Abner B. Lall

Spectral correspondence between visual spectral sensitivity and bioluminescence emission spectra in the click beetle Pyrophorus punctatissimus (Coleoptera: Elateridae)

The presence of two spectral mechanisms, near-ultraviolet and green (lambda(max)=545nm), is strongly suggested by electroretinographic visual spectral sensitivity curves obtained under dark and red chromatic adaptation conditions in the compound eyes of the click beetle Pyrophorus punctatissimus. The bioluminescence emission of the dorsal prothoracic lanterns is deep green (lambda(max)=543nm) and that of the ventral abdominal lantern is lime green (lambda(max)=556nm) in colour in P. punctatissimus. A broad green visual receptor would detect both deep green and lime green bioluminescent optical signals.

Vision in click beetles (Coleoptera: Elateridae): pigments and spectral correspondence between visual sensitivity and species bioluminescence emission

Among lampyrids, intraspecific sexual communication is facilitated by spectral correspondence between visual sensitivity and bioluminescence emission from the single lantern in the tail. Could a similar strategy be utilized by the elaterids (click beetles), which have one ventral abdominal and two dorsal prothoracic lanterns? Spectral sensitivity [S(λ)] and bioluminescence were investigated in four Brazilian click beetle species Fulgeochlizus bruchii, Pyrearinus termitilluminans, Pyrophorus punctatissimus and P. divergens, representing three genera. In addition, in situ microspectrophotometric absorption spectra were obtained for visual and screening pigments in P. punctatissimus and P. divergens species. In all species, the electroretinographic S(λ) functions showed broad peaks in the green with a shoulder in the near-ultraviolet, suggesting the presence of short- and long-wavelength receptors in the compound eyes. The long-wavelength receptor in Pyrophorus species is mediated by a P540 rhodopsin in conjunction with a species-specific screening pigment. A correspondence was found between green to yellow bioluminescence emissions and its broad S(λ) maximum in each of the four species. It is hypothesized that in elaterids, bioluminescence of the abdominal lantern is an optical signal for intraspecifc sexual communication, while the signals from the prothoracic lanterns serve to warn predators and may also provide illumination in flight.

Blue through UV polarization sensitivities in insects

A Signal-to-Noise optimization model has now been extended to explain the range of species-specific polarization sensitivities of insects. The different polarization sensitivities are shown to represent optimizations for the detection of plane polarized (Rayleigh-scattered) skylight over a range of atmospheric polarization conditions. Rhodopsin absorption spectra with peaks in the Blue (λmax≈450 nm) maximize detection efficiencies under conditions of high polarization. Rhodopsin absorption spectra peaking in the UV (λmax≈350 nm) maximize Signal-to-Noise Ratios for the detection of polarized skylight at the other extreme of low polarization.

Action spectra for the initiation of bioluminescent flashing activity in males of twilight-active firefly Photinus scintillans (Coleoptera: Lampyridae)

Abstract The action spectra [S(λ)-functions] for the initiation of bioluminescent flashing were determined in males of twilight-active firefly Photinus scintillans, using horizontal and vertical beams of spectral lights to simulate closed and open space in nature, respectively. The peak of the S(λ)-function in the horizontal beams was in the long (yellow, Fig. 3) and that for the vertical in the short (near-u.v. and blue, Fig. 5) wavelength region. It is concluded that both short and long wavelength visual receptors mediate the initiation of flashing behavior in males of those fireflies which restrict their flashing to twilight-hours. Furthermore under dim illumination conditions as in a closed space, the long wavelength receptor dominate the behavioral response, while in an open space with bright illumination conditions, the short wavelength receptors dominate.

The spectral sensitivity of the ocellar system in the cricket Gryllus firmus (Orthoptera: Gryllidae)

In the field cricket Gryllus firmus, the electroretinographic visual spectral sensitivity functions [S(λ)] of the median and lateral ocelli show the presence of a single receptor system sensitive to the green region with a maximum at 520 nm. The S(λ) functions match the nomogram for a P520 visual pigment. The waveforms of the electroretinogram elicited by light stimuli across the spectrum are similar. The slopes of the Vlog I curves are also similar at different stimulus wavelengths across the spectrum. The ocelli are capable of responding over 3–5 log units of change in the stimulus intensity.

Spectral cues for the regulation of bioluminescent flashing activity in the males of twilight-active firefly Photinus scintillans (Coleoptera: Lampyridae) in nature

Abstract Males of the twilight-active firefly Photinus scintillans initiate bioluminescent flashing when a threshold intensity of ambient light is reached, irrespective of the type of habitat and the spectral cues available. Under dense shrubbery (closed space) the flashing period on average is about one-and-half times or more longer than in the meadows (open space). Long wavelength spectral cues dominate in closed space while both short and long wavelength cues are present in open space. Twilight-active fireflies use long wavelength spectral cues alone or short and long wavelength spectral cues together for the regulation of flashing in nature.