Nightshade plants bleed sugar as a call to ants for backup

nightshade leaf with goo and ant

Tests suggest that nightshade goo contains lots of sugar and some amino acids that may help attract protective ants like Lasius niger (shown). Researchers suspect that a common hormone called jasmonic acid induces its production. 

Tobias Lortzing

Herbivores beware: Take a bite out of bittersweet nightshade (Solanum dulcamara), and you might have an ant problem on your hands. The plants produce a sugary goo that serves as an indirect defense, attracting ants that eat herbivores, Tobias Lortzing of Berlin’s Free University and colleagues write April 25 in Nature Plants.

Observations of wild nightshade plants in Germany suggest that plants that ooze goo attract more ants (mostly European fire ants, or Myrmica rubra) than undamaged plants. In greenhouse experiments, those ants fed on both the goo and roving slugs and flea beetle larvae, substantially reducing leaf damage. Leaf-munching adult flea beetles and, to a lesser degree, slugs prompted the goo production. The ants didn’t attack the beetles but did protect the plant from slugs and beetle larvae.

Plenty of other plants produce defensive nectars via organs called nectaries, and nightshades’ bleeding may be a unique, primitive version of that protective strategy, the scientists report. 

Helen Thompson

Helen Thompson is the associate digital editor. She has undergraduate degrees in biology and English from Trinity University and a master’s degree in science writing from Johns Hopkins University.

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