Anatomic and acoustic sexual dimorphism in the sound emission system of Phoenicoprocta capistrata (Lepidoptera: Arctiidae).

Both sexes of Phoenicoprocta capistrata have functional tymbals. The scanning electron microscopy revealed differences in the morphology of these organs in males and females. Male tymbals have a well-developed striated band, constituted by 21 +/- 2 regularly arranged striae whereas female tymbals lack a striated band. This type of sexual dimorphism is rare in Arctiidae. The recording of the sound produced by moths held by the wings revealed that while males produced trains of pulses organized in modulation cycles, females produced clicks at low repetition rate following very irregular patterns. Statistically, there are differences between sexes in terms of the duration of pulses, which were 355 +/- 24 micros in the case of males and 289 +/- 29 micros for females. The spectral characteristics of the pulses also show sexual dimorphism. Male pulses are more tuned (Q(10) = 5.2 +/- 0.5) than female pulses (Q (10) = 2.7 +/- 0.5) and have a higher best frequency (42 +/- 1 kHz vs. 29 +/- 2 kHz). To our knowledge, this is the first report on an arctiid moth showing sexual dimorphism in tymbal's anatomy that leads to a best frequency dimorphism. Males produce sound at mating attempts. The sounds recorded during mating are modulation cycles with the same spectral characteristics as those recorded when males are held by the wings. The morphological and acoustic features of female tymbals could indicate a process of degeneration and adaptation to conditions under which the emission of complex patterns is not necessary.

Otoacoustic emissions from insect ears having just one auditory neuron.

Sensitive hearing organs often employ nonlinear mechanical sound processing which produces distortion-product otoacoustic emissions. Such emissions are also recorded from insect tympanal organs. Here we report high frequency distortion-product emissions, evoked by stimulus frequencies up to 95 kHz, from the tympanal organ of a notodontid moth, Ptilodon cucullina, which contains only a single auditory receptor neuron. The 2f1-f2 distortion-product emission reaches sound levels above 40 dB SPL. Most emission growth functions show a prominent notch of 20 dB depth (n = 20 trials), accompanied by an average phase shift of 119 degrees , at stimulus levels between 60 and 70 dB SPL, which separates a low- and a high-level component. The emissions are vulnerable to topical application of ethyl ether which shifts growth functions by about 20 dB towards higher stimulus levels. For the mammalian cochlea, Lukashkin and colleagues have proposed that distinct level-dependent components of nonlinear amplification do not necessarily require interaction of several cellular sources but could be due to a single nonlinear source. In notodontids, such a physiologically vulnerable source could be the single receptor cell. Potential contributions from accessory cells to the nonlinear properties of the scolopidial hearing organ are still unclear.

Threshold minima and maxima in the behavioral audiograms of the bats Artibeus jamaicensis and Eptesicus fuscus are not produced by cochlear mechanics.

Behavioral audiograms of Artibeus jamaicensis and Eptesicus fuscus are characterized by two threshold minima separated by a threshold maximum at 40 kHz, for A. jamaicensis, and 45 kHz, for E. fuscus [Koay, G., Heffner, H.E., Heffner R.S., 1997. Audiogram of the big brown bat (Eptesicus fuscus). Hear. Res. 105, 202-210; Heffner, R.S., Koay, G., Heffner H.E., 2003. Hearing in American leaf-nosed bats. III: Artibeus jamaicensis. Hear. Res. 184, 113-122.]. To investigate whether these characteristics are due to cochlear properties, we recorded distortion product otoacoustic emissions (DPOAEs) and calculated DPOAE threshold curves. We found that in both species cochlear sensitivity, assessed by DPOAE recordings, does not show local threshold maxima. The DPOAE threshold curve calculated for A. jamaicensis reveals a broadly tuned minimum for frequencies between 20 and 50 kHz and the threshold curve of E. fuscus shows a broad sensitive area for frequencies between 15 and 60 kHz. In none of the two species any pronounced threshold irregularities were found. The characteristic pattern of a threshold maximum followed by a minimum observed in behavioral studies seems to be shaped by transfer characteristics of the outer ear and/or neuronal processing in the ascending auditory pathway rather than by cochlear mechanics.

L1,L2 maps of distortion-product otoacoustic emissions from a moth ear with only two auditory receptor neurons.

The tympanal organ of the moth Empyreuma affinis emits physiologically vulnerable distortion-product otoacoustic emissions. To assess the nature of underlying mechanical nonlinearities, we measured L1,L2 maps by varying both stimulus levels. Two types of maps were found: (1) Maps containing dominant islands centered at the L1=L2 diagonal as it is typical for saturating nonlinearities that can be described by Boltzmann functions. In contrast to maps published for mammals and frogs, the shape of such islands includes sharp ridges at L1 or L2 levels close to 70 dB sound pressure level. This could be produced by a strongly asymmetric operating point of the respective transfer functions, consistent with the fact that the auditory sensory cells are not hair cells but primary mechanoreceptors with a single cilium. The saturating map components could be selectively reduced by acoustic suppression. (2) Maps where separated islands were less conspicuous but in which the dominant feature consisted of contour lines which were orthogonal to the L1=2L2 diagonal and could be generated by an expansive nonlinearity. Maps showing strong islands were found for f2 frequencies between 26.7 and 45 kHz, maps without strong islands for f2 between 42 and 57.5 kHz. This suggests a frequency-dependent change regarding the involved mechanical nonlinearities.

Repelentes electrónicos contra mosquitos: propaganda y realidad

Se presenta una revisión bibliográfica acerca del uso de dispositivos electroacústicos con supuesta acción repelente sobre las hembras de diferentes especies de mosquitos hematófagos. Se dan 15 referencias directas y 2 indirectas, en todas se concluye que estos dispositivos no protegen a quienes los portan de las picadas de los mosquitos. Se dan los nombres de 9 de los dispositivos probados, así como de 16 de las principales especies de mosquitos presentes en las pruebas de campo. Estas pruebas de campo se han realizado en condiciones ecológicas muy diferentes, que van desde alaska hasta el África Ecuatorial. También se menciona el efecto potencialmente dañino al hombre de los dispositivos que emiten frecuencias a alta intensidad.

A bibliographic review about the use of electroacustic devices with a supposed repellent action on the females of different species of hematophagous mosquitoes is presented. 15 direct references and 2 indirect ones are given, in which it is concluded that these devices do not protect those who have them from the stings of mosquitoes. The names of 9 of the tested devices as well as of 16 of the main species of mosquitoes present in the field tests are mentioned. These tests have been carried out in very different ecological conditions from Alaska to Equatorial Africa. It is also stressed that the high intensity ultrasonic frequencies emitted by these devices produces a potentially harmful effect on man.