Eucalypt psyllids put their feet up
From Forest Health News 117, April 2002.
The blue gum psyllid, Ctenarytaina eucalypti , fancies the juvenile leaves of its host, Eucalyptus globulus. It can eat and feed just as well on the adult foliage, yet it mates, lays its eggs, and generally prefers to hang about on the waxy juvenile leaves. But the eucalyptus psyllid, Ctenarytaina spatulata , also present in New Zealand, favours the adult
foliage. It mates, lays its eggs, and by and large frequents only the adult leaves. If placed on waxy juvenile foliage, C. spatulata is unable to feed.
Now a Ph.D. student from University of California Davis, Eric Brennan*, has discovered that the host foliage preferences of Ctenarytaina psyllids apparently depend on the size of their feet! He has found that per unit of body weight, C. eucalypti has a foot (pulvillus) area approximately ten times larger than does C. spatulata. He believes that the slippery epicuticular waxes present on the juvenile foliage prevent the psyllids with smaller feet from gripping the leaf surface. They are unable to maintain their hold, and simply fall off! The psyllids with the larger foot area can cope with the waxy leaf surface, and effectively live their lives with both feet planted firmly on the ground.
Toni Withers, Forest Research
* Brennan, E.B.; Weinbaum, S.A. (2001): Aust. J. Entomology 40: 270-277.