86 REPORT OF THE COMMISSIONER OF AGRICULTURE. 



Apbides, as is well known, are found upon a great variety of plants, 

 both wild and cultivated, and tbeir power to secrete a sweet tluid or 

 nectar from tlie juices tliey draw from plants is also a well-known I'ncr. 

 This liuid is j^iven off by these insects in ;:reat quantities, so that the 

 leaves below those upon which they are stationed are often covered with 

 the substance, and not unfrequently it may be seen actually fallinir from 

 such trees as the maple or elm like a miniature shower, drcnchin;;- all 

 objects upon the piround beneath. The nectar thus produced has a 

 sweet and pleasant taste, and unquestionably forms at times no incon- 

 siderable portion of our best honey, for bees are very easier in .gather- 

 ing it. The honey it yields is light colored, has a pleasing taste, and 

 is perfectly safe, as a winter food for bees."* 



It has been shown that various species of bark-lice (ord(;r Goccidw) 

 also foi-m and excrete a honey like substance, quite as copiously some- 

 times as do the aphides themselves, so that a like ai)pearance is given 

 to the plants they iuiect, the leaves sometimes fairly dripi)ing with 

 the Tieetar and the grass and walks beneath becoming sticky with tin', 

 unctuous tluid. IJees also gather this nectar, but only when other food 

 fails, for they evidently do not like it. The honey produced is dark- 

 colored, has a disagreeable taste, and imparts an extremely unpleasaiit 

 odor to the ai)iary.t 



That houeydew is oltentimes a true excreta from the tissues of the 

 leaves themselves is pro\en by the fact of its a])pcarance upon plants 

 entirely free innn all insects. Its production is not confined to excretory 

 glands, or to any set of organs, but takes jilace over the entire surface 

 of the leaves or fresh and green twigs, and nniy bo regarded as a veri- 

 table disease. A great variety of plants have been observed to x)roduce 

 this honey-dew : among them nniy be mentioned the linden, poplar, elm, 

 willow, orange, olive, walnut, tir, and several species of mai)le. A num- 

 ber of shrubs and herbaceous plants may also be included in the list. 



To what extent the production of this honey-dew is injurious is not 

 well known. Sometimes the affected iilants do not appear to suffer, but 

 it has been skown that in some instaiu-es the leaves become discolored 

 through the destruction of the chlorophyl grains in the cells, and there 

 are also other changes that take place within the leaf in consequence 

 of this. aS'o further injury has been noted, yet indirectly \i is liable to 

 occasion serious damage, inasmuch as it may attract aphides and other 

 insects, as well as various kinds of parasitic fungi. 



The composition of honey-dew. as given by Bossingault and Zoeller, ■ 

 is 48 to 55 percent, cane sugar, 28 to L'4 per cent, of inverted sugar, and 

 22 to 19 per cent, dextrine. A little of the substance called maunite 

 h IS also been detected in it. This composition is exactly the same as 

 that of the manna collected by the monks at Mount Sinai, upon the 

 ta-»narisk stung by Coccus manniparus. 



Very little is known Jis to the cause of this malady. It a|)pears most 

 frequently in hot, dry weather, more particularly on jilants that are ex- 

 posed to the direct rays of the sun. Some think that it may be due to 

 the nature of the soil in which the plants grow; others that it is a 



* Scicrire, January 2;?, IHS'j. 



I JJr. II. S. I{nl>l)ar(l, ot tbc entomological divisiou of the IJnifod Statos Dcpiiifnient 

 of Agriculture, Las o'!>ervt(l several sjiecies of leaf liop))crs (;;en'us I'roconia) upon 

 the cotton-plant and the pear tree, \vhich secreted a sweet substance similar in nature 

 to tliat produced by apbides. They possess the power of ejecting the fluid fnnii 

 their liodie.s with considerai)le force. Tiiis is done at short and regular intervals, anil 

 til" "inantity thrown out is often sutiQcionr to eovei' tlie leaves and tlie objects licrieatb 

 tho plantM, making them appear as if wet with dew. 



