1922.] 233 



heaves then began, and wilhin twenty uiiuutes from the commencement the 

 whole insect was free save for the last two segments of its abdomen, which 

 were eventually cleared by the posterior tarsi forcing the skin off. Since 

 hardening the bug has proved to be Picrovierus bidensL. — II. K. P. Collett : 

 AuyiistSth, 1922. 



How the Honey-dew of Plaiit-Hce is excreted. — In the August number of 

 ihe Ent. Mo. Mag., Mr. E. A. Butler records that he saw a small slender- 

 bodied but ample-winged Ilymeuopteron stroking and tickling the body of a 

 plump-bodied but not very large green aphis on a rose-bush ; and he asks if 

 anyone can throw some light on the matter. I should say without any hesita- 

 tion that the Ilymeuopteron was endeavouring to milk the Aphid in the same 

 manner as that used by ants when they wish to obtain the sweet secretion 

 which is excreted by plant-lice. This, after all, would not be very surprising 

 — certain beetles and their larvae ( Coccidotrophus socialis) milk coccids ; 

 gnats {Hdiyayomyia spp.) solicit food from, and are fed b}^ ants ; and even 

 Lepidoptera have been seen to milk aphids and coccids. Mr. Butler's aphis 

 would, no doubt, be the common rose aphis, and his Hymenopteron a Braconid, 

 or perhaps a Proctotrypid. The reason which probably prevented him from 

 understanding what was in progress was his evident belief in the old error 

 perpetuated by some of the earlier writers — lieaumur, Limiaeus, etc., and 

 also by some of the more recent ones, such as McCook, Buckton, and even 

 Comstock — that the sweet secretion or honey -dew obtained by ants from 

 aphids comes from the cornicles ; as he writes : " On the cornicles of the aphis 

 there were two small light-coloured masses of what looked like some solid 

 matter, but tiie Hymenopteron took not the slightest notice of these." It has 

 been proved, and anyone can satisfy himself by watching ants, with a low- 

 pocket lens, milking aphids, that the sweet secretion is excreted from the anus 

 and not from the cornicles. Moreover, many of the true myrmecophilous 

 aphids, which pass nearly the whole of their lives in ants' nests and supply the 

 bulk oi the food of their hosts, do not possess cornicles at all ; and as we shall 

 see later on, they would not require them in the safety of an ant's nest, 

 Biisgen, Donisthorpe, Forel, Kolbe, Wheeler, and others have all disproved 

 the statement that the honey-dew is a secretion of the cornicles, and have 

 shown that it is simply the excrement of the plant-lice. Darwin, in the 

 "Origin of Species," well describes how aphids voluntarily yield their sweet 

 excretion to ants. He writes : " I removed all the ants from a group of about 

 a dozen aphides on a dock-plant, and prevented their attendance during several 

 hours. After this interval, I felt sure that the aphides would want to excrete. 

 I watched them for some time through a lens, but not one excreted. I then 

 tickled and stroked them with a hair in the same manner, as well as I could 

 as the ants do with their antennae ; but not one excreted. Afterwards 1 

 allowed an ant to visit them, and it immediately seemed, by its eager way of 

 running about, to be well aware what a rich flock it had discovered ; it then 

 began to play with its antennae on the abdomen first of one aphis and then of 

 another ; and each, as soon as it felt the antennae, immediately lifted up its 

 abdomen and exci'eted a limpid drop of sweet juice, which was eagerly 

 devoured by the ant." The liquid secreted by the cornicles is of a sticky and 

 wax-like nature, and is of a yellower colour than that excreted by the anus. 



X 



