Friday, December 14, 2007
Milkweed Community #5: Sharpshooter
A few glassywinged sharpshooters (Homalodisca vitripennis) have staked out stems on the Asclepias which raised my left eyebrow. As you know these leaf hoppers are xylem feeders known for a few unpleasant qualities, one of those being the droplets of minimally digested sap they emit as they feed. The mouth part inserted into the xylem connects the insect's digestive system with the vascular system of the plant, and so sap flows through the insect in much the same way it flows through the plant. The insect cannot process the sap that quickly and so eliminates droplets as the pressure builds. So, I was thinking (or rather not thinking) how does that thick milky sap of the milkweed become a thin clear liquid capable of being squirted as it passes through the sharpshooter? Um, oops! The milky substance is latex and is carried through the milkweed plant in a different set of vessels, the lactifers. The sap of milkweed is not milky. A common misconception, I fear but easily dispelled if we just give it some thought.
Here is a nice shed exoskeleton to go with that thought.