Searching behaviour and mate recognition by males of the two-spot ladybird beetle, Adalia bipunctata

1. Adult males of the two-spot ladybird beetle, Adalia bipunctata, did not show a functional response to increase in aphid abundance and consumed markedly fewer aphids than do the females. 2. At high densities of prey, females spent more time in area-restricted search than when prey was scarce. Males were always less active than females and they did not respond to an increase in prey abundance by a change in searching behaviour. 3. After a brief encounter with a female, a male showed area-restricted searching behaviour. This behaviour occurred in response to encountering a female's elytra and in particular to a chloroform-soluble component (sex pheromone) present on or in the elytra. 4. Males needed to encounter a female in order to respond to her presence, which indicated the pheromone is a contact pheromone. 5. The searching behaviour of males appeared to be mainly directed towards locating females; that of females towards locating aphids. This difference between the sexes should be taken into account when quantifying the predatory response of ladybirds to aphid abundance in the field.