Hind femora influence directionality of the locust ear
Whereas usually sensory effects on behaviour were investigated, here the reverse, the influence of hind leg position on the acoustic input to the locust ear has been measured with a probe microphone. The large hind femur has considerable mobility in all 3 planes of rotation; it covers the ear as it is lifted (Fig. 1) and closes or opens it when straddled or tilted. In the lower frequency range of locust hearing no effects are found (Fig. 8; 7 kHz). In the high frequency range (20 kHz) femora cause sound pressure changes of a magnitude equal to the known body-induced directionality effects: With increasing straddling (σ) and lifting (λ), amplifying effects are found which develop nearly parallel for ipsi- and contralateral sound direction (Fig. 5). Opposing effects are found for caudal and frontal sound direction. The more the femora are straddled and lifted the stronger caudal sound is amplified (up to + 6 dB) and frontal sound attenuated (up to −6 dB; Fig. 5); this shifts the directionality characteristic of the ear towards the caudal hemisphere (Fig. 6).
Since the two frequency ranges are both stimulated by species-specific sound spectra, since they are both independently represented by different receptors and since they are influenced in different ways by the femora, the animal could perform the ipsi-/contralateral decision with the help of low frequencies while the frontal/caudal decision could be performed simultaneously with the additional use of high frequencies — thereby solving the old front/back ambiguity of directional hearing in the azimuth plane. In the range of leg postures observed in walking or climbing animals (Fig. 3), ear directionality is nearly unchanged (Fig. 4).
KeywordsAzimuth Sound Pressure High Frequency Range Hind Femur Sound Spectrum
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- Adam L-J (1969) Neurophysiologie des Hörens und Bioakustik einer Feldheuschrecke (Locusta migratoria). Z Vergl Physiol 63:227–289Google Scholar
- Adam L-J (1977) Preferential directions of nervous ‘intensity filters’; auditory neurons in the brain ofLocusta migratoria (Acrididae). Zool Jb Physiol 81:250–272Google Scholar
- Busnel MC, Degrois M, Busnel RG (1953) Variations des stridulations deLocusta migratoria, mâle, selon la patte utilisée par l'insecte. Physiol Comp Oecol 3:18–24Google Scholar
- Busnel RG, Chavasse P (1950) Recherches sur les émissions sonores et ultra-sonores d'Orthoptères nuisibles à l'agriculture: Étude des fréquences. Nuovo Cimento 7 (Suppl) Ser 9:1–17Google Scholar
- Dahmen H-J (1980) A simple apparatus to investigate the orientation of walking insects. Experientia 36:685–686Google Scholar
- Haskell PT (1957) The influence of flight noise on behaviour in the desert locustSchistocerca gregaria (Forsk.). J Insect Physiol 1:52–75Google Scholar
- Kalmring K (1975) The afferent auditory pathway in the ventral cord ofLocusta migratoria (Acrididae). II. Responses of the auditory ventral cord neurons to natural sounds. J Comp Physiol 104:143–159Google Scholar
- Michelsen A (1971a) The physiology of the locust ear. I. Frequency sensitivity of single cells in the isolated ear. Z Vergl Physiol 71:49–62Google Scholar
- Michelsen A (1971b) The physiology of the locust ear. III. Acoustical properties of the intact ear. Z Vergl Physiol 71:102–128Google Scholar
- Miller LA (1977) Directional hearing in the locustSchistocerca Gregaria Forskål (Acrididae, Orthoptera). J Comp Physiol 119:85–98Google Scholar
- Payne RS, Roeder KD, Wallman J (1966) Directional sensitivity of the ears of noctuid moths. J Exp Biol 44:17–31Google Scholar
- Römer H (1976) Die Informationsverarbeitung tympanaler Rezeptorelemente vonLocusta migratoria (Acrididae, Orthoptera). J Comp Physiol 109:101–122Google Scholar