Abstract
Aphids are destructive insect pests worldwide, and alarm pheromones play a key role in their chemical ecology. However, the composition and key active components of alarm pheromone differentiate among aphid species. Here we conducted a detailed analysis of the terpenoid compounds in the vetch aphid Megoura viciae and its host plant Pisum sativum by using gas chromatography-mass spectrometry. The results showed that a variety of terpenoid compounds existed in the aphid, with four major terpene components, i.e., (-)-β-pinene (49.74%), (E)-β-farnesene (32.64%), (-)-α-pinene (9.42%) and (+)-limonene (5.24%), in addition to a trace amount of minor terpenoid components (3.14%). In contrast, the terpenoid compounds were relatively scarce in the host plant, mainly consisting of squalene (66.13%) and its analogue 2,3-epoxysqualene (31.59%) in addition to some minor components. Quantitative analysis of the dynamics of four major terpene components during different developmental stages showed that the monoterpenes increased with continuous development, while the sesquiterpene reached peak at the 3rd -instar; all terpene components remained at a high level in the 4th -instar, with (-)-β-pinene accounting for the highest proportion during all developmental stages. Behavioral assays with single components and mixtures at different concentrations were conducted in a three-compartment olfactometer, revealing that the repellent activities of single components varied in a concentration-dependent manner, but two mixtures (1:44.4:6.5:2.2 and 1:18.4:1.3:0.8) prepared according to the proportions of four major components at the 3rd - and 4th -instar stages maintained a significant repellent activity at all concentrations tested. Our results suggested that (-)-α-pinene and (-)-β-pinene were the major active components of alarm pheromone in M. viciae, but the mixtures of single components play a key role in the alarm behavior of M. viciae. Our study helps to understand the chemical ecology of insects and design alternative control strategies against aphids.
Identification of the Terpenoid Compounds and Behavioral Assays of Alarm Pheromones in the Vetch Aphid Megoura Viciae
