ABOVE: Aphids have covered the tiny hairs in this cross-section of a plant gall with powdery white wax particles.

Social aphid species such as Colophina clematis inhabit galls on their host plants and engage in a range of colony-protecting behaviors including the collective removal of waste. The behavior is potentially dangerous because aphid waste, or honeydew, is a liquid, and unless the dew is stored and removed as tiny, individual droplets, it could easily contaminate or even drown the galls’ inhabitants.

Researchers now report that aphids help to maintain the integrity of honeydew droplets by making sure their homes are water-repellent. The aphids’ presence in the host induces plants to produce tiny hairs, or trichomes, on the inner surface of the galls, according to a study published in Biology Letters. Onto these hairs, the insects deposit tiny, hydrophobic wax particles, which then coat the honeydew droplets...

Scanning electron micrograph of wax-coated plant hairs (scale bar 20 µm)

K. Uematsu et al., “Water-repellent plant surface structure induced by gall-forming insects for waste management,” Biol Lett, 20180470, 2018.

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