The olfactory responses of coccinellids to aphids on plants

Our understanding of the foraging behaviour of predaceous coccinellids is limited, despite the importance of this information to the use of coccinellids in the biological control of insect pests (Obrycki & King, 1988). Laboratory studies have revealed that coccinellids use multiple cues, especially olfaction and vision, to locate prey (e.g. Hattingh & Samways, 1995; Hamilton et al., 1999; Harmon et al., 1998; Obata, 1997) and that their responsiveness to prey is influenced by intrinsic factors, especially relating to hunger, age and sex (e.g., Sengonca & Liu, 1994; Sengonca et al., 1995), and extrinsic factors, including prey species, temperature and light intensity (e.g., Ferran & Dixon, 1993; Kalushkov, 1999). Feeding experience can also affect the searching activity and prey preference of coccinellids. For example, Harmonia axyridislarvae changed from ‘extensive’ to ‘intensive’ search mode only when the larvae encountered familiar prey (Ettifouri & Ferran, 1993) or their odour tracks (Ferran et al., 1997); andAdalia decempunctata l rvae that encountered the toxic aphidHyalopterus pruni(including penetration of the aphid cuticle) subsequently rejected this aphid (Dixon, 1958). In the field, coccinellid-prey interactions generally occur on plants. Coccinellids forage on many different plant species and their foraging success is influenced by the architecture and surface features of the plant (e.g., Carter et al., 1984; Clark & Messina, 1998; Eigenbrode et al., 1996). Little consideration, however, has been given to the effect of the plant and feeding experience on the olfactory responses of foraging coccinellids. To address this last issue, we investigated the olfactory responsiveness of the aphidophagous coccinellidAdalia bipunctataL. to the prey/plant complex and how this may be affected by experience.Aphis fabaeScop. was used as the prey item. AlthoughA. fabaehas been reported as a food of relatively low suitability forA. bipunctatain the laboratory (Blackman, 1967; Kalushkov, 1999), wild populations of this coccinellid forage extensively on A. fabaecolonies on various plant species in the field (Banks, 1955; unpub. obs. of authors).