Family GELASTOCORIDAE

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Family GELASTOCORIDAE

Compiler and date details

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

Introduction

The Gelastocoridae, or toad bugs, are a family of Nepomorpha found in all major zoogeographic regions, except the Palaearctic. The majority of species occur in the Neotropical Region, Australia and Melanesia. The world fauna presently comprises three genera and 111 species (Menke 1979; Zoological Record 1979–1994; Henry 2009; Polhemus, J.T. pers. comm.).

Toad bugs are medium sized (6–10 mm in length) and are characterised by an ovoid body with a dull, roughened surface, often with a warty appearance. The eyes are large, protruding and reniform, and ocelli are usually present. The head is subtriangular and somewhat depressed. The antennae are 4-segmented, short, and not visible from above. The labium is 4-segmented, short, and does not extend beyond the forecoxae. The pronotum is large, transverse and wider than the head. The scutellum is triangular and large. The metathoracic scent glands are well developed in the Gelastocorinae, and absent in the Nerthrinae. The larvae lack dorsal abdominal gland openings. The forewings are mostly divided into clavus, corium and membrane. Menke (1979) reported wing polymorphism as common, with flight rare, particularly in Nerthra Say species. In some species the hemelytra are fused along the midline (Todd 1960). Parsons (1960) records a reduction in hind wings and wing musculature in Gelastocoris Kirkaldy. The mid and hind legs are slenderand the forefemora are incrassate. The foretarsi are diagnostic at the subfamily level, the Gelastocorinae having a fully articulated, 1-segmented tarsus, with the foretarsus and tibiae fused and a single claw on the pretarsus. The pretarsi of the forelegs are asymmetrical, with the inner claw reduced. The hind tarsus is 3-segmented. The abdominal sternites are asymmetrical, particularly in the males. The male genitalia are asymmetrical with the left paramere reduced or absent. Females lack a laciniate ovipositor (Parsons 1959, 1960; Slater 1982).

Gelastocoris species are found on the muddy banks of streams, ponds, lakes, swamps and roadside ditches. Hungerford (1922) gave an account of the biology of the North American species, Gelastocoris oculatus (Fabricius). Nerthra species are found in a wide variety of habitats, including semiaquatic habitats, but are sometimes found far from water. Todd (1955) reported Nerthra species from leaf litter, under debris, in soil, and sometimes in decomposing plant material, or cow dung. He reported the Neotropical species, Nerthra nepaeformis (Fabricius), from banana plantations. Burrowing has been given as a common behaviour of toad bugs, in both wet and dry conditions (Bennett & Cook 1981). Both larvae and adults of the widespread species Nerthra macrothorax (Montrouzier) are found in and under decaying vegetation of Pandanus Parkinson and Erythrina indica Lam. (Todd 1960). The habitats of other Australian species are poorly known. Carver et al. (1991) report that most Australian species are found near water; a few species are collected away from water, particularly in rainforest habitats, and N. plauta Todd is found in association with spinifex. Toad bugs are considered to be opportunistic predators and scavengers (Bennett & Cook 1981). Hungerford (1922) recorded them feeding on a variety of arthropods including leafhoppers, various flies and a locust species.

Todd (1955) discussed the phylogeny of the gelastocorids and suggested a relationship with the Naucoridae. He proposed that toad bugs represent an intermediate taxon between terrestrial and truly aquatic bugs. Popov (1971) and Rieger (1976) provided phylogenetic schemes for the Nepomorpha and indicated a sister-group relationship between the Ochteridae and Gelastocoridae. Rieger (1976) indicated that the Ochteroidea are a plesiomorphic group in the Nepomorpha, with the Nepoidea being the only group which is more basal.

Štys & Jansson's (1988) classification of the Gelastocoridae recognised two subfamilies (Gelastocorinae and Nerthrinae), and three genera (Gelastocoris, Montandonius Melin and Nerthra). Todd (1955) revised the Gelastocoridae of the world, and described and keyed all the taxa, including many new species. Todd (1959) revised the Gelastocoridae of Melanesia, and recognised 23 Melanesian Nerthra species in two major species groups. Todd (1961) provided a checklist of the Gelastocoridae.

The Australian toad bug fauna comprises 25 Nerthra species. Todd (1960) revised the Australian fauna and recognised four species groups. Cassis & Silveira (2001, 2002, 2003) described four new species of Nerthra and redescribed species from the N. alaticollis (Stål), N. elongata (Montandon) groups and the enigmatic species N. tuberculata (Montandon). Many species are widely distributed in eastern Australian, a few species are endemic to south-western Western Australia, and one species is endemic to Tasmania. The elongata and alaticollis species groups are endemic to Australia. The laticollis species group also occurs in Melanesia and the rugosa-group is also found in the Oriental and Afrotropical regions, and in the Western Hemisphere. Only one species, N. macrothorax, is also found outside Australia. Andersen & Weir (2004b) provided a key for the Australian gelastocorids.