We searched the native forests of Oʻahu to look for ʻakoko planthoppers, a curious-looking insect with a distinctive horn on its forehead longer than the bug itself.
The Hawaiian Islands are home to 22 species of ʻakoko — Chamaesyce — 15 of which are endemic, and 6 of which are endangered. ʻAkoko belongs to the Euphorbiaceae family of plants all of which produce a poisonous milky sap to ward off herbivores. The sticky white sap is caustic and irritating to the skin and eyes.
The amazing thing about this planthopper is that it feeds on the poisonous sap of ʻakoko. Hence its name, the ʻakoko planthopper or delphacid planthopper. I learned from Betsy Gagne that a Hawaiian nickname — “umiʻi ʻakoko” — was coined for the planthopper. “Umiʻi” is a sharp pain in the side like the piercing of a needle. “ʻAkoko” is the planthopper’s host plant.
The ʻakoko planthopper — Dictyophordelphax mirabilis — is tiny — under a quarter inch long — and is endemic to Oʻahu. There is also an ʻakoko planthopper endemic to Kauaʻi — Dictyophordelphax swezeyi — whose horn is slightly shorter than its Oʻahu cousin. These creatures are tiny, not easy to find, and skittish. You must be quiet and move slowly in order to not scare them away.
When I posted video and photos to the Hawaiian Entomology Society facebook page, I learned from Sam Gon III that like other delphacids, the ʻakoko planthopper is a piercing and sucking insect. But curiously, is it not the long horn that does the piercing and sucking.
Karl Magnacca said that the mouth, beak, stylet, or rostrum of the insect is located between the front legs — the dark area under the bug in the photo above.
Will Haines said that the cephalic horn extends from the forehead of the insect, and is not a nose or mouth-part of any kind. A branch of the gut extends up to the tip of the horn, and one theory is that the horn detoxifies the sap prior to digestion. Other planthoppers in other families around the world have similar horns and another theory is that the horns have musculature that helps the insect suck up sap.
Still more theories include that the horn plays a protective function — the ingested sap in the horn makes it unpalatable to predators and that the elongated head camouflages the insect as a thorn or twig.
Feeding on sap can be dangerous. We saw a dead ʻakoko planthopper that appeared to have gotten stuck on some sticky sap, could not free itself, and died.
The tiny insects are fascinating to watch. Take a look at this video of the planthoppers as they scurry about branches of ʻakoko. Such neat little creatures.
Thanks to Chris Wong who spotted all 6 of the planthoppers we saw and who “took one for the team”.
Thanks to members of the Hawaiian Entomology Society who responded to my inquiries about the ʻakoko planthopper. Mahalo for the great information!
Personal communication with Betsy Gagne
Personal communication with Karl Magnacca
Personal communication with Sam Gon III
Personal communication with William Haines
Delphacid Planthopper, Bishop Museum
Hawaiian Insects and Their Kin by F.G. Howarth and W.P. Mull, pg 98, University of Hawaii Press
Hawaiian Natural History, Ecology, and Evolution By Alan C. Ziegler
Umii – Parker Hawaiian Dictionary