SUBSTRATE VIBRATIONS ELICIT DEFENSIVE BEHAVIOR IN LEAFMINER PUPAE

Late instar larvae and pupae of the spotted tentiform leafminer Phyllo norycter malella (Ger.) (Lepidoptera: Gracillariidae) react with defen sive behaviour when attacked by one of their parasitoids, the eulophid wasp Sympiesis sericeicornis Nees (Hymenoptera: Eulophidae). Vibratio ns produced during the insertion of the ovipositor into the mine are k nown to be important cues by which larvae detect the presence of their enemies, The aim of this study was to investigate which frequency com ponents elicit defensive reactions in leafminer pupae using synthetic vibrations, Sine vibrations and bandlimited noise stimuli were offered to both free pupae and pupae concealed in their leafmines. Using lase r vibrometry we measured the vibrations experienced by pupae inside th eir mines and assessed the influence of the mine, Pupae were shown to react to substrate vibrations, and do so over a broad range of frequen cies, Behavioural reactions to noise stimuli were stronger than to pur e sine stimuli, Mine tissue attenuated vibration amplitudes of the inp ut signal from 5.1 to 22.6 dB, However, as response thresholds of conc ealed pupae were only twice as high as thresholds of free pupae (which is adequate to 3 dB) pupae inside their mine were more sensitive than expected, This discrepancy is discussed both in terms of the conditio ns of pupae and in terms of mine structure, The results indicate that broadbandedness of vibrations produced by hunting parasitoids during o vipositor insertion into the mine may be a major criterion used by lea fminers to perceive parasitoid presence and to escape ovipositor sting s. (C) 1997 Elsevier Science Ltd. All rights reserved.