JOURNAL

OF THE

ROYAL HORTICULTURAL SOCIETY.

VOL. XXII. 1898.

PART II.

INSECT "BLIGHTS AND BLESSINGS.”

By Mr. FRED ENOCK, F.L.S., F.E.S.

[Read April 12, 1898.]

TIME is so very precious to all of us nowadays that we have great difficulty in paying much attention to things which we think do not concern our own interests. This is specially noticeable in floriculture, in which the demands of fashion compel horticulturists to produce flowers in, as well as out of season (mostly the latter), and the florist who can show the largest collection generally carries off the palm. This remark applies equally well to entomologists who amass large collections of specimens. A great deal more might be done if both would pay more attention to the habits and economy of insects, whose life-histories (if we omit Lepidoptera) are, comparatively speaking, unknown. I refer to such insects as come under the eyes of the horticulturist, and which generally fall between his finger and thumb or under his heel.

For years I have been studying, drawing, writing, and speaking of the life-histories of insects and the indisputable fact that is constantly brought home to me is our lamentable

B

ignorance. Now in the very short time placed at my disposal to-day I can only call your attention to a few of the insects which I have watched and carefully drawn or photographed from nature. The first of these shown upon the screen is a very small piece of a leaf from a Sycamore tree containing winged and wingless specimens of the Sycamore "Green Fly" (fig. 18). I really do not think a gardener could be found who was ignorant of the insects known as "Blight," or "The Fly," of

which there are hundreds of named species figured in British Aphidæ by Buckton; but even in our wholesale destruction of these a very little time spent in studying their habits would be of value, and enable us to distinguish valuable friends and helpers in the very camp of our enemies, where may be noticed white eggs of an oval form nesting between the ribs of the leaf: these are the eggs of the gardener's greatest friend. The Wasp Fly, or Hoverer Fly, belonging to the genus Syrphus (fig. 19), shows the maggot-like larva of this "blessing," which when

full grown is half an inch long, its body thickest at the tail end, gradually tapering towards the head, in which the mouth, formed much like a hook, is found. Attaching itself firmly to the midrib by means of its anal claspers, or "feet," the maggot moves its attenuated body about, swaying from side to side, much after the manner of a leech. I have frequently watched the emergence of these larvæ from the eggs scattered over the leaf, and sometimes, even before it has become clear of the eggshell, its head has touched a Green Fly, which it immediately seizes and sucks dry. The flavour is so acceptable to its palate

that for the rest of grub-life it feeds on nothing else. Its appetite is astounding: I have watched one specimen hoist up into midair (fig. 19) and suck dry over one hundred and twenty Green Flies in one hour. I look upon this as a record meal, but the number destroyed by one larva of Wasp Fly during its life of ten to thirteen days is simply prodigious. At the end of this time the maggot attaches its claspers to either a leaf or stem, where it undergoes its change to the chrysalis (fig. 20), the form and colour of which so much resemble a shoot that this protective resemblance preserves it from attack by birds. In a few days the matured Fly bursts forth from its shroud a living

and active Wasp Fly (fig. 21), and soon meets its partner, and again another batch of eggs is laid where Green Flies most do congregate. I consider it the bounden duty of every gardener to become acquainted with the Wasp Flies in all their changes, and to conscientiously avoid killing them.

Some of the Green Flies may even contain "blessings " in the

at fig. 22.

FIG. 20.

shape of minute parasitic

Flies.

One of these is shown at fig. 22. A little experience and patience will soon enable anyone to detect these very fat Flies, which generally lose their green colour, and attach themselves somewhat apart from their fellows, and gradually become of a dry appearance and brown or white in colour. From each of these emerge small four-winged Flies of different

species, the most plentiful (Aphidius) being shown

These and other allied species are in the habit of running about the green Flies, tapping them on the back with their long antennæ and sounding them to ascertain if they already contain a parasitic grub; if not a rapid leap is taken upon the back of one, and nolens volens a hole bored through the skin and an egg of the parasite deposited in the stomach of the Green Fly. This egg soon hatches to a maggot which feeds upon the juices contained, and of course in due time destroys

the Green Fly, whose dried skin then forms a protection to the chrysalis of the parasitic Fly, which when mature bites a circular hole in the skin (fig. 23) and escapes to continue its species in due course. There is a large field open to anyone desirous of studying the parasitic Hymenoptera of the British Aphide.

If I did not know it to be a fact, I should not venture to say that the disease known as "The Black Currant Gall" is utterly unknown to a large number of gardeners having hundreds and

thousands of trees under their care; and yet every bush has been more or less affected, the common excuse for the scarcity of fruit being "Oh! the birds take them." It is not to be expected that gardeners should know the Gall Mite, which is but the one four-hundredth part of an inch long; but every gardener in Great Britain ought to know the "gall" itself-a sketch of which I give at figs. 24 and 25-a photograph of twigs showing innumerable galls of from a quarter to three-eighths of an inch in diameter, much resembing a hard-hearted cabbage.