Molecular Basis of Sucrose Perception Differs Between Larval and Adult Stages of the Cotton Bollworm Moth

Core Concepts

Larval and adult Helicoverpa armigera use different gustatory receptor genes, Gr10 and Gr6, to detect and respond to sucrose in their respective food sources.

Abstract

The study investigated the molecular basis of sucrose perception in the cotton bollworm moth, Helicoverpa armigera, across its larval and adult stages. Key highlights: Larval lateral sensilla styloconica had sugar-sensing neurons that were 100-1000 times more sensitive to sucrose compared to adult taste sensilla. Gr10 was highly expressed in larval maxillary galea and specifically tuned to sucrose, while Gr6 was highly expressed in adult antennae, tarsi and proboscis, and responded to sucrose, fucose and fructose. Knockout of Gr10 significantly reduced sucrose sensitivity and feeding preference in larvae, while knockout of Gr6 impaired sucrose, fucose and fructose detection and proboscis extension reflex in adults. The findings demonstrate that H. armigera larvae and adults evolved distinct sugar receptor systems to adapt to the different sugar compositions in their respective food sources - plant tissues for larvae and nectar for adults.

Stats

Larvae had sugar-sensing neurons in lateral sensilla styloconica that responded to 0.1 mM sucrose, while the threshold for adult taste sensilla was 10-100 mM. The firing rates of larval sugar-sensing neurons to 1 mM, 10 mM and 100 mM sucrose were 40%, 20% and 28% of wild-type in Gr10 knockout, respectively. Gr6 knockout adults showed significantly reduced proboscis extension reflex to 10 mM, 100 mM and 1000 mM sucrose, fucose and fructose compared to wild-type.

Quotes

"The sugar GSNs in lateral sensilla styloconica of larvae responded strongly to sucrose with high sensitivity, and weakly to fucose; while the sugar GSNs of adults responded to sucrose, fucose, and fructose (except for those on tarsi) with lower intensity and sensitivity." "Gr10 plays a key role in sucrose reception by the sugar GSNs in the larval lateral sensilla styloconica, and mediates the feeding preference of larvae to sucrose, whereas Gr6 plays a key role in sensing sucrose, fucose, and fructose by the sugar GSNs in contact chemosensilla of the adult antennae, foreleg tarsi and proboscis, and mediates the related PER behavior of adults."

Key Insights Distilled From

The larva and adult of Helicoverpa armigera use differential gustatory receptors to sense sugars

by Zhang,S.-S.,... at www.biorxiv.org 09-21-2023

https://www.biorxiv.org/content/10.1101/2023.09.19.558417v2

Deeper Inquiries

How do the sugar receptor genes Gr10 and Gr6 evolve to enable the larval and adult stages of H. armigera to adapt to their respective food sources

The sugar receptor genes Gr10 and Gr6 in H. armigera have evolved to enable the larval and adult stages to adapt to their respective food sources through specialization and sensitivity to different sugars. Gr10, highly expressed in larval sensilla, is specifically tuned to sucrose, allowing larvae to detect lower sucrose concentrations found in young leaves and flower buds. On the other hand, Gr6, highly expressed in adult sensilla, responds to fucose, sucrose, and fructose, enabling adults to detect higher sucrose concentrations present in nectar. This specialization in sugar reception allows the insect to effectively identify and feed on the appropriate food sources at different life stages, enhancing their survival and reproductive success.

What are the potential tradeoffs or constraints that shape the specialization of Gr10 and Gr6 in larval and adult stages

The specialization of Gr10 and Gr6 in larval and adult stages of H. armigera may be shaped by potential tradeoffs and constraints in their evolutionary adaptation. One constraint could be the availability and diversity of sugar sources in the environment. Larvae primarily feed on plant tissues with lower sucrose content, necessitating a high sensitivity to detect these lower concentrations, which is facilitated by Gr10. In contrast, adults feed on nectar with higher sugar concentrations, requiring a broader response spectrum to detect various sugars, including sucrose, fucose, and fructose, as mediated by Gr6. Tradeoffs may arise in the form of energy allocation and resource utilization, where the insect invests in specific sugar receptors based on the predominant food sources available at each life stage, optimizing their foraging efficiency while balancing metabolic costs.

Could the insights from this study on sugar perception be applied to understand feeding behaviors and host plant selection in other phytophagous insect species

The insights from this study on sugar perception in H. armigera could be applied to understand feeding behaviors and host plant selection in other phytophagous insect species. By investigating the molecular mechanisms of sugar reception and the specialization of sugar receptor genes in different life stages, researchers can gain valuable insights into how insects adapt to diverse food sources. This knowledge can be extrapolated to study the feeding preferences, foraging strategies, and host plant selection of other phytophagous insects. Understanding the genetic basis of sugar perception can provide a framework for exploring the ecological interactions between insects and plants, shedding light on the co-evolutionary dynamics and behavioral adaptations of phytophagous insects in response to changing environmental conditions.