Enithares Spinola, 1837

Nieser, Nico, 2004, Guide To Aquatic Heteroptera Of Singapore And Peninsular Malaysia Iii. Pleidae And Notonectidae, Raffles Bulletin of Zoology 52 (1), pp. 79-96 : 91-93

Enithares Spinola, 1837

Remarks. - The genus Enithares has been revised for Asian and Australian species by Lansbury (1968) who provides keys to males and females. Since then several other species have been described but these are nearly all restricted to Insular Asia (Liu & Zheng, 1991; Nieser & Chen, 1991, 1996; Nieser & Zettel, 1999; Zettel, 2003).

Four species are actually known from the Malay Peninsula. Most live in virtually stagnant bays of streams or ponds associated with streams. An exception is E. mandalayensis which can be found in ponds and marshes away from streams. In smaller pools there may be only one or two adult specimens. Like many Notonectinae they usually float against the underside of the surface film when resting or awaiting prey. Most species are easily disturbed and then hide under water. Most species have a dark coloured and a pale form.

Both males and females can be identified although males show more characteristics their identification is consequently more reliable. Males and females can be distinguished by differences in the caudal abdominal sternites but unfortunately the characteristic sternite VIII, which in the males is more elongate, is usually hidden inside the apex of abdomen. The easiest way to separate males and females is to lift the caudal sternites of the abdomen in fresh or relaxed specimens to reveal the male genital capsule ( Figs. 30 , 31 ) or the paired short and blunt ovipositors (first gonapophyses) which are strongly sclerotized and beset with stout spines ( Figs. 32 , 33). Dry specimens can be relaxed in the vapour of acetic acid, see introduction. Males of many species have modified tibiae and tarsi on fore- and or middlelegs ( Fig. 38 ). The shape of the metasternal xiphus is the most important non sexual character used for identification ( Figs. 34 , 35 ). Some males have various leg segments modified ( Figs. 8 , 37 , 38 ). The genital capsule or pygophore ( Fig. 31 ) also provides specific characteristics. In Enithares it is laterally cleft, the symmetrical parameres lie at the base of the cleft ( Fig. 31 ). Behind the cleft lies the posterior lobe, which is dorsally open and encloses the aedeagus. The basal plate ( Fig. 31 ) aids in specific identification in some species. In order to expose the aedeagus the capsule can be softened by soaking the capsule for a few hours in 10% potassium hydroxide (KOH) at room temperature, or boil for some minutes. Females do not show specialized external characters.

KEY TO ENITHARES SPECIES OF WEST MALAYSIA AND SINGAPORE

1. Males ...................................................................................... 2

– Females .................................................................................... 5

2. Mesotrochanter forming a distinct spur at inner ventral margin ( Fig. 8 ) ................................................................ E. malayensis

– Mesotrochanter rounded or bluntly angulate .......................... 3

3. Small species, length up to 7; outer claw of mid-tarsus conspicuously thickened and bent inwards ( Fig. 37 ) ....................................................................... E. mandalayensis

– Larger species length 8 or more ............................................ 4

4. Length 8.5-9.6, second segment of intermediate tarsus widened, about as wide as long ( Fig. 38 ) (in lateral view the first tarsal segment is largely to entirely hidden by the tibia so the actual second segment is apparently the first, see Fig. 7 ) ... E. ciliata

– Length 10.2-12, second segment of intermediate tarsus not widened, twice as wide as long ............................ E. metallica

5. Length 7.0-8.0; metaxiphus as fig 35mn ......... E. mandalayensis

– Length over 8.5 ...................................................................... 6

6. Length less than 10.0, metasternal xiphus with convex lateral margins or with small blunt subapical projections, apex blunt ( Figs. 35c, 35 ml) .................................................................... 7

– Length over 10.5, metasternal xiphus with concave lateral margins and a long acute apex ( Fig. 35 me) .... E. metallica

7. Metasternal xiphus with smoothly convex lateral margins ( Fig. 35 ml) ................................................................... E. malayensis

– Metasternal xiphus with small blunt subapical projections and blunt apex ( Fig. 35c ) .................................................. E. ciliata

Figures

Fig. 30. Apex of abdomen of male Enithares, ventral view, semidiagrammatic.

Fig. 31. Genital capsule of male Enithares metallica, lateral view. b = basal plate of aedeagus, p = paramere.

Fig. 32. Apex of abdomen of female Enithares, ventral view, semidiagrammatic.

Fig. 38. Enithares ciliata male, tarsus of middle leg.

Fig. 34. Enithares metasternum, semidiagrammatical ventral view, caudad upwards. c = hind coxa, p = coxal plate, t = hind trochanter, x = metasternal xiphus (dotted).

Fig. 35. Enithares species, metasternal xiphus. c = E. ciliata, mn = E. mandalayensis, ml = E. malayensis, me = E. metallica.

Fig. 8. Enithares malayensis middle femur and trochanter.s = spur at inner ventral margin of trochanter.

Fig. 37. Enithares mandalayensis male, tarsus of middle leg. Thickened and bent inner claw dotted.

Fig. 7. Middle leg of male Enithares ciliata. cl = tarsal claws; co = coxa; f = femur; p = anteapical pointed protuberance of femur; ta1, ta2, ta3 = first, second and third tarsal segment; ti = tibia; tr = trochanter.