Tuesday, September 11, 2012

Making more music-makers

A Davis's tree cricket, Oecanthus exclamationis, in between fiddles. This little fellow is a contributor to the great musical backdrop of late summer and fall, courtesy of the Orthopteran symphony. Most tree crickets produce long droning trills, and as there are generally many of them in close proximity, tree crickets are major contributors to the sounds of the night.

The males are singing to attract mates, just as songbirds do. Tree crickets and other Orthopterans have their "ears" or hearing organs located just below the "knee" on the foreleg. This odd placement allows the ears to be about as far apart as possible, and that allows the animal to more accurately triangulate on sounds. And in the case of females, to better locate singing studs such as the guy above.

Ah! His melodious charms have worked! He's successfully wooed a mate, and she has joined him on the leaf. That's the female on top, which may seem to be an odd position. They are engaged in courtship feeding, a bizarre quirk of tree cricket reproduction. The male has an organ called a melanotal gland on his back, just behind the wings. This structure produces a tasty nutrient-rich substance that lures the female into an optimal position, and she is feeding from the melanotal gland in this photo. Once she's settled in, he'll curve his abdomen upwards to contact her genitalia and transform his spermatophores to her. Sometime after she's been successfully fertilized, she'll use her ovipositor to puncture bark on twigs and inject her eggs. Come the following spring, the eggs will hatch and a new crop of tree crickets will begin life.

While on a nocturnal field trip a week or so ago, Cheryl Harner spotted this scene and alerted the rest of us. It's a pair of short-winged meadow katydids, Conocephalus brevipennis, caught in the act of mating. The female is on the right, kindly holding her swordlike ovipositor aloft so as to not impale her mate. The male has managed to contort himself into a rather spectacular position; he must have studied the insect Kama Sutra.

The white globule is the spermatophore - we've caught him just as he was transferring his reproductive material to his mate. At the tip of his abdomen, just to the right of the spermatophore, we can see the specialized claspers that he uses to grasp and hold the female. These are called cerci, and each species of meadow katydid has uniquely shaped cerci.

The scenes in these photos are the fruition of the male's songs - successful courtship with a female, and perpetuation of the species. These Orthopteran romances play out by the score each night, all around us, but we seldom get to see them in action.


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