176 



GLEANINGS IN BEE CULTURE 



Mar. 15 



General 

 Correspondence 



THE SOURCE OF HONEY-DEW. 



D. M. Macdonald's Opinions Disputed. 



BY DR. C. GORDON HEWITT, 

 Dominion Entomologist. 



[This article by Dr. Hewitt, and the one which fol- 

 lows it, by Dr. E. F. Phillips, were received by us at 

 practically the same time. Both writers agree very 

 well in regard to the source of honey-dew, and, com- 

 ing from such authorities, we feel quite sure that 

 these opinions, together with that from Prof. H. A. 

 Surface, may be taken as the final answer to the ques- 

 tion, viz., that most of our honey-dew is an excretion 

 from the aphides.— Ed.] 



I have read with interest the recent com- 

 munications in Gleanings on the above sub- 

 ject which appears to have been stimulated 

 by the remarks of Prof. H. A. Surface in 

 your issue of October 15, p. 623. In your is- 

 sue of December 15, p 768, an article by Mr. 

 D. M. McDonald, in the British Bee Journal, 

 was published which tended to disprove the 

 views of Prof. Surface; and in the last issue 

 of your journal which I have just received, 

 Feb. 1, p. 89, Mr. J. L. Byer expresses the 

 pleasure that he will feel should Mr. Mac- 

 donald's view be established — namely, 

 that honey-dew is not an excretion. 



It is a matter of regret that there should be 

 any doubt in the minds of your readers as to 

 the nature and source of the honey dew in 

 aphides, as this has been established as a 

 scientific fact for many years: and it is on 

 this account, and in order to set the matter 

 at rest in the minds of those who may not 

 have the advantacre of being acquainted 

 with the scientific literature on the subject, 

 that T am taking this opportunity of placing 

 the true facts before your readers. 



Some writers have believed that the sugary 

 matter called "honey-dew" was produced 

 (I will refer to the use of the two terms 

 "secreted" and "excreted" later) by the 

 pair of peculiar tubes or siphons which exist 

 in certain sub-famihes of the aphides: but it 

 has been proved by many authorities that 

 this view is erroneous. It has been shown 

 that honey-dew is a product of the alimen- 

 tary or digestive tract, and escapes by way 

 of the anus, or vent. Certain species of 

 aphides produce large quantities of honey- 

 dew which is so prized by ants and certain 

 other insects, including bees 



In the early half of the 18th century the 

 famous entomologist Reaumur expressed the 

 view that honey-dew does not issue from the 

 siphons but from the anus; and. later, Kal- 

 tenbach supported the idea. Forel states 

 definitely that the siphons do not secrete a 

 sweet fluid but a gluey wax which is not 

 sought by the ants: the sugary matter which 

 they lick up is rather an excretory product 

 of the digestive tract. 



In 1891 Busgpn observed a single individ- 

 ual produce 48 drops, each drop being about 

 1 mm. (i. e., ^V of ^^ inch) in diameter in 24 



hours (p. 193, Biologisches Centralblatt, vol. 

 9). The production of this honey dew is 

 also affected by the temperature; and Bran- 

 des (Die Blattlaus und der Honigbau, in 

 Zeitschr. fur Naturwiss., vol. 66, pp. 98-103, 

 1894) found that the greatest activity was in 

 the middle of the day. Th s fact of the ef- 

 fect of temperature on the production of 

 honey dew by the aphides is taken advan- 

 tage of by certain species of ants which keep 

 the aphides warm by erecting small tents or 

 shelters over them which may be compared 

 to cow-sheds. 



In the article of Mr. Macdonald's, to which 

 reference bas been made, he says, p. 764, 

 " It, like the honey-bee, has something in the 

 nature of a honey-sac, quite separate from 

 its ordinary stomach, and from which, when 

 the sac gets overcharged, it regurgitates or 

 rejects aphidian honey by means of two 

 tubes used for no o/Zzer purpose." Although 

 the author of that statement may be an ex- 

 cellent bee keeper he is not a scientific en- 

 tomologist, or he would never have made 

 such a statement, which is absolutely inac- 

 curate. The honey-sac of the bee is the 

 fore- stomach, and is part of the digestive 

 tract. The digestive tract of the aphid has 

 no connection with the two tubes or s'phons 

 by which it has been wrongly thought the 

 hon^-y dew is produced. The gluey waxlike 

 substance which appears in drops at the end 

 of these tubes is secreted by a group of small 

 gland cells situated at their bases. Certain 

 aphides, such as the woolly aphis, chermes, 

 etc., do not possess these sipnons or tubes, 

 but have, instead, simple pores on the upper 

 side of the body which produce waxlike 

 threads from wax-glands. If Mr. Macdonald 

 will consult a piper by A. J. Grove, on "The 

 Anatomy of Siphonophora rosarum, Walker, 

 Part 1, the Apterous Viviparous State," in 

 Parasitology, Vol. II., pp. 1—28. 1909, he will 

 find two excellent figures of the alimentary 

 or digestive canal of this rose aphis on page 

 7, from which he will see that it is a very 

 simple structure. 



Honey-dew is an excretory product of the 

 digestive tract of the aphid which is natural- 

 ly expelled by the usual aperture. It is 

 elaborated in the digestive processes from 

 the very large amount of sap which the 

 aphids sufk up by means of their probos- 

 cides; and as it can not be made use of by 

 the insects in building up the body tissues 

 and producing young, it is excreted in a 

 changed form as a waste product. I entire- 

 ly fail to understand why the idea of its be- 

 ing an excreti n instead of a secretion 

 should be repellant to any one: it is merely 

 changed cell sap, as also is honey, both of 

 which undergo a change in the digestive 

 tract of the insect. The difference between 

 an excretirin and a secretion is really not so 

 great as at first sight appears. The cells of 

 an animal's body produce certain chemical 

 substances according to their nature. The 

 cells of the salivary glands produce by their 

 a>tivity a secretion known as the saliva; the 

 wax-cells of the aphid and of the bee pro- 

 duce a wax secretion. Many of the cells of 



