Laboratory studies of plant searching behaviour by Coccinella septempunctata L. larvae

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Abstract
Movements of individual fourth instar Coccinella septempunctata L. larvae on pot-grown broad bean plants in England were recorded continually to assess plant recognition and the effects of prey capture. Prey capture was also studied in a 25X25 cm artificial arena. Approximately 80% of the total distance moved by larvae on plants was along leaf edges and mid-veins. Typical search speeds were 0−38−0−51 cm s−1. An average of only 3−2% of larval search time on plants was spent on leaf laminae on which movement was considerably slower, about 0−15 cm s−1. Discovery of Acyrthosiphon pisum (Harris) nymphs on plants induced intensive re-searching of the general area of discovery for periods of up to 12 min whereas in the arena the intensive search following prey capture lasted only up to 72 s and was much more localised. Examination of larval search times on plants revealed that 64% and 36% of maximum search times were recorded for the first and for the second or third searches, respectively, in a sequence of searches of the same plant. Only after prey capture was a fourth or subsequent search the longest. Plants previously searched unsuccessfully were recognised by detection of a chemical marker, specific for each individual, secreted via the anal disc during searching. Since C. septempunctata larvae are unable to detect aphids by sight or smell, recognition of areas previously searched unsuccessfully minimises wasteful energy expenditure.