SCALE-INSECTS. 15 



believe that the Coccididae of this country are likely to furnish 

 any products of a useful or commercial character. 



There is, however, one substance produced by these insects 

 which has an injurious effect upon the plants they grow on. 

 This is a transparent glutinous fluid, apparently analogous to 

 that exuding from Aphides, and which may receive the name of 

 " honeydew/' as in that family. In fact, this fluid would seem 

 to be produced by most of the Rhynchota, for the Psyllidse arid 

 Aleurodidse also excrete it. The quantity issuing from Coccids 

 seems to vary greatly. In some cases e.g., Lecanium hesperidum, 

 Ctenochiton viridis or perforatus, Fiorinia astelice the insects 

 appear to discharge " honeydew " freely ; in others e.g., My- 

 tilaspis pomorum, Rhizococcus fossor none, or scarcely any fluid, 

 is excreted. But in no case does it appear that our Coccids"* 

 form honeydew to the same extent as the Aphides, which are 

 stated to produce sometimes quantities that may be gathered 

 from the leaves or the soil by the pound weight. It is not 

 so much the amount exuding from each insect as the great 

 number of insects on a plant which renders the Coccid honeydew 

 obnoxious : each individual may excrete only a little, but when, 

 as usually happens, there are many hundreds of individuals 

 together, the result, for the reasons given below, becomes 

 important to the tree. 



There is every reason to believe that the honeydew of Coe- 

 cididse is of similar character to that of the Aphididse, and, 

 according to analyses by Boussingault, of Paris, and Gunning, of 

 Amsterdam (Bucktoii, "Brit. Aphides/' Vol. I., pp. 42, 43), the 

 Aphidian hcneydew contains a very large quantity of sugar, and, 

 curiously enough, cane-sugar. Some observers, noticing in its 

 composition also glucose and dextrine, have considered it as 

 of vegetable rather than animal origin ; but the weight of 

 evidence appears to make it certainly the product of the Aphides. 

 As the present work is intended rather as a manual for gardeners 

 and tree-growers than as a purely scientific publication, there is 

 no need to enter more fully into the subject here : it may there- 

 fore be simply stated that the honeydew of Coccididse probably 

 contains a large proportion of sugar in various forms. 



The mode in which this substance is excreted by the insects 

 differs somewhat from that of the Aphididse. On the abdomen 



* Gossyparia mannipara, .an Arabian Coccid, is said to excrete so much that 

 the Arabs " eat it with their bread like honey." Buckton, " Brit. Aphides," 

 Vol. I., p. 42. 



