Egg surface structure of Ochlerotatus albifasciatus (Macquart, 1838) and Ochlerotatus scapularis (Rondani, 1848) (Diptera: Culicidae) by Scanning Electron Microscopy (SEM).

SANTOS-MALLET J.R.; GLEISER, R.M.; MULLER, G.A.; ALENCAR, J.; MARQUES, W.A.; SARMENTO J.S.; MARCONDES C.B.

Foz do Iguacu, Brasil

Congreso; XXI Congresso Brasileiro de Parasitologia. II Encontro de Parasitologia do Mercosul.; 2009

The description of mosquito eggs by SEM can be utilized for the identification of breeding places, being particularly important for medically-important species, like Ochlerotatus albifasciatus and O. scapularis. Eggs of O. albifasciatus and O. scapularis from females collected in Córdoba city and at Florianópolis (SC), Brazil were analyzed by SEM. They were fixed in 2.5% glutaraldehyde and post-fixed in 1% osmium tetroxide, both in 0.1M sodium cacodylate buffer at pH 7.2, dehydrated in ethanol and after the critical-point drying method they were mounted on gold-plated metal supports and observed under a Jeol 5310 SEM. The eggs O. albifasciatus were elliptical in outline, measuring approximately 615.7 ± 37.24 µm long and 180.7 ± 22.87 µm wide, with an egg index (l/w ratio) of 2.9 ? 3.7 µm. The chorionic coating in general presented cells shaped as racquets, consisting of a central small tubercle, surrounded by larger tubercles and followed by a row of smaller tubercles. The micropylar apparatus in the anterior region presented a collar with very evident molding with a thickness of around 10.7 µm. The margins of the micropyle disc were raised and measured around 21.1 µm in diameter. The micropyle orifice was very evident. O. scapularis eggs were laid singly and are black and elliptical in outline showing a length of approximately 620,4 (±16,74) µm and a width of 163,7(±16,90) µm at the midlle of the egg, with an egg index (l/w ratio) of 3,79 µm. The ventral surface of the chorionic coating presented cells with tubular aspect containing tubercles in row with a density of 5 to 9 per cell. Inside the chorionic cells the tubercles presented two different sizes, the largest measuring in the longitudinal diameter 7,23 ± 0,98 and the minors 4,15 ± 0,53 µm. In dorsal surface the reticulum the tubercles present in the central region tubercles with 8,45. ± 0,67 µm  and around them 3 to 5 minors tubercles measuring 2,57 ± 0,26 µm. The micropylar apparatus presented a collar with very evident molding with defined margins and a thickness of around 11.1µm. The micropyle disc presents raised margins and has 17.8 in diameter and the micropyle orifice around 1.41µm. With full knowledge of the morphology of the eggs it will be possible to develop keys for the identification of mosquito eggs collected during ovitrapping programs and thus reduce cost and time required for hatching and rearing immature stages to adults for identification.