Life on Earth runs on a 24-hour cycle as the planet turns. Animals and plants have built-in circadian clocks that synchronize metabolism and behavior to this daily cycle. But one beetle is out of sync with the rest of nature. A new study, published Jan. 18 in Current Biology, looks at a beetle with a unique, 48-hour cycle. The large black chafer beetle, Holotrichia parallela, is an agricultural pest in Asia. Many insects, from moths to mosquitoes, use scent to attract a mate. Insects "smell" with their antennae, which contain specialized receptors that react to specific chemicals wafting through the air.

The researchers initially cloned 14 candidate genes. A series of experiments led them to a gene called HparOR14 as the sex pheromone receptor -- incidentally, the first such to be identified in a beetle species. Having identified the receptor gene, they could measure levels of HparOR14 gene transcripts throughout the beetle's life and its activity over 48 hours. They found that on "date night," when females would be climbing plants to release scent, HparOR14 transcription was higher after dark. But receptor activity was low on the alternating days. The results show that male chafer's ability to detect the female sex pheromone does run on a 48-hour, circabidian cycle that matches the female mating behavior.

Why, and how, large black chafers have these 48-hour cycles is unknown. But there are no 48-hour cues in nature, so exactly how the circabidian cycles of large black chafers are set -- including how males and females can synchronize with each other, so they all know which night is date night -- is a mystery still to be solved. Twenty-four hour rhythms in physiology and behavior are commonly observed in organisms from bacteria to humans, but observations of 48-hour rhythms in nature are rare. This elegant study has provided us with an in-depth description of how the circabidian rhythm of pheromone detection in this beetle is generated.