Aphid and Plant Volatiles Induce Oviposition in an Aphidophagous Hoverfly

Abstract

Episyrphus balteatus DeGeer (Diptera, Syrphidae) is an abundant and efficient aphid-specific predator. We tested the electroantennographic (EAG) response of this syrphid fly to the common aphid alarm pheromone, (E)-β-farnesene (EβF), and to several plant volatiles, including terpenoids (mono-and sesquiterpenes) and green leaf volatiles (C6 and C9 alcohols and aldehydes). Monoterpenes evoked significant EAG responses, whereas sesquiterpenes were inactive, except for the aphid alarm pheromone (EβF). The most pronounced antennal responses were elicited by six and nine carbon green leaf alcohols and aldehydes [i.e., (Z)-3-hexenol, (E)-2-hexenol, (E)-2-hexenal, and hexanal]. To investigate the behavioral activity of some of these EAGactive compounds, E. balteatus females were exposed to R-(+)-limonene (monoterpene), (Z)-3-hexenol (green leaf alcohol), and EβF (sesquiterpene, common aphid alarm pheromone). A single E. balteatus gravid female was exposed for 10 min to an aphid-free Vicia faba plant that was co-located with a semiochemical dispenser. Without additional semiochemical, hoverfly females were not attracted to this plant, and no oviposition was observed.The monoterpene R-(+)-limonene did not affect the females' foraging behavior, whereas (Z)-3-hexenol and EβF increased the time of flight and acceptance of the host plant. Moreover, these two chemicals induced oviposition on aphid-free plants, suggesting that selection of the oviposition site by predatory hoverflies relies on the perception of a volatile blend composed of prey pheromone and typical plant green leaf volatiles.

Fast gas chromatography characterisation of purified semiochemicals from essential oils of Matricaria chamomilla L. (Asteraceae) and Nepeta cataria L. (Lamiaceae)

“…Three isomers of nepetalactone were present in the essential oil of N. cataria, but could not be identified with absolute configuration certainty by GC-MS. The stereoisomery of (Z,E)-nepetalactone was confirmed by 1 H and 13 C NMR spectrometry (data not shown) and by comparison of the chemical 13 C displacements with those of the literature [26]. Ten minor compounds of the essential oil could not be identified with the spectral library and retention index.…”

“…Moreover, β-caryophyllene is a molecule of interest having biological activity against aphid reproduction [2] and was identified as the aggregation pheromone of the Asian lady beetle Harmonia axyridis [8]. One of the main interest of these compounds is that they could act as attractants and oviposition inductors of some aphid predators (Episyrphus balteatus De Geer (Diptera: Syrphidae)) and parasitoids (Aphidius ervi Haliday (Hymenoptera: Braconidae)) [9][10][11][12][13]. The essential oil of Matricaria chamomilla L. (Asteraceae), popularly known as German chamomile (other synonyms: Matricaria recutita L. and Chamomilla recutita L), was reported to contain a high proportion of E-β-farnesene.…”

Tuned protection of aphids by ants against a predatory hoverfly

“…Female hoverflies are known to choose oviposition sites according to available aphid resources. They adjust the number of eggs that are laid depending on the growth performance of their larvae on different aphid species or the size of aphid colonies (Scholz & Poehling, 2000;Almohamad et al, 2007Almohamad et al, , 2010Verheggen et al, 2008). The present results strongly suggest that the presence of aphid-tending ants should be another key criterion for the selection of oviposition sites so that female hoverflies could decrease the predatory pressure exerted by ants on the first instars of their offspring.…”

“…The present results strongly suggest that the presence of aphid-tending ants should be another key criterion for the selection of oviposition sites so that female hoverflies could decrease the predatory pressure exerted by ants on the first instars of their offspring. For instance, the search for oviposition sites by hoverfly females should be guided not only by plant-or aphid-derived semiochemicals (Budenberg & Powell, 1992;Verheggen et al, 2008) but also by ant-related volatile compounds. In the latter case, compounds such as footprints' cuticular hydrocarbons (Devigne & Detrain, 2002;Devigne et al, 2004;Lenoir et al, 2009) or trail pheromones laid by ants (Mailleux et al, 2005;Detrain & Deneubourg, 2009;Morgan, 2009) could be used as kairomones by syrphid females to avoid locations that are heavily patrolled by ants, just like they avoid laying eggs in the presence of other aphidiphages (Almohamad et al, 2010).…”

“…In this guild of aphidophagous insects, the hoverfly Episyrphus balteatus De Geer (Diptera: Syrphidae) is frequently encountered at aphid-infested sites in the temperate regions of the Northern Hemisphere (Schneider, 1969;Gilbert, 236 Claire Detrain, Melanie Fichaux andFrançois Verheggen 1986, 2005;Tenhumberg, 1995). Just like aphid-tending ants, hoverfly females use semiochemicals to locate aphid colonies and to oviposit eggs from which aphidophagous larvae hatch (Harmel et al, 2001;Almohamad et al, 2007;Verheggen et al, 2008;Leroy et al, 2014). Therefore, both actors are likely to encounter each other.…”