Cornicle

Abstract: Analysis of single cornicle droplets from six species of aphid showed the presence of volatile components in addition to (E)-β-farnesene. Compounds identified included (Z,E)-α- and (E,E)-α-farnesene forMyzus persicae and α- and β-pinene forMegoura viciae. WithMegoura viciae, (−)-α-pinene was most important for alarm activity. The major component of the alarm pheromone ofPhorodon humuli was (E)-β-farnesene even though farnesenes are present in the summer hostHumulus lupulus.

Abstract: The aphids Aphis coreopidis (Thomas), Acyrthosiphon pisum (Harris), Acyrthosiphon soiani (Kaltenbach), and Myzus persicae (Sulzer) produce droplets at the tips of their cornicles when attacked by several species of insect predators. Alarm pheromones volatilizing from these cornicle droplets repel nearby aphids from their feeding sites. The release of cornicle droplets can also be elicited by various physical stimuli. Depending upon the type of stimulus and the aphid species involved, 50 to 90% of aphids produce droplets and 62 to 76% of droplets emit biologically active levels of pheromone. Aphids respond to the alarm pheromones at a distance of 1–3 cm from freshly secreted droplets and repellent activity is retained up to 60 minutes after secretion. Alarm pheromones are perceived by primary and secondary sensoria located on the aphids antennae.

Abstract: THE chemical structure of the repellent odour found in the cornicle secretion of the aphid M. persicae1 has been identified as trans-β-farnesene.

Abstract: The oviposition behaviour of the aphid parasitoid Aphidius ervi Haliday is influenced by both chemical and physical cues. Oviposition attack responses were elicited by paint pigments sealed into the tip of a glass capillary tube. Parasitoids reacted to yellow pigments with repeated oviposition attack responses, but they did not react to green pigments. The spectrum of reflected light from the yellow pigments was very similar to that from the `green' natural host Acyrthosiphon pisum (Harris), with a high proportion of the total radiation energy being emitted in the yellow-orange wavebands (580-660 nm). Pea aphid cornicle secretion also elicited oviposition attack responses, which were not exclusively induced by its pale yellow-green colour. In fact, the oviposition attack response to capillary tips coated with cornicle secretion remained evident under red light conditions, which, in contrast, nearly completely suppressed the response to yellow pigments. Chemical compounds from cornicle secretion do not appear to be involved in parasitoid orientation, even though they stimulate intense oviposition attack responses. Olfactometer experiments showed that the putative kairomone involved acts only at very short range or on contact. Host exuviae, which also elicited strong and persistent oviposition reactions from A. ervi females, appear to be a good alternative source of ovipositional kairomone(s). This work confirms the existence of an aphid cuticular kairomone.