Halobates formidabilis ( Distant, 1910 )

Anderson, R. Charles, Adam, M. Shiham & Cheng, Lanna, 2023, Marine insects of the Maldives (Heteroptera: Gerridae, Hermatobatidae and Veliidae; Diptera: Chironomidae) with notes on taxonomy, Indo-Pacific distribution, and ecology, Raffles Bulletin of Zoology 71, pp. 478-490 : 480

Halobates formidabilis ( Distant, 1910)

Halobates formidabilis is the only coastal species of Halobates we found in the Maldives. It was first described from the Andaman Sea ( Distant, 1910) and also occurs along the coasts of India and Sri Lanka ( Andersen & Foster, 1992; Andersen & Cheng, 2004). It is one of the largest of coastal Halobates species known, measuring over 5 mm in body length. Both adults and nymphs show distinct colour patterns dorsally ( Figs. 3A , 4A, B ) and males are easily distinguished from other coastal Halobates species by their genitalia ( Fig. 4C, D ). The male is further characterised by a strongly modified front femur and a prominent spine on the inner margin of its front tibia ( Andersen & Cheng, 2004: fig. A45), which is presumably used for holding the female during mating, although little is known about the biology of this species. It was first reported from the Maldives by Phillips (1959) who collected it from Gan Island, Seenu (=Addu) Atoll, in February 1959, reporting it as Halobates sp. His samples were subsequently identified as Halobates formidabilis by Herring (1961: 241) and confirmed by Andersen & Foster (1992). This species can be easily distinguished from the two open-ocean species of Halobates found in the Maldives by its much larger size and completely pale venter ( Fig. 3B ). It does not appear to be especially common in Maldives (it was found in just 3 of our 55 samples) but is widely distributed. We collected it at the same location as Phillips (1959), i.e., in Seenu (=Addu) Atoll in the south of Maldives, and from two other locations in the middle and north of the archipelago ( Fig. 2A). It was only abundant in one sample, from a sheltered lagoon with mangroves, where it possibly breeds (sample 54, Maalhendhoo Island, Noonu Atoll, Table 1). All of our samples, and those of Phillips (1959), were from shallow lagoons or reef flats ( Table 2), as expected for this coastal species.

Figures

Fig. 3. Halobates formidabilis. 5th instar nymph, live individual, Dhidhdhoofinolhu Island, Alifu Dhaalu Atoll, 13 May 2006; not measured, approximate length 5 mm. A, dorsal view; B, ventral view, note uniform pale colouration.

Fig. 4. Halobates formidabilis. Specimens from Maalhendhoo Island, Noonu Atoll, 5 May 2013. Scale bars = 0.5 mm. A, 5th instar nymph, dorsal view, showing colour pattern (length = 4.2 mm); B, adult male, dorsal view (length = 5.6 mm); C, male genitalia, dorsal view (genital segment length = 2.0 mm); D, male genitalia, ventral view (genital length = 1.4 mm).