Fig. 355.—Wax disks of social bees: a, Apis mellifica, worker; b, do., queen; c, Melipona, worker; d, Bombus, worker.—From Insect Life, U. S. Dept. Agr.
The wax-glands in the honey-bee are scale-shaped organs situated on the under side of the four last abdominal segments (Fig. 355). These secrete the wax, which appears as whitish scales, and secretion is only possible when the bees have sufficient honey and pollen. The wax is secreted by the hypodermal cells rather than by glands within the abdominal cavity; the wax traverses the cuticular layer, and accumulates on its outer surface (Carlet). According to Fritz Müller, in the stingless bees (Trigona) which he observed, the wax-glands are situated on the back of the abdomen, but Ihering states that in many species of Trigona and Melipona there are also slightly developed wax-organs on the ventral side.
It has been found that certain caterpillars secrete wax. Thus the cells of the Tortrix of the fir (Retinia resinella) formed of resin are lined with wax, as on dissolving away the resin with alcohol, Dr. Knaggs found a slight film of wax; also a secretion of wax has been detected in the larva of a butterfly (Parnassius apollo). The bodies of certain saw-fly larvæ are covered with a white powdery secretion, while the remarkable larva of a Selandria is clothed with snow-white, long, flocculent, waxy masses, nearly concealing the body (Fig. 356).
h. “Honey-dew” or wax-glands of Aphids
The so-called “honey-dew” of Aphids which oozes from two wart-like tubercles or tubes situated near the end of the body, is secreted by hypodermal unicellular glands which open into a modification of a pore-canal, the tube itself being an outgrowth of the cuticula.
Witlaczil states that both in the “honey” tubes and in the body beneath, the sugary matter exists in cells of the connective tissue in the form of granules. “These large ‘sugar-cells’ in contact with the air undergo destruction, while the sugar crystallizes into needles, and thus each cell is transformed into a radiated crystalline mass.”
“A muscle extends from a horseshoe-shaped place (a valve?) in the middle of the flat terminal plate of the honey tube, through this and down through the abdomen to the ventral surface. By this muscle the honey tube is at times erected, and we then find, as also when we lightly press the body of the insect, lumps of crystallized sugar which have been expressed through the tips of the honey tubes.” (Zool. Anzeiger, 1882, p. 241.)
Fig. 356.—Wax-secreting larva of a saw-fly.
