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 Major Groups | Insecta (insects) | Hemiptera (bugs)
 

Hemiptera (bugs)

Major Group: Insecta
Order: Hemiptera

Aquatic Hemiptera belong to the suborder Heteroptera (true bugs). They can be further divided into 3 groups based on the niche they favour and the adaptations they exhibit. Gerromorpha are semi-aquatic bugs that live on the water’s surface and have modified legs and claws that do not break the surface tension enabling them to tread, skate or stride atop the water. Nepomorpha are true aquatic bugs that live beneath the water’s surface and exhibit a range of breathing and swimming strategies. 3 families from Dipsocoromorpha and Leptopodomorpha are shore dwellers that can cope with periods of flooding. They have been included in this guide because they are often found in aquatic samples. Bugs generally form a small part of fish diet although some species will defend themselves by secreting a noxious substance from scent glands. In turn hemipterans can significantly influence populations of other aquatic insects and even small fish by predation.

Descriptive Features:

  • head shape variable, points forward with rostrum clearly visible
  • eyes prominent, globular
  • antennae are short or long, 3 or 4-segmented, inserted in front of eyes
  • mouthparts adapted for piercing and sucking
  • rostrum long and slender or short and stout, typicaly composed of a 4-segmented labium which is indented medially to form a groove enclosing the pairs of mandibular and maxillary stylets
  • pronotum is a broad plate with posterolateral margin expanded into large pronotal lobe that covers the mesonotum
  • 3 pairs of segmented legs, variously modified
  • macropterous (winged) and apterous (wingless) adult forms
  • wings folded flat on body, forewings may be hemelytra (hard anteriorly, membranous posteriorly) or coriaceous (leather-like), hindwings membranous
  • abdomen 10-segmented, in females 8–10 form genitalia, in males 9-10 form genitalia
  • only 6 visible abdominal sterna, sternum 1 fused with metasternum
  • Total length: 1.0 mm -11 cm
  • Nymphs: similar to adults but smaller, paler, soft bodied, tarsal segmentation absent or indistinct, wings absent
  • Taxonomic Checklist:

    Families

    Aphelocheiridae
    Belostomatidae
    Corixidae
    Dipsocoridae
    Gelastocoridae
    Gerridae
    Hebridae
    Hydrometridae
    Leptopodidae
    Mesoveliidae
    Micronectidae
    Naucoridae
    Nepidae

    Notonectidae
    Ochteridae
    Pleidae
    Saldidae
    Veliidae
     

      

    Distribution: Australia wide

    Sensitivity Rating: SIGNAL grade 2

    Functional Feeding Group: predators, scavengers, macrophyte piercers

    Ecology: Instream habitat: Aquatic bugs occur in a wide variety of lentic waters, from temporary pools to lakes, and lotic waters, from small streams to rivers. The greatest species richness is found in small to medium sized waterbodies of slow flow that are rich in submerged and emergent macrophytes.
    Feeding ecology: Hemipteran nymphs and adults are generally predators or scavengers feeding on live or dead zooplankton, other aquatic insects, terrestrial insects that “fall in” and some larger hemipterans will feed on small fish. Bugs harpoon the prey with the rostrum and the maxillary stylets deliver paralysing saliva that also predigests the tissue of the prey animal. The predigested tissue is sucked up one of the canals formed by the maxillary stylets, hence the term “piercing and sucking mouthparts”. Semi-aquatic bugs are typically opportunistic, with soft bodied arthropods being preferred. They either sit and wait, or troll the surface, detecting vibrations from other animals on the surface film. Fully aquatic bugs sense underwater vibrations to catch prey and will either ambush prey animals from amongst the submerged vegetation or swim about actively searching for prey. Only Corixidae species have been reported to feed on plants and algae but they will also feed on living or dead microscopic invertebrates and have been observed catching mosquito larvae, when available. Corixid bugs forage on the substratum in the ooze and detritus using modified fore tarsi to scoop bits past their rostrum, reflecting its shorter stouter shape. Plant particles are ingested through the stylet and then ground with predigestive saliva inside the head capsule.
    Habit: Hemipterans exhibit a range of adaptations for life in the water. The abdomens of aquatic bugs are covered with a fine layer of microtrichia (non-wettable hairs and setae), forming the hydrofuge. Legs of surface dwelling bugs are also covered with hydrofuge, giving them a characteristic dull, velvety appearance and enabling them to sit on the water without breaking the surface tension. They must regularly groom the hydrofuge, with specialised structures on the tibiae, to keep the microtrichia layers arranged so as to maintain its hydrophobic nature. Semi-aquatic bugs breathe through spiracles located on the thorax and abdomen with no specialised strategy for underwater breathing. Fully aquatic hemipterans exhibit three main underwater breathing strategies; 1) an air bubble is taken from the surface and trapped beneath the elytra within the hydrofuge, these bugs can stay submerged for hours even days before they return to the surface to take another bubble; 2) a respiratory siphon or a pair of air straps at the abdominal tip is held above the bug to the water’s surface like a “snorkel”, these bugs appear to hang from the surface usually clinging to a submerged object; 3) a plastron is a layer of air that forms around the bug within the hydrofuge and is replenished by diffusion from the surrounding water, allowing these bugs to stay under water for long periods but eventually the air disperses and must be replenished. Aphelocheiridae: Aphelocheirus australis is an exception, having a hydrofuge that consists of numerous very small close set microtrichia with the tips bent over at right angles such that the plastron does not diffuse enabling this species to stay submerged indefinitely. There are four main types of leg modifications that reflect bug habits; 1) cursorial for running where the femora and tibiae are elongate and slender; 2) raptorial for grasping where the fore femora are greatly enlarged; 3) natatorial for swimming where the mid and hind femora and tibiae are flattened and fringed with hairs; 4) for rowing where the midlegs are longer than hindlegs.
    Life history: Knowledge of reproductive biology in Australian bugs is not well known and tends to be assumed from northern hemisphere taxa until specific differences are recorded in Australian taxa. Male hemipterans in Australia have been observed to produce sound. Males of some Notonectidae species have well developed stridulatory combs which when moved rapidly over the rostral prong produces a sound audible to humans, described as “a distant grind stone”. Some Corixidae males produce species specific sounds by rubbing palar pegs on the forelegs against a sharp edge of the head. Male sounds are used for defence and courtship, often in conjunction with surface vibrations. Hemipteran males may mate and leave, or mate and stay to guard the female from being mated by other males, or in the case of Belostomatidae: Diplonychus the female lays eggs on the back of a male and he cares for them until hatching. Bug egg sizes and shapes are as diverse as the many egg laying strategies. Typically the size of an egg increases at about half rate of size of female’s abdomen. Therefore, females of larger bug species tend to mature more eggs at one time because the eggs are relatively smaller to her body size, whereas smaller species will only mature two or three eggs at one time. Eggs are laid in a range of places; under water glued to any substrata, attached to the underside of leaves, standing upright on stalks on substratum, embedded in plant stems or leaves by drilling a hole with a serrated ovipositor, or above the water’s surface in small holes of moist sand or mud, glued onto floating objects in regular rows. Generally there are five nymphal instars from egg to adult, the nymphal stage closely resemble the adults in structure and feeding with the newly emerged adults being very pale and soft. It can take several days to achieve full adult colour and a hard exoskeleton.
    Nepidae 

    breathing through a siphon

    Notonectidae 

    replenishing the plastron

    Ochteridae 

    cursorial legs

    Nepidae 

    raptorial legs

    Naucoridae 

    natatorial legs

    Gerridae 

    rowing legs

     
    Information Sources: Tinerella 2013, Andersen & Weir 2004, Lansbury & Lake 2002, Ingram et al 1997, Zborowski & Storey 1995, Davis & Christidis 1997
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