Identification of the Terpenoid Compounds and Behavioral Assays of Alarm Pheromones in the Vetch Aphid Megoura Viciae

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.

PATHOGENIC POTENTIAL OF ENTOMOPATHOGENIC FUNGI OF THE GENUS LECANICILLIUM AGAINST HEMIPTERA

The virulence of the species of the entomopathogenic fungi Lecanicillium psalliotae (strain Vl 78), L. dimorphum (Vl 79) and L. pissodis (ARSEF 8057) against bean aphid Megoura viciae Buckt and greenhouse whitefly Trialeurodes vaporariorum Westwood has been compared with the virulence of well-studied species L. muscarium (Vl 21, Vl 72), L. lecanii (Vl 5), L. longisporum (Vl 13). Species L. longisporum (Vl 13), L. muscarium (Vl 72), L. psalliotae (Vl 78) had a virulence of more than 80% against bean aphid, other strains showed the virulence less than 60%. All strains except L. longisporum (Vl 13) had a high virulence about 75–100% against the greenhouse whitefly. As appeared, the species L. psalliotae (Vl 78) has the perspectives against the both insect species. Its virulence corresponds to the similar level of mortality caused by the well-studied species L. muscarium.

The influence of natural enemies on wing induction in Aphis fabae and Megoura viciae (Hemiptera: Aphididae)

Previous studies have shown that the aphid species, Aphis fabae Scopoli and Megoura viciae Buckton, do not produce winged offspring in the presence of natural enemies, in contrast to results for the pea aphid (Acyrthosiphon pisum (Harris)) and the cotton aphid (Aphis gossypii Glover); but these studies did not involve exposing aphids directly to natural enemies. We exposed colonies of both A. fabae and M. viciae to foraging lacewing (Chrysoperla carnea (Stephens)) larvae and found that the predators did not induce winged morphs among offspring compared to unexposed controls. Colonies of A. fabae responded to an increase in aphid density with increasing winged morph production, while such response was not found for M. viciae. We suggest that different aphid species differ in their susceptibility to natural enemy attack, as well as in their sensitivity to contact.