Saturday 6 July 2013

A new species of Diving Beetle from New Guinea.

Diving Beetles (Dytiscidae) are often largish predatory Beetles with an aquatic lifestyle. Both the adults and larvae are predatory, though they are otherwise quite different. The young are aggressive shrimplike animals that emerge from eggs laid on plant stems. When fully grown these pupate in mud (above the water table), emerging as oval, brownish Beetles, capable of both flying to disperse and diving to lay eggs and feed. Both adults and young deliver a powerful bite, and inject digestive enzymes into their prey, which can include other Insects, Crustaceans, Worms, Leeches, Mollusks, Tadpoles and small Fish. The Beetles then feed by sucking fluids out of their victims.

In a paper published in the journal ZooKeys on 28 May 2013, Helena Shaverdo of the Naturhistorisches Museum in Vienna and Lars Hendrich and Michael Balke of the Zoologische Staatssammlung München, describe a new species of Diving Beetle from the Indonesian province of West Papua.

The new species is placed in the genus Exocelina, and given the specific name baliem, after the site where it was found, a pond in the Baliem River Valley. Exocelina baliem is a medium sized (4.1-5.5 mm) reddish brown Diving Beetle. It is known from a single location, an ephemeral pond in a riverine relic forest in the Baliem River Valley, roughly 1 km from Wamena Airport, at an altitude of 1700 m.

Exocelina baliem, female. Shaverdo et al. (2013).

Shaverdo et al. observe that this is the first species of Exocelina known from ponds in New Guinea, with other members of the genus being found in directly stream related stagnant water, such as rockpools, stagnant backflows, marginal puddles and waterholes along stream banks, and at the immediate stream margin. It is difficult to assess if this is a genuine novelty, since the species was only observed at a single location, which may have been exceptional, and, similarly, occasional use of ponds by other species of Exocelina in New Guinea cannot confidently be ruled out.

Although the species has only just been described, the specimens from which it was described were collected in 1992. The pond in which it was found had disappeared by 1993, when only a single specimen could be found, on a tuft of reeds. The site was revisited in 2011, when it was found that the woodland had been cleared, and all ponds in the area were showing signs of eutrophication (excess nutrients, often leading to blooms of algae which block the light to other plants), presumably associated with agricultural runoff. Whether the Beetles survive elsewhere is uncertain.

The original pond where Exocelina baliem was discovered in 1992. Shaverdo et al. (2013).

Map of New Guinea showing the location where Exocelina baliem was discovered (red circle). Shaverdo et al. (2013).

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