HOST LOCATION BY A PARASITOID USING LEAFMINER VIBRATIONS - CHARACTERIZING THE VIBRATIONAL SIGNALS PRODUCED BY THE LEAFMINING HOST

The aim of this study was to characterize the vibrations produced by t he apple tentiform leafminer Phyllonorycter malella (Ger.) (Lepidopter a, Gracillariidae). Host location using vibrations by one of its paras itoids Sympiesis sericeicornis Nees (Hymenoptera, Eulophidae) was post ulated by Casas (1989) on the basis of detailed quantitative behaviour al observations and has also been suggested by other authors on simila r systems. Both host and parasitoid send and may receive vibratory sig nals; consequently we first attempted to characterize and classify the signals, one of the first steps required in the design of an adequate vibrational biotest. In this respect, our approach differs fundamenta lly from the familiar setting of host location via semiochemicals and is best framed within the context of vibratory communication. Vibratio nal signals produced by a moving larva and pupa were measured on sever al spots on the leaf using a laser vibrometer. The emitted signals wer e characterized by their temporal patterns of change in amplitude and frequency spectra. The vibrational patterns released by a moving larva were different from those released by a wriggling larva and a wriggli ng pupa in the time as well as in the frequency domains. Wriggling lar vae and wriggling pupae triggered vibrations that were similar in freq uency, but differed in their temporal pattern. Frequencies up to 15 kH z could be identified. The amplitudes and frequencies df the signals b oth decreased significantly from the tip to the base of the leaf. A wr iggling pupa and a wriggling larva produced stronger signals than a fo raging larva. All calculated parameters (displacement, velocity, accel eration, and duration of the signal components) of the vibrational sig nals were found to be in a range comparable with others used for well- known arthropod communication systems. The vibrations produced by the host displayed distinct characteristics: they could usually be disting uished easily from background noise; could be perceived anywhere on th e leaf; and were specific for a certain host stage and activity. Our f indings support the hypothesis that vibration signals represent a reli able source of information to foraging parasitoids and, therefore, exp lain certain behavioural patterns observed in a population of S. seric eicornis females foraging in the field.