Origin of Honey-Dew—White Flies — Jumping Plant-Lice — Sugar-Cane Leaf-Hopper — Bark-Lice or Coccidae — Plant-Lice or Aphididae — Life Cycle of Plant-Lice — Excretion of Honey-Dew — Mouth-Parts of Hemiptera — Chemical Analysis of Honey-Dew — Exudation of Sugars — Water Excretion.
Honey-dew is a sweet glutinous liquid excreted in large quantities on the foliage of plants by Hemipterous* insects, chiefly by plant-lice and scale-insects. it is often so abundant on the leaves of trees and bushes that it drops upon the grass and sidewalks, covering them with a glistening coating resembling varnish. At times it falls in minute globules like fine rain. Although readily gathered by honeybees, it has an inferior flavor, and is detrimental to beekeeping. The ancient Roman naturalist, Pliny, supposed that honey-dew fell from the stars, and this belief was generally accepted for centuries. The larger part of the honey-dew gathered by bees is produced by five families of insects belonging to the suborder Hemiptera of the order Hemiptera or bugs: plant-lice (Aphididae), bark-lice (Coccidae), lantern-flies (Fulgoridae), jumping plant-lice (Psyllidae), and white flies (Aleyrodidae). A small amount of honeydew is also excreted by a few species of tree-hoppers (Membracidae), but they are seldom sufficiently numerous to do much harm.
The white flies (Aleyrodidae), small winged insects covered with a whitish powder, were formerly classed with the scale-insects, as in their immature state they are scale-like in form. They are widely distributed in both temperate and tropical regions, and infest many common cultivated plants. Honey-dew is deposited in large quantities by the larvae, pupae, and adults, and forms a medium on which grow several fungi. Only the adult females of plant-lice and scale-insects produce honey-dew. In Florida the larvae, pupae, and adults of the woolly white fly (Aleurothrixus howardi) excrete such large quantities of honey-dew on the under side of orange leaves that the smaller branches droop slightly under its weight. When an infected branch is jarred, the drops fall in a shower, and the branches and leaves become very sticky. The accumulation of honey-dew causes much annoyance to orange-pickers and to the men and mules engaged in cultivating the groves. The drops are often one-eighth of an inch in diameter, and become overgrown with a dark-colored fungus.
The jumping plant-lice (Psyllidae) are small winged insects about one-sixth of an inch in length. Many of the species form galls. The pear-tree Psylla often destroys pear trees by sucking the sap from the twigs. According to Slingerland it excretes honey-dew copiously: “It literally rained from the trees upon the vegeta-
* The mouth-parts of the order Hemiptera form a beak, which is used for piercing and sucking. It is divided into three suborders: 1. The Parasitica (lice) are wingless insects parasitic on man and other mammals. 2. The Heteroptera have two pairs of wings, but the first pair are thickened at the base, while the tips are thin and transparent. They include water boatmen, water-bugs, water-striders, bed-bugs, lace-bugs. and chinch-bugs. 3. The Homoptera have the wings of the same thickness throughout their entire length, and include cicadas, spittle-insects, leaf-hoppers, plant-lice, and bark-lice.