Gyretes minax Ochs, 1967

Colpani, Daniara, Benetti, César João, Hamada, Neusa, Andrade-Souza, Vanderly & Michat, Mariano C., 2018, Gyretes Brullé (Coleoptera: Gyrinidae) from Brazil: Morphology of eggs and early instars, Zootaxa 4526 (3), pp. 331-346: 335

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Gyretes minax Ochs, 1967


Gyretes minax Ochs, 1967 

(Figs. 6–9)

Description. Eggs. Cylindrical, length 1.16–1.18 mm, width 0.29–0.31 mm (n = 10); dark brown (just before eclosion) (Fig. 6). The chorion is sculptured, except for the ventral surface, which is smooth and flat. The chorion consists of reticulation with variable shape (triangular, rounded, cylindrical, rectangular); the edges of these cells are smooth, without layers (Figs. 6–9). The micropylar projection is inserted into the anterior pole, is stem shaped and has a round apex (Figs. 7, 9).

Comparative notes. Generally, Gyrinidae  eggs have the chorion very strongly sculptured, usually ribbed or sculptured in honeycomb format ( Hinton 1981).

The general structure of the eggs of both species of Gyretes  agrees with previous descriptions for the family ( Baker & Wai 1987; Komatsu & Kobayashi 2012; Saxod 1964) such as length, width, shape, color, presence of sculpture on the chorion, longitudinal splitting-slit and micropylar projection. Newly laid eggs are white, long ellipsoid, and loosely fixed to the substrate by a mucous-like substance.

The eggs of the two species analyzed have morphological differences. Although both species have a sculptured chorion, it is of different shapes. In G. nubilus  the reticulation of the chorion is rounded or quadrangular with uneven edges along its height and, in some of them, the lower portion of the edge covers part of the cell bottom, whereas in G. minax  the reticulation is more variable and its edges are smooth, without layers. Both species also differ in the apex of the micropyle, which is pointed in G. nubilus  and rounded in G. minax  .

There are only three descriptions of whirligig beetle eggs in the literature based on scanning and transmission electron microscopy: Gyrinus substriatus Stephens, 1829  ( Saxod 1964), Dineutus mellyi Régimbart, 1883  ( Komatsu & Kobayashi 2012) and Dineutus hornii Roberts, 1895  ( Baker & Wai 1987). Comparing the morphology of the eggs of Gyretes  and those of other genera, several differences are found. For example, Dineutus  eggs are much larger, reaching 1.5–2.0 mm; also, chorionic sculpture is well differentiated in D. hornii  and D. mellyi  , formed by conical projections that can be either little or well developed, differing from Gyretes  and Gyrinus  , in which the sculpture of the chorion forms cells that are similar to a honeycomb ( Hinton 1981). The sculpture of the chorion of G. substriatus  differs from those of G. minax  and G. nubilus  in having hexagonal-shaped cells (Sadox 1964). Other features, such as the presence of a micropylar region in the anterior pole and presence of a longitudinal fissure, are common to all gyrinid genera. As noted in the literature, gyrinid eggs do not have aeropyle. According to Hinton (1981), these openings are commonly found in eggs of aquatic insects and are probably related to respiration, facilitating the exchange of gases between the egg and the external environment.