Social feeding in ladybird beetles: adaptive significance and mechanism

Young larvae of Adalia bipunctata search an area more intensively when expo sed to the odour from other larvae feeding on aphids than when exposed only to the odour of aphids. In an olfactometer young larvae were significantly attracted either to the odour of crushed aphids or larvae feeding on aphid s, but not to that of aphids, larvae, larvae plus aphids or larvae feeding on an artificial diet. That is, the change in searching behaviour appears i n response to a volatile released by aphids when attacked. The odour releas ed by crushed aphids is made up entirely of aphid alarm pheromone, beta -fa rnesene. It is likely that the adaptive significance of this response is th at it increases the ability of larvae to locate larvae that have already ca ught prey. By sharing the aphid kill of another larva it is likely that a f irst instar ladybird larva greatly increases its probability of surviving t o the next instar. It is suggested that this social feeding is facilitated by egg clustering, which also may additionally account for why aphidophagou s ladybirds lay their eggs in clusters.