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Notes from Planet Earth

Maternal behavior of a different sort

Watching National Geographic Nature programs and “Nature” on PBS has allowed us to witness numerous examples of the strenuous efforts that the mothers (and sometimes fathers as well) of different species undertake to care for and protect their young. And we’re certainly familiar with the outpouring of stinging or biting workers when intruders threaten the nests of bees and ants. However, when it comes to fruit flies, those tiny, non-social, non-biting, and rapidly reproducing, flying insects that arrive unbidden to feed and lay their eggs on our ripening fruit, one wouldn’t think of expecting much in the way of protective action by the female parents of these insects.

Some recent research, however, has informed us of the unexpected maternal behavior these insects are capable of. These little pests (which, it should be acknowledged, have played a vital role in helping us understand genetic mechanisms) are themselves plagued by parasitic wasps. When such wasps find these fruit flies they seek out their developing larvae (the second stage of embryonic development) and inject their eggs into these larvae. There the wasps’ young develop while eating the fruit fly’s larvae from the inside out.

As shown by this new study, however, if the female fruit fly sees a female parasitic wasp in the neighborhood it stops laying its eggs on newly ripening fruit and seeks out fruit in which the sugars have had a longer time to ferment. This means the alcohol content of the food their larval offspring feed upon will be high. And because alcohol is toxic to the wasp’s larvae, the fruit fly’s larvae are protected from this gruesome infection. In this way these fruit fly mothers are immunizing (or medicating) their offspring against the parasitic wasps larvae. Indeed, the larvae themselves will seek out food with more alcohol content if they get infected by the parasitic wasp, and thus are capable of self-medicating when given the opportunity.

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