These beetle larvae attract bees by imitating flowers

Like cunning perfumers, the larvae of a parasitic beetle create floral aromas to attract bees. Plants are known for cosplay as animalsbut this rare discovery could be the first known example of an animal chemically mimicking a plant.

European beetle larvae (Meloe proscarabaeus) emerge from the ground in spring, climb grasses, and clump together to form bright orange masses that resemble flowers. When a bee approaches, the larvae quickly latch on to return to its nest, before eating its eggs and continuing their life cycle. How exactly the larvae attracted the bees was a mystery.

The results, published on January 15 at biorXiv.orgreveal that beetles produce a range of aromatic compounds normally associated with plants and known to attract pollinators. “They weren’t just producing a compound and then vaguely trying to imitate a flower,” says Ryan Alam, a synthetic chemist at the Max Planck Institute for Chemical Ecology in Jena, Germany. “It was like their own personal larva scent.”

Alam collected male and female adults and raised them in tanks in a greenhouse, feeding the voracious beetles wheatgrass, broad beans and clover. After mating, the females laid their eggs, and a few weeks later the larvae emerged and immediately crawled onto the plants. The researchers picked them up with a paintbrush and performed a series of chemical analyzes on the compounds they emitted.

The beetles give off a complex aroma of 17 plant compounds, including linaloola spicy lavender scent widely used in commercial perfumes, the results showed. Further analysis revealed that the larvae synthesize scents from scratch, using two enzymes to tinker with linalool and diversify the bouquet.

The researchers then created synthetic versions of the flavors and conducted choice experiments with wild red mason bees (bicornuate osmia). A few were particularly attractive to females, which may be an advantage for the larvae, as it increases their chances of being transported directly to a nest.

The compounds also attracted larvae and may be a signal for them to congregate, according to the study. This suggests that deep in their evolutionary past, larvae may have followed scents to find a flower and wait for a bee. After a while, they began producing the compounds themselves to enhance the floral aroma, before eventually removing the plants altogether.

This may have allowed the larvae to emerge in very early spring, when there are not many flowers, and become the closest apparent food source. And the bees don’t seem to be any wiser.