Parasite that forces trees to do its bidding gets enslaved itself
S.P. Egan et al/ZooKeys 2017
Parasites can drive their hosts to do weird, dumb things. But in certain oak trees, the parasites themselves get played.
“Creepy and awesome,” says Kelly Weinersmith of Rice University in Houston, who has helped reveal a Russian doll of nested parasitisms.
The saga begins when two majestic live oak species in the southeastern United States send out new shoots, and female crypt gall wasps (Bassettia pallida) arrive to lay eggs. A wasp mom uses the delivery end of her reproductive tract to drill through tree bark, injecting each of her eggs into a separate spot in the oak.
Wasp biochemistry induces the tree to form a botanical womb with an edible lining largely free of oak defense chemicals. The tree is hijacked into nurturing each larva, and wasp life is good — until the unlucky ones get noticed by a second exploiter.
Another wasp species, a newly discovered Euderus, arrives, barely visible to the naked eye but “amazingly iridescent,” Weinersmith says. Her colleague at Rice, Scott Egan, named these jewel blue and green specks after Set, an Egyptian god of evil and chaos.
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E. set wasps enslave the B. pallida as laborers and living baby food. E. set females sense their prey inside the gall and inject eggs that hatch and feed on the original occupant. When the invaders mature, they are typically too frail to dig themselves out of the tree.
But that’s not a problem, Weinersmith, Egan and colleagues report in the Jan. 25 Proceedings of the Royal Society B. That’s because, despite having a gnawing parasite inside, B. pallida wasps dig a tunnel to freedom.
Almost. When infested with E. set, the tunnelers don’t manage a large enough hole for their own escape. They die with their heads plugging the tunnel exit, perfect for the E. set attackers, who chew an escape hole through the stuck noggins.
Weinersmith and Egan may be the first to describe E. set’s manipulation, but what could be a much earlier example was collected by Alfred Kinsey — yes, that Kinsey. Before shocking mid-20th century America with explicit chronicles of human sexual behavior, he specialized in gall wasps.
Kinsey named more than 130 new species in just three years, collecting at least 5.5 million specimens, now at New York’s American Museum of Natural History. One of his Bassettia has its head stuck in a too-small exit hole in a stem, suggesting a chaos-and-death wasp lurks inside.
S.P. Egan et al. Description of a new species of Euderus Haliday from the southwestern United States (Hymenoptera, Chalcidoidea, Eulophidae): the crypt-keeper wasp. ZooKeys. Vol. 645, January 12, 2017, p. 37. doi: 10.3897/zookeys/zookeys.645.11117.
K.L. Weinersmith et al. Tales from the crypt: a parasitoid manipulates the behavior of its parasite host. Proceedings of the Royal Society B. Vol. 284, January 25, 2017, p. 20162365. doi: 10.1098/rspb.2016.2365.
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