Plant tissues differ dramatically in their nutrient content. Leaves rich in proteins, minerals, and vitamins are favored food of many caterpillars and beetles. Phloem sap transports the products of photosynthesis from one cell to the next and is a rich source of sugars and amino acids. Sucking insects like mealybugs, whiteflies, soft scales, and aphids tap into phloem for their daily nutrition.
Among the most nutrient poor plant tissues is xylem sap, the lifeblood of a plant that transports water from the soil, up the stem, and into the leaves to power the magical process of photosynthesis. Dissolved in xylem sap are minerals, amino acids, the building blocks of proteins, and other organic acids essential for life. The powerful negative pressure created by transpiration, the loss of water from leaves, draws xylem fluid from the roots to the top of the tallest trees. Some insects like cicadas, spittlebugs, and froghoppers we visited in previous episodes evolved to use xylem sap as their source of food. To obtain sufficient nutrients from this nutrient-poor xylem, large quantities of xylem fluid must be imbibed. One fascinating report suggests that some xylem feeders process the equivalent of a human drinking 400 gallons of water a day – yikes!
What goes in must come out and the obvious outcome of xylem feeding is the production of large quantities of excess fluid waste expelled from the rear end of the insect. Among these xylem feeders are some of the most interesting and beautiful of all insects, the sharpshooters. Sharpshooters are a part of the leafhopper clan. The origin of their name is shrouded in mystery. Some early entomologists described the appearance of their feeding injury as if caused by “minute bullets.” Another allegory holds that the “rapid and forcible ejection of minute drops of fluid” from their anus is reminiscent of gunfire of a sharpshooter. Check out the videos that accompany this episode and see if you agree.
Watch as a lovely Oncometopia sharpshooter shoots a liquid bullet from its rear end almost every second.
Sharpshooters can be found on many herbaceous and woody plants throughout the land. On the front range of the Rocky Mountains near Denver, Colorado gorgeous Cuerna sharpshooters busily process xylem sap from the stems of thistles. This week on a scorching summer day a towering cup plant in my flower bed served as a liquid feast for a beautiful Oncometopia sharpshooter. While these sharpshooters cause no real harm to my plants, some sharpshooters carry serious disease agents including viruses and bacteria. For example, the glassy winged sharpshooter is the vector of a bacterium called Xylella, the causative agent of bacterial leaf scorch in trees and Pierce’s disease of grapes. Nonetheless, if you happen to spy one of these beauties on a plant, take a moment to observe glistening drops of fluid shot by these tiny riflemen.
On a hot summer’s day a gaggle of Cuerna sharpshooter adults and one nymph extract xylem fluid from a thistle stem and eject a steady stream of liquid.
Bug of the Week thanks Dr. Shrewsbury for providing the inspiration for this episode. The information rich Featured Creature “Common name: sharpshooters, leafhoppers, scientific name: Cicadellidae (Insecta: Hemiptera: Auchenorrhyncha: Cicadellidae)” by Chris Tipping and Russell F. Mizell III was used to prepare this episode.