Researchers have identified a particular class of structurally similar, queen-specific hydrocarbons that suppress the reproduction of ant, wasp and bumblebee workers alike — and they suggest that these pheromones have been around, signaling fertility in social insects, for nearly 150 million years. Previous studies have shown that when it comes to such social insects, queens maintain their monopoly on reproduction by emitting chemical signals that render their loyal workers infertile. But, even though these signals, called pheromones, achieve the same end in various species, they are structurally diverse. Annette Van Oystaeyen and colleagues studied the chemical profiles of the outer skeleton, or cuticle, of the desert ant, the common wasp and the buff-tailed bumblebee and found several compounds that were specifically overproduced in the queens of each species. They tested those chemicals on workers and discovered that, even when their queens were gone, the presence of saturated hydrocarbons kept the workers infertile. (Meanwhile, however, control groups of the insect species rapidly developed ovaries in the absence of their queens.)
Van Oystaeyen and her colleagues compared their findings to those of 90 other published studies and investigated the chemicals that have been consistently overproduced by queens across 64 different species. Their findings reveal that saturated hydrocarbons are, by far, the most common class of chemicals overproduced by social insect queens. In fact, their study suggests that similar hydrocarbons were used by the solitary ancestors of ants, wasps and bumblebees to indicate their reproductive status millions of years ago. The study suggests that these chemicals have been evolutionarily stable, and that queen pheromones are honest signs of the queen’s fertility (not manipulative signals, variable over time, meant to actively suppress worker reproduction). A Perspective article by Michel Chapuisat explains this study in more detail and highlights its implications regarding the ancient origins of eusociality.