Searching behaviour of the sevenspotted ladybird, Coccinella septempunctata– effects of plant-plant odour interaction

In the present study the main aim was to investigate the odour mechanisms affecting habitat preferences of Coccinella septempunctata (L.). In a field study, the frequency of adult C. septempunctata was higher in barley plots containing high densities of the common weeds Cirsium arvense (L.) Scop. and Elytrigia repens (L.) Nevski. than in control plots with only barley. In olfactometer experiments in the laboratory, adult C. septempunctata showed a significantly more positive response to mixed odours of barley and each of the two weeds than to barley alone. Ladybirds responded differently to barley plants that were previously exposed to volatiles from the two weeds. The E. repens -exposed barley plant lost its attractivity while the C. arvense -exposed barley plants maintained attractivity. As no aphids or pollen resources were present in the plots during the experiment, the results show that C. septempunctata responds to the botanical characteristics of the habitat even if no food resources are available. These results strongly suggest that olfactory cues and plant-plant communication from diversified plant stands can be important mechanisms in predator attraction to sites with a complex botanical diversity.