Odonatological Abstracts

(16851) FRANK, J.H. & E.D. McCOY, 1995. Precinctive insect species in Florida. Fla Ent. 78(1): 21-35. — (First Author: Ent. & Nematol. Dept, Univ. Florida, Gainesville, FL 32611, USA). The Florida (USA) insect spp. are classified into 6 categories, for which the following terminology is used; (1) Indigenous (native): (a) precinctive (native and restricted to the area specified), (b) indigenous but not precinctive (native to the area specified and elsewhere); (2) Adventive (non-indigenous, arrived from elsewhere): (c) immigrant (not native to the area specified, and arrived there by means other than purposeful introduction), and (d) introduced (not native to the area specified and arrived there by purposeful introduction. – An estimated 144odon, spp. were indigenous to Florida at the time of the European discovery (40 Zygopt., 104 Anisopt.). Of these, 1 Zygopt. and 4 Anisopt. spp. are precinctive. There are now 12 established spp. of immigrant Odon.: 1 from Asia, 3 from N America, and 8 from neotropics. No odon. sp. has been (deliberately) introduced to Florida. Additionally, 7 spp. have been found as vagrants, without breeding populations. (16852) LABHARXT.&D.-E. NILSSON, 1995. The dorsal eye of the dragonfly Sympetrum: specializations for prey against the blue sky. J. comp. Physiol. (A) 176:437-453. — (First Authr: Zool. Inst, Univ. Zurich, Winterthurerstr. 190, CH-8057 Zurich). Dragonflies of the genus Sympetrum have compound eyes conspicuously divided into dorsal and ventral regions. Using anatomical, optical, electro-physiological, in-vivo photochemical and microspectrophotometrical methods, the design and physiology of the dorsal part which is characterized by a pale yellow-orange screening pigment and extremely large facets were investigated in S. vulgatum. The upper part of the yellow dorsal region is a pronounced fovea with interommatidial angles approaching 0.3°, contrasting to the much larger values of l.5°-2° in the rest of the eye. The dorsal eye part is exclusively sensitive to short wavelengths (below 520 nm). It contains predominantly blue-receptors with a sensitivity maximum at 420 nm, and a smaller amount of UV-receptors. The metarhodopsin of the blue-receptors absorbs maximally at 535 nm. The yellow screening pigment transmits longwavelength light (cut-on 580 nm), which increases the conversion rate from metarhodopsin to rhodopsin. It is demonstrated that because of the yellow pigment screen nearly all of the photopigment is in the rhodopsin state under natural conditions, thus maximizing sensitivity. Theoretical considerations show that the extremely long rhabdoms (I. I mm) in the dorsal fovea are motivated for absorption reasons alone. A surprising consequence of the long rhabdoms is that the sensitivity gain, caused by pumping photopigment into the rhodopsin state, is small. To explain this puzzling fact, arguments are presented for a mechanism producing a gradient of rhodopsin concentration along the rhabdom, which would minimize saturation of transduction units, and hence improve the signal-tonoise ratio at high intensities. The latter is of special importance for the short integration time and high contrast sensitivity these animals need for spotting small prey at long distances.