Pea aphid youngsters use piggyback rides to escape a crisis

First it’s mammal bad breath. Then it’s babies pestering for piggyback rides. A near-death experience is tough on pea aphids.

When warm, moist breath signals that some cow or other giant is about to chomp into foliage, tiny green aphids feeding on that foliage drop toward the ground by the hundreds (SN Online: 8/10/10). “It literally rains aphids,” says ecologist Moshe Gish, who in 2010 described the breath cue.

Now Gish and Moshe Inbar, both at the University of Haifa in Israel, describe what pea aphids (Acyrthosiphon pisum) do after they hit the ground. There’s “a climbing frenzy,” Gish says. “Frantic” newborns scramble onto adults for a piggyback ride to safety.

Open ground may be a better bet than certain death in cow cud. But exposure still brings risks from other predators as well as dehydration or even starvation if the aphids can’t find another plant to suck sap from. In a lab setup, hitchhiking got very young aphids safely across open ground about four times faster than scrabbling to safety on their own, the researchers found. These newborn aphids, not even 12 hours old, were not just seeking some object to clamber onto. They soon lost interest if presented with beads or dead adults but held on to live grown-up aphids in motion, the researchers report December 6 in Frontiers in Zoology.

When catching a ride, kinship didn’t seem to matter. Closely related or not, most adults resisted vigorously, bobbing heads or rears up and down. Some just lowered that head or rear and waited. In the end, only about 5 percent of youngsters got their much sought-after piggyback ride.

Two other aphid watchers had reported piggybacking previously but proposed youngsters were cannibalizing their rides. Gish, however, rarely saw riders poke mouthparts into adults and thinks any jabs were just natural “tasting” of what the babies were standing on.