Family GERRIDAE

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Family GERRIDAE

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October 2010 - Dr G. Cassis, University of New South Wales, Sydney, NSW

Introduction

The Gerridae, or water striders, are a cosmopolitan family of gerromorphan semiaquatic bugs. The family presently comprises 67 genera and 751 species (Andersen 1982; Zoological Record 1980–1994; Henry 2009; Polhemus, J.T. pers. comm.).

Gerrids are elongate to ovoid and covered with several types of water-proof hairs, giving a velvety appearance (Andersen 1977). Species vary in length from 2 to 16 mm. The body is usually black or brown, occasionally with pale markings, and the venter is often silvery. The head is short and conical. The eyes are large and globular and ocelli are absent. The antennae and labium are 4-segmented. The pronotum is prominent, either covering the mesonotum or sometimes fused with it. The forewings lack a clavus or differentiated membrane. Wing polymorphism is common, with apterous, brachypterous and macropterous conditions known. The metathoracic scent glands are of the omphalium type, with a single sternal opening, two lateral glands and a median reservoir. The larvae lack dorsal abdominal glands. The legs are long and slender, with the hind femora extending beyond the abdomen, and are adapted for locomotion on water. The midlegs are primarily concerned with propulsion. The tarsi are 2-segmented and the claws of the forelegs are often inserted preapically (Slater 1982).

Gerrids inhabit the surface of lentic and lotic waters, including temporary pools, ponds, lakes, small streams and rivers. Halobatinae species are found in coastal waters or the open sea. Rhagadotarsus anomalus Polhemus & Karunarate is found in lakes, temporary waters or in quiet portions of flowing waters. Rheumatometra philarete Kirkaldy is found in large aggregations in the quiet parts of streams. Aquarius Schellenberg species occur in flowing waters and species of Limnogonus Stål occur in still waters.

Gerrids are obligate predators, feeding on organisms on or below the water surface. Prey items are held by the forelegs and pierced by the labium. Most gerrids lay their eggs below the water surface, mostly on vegetation. Halobatinae species lay their eggs on floating material and have been observed ovipositing on a living sea bird (Herring 1961). Andersen & Foster (1992) observed Halobates micans Eschscholtz eggs on a cuttlefish shell. Rhagadotarsinae lay their eggs in plant tissue. Cheng (1985) reviewed the biology of Halobates and Cheng & Schmitt (1982) described the biology of Halobates Eschscholtz species known from the Great Barrier Reef. The gerrid life cycle typically has five larval stages. Multivoltine species are known, particularly in tropical climates, where generations are continuous. In temperate regions, univoltine and bivoltine species are known and the adults are usually the hibernating stage. North American Gerris Fabricius species are known to overwinter under dead leaves, in holes, in stream banks and other sheltered places near water (Polhemus & Chapman 1979). Wing polymorphism has been examined in relation to habitat stability, photoperiod and temperature. Vepsäläinen (1971, 1973) reported aptery in European species found in stable habitats. Wing polymorphism has also been observed in different generations of the same species (Callahan 1974).

Hungerford & Matsuda (1960) gave an overview of the higher classification of the Gerridae, with keys to the suprageneric and generic groups. Matsuda (1960) provided a detailed description of gerrid morphology and divided the family into five subfamilies. Andersen (1975) revised the higher classification, raising three Gerrinae tribes to subfamily status. Calabrese (1980) provided a cladistic analysis of the gerrid genera of the world and discussed the biogeography of the group. Andersen (1982) reviewed the Gerridae, covering morphology, classification, phylogeny, ecology and biogeography. He claimed that gerrids are a monophyletic group on the basis of the frontal embryonic egg burster, absence of ocelli, prolonged mesothorax and two tarsal segments. He also analysed the gerrid subfamilies, refuting some of the sister-group relationships of Matsuda (1960) and Calabrese (1980). Andersen's classification recognises the following subfamilies: Rhagadotarsinae, Trepobatinae, Charmatometrinae, Cylindrostethinae, Eotrechinae, Gerrinae, Halobatinae and Ptilomerinae. Among the recent taxonomic works Polhemus & Polhemus (1993, 1994, 1995 1996) revised the subfamily Trepobatnae from Papua New Guinea with the review of worldwide fauna. Chen and Zettel (1998) revised the Oriental genus Ventidulus Distant. Polhemus (2001) and Polhemus & Polhemus (2001) revised species of the genus Ptilomera Amyot & Serville from Indochina and Papua New Guinea. Moralis-Costano & Molano-Rendon (2009) revised neotropical species of Tachygerrini. Andersen & Weir (2004) discussed the position if the family Gerridae among the other groups of Gerromorpha and incuded them to the identificational key of water bugs of Australia (Andersen & Weir 2004b).

The Gerridae are represented in Australia by four subfamilies, 11 genera and 37 species. The Gerrinae in Australia are represented by four genera and 14 species. Andersen (1990) reviewed the mostly Holarctic genus Aquarius, with two species known from Australia, A. fabricii Andersen from the Kimberley region and A. antigone (Kirkaldy), which is widely distributed in eastern Australia. Andersen (1975) revised the genus Limnogonus, recognising four Australian species, three of which are also known from the Oriental Region and/or Melanesia. The other Australian gerrines belong to Tenagogerris Hungerford & Matsuda and Limometra Mayr; Hungerford & Matsuda (1958) and Andersen (1964) revised the latter genus (as a subgenus of Tenagogonus Stål). Herring (1961) described all species, and provided a detailed discussion of their distribution and phylogeny. Malipatil (1988) reviewed the Australian species of Halobates, recognising 13 species in two ecological groups—coastal and open ocean. Polhemus & Polhemus (1991) reviewed some of the Australian Halobates and synonymised two Halobates species described by Malipatil. Andersen (1991) reviewed the genital morphology and phylogeny of Halobates, recognising a number of monophyletic species groups. He questioned the validity of the subgeneric classification, particularly the validity of Hilliella China, which is retained in the Catalogue. Andersen & Foster (1992) revised the Indian Ocean species of Halobates and Asclepios Distant. Andersen & Weir (1994a) described a freshwater halobatine Austrobates rivularis, from Cape York Peninsula, and provided a cladistic analysis of halobatine genera. Andersen & Weir (1994b) revised the Australian Halobates species, describing a new species from the Northern Territory, H. (Hilliella) lannae, redescribing all endemic species, and giving a phylogenetic analysis.

Polhemus & Polhemus (1991) reviewed some Trepobatinae, recording Stenobates Esaki from Australia, and describing two new species of the genus from northern Queensland and the Northern Territory; S. carpentaria is now assigned to Rhinometra Kirkaldy. Polhemus & Polhemus (1993, 1994) reviewed the world Trepobatinae fauna and described three species of Calyptobates Polhemus & Polhemus from northern Australia. The only other trepobatine known from Australia, Rheumatometra philarete, is found in eastern Australia. The Rhagadotarsinae is represented by one species, Rhagadotarsus anomalus, which is known from tropical Queensland and the Oriental Region.