ORDER ODONATA Greek origins of name: Odanata is derived from the Greek word “Odonto-“meaning tooth refers to the strong teeth found on the mandibles of most adults. Odonata or damselflies and dragonflies are well known, commonly seen insects with terrestrial adults and aquatic nymphs they are closely related to the Ephemeroptera (mayflies). Odonata is a very ancient order of insects and its fossils exist from more than 300 million years ago they are also relatively large insects even now, but in their past they were much larger. Fossils remains of the largest flying insects to have ever existed are Dragonflies, one species meganeura monyi had a wing span up to 75cm. Classification Taxonomy of order odonata includes two suborders such as zygoptera (damselflies) in which the front and hind wings are similar in shape. Anisoptera (dragonflies) the hind wings are broader near the base than the front wings. It follows the following taxonomic ranks, kingdom animalia, phylum arthropods, class insect, order odonata and two sub-orders (suborder anisopteradragonflies, suborder zygotera – damselflies). Distribution and diversity Dragonflies and damselflies are widely distributed and common components of most fresh water and riparian ecosystems across Australia. Just over 600 genera and about 6,500 species of odonata are recognized worldwide. In Australia they are relatively well known taxonomically. Around 320 described species in 110 genera, assigned to 30 families are recorded with estimates of only another 10 or 50 species as yet undescribed. Main characteristics of order odonata (dragonflies and damselflies) (i)

Two pairs of wings of similar size and have a dark mark, or pterostigma, near the tip of each.

(ii)

Long and slender abdomens

(iii)

Large heads

(iv)

Very large compound eyes

(v)

Small, hair – like antennae

Life cycle/development stages The odonata insects like damselflies and dragonflies are hemimetabolous means that they pass into life stages during their development. From eggs to nymphs and then to the adult or imago. The eggs are laid in batches (one at a time in quick succession), the eggs are laid in two general ways, some species females have their sharp ovipositor which can cut into plants and deposit eggs into there. Some species do not have their sharp ovipositor and simply drop their eggs into waters. Larvae or nymphs Larvae are aquatic normally in rivers, streams, ponds and lakes. For instance, zygopteran larvae swim by flexing their abdomen from side to side but anisopterans tend to walk. Zygopteran larvae like other aquatic insects breath through caudal gills (their tails), but anisopteran larvae breath through their anus which is an enlarged cavity with special internal folds to increase the surface area, water is pumped in and out of this muscularly to increase water flow across the respiratory membranes. Larvae are carnivorous detecting their prey by sight, in most cases and catching it by means of rapidly extensible grasping modification of the Labium. Adults or imagos In any given set of climatic conditions most species emerge at well synchronized times of year over a period of about a month. After emerging most dragon flies leave the vicinity of the water and go through a period of maturation, this generally lasts about one month during which time the gonads finish developing and the body color brightens. But others in tropical regions maturation may take only five days.

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Feeding Dragonflies and damselflies are both as immature and adult. The adults are quick agile fliers that are generally considered beneficial because they fed on large numbers of small flying insects like gnats and mosquito legs are used either as a basket for catching prey or as grapples for dinging to emergent vegetation. Adults are aerial predators that hunt aided by their extremely acute eyesight. They catch flying insects with their legs, or glean sedentary insects. And use their mandibles to break apart their prey. The aquatic nymph are also predaceous and are generally ambush predators that remain concealed in silt or under rocks and plants waiting for slow moving prey. The larvae have a unique, hinged prehensile lower mouthpart (labium) that they shoot forward to capture their prey and bring it to the mandibles. Odonate nymphs are relatively indiscriminate predators and will eat anything up to and as large as themselves including other odonate nymph and small vertebrates such as tadpoles and fish fry. Mating and reproduction in odonata Their reproduction and associated behavior is unique among the animal world. In dragonflies and damselflies the territory will usually be a good egg-laying site. In most dragonflies and some damselflies females only visit their breeding site to mate and lay eggs. Courtship and recognition includes the male showing its ovipositing site to the female. The female may reject the mating if it thinks the ovipositing site is not good enough. The dragonflies and damselflies males have their secondary genitalia on the second segment of the abdomen. And the first genitialia are found on the last abdominal segment. The male bend its abdomen forward to touch the secondary genitialia to move sperms for primary genitalia into the secondary genitalia before copulation. The female responds with bending up its abdomen to the genitalia of the male and form the wheel position. The female then curls its abdomen forward to contact with the secondary genitalia in order to receive sperm. Most dragonflies start copulation in flight some may continue in flight and some may settle. Settle copulation usually last longer, from minutes to hours. Air copulation may last only a few seconds. Before transferring its sperm the male will remove the existing sperm from earlier mate, and then replace it with its own. After 2

the copulation the couple may separate or remain in tanden. The couple maybe at rest or in flight and there is no genital contact. The reason could be the male waiting for the female for the readiness of oviposition. By holding the female it can make sure it does not mate with other male before laying eggs. Oviposition takes place usually immediately after copulation. The male often accompanies the female when she oviposits. Eggs are laid in two general ways some species females, they have their sharp ovipositor which can cut into plants and deposit egg into their, some species do not have their sharp ovipositor and simply drop their eggs into water. A female may lay several batches of eggs, each batch it may lay a few hundreds to a few thousands eggs, depends on species. Those eggs may hatch after 5 – 40 days depend on species, temperature and other conditions. There are about 10 –19 instars stages may take one to ten years living in waters then they emergence and become adults. Economic importance of order odonata Dragonflies and damselflies play key roles in both terrestrial and aquatic habitats. (i)

They are predators; as both nymphs and adults, feed on a variety of prey including nuisance species such as mosquitoes and biting flies. Nymphs can be top predators on fishless wetlands and helps to structure the wetland community.

(ii)

Dragonfly and damselfly nymphs in turn are an essential food resource for fish and amphibians and adults are eaten by upland predators such as birds, bats, lizards and spiders.

(iii)

Dragonflies can also be used to help diminish diseases spread by mosquitoes, horseflies and deerflies, by releasing dragonflies in areas where infestations of these insects exist. These insects spread such diseases as malaria, yellow fever, dog heartworms, anthrax and tularemia. However, dragonflies are voracious and indiscriminate eaters so they might eat other species that are beneficial.

(iv)

Researchers also look to dragonflies as ecological indicators. The presence of dragonflies indicates fresh water. One of the most useful dragonfly facts is that they reside low in the food chain, so scientific study of their numbers and their health can 3

reveal changes in water ecosystems more quickly than studying other animals or plants. Some national parks are beginning to use this species to survey and document the health of the parks water ecosystems. (v)

They also provide charming visual appeal for ponds, streams and other fresh water bodies, due to the fact that these insects come in many brilliant colors that are copper, emerald, amethyst, sapphire and others.

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REFERENCES Grimaldi, D. & Michael, E. (2005). Evolution of Insects. Cambridge University Press. Hammond, P. (1992). Species Inventory. In Groombridge Brain (ed). Global Biodiversity. Springer: Netherlands. Kukalova’ – Peck, J. (1991). The Insects of Australia. Carton: Melbourne University Press. Labandeira, C. & Phillips, T. L. (1996). ‘A Carboniferous Insect Gall: Insight into Early Ecologic History of the Holometabola’. Proceeding of the National Academy of Science.