chemical that typically repels other insects? Researchers at Nanjing Agricultural University[1] investigated this question, aiming to understand how O. achatina perceives and responds to camphor at a behavioral and molecular level. The study began by observing the moths’ behavior. Contrary to expectations, both male and female O. achatina moths were attracted to camphor, rather than repelled. This suggests the moths have evolved to recognize camphor not as a warning signal, but as an indicator of a suitable host plant – the camphor tree itself. This finding is particularly interesting when considered alongside earlier work demonstrating the insecticidal properties of camphor against other pests[2]. While camphor effectively deters many insects, O. achatina has seemingly reversed this relationship. To understand how the moths detect camphor, the researchers examined the antennae – the sensory organs responsible for smell. They analyzed the genes active in the antennae and identified 40 genes related to olfactory receptors (ORs), which are proteins that bind to odor molecules. Of these, only one – OachOR16, working in conjunction with Orco – showed a significant response to camphor when tested in a laboratory setting using Xenopus oocytes (frog eggs used as a system to study gene function). This indicates OachOR16 is likely the primary receptor responsible for detecting camphor in O. achatina. Further investigation focused on the structure of the OachOR16 protein. Using computer modeling (molecular docking) and genetic modification (site-directed mutagenesis), the researchers pinpointed a specific amino acid, Serine 209 (Ser209), as crucial for camphor binding. Changing this single building block of the protein significantly reduced its ability to interact with camphor, confirming its importance in the detection process. This research builds upon previous phytochemical studies of C. camphora[3], which identified camphor as a major component of the tree’s essential oils, alongside other compounds like 1,8-cineole and α-terpineol. While those earlier studies focused on the overall chemical composition and antibacterial/insecticidal properties of the oils, this new work delves into the specific molecular mechanisms allowing one insect species to overcome those defenses. The findings also complement research identifying other volatile compounds that influence insect behavior[4], demonstrating how specific chemical signals can drive host plant selection. The study’s findings have implications for pest control. By identifying the specific receptor and amino acid involved in camphor detection, researchers have created a potential target for developing new insect repellents. Compounds that interfere with the binding of camphor to OachOR16 could disrupt the moth’s ability to locate host plants, offering a novel approach to managing this pest.

BiochemEcologyPlant Science

References

Main Study

1) The Odorant Receptor Recognizing Camphor in a Camphor Tree Specialist Orthaga achatina (Lepidoptera: Pyralidae).

Published 24th January, 2024

https://doi.org/10.1021/acs.jafc.3c08877

Related Studies

2) The Chemical Composition of Essential Oils from Cinnamomum camphora and Their Insecticidal Activity against the Stored Product Pests.

Journal: International journal of molecular sciences, Issue: Vol 17, Issue 11, Nov 2016

3) Sub-Tissue Localization of Phytochemicals in Cinnamomum camphora (L.) J. Presl. Growing in Northern Italy.

https://doi.org/10.3390/plants10051008

4) Electrophysiological and Behavioral Responses of Plutella xylostella (Lepidoptera: Plutellidae) to Volatiles from a Non-host Plant, Geranium, Pelargonium × hortorum (Geraniaceae).

https://doi.org/10.1021/acs.jafc.1c08165


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