Sexual deception of a beetle pollinator through floral mimicry.

Sexual mimicry is a complex multimodal strategy used by some plants to lure insects to flowers for pollination. ^1-4 It is notable for being highly species-specific and is typically mediated by volatiles belonging to a restricted set of chemical compound classes. ^{3 , 4} Well-documented cases involve exploitation of bees and wasps (Hymenoptera) ^{5 , 6} and flies (Diptera). ^7-9 Although beetles (Coleoptera) are the largest insect order and are well known as pollinators of both early and modern plants, ^{10 , 11} it has been unclear whether they are sexually deceived by plants during flower visits. ^{12 , 13} Here we report the discovery of an unambiguous case of sexual deception of a beetle: male longhorn beetles (Chorothyse hessei, Cerambycidae) pollinate the elaborate insectiform flowers of a rare southern African orchid (Disa forficaria), while exhibiting copulatory behavior including biting the antennae-like petals, curving the abdomen into the hairy lip cleft, and ejaculating sperm. The beetles are strongly attracted by (16S,9Z)-16-ethyl hexadec-9-enolide, a novel macrolide that we isolated from the floral scent. Structure-activity studies ^{14 , 15} confirmed that chirality and other aspects of the structural geometry of the macrolide are critical for the attraction of the male beetles. These results demonstrate a new biological function for plant macrolides and confirm that beetles can be exploited through sexual deception to serve as pollinators.
Competing Interests: Declaration of interests The authors declare no competing interests
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