Monday, January 12, 2009

Egg laying in fast flowing water.
Dragonflies and damselflies collectively called odonates, are one of the most common insects flying over forest, fields, meadows, ponds and rivers. About 6,000 species are distributed all over the world. India is highly diverse with more than 500 known species. The life history of odonates is closely linked with water bodies. They use a wide range of flowing and stagnant water bodies. Even though most species of odonates are highly specific to a habitat, some have adapted to urban areas and make use of man-made water bodies.
Dragonflies lay their eggs in one of two ways. Either they lay them directly in water or they insert them into the stems or leaves of plants that grow in or near water. The method of laying eggs directly in water is called exophytic deposition while the method of laying eggs on plants is called endophytic deposition.
Females of the darner family species have serrated ovipositors that they use to cut small holes in plant tissues where they then insert their eggs. This method of egg laying is useful because it allows the dragonfly to carefully chose the appropriate location for its eggs and once they are lodged into the vegetation there is very little chance of them getting moved to an unfavorable location. Dragonflies that deposit their eggs freely in water do not have the specialized ovipositor that darners have. Generally they simply dip the tip of their abdomen into water, while still in flight, and release their eggs. These eggs then sink to the bottom of the lake, stream, pond or puddle they were dropped in and then continue to develop. Some species lay their eggs in a gelatinous mass that sticks to rocks or vegetation, while others have long filamentous strands attached to their eggs that are used to wrap around aquatic plants and anchor the eggs. Since this type of egg laying is much less precise than the other method, these species must lay a much larger number of eggs to ensure that at least some of their offspring survive to maturity. Generally dragonfly eggs hatch about 4 weeks after they have been laid. This damselfly was egg laying in the fast flowing current of river. Her male mate was observing her and ensured that she deposited all the eggs in the water and their life cycle will continue.
Yuwaraj Gurjar.

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