In many insects, mate finding is mediated by volatile sex pheromones, but evidence in nabids is still fragmentary. The role of odour-mediated sexual attraction in two nabid species, Nabis pseudoferus and N. rugosus, was studied in a Y-tube olfactometer. Females of the two species were significantly attracted by odours of conspecifics males, and males of N. rugosus, but not of N. pseudoferus, were attracted by odours of conspecific females. Odours of conspecifics of the same gender were unattractive. These results suggest the existence of male pheromones in both species and a different female pheromone in N. rugosus.
The olfactory orientation of the aphidophagous ladybird Coccinella septempunctata L. was assessed in a Y-tube olfactometer and a choice arena. The response of the predator to 22 plants, aphid prey and conspecifics was tested. The ladybird was attracted to the odour of chopped Berberis vulgaris L. leaves, and of Tripleurospermum inodoratum (L.) Sch.-Bip. flowerheads, and males were attracted to females. Methanol extracts of B. vulgaris leaves were also attractive.
The foraging behaviour of beneficials such as aphidophagous predators depend largely on volatile compounds emitted by potential preys. Even if polyphagous predatory species are considered, all the potential preys are not systematically localised and accepted. In this work, chemical cues from different aphids and plants, each alone or in association, were studied to elucidate their role in prey location. Using a four-arm olfactometer, attraction of combinations of three aphid (Megoura viciae, Acyrthosiphon pisum and Aphis fabae) and one plant (Vicia faba) species for Episyrphus balteatus larvae was observed. Predatory hoverfly larvae were attracted by all tested stimuli in the presence of aphids, whatever the species. Whole or crushed aphids and also aphids on bean plant parts were attractive to syrphid larvae, but the host plant alone did not present any infochemical role for E. balteatus. Identification and quantification of the volatile releases from aphid and plant species, alone or in association, were performed using SPME and GC-MS methods. Aphid alarm pheromone, (E)-β-farnesene, was found in the volatile pattern of each aphid and was tested for its role as an effective kairomone for the hoverfly.
The tritrophic interactions between two different plant-host complexes, Avena sativa-Sitobion avenae, Triticum aestivum-S. avenae and the aphid parasitoid Aphidius rhopalosiphi were studied with respect to odour learning and recognition by the parasitoid. The orientation behaviour of females towards odours from either uninfested or aphid-infested oat or wheat plants was tested in a series of dual choice Y-tube olfactometer experiments. Female parasitoids had the opportunity to gain a single oviposition experience on either the oat-S. avenae or wheat-S. avenae complex before the experiment. In the first set of experiments, where A. rhopalosiphi was reared on the oat-S. avenae complex, eight odour-bait combinations were tested. The females did not discriminate between uninfested oat and wheat. After oat complex experience, females responded to odours from the oat complex, but not to odours from the wheat complex. Consequently, in a direct comparison the oat complex was preferred over the wheat complex. After wheat complex experience, the parasitoid's orientation responses gave a different picture. Both, the wheat complex and the oat complex, were then shown to be equally attractive. Hence, in direct comparison no preference was recorded between the oat and wheat complexes. In a second set of experiments, where A. rhopalosiphi was reared on the wheat- S. avenae complex, a possible influence of any pre-adult or emergence-related host plant experience could be excluded as the same results were obtained as before. At first glance the responses towards the different odour baits seem inconsistent. However, the results may be explained using a simple model with two key odour components.