Aleeta - Description

Description

Measuring 9–10 cm (4 in) in length, with forewings between 3 and 5.1 cm (1.4–2 in) long, the adult floury baker is brown with a white dusted appearance. The white downy filaments cover much of the body, legs, and some wing veins, but this silver body fur is easily rubbed off, and so is often substantially diminished in older adults and museum specimens. Individuals have a variety of body markings, but all have a pale midline on their pronotum. Their legs are brown, sometimes yellowish, but with no distinct markings. Their eyes are dark brown, and the opercula are yellowish and extend laterally well beyond the body. The female is slightly larger than the male, She has generally similar colourings, slightly paler in some areas. Her ninth abdominal segment is long and dark reddish-brown, sometimes partly tending toward black. Her ovipositor is long, with a downward tilt, and the ovipositor sheath is black or dark reddish-brown. The size of individuals varies markedly by region, depending strongly on the local rainfall. Areas with an average annual rainfall of over 1000 mm (40 in) – mostly coastal – have much larger individuals, with average forewing lengths about 1 cm (0.4 in) longer than those in low-rainfall areas.

The wings are transparent, with black or sometimes brown veins, and a brown-black patch at the base of apical cells 2 and 3, these patches are sometimes fused into a continuous zigzag infuscation (dark brown to black discoloration). The basal cell is often opaque and amber-coloured. As on many insects, the wing membranes are coated on both sides by a periodic array of cuticular nanostructures, about 200 nm in height, separated by about 180 nm. These are thought to aid in anti-reflective camouflage, anti-wetting, and self-cleaning.

Heard at any time of day, the male floury baker's call is an unusual hissing-type sound, starting as a series of one second sibilant bursts about a second apart repeated more rapidly until they become a constant hiss, a tune which has been described as "rp, rp, rp, rp, rrrrrp". The sound is produced when single muscular contractions click the tymbal inward, buckling 7–9 of the tymbal ribs, each producing a sound pulse. This occurs alternately on the two tymbals, and is rapidly repeated (in groups of four except during the distress call when they are ungrouped and at a lower frequency), giving a pulse repetition frequency of around 1050 per second, with a relatively broad sound frequency range of 7.5–10.5 kHz, with a dominant frequency of 9.5–9.6 kHz. The abdominal air sacs act as a resonant chamber to amplify the sound, and are rapidly extended or raised to modulate the volume of the call during the introduction to the free song. Male cicadas use these calls to attract females, but when clustered together can attain sufficient volume to repel birds. The floury baker is one of Australia's loudest cicadas, and has been rhetorically termed "the best musician of them all".

A. curvicosta is distinguished from a similar undescribed species A. sp. nr curvicosta (the little floury baker) by the structure of the male genitalia, and an audibly distinct call. The morphological distinction between Aleeta and Tryella is based on two factors: A. curvicosta has a larger forewing size – rarely less than 3.2 cm (1.3 in) and usually over 4 cm (1.6 in), whereas Tryella is never above 3.2 cm (1.3 in); the uncal lobes of Aleeta's very distinctive male genitalia are downturned at their distal ends, whereas Tryella's are upturned. These two genera are easily distinguished from all other Australian cicadas because they lack tymbal covers and because the costal margin of their forewings gets larger toward the point where the wing is attached to the body, in these genera it is clearly wider than the costal vein.