Australasian Science: Australia's authority on science since 1938

Costly Copulation

By Magdeline Lum

Wasps and bats upsize their meals when they catch prey that are in the act of mating.

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In 2010 Australian plague locusts (Chortoicetes terminifera) descended on farming land and communities throughout Queensland, New South Wales, South Australia and Victoria after a decade of drought had been broken by rainfall. While the locusts were feeding and damaging grazing areas and gardens in agricultural areas, Dr Darrell Kemp from the Department of Biological Sciences at Macquarie University was observing parasitoid digger wasps (Sphex cognatus) entombing mating pairs of locusts.

Increased vulnerability to predation during mating is often mentioned as a cost of reproducing, but there are limited data showing this. However, in December 2010 Dr Kemp observed female digger wasps capturing and burying paralysed locusts in south-eastern Australia. He saw that the wasps caught 43 individual female locust and 19 mating pairs. The female digger wasp’s catch of locusts (30.6% were mating pairs) was far greater than the relative availability of mating pairs in the hunting environment (less than 3.0%).

The data show that there is a cost involved with copulation that is most likely due to being more visible to predators and the reduced ability to escape. Dr Kemp noted that it was only the female locust that was stung and paralysed before burial. The male locust was never stung but, unable to detach himself, was dragged along and buried alive with his mate.

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