Family BELOSTOMATIDAE

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Family BELOSTOMATIDAE

Compiler and date details

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

Introduction

The nepomorphan family Belostomatidae comprises nine genera and 160 species (Menke 1979, Slater 1982, Štys & Jansson 1988, Polhemus, J.T. pers. comm., Henry 2009). The family is found in all major zoogeographic regions and is most diverse in the tropics. These insects are colloquially referred to as giant waterbugs, tadpole killers, electric light bugs and toe biters. Cantonese and Laotian people are known to eat Lethocerus indicus (Lepeletier & Serville) after boiling them in salted water (Miller 1956; Gope & Prasad 1983).

Belostomatids are generally very large, ranging in length from 25 to 110 mm. They are mostly elliptical, in shape and moderately dorso-ventrally flattened. The head has a triangular anteoculus, lacks ocelli, and has large eyes. The antennae are usually 4-segmented and housed in grooves below the eyes; AII and AIII have various lateral projections, which are diagnostic at the subfamilial level. The pronotum is divided into two lobes. The hemelytral membrane has reticulate veins. The Horvathiniinae and Lethocerinae have metathoracic scent glands, which are absent in the Belostomatinae. Belostomatid larvae lack dorsal abdominal glands (Staddon 1971; Aldrich 1988). The metepimeron extends posteriorly over the first two or three abdominal sterna and is fringed with long hairs. The forelegs are raptorial, strongly incrassate, with the femora often grooved to accept the tibiae. The foretarsi are either 2 or 3-segmented. The middle and hind legs are modified for swimming, being flattened and fringed with hairs. In the male, the phallus is articulated with the genital capsule and the aedeagus is divided into a phallosoma and endosoma. The eighth abdominal segment has two long, flattened, retractile respiratory straps, each with a basal spiracle (Lauck & Menke 1961; Menke 1979; Slater 1982; Aldrich 1988).

Belostomatids are voracious predators and have a varied diet that includes other insects, snails, tadpoles, small frogs and fish. Species of Lethocerus Mayr can be important pests in fish hatcheries (Wilson 1958). Species of the African genus Limnogeton Mayr are obligate feeders on freshwater snails (Voelker 1968). Belostomatids are known to inject their prey with toxins causing prey paralysis and tissue necrosis. The salivary secretions are known to contain proteases and amylases (Rees & Offord 1969). There are also incidental records of belostomatid "bites" on humans, producing painful and local reactions (Menke 1979).

The genus Lethocerus is known mostly from lentic waters, usually the deep waters of lakes, and rarely from streams and rivers. The genus Diplonychus Laporte is known throughout the Old World tropics and can be very common in quiet bodies of water. Some members of the Western Hemisphere genus Belostoma Latreille are known from the vegetated banks of streams.

Females of the Belostomatinae lay their eggs on the dorsum of males. The eggs are glued to the male who cares for them until they emerge. The eggs are intermittently wetted, exposed to air, and stroked, which maintains gaseous exchange and enhances egg survival (Smith 1976; Menke 1979). The Lethocerinae usually lay their eggs on exposed vegetation. The oviposition behaviour of the Horvathiniinae remains unknown. The respiratory behaviour of belostomatids is similar to that of Nepidae. The straplike abdominal siphons are used to trap air which travels along marginal hairs and is stored in the sub-hemelytral airstore (Parsons 1972). Life history studies of North American belostomatids have been reviewed by Menke (1979). McKeown (1942) has provided anecdotal information on some Australian species.

The Belostomatidae are divided into three subfamilies: Belostomatinae, Horvathiniinae and Lethocorinae (Lauck & Menke 1961; Štys & Jansson 1988). The Belostomatinae are cosmopolitan and comprise six genera: Abedus Stål, Belostoma Latreille, Diplonychus Laporte, Hydrocyrius Spinola, Limnogeton and Weberiella De Carlo. The Horvathiniinae are monogeneric (Horvathinia Montandon, Neotropical Region, nine species). The Lethocerinae are also monogeneric, contain numerous gigantic species, and are most diverse in the tropical Americas (Lauck & Menke 1961). Perez Goodwyn (2006) revised the subfamily Lethocerinae, recognising three genera within it: BenacusStål, KirkaldyiaMontandon, and Lethocerus Mayr. He also provided a key for all species of the subfamily in the same paper.

Larsén (1938) indicated that Belostomatidae and Nepidae are sister groups based on similarities of the genitalia, caudal respiratory appendages and abdominal musculature. This is supported by characters of the head (Spooner 1938), the spermatheca (Pendergrast 1958) and the antennae (Lauck & Menke 1961). China (1955) suggested that the belostomatids arose from an ancestor that had siphon respiration and metathoracic scent glands.

Significant regional taxonomic works include Poisson's (1949) review of the Afrotropical species and De Carlo's (1964) and Froeschner's (1981) treatments of the South American fauna. Polhemus et al. (1988) catalogued the Nearctic fauna andEstevez et al. (2011) revised the New World genus Weberella. Menke (1960) reviewed the Eastern Hemisphere species of Lethocerus, provided a key and checklist, described a new Australian species, L. distinctifemur, and clarified that L. insulanus (Montandon) had been misidentified in Australia as L. indicus.

The Australian fauna includes four species: Diplonychus eques (Dufour), D. plana (Sulzer), and the two Lethocerus species. Polhemus (1994) clarified the identity of D. plana, which was known previously as D. rusticum in the Eastern Hemisphere. He concluded that Nepa rustica Fabricius, 1775 and Nepa rustica Fabricius, 1781 are separate species. Polhemus (pers. comm.) believes that D. plana does not occur in Australia. It is retained in the Catalogue, however, pending a taxonomic revision of the group. Andersen & Weir (2004b) provided a key for the Australian fauna of belostomatides.