Sticky bugs on the tree: Evolution of sticky trap predation in the assassin bugs (Hemiptera: Reduviidae)

With about 300 genera and more than 2,000 species, Harpactorini is the largest tribe in the Reduviidae, or assassin bugs. A predation strategy called sticky trap predation, using sticky secretions produced from specialized dermal glands on the fore tibia called sticky glands to assist in prey capture was found in a New World harpactorine genus, Zelus Fabricius. Morphological investigations of homologous glandular and cuticular structures in 56 genera and 64 species were carried out to infer the presence of the sticky trap predation strategy in the Reduviidae. Sticky glands were found in 11 additional genera of the Harpactorini, namely, Atrachelus Amyot & Serville, Atopozelus Elkins, Castolus Stål, Corcia Stål, Graptocleptes Stål, Heza Amyot & Serville, Hiranetis Spinola, Mucrolicter Elkins, Myocoris Burmeister, Repipta Stål, and a Zelus-like possibly new genus. All of them are from the New World. Sundew setae resembling trichomes on leaves of the sundew flowers were found in all the genera with sticky glands, except for Heza. With a genus-level molecular phylogeny of the Harpactorini, the evolution of sticky trap predation was inferred. Three scenarios were proposed for the evolution of the sticky glands involving multiple gains and losses, and sundew setae appeared to have evolved twice independently.