INSECTS AT WAR.

Dominion, Volume 1, Issue 67, 12 December 1907, Page 2

INSECTS AT WAR.

ANOTHER APHIS KILLER j OXJR LACE-WING FLY. < Tho nenropterous inscct illustrated to-day ■ is a valuable natural enemy of our aphides, 1 but is yet vory little known among our hor- : tioulturists. It is oxcocdingly valuable, 1 being voracious in the destruction of aphides of many plants. In the larva form wo have found it abundant at Auckland, 1 To Aroha and Welliugton, and no doubt it exists also im tho south, where, however, we leave it to our readers to discover. News of their success will be welcomed by all roaders interested in tho subject. Tho. larva is not easily seen. Its colour and minute size almost 'deceive the eye at tho first glance, even when one is looking straight at it. It has a wide range of habitats, being quite happy, apparently, on any plant where aphides exist. On a wild dogrose bush one can generally depend on finding one or two sjjecimens without any difficulty.' It' also visits comato; cosmos, dahlia, chrysanthemum and other flower plants, and among the turnip-flower ( aphides, recently described, it revels in abundanco. It is scarcely more than an eighth of, an inch in length, greyish' in colour, almost transparontj and no one who was not absolutely looking for it would bo likely to notice such a small and unobtrusive object. When still, it is like a. very minute bit of a dried leaf, but under a pocket lens it becomes a beautiful creature. So soon as it moves, its lizard-like wriggling gait is at once apparent. If you are fortunate enough to find one, you will be sure to notice the skilful way in which it uses its tail as a foot by pncking.it into the bark of tho twig or into the leaf on which it happens to be travelling. The lateral spread of its six legs enables its body to lie close to tho leaf, giving it the lizard-liko attitudo again. Its tail and feet have a wonderful power of holding tightly to a branch or leaf when an oncounter . with an aphis necessitates a stroiig pull. Yet when not at work it lies so lightly that a slight jerk, such as niight bo causod in breaking off a twig, will cliplodge it and make. it fall to. the ground—a matter which it is well to bear in mind when endeavouring to secure a specimen. '

Under a good. lens you will be able to observes—as shown in Fig. I—the terrible-look-ing mandibles. _ These are his weapons against the aphis. Ho knows no fear, and will attack an aphis twice his own size without the slightest hesitation or preliminary skirmishing. Ho just grips it with his mandibles. Those penetrate the soft bag of juico of which an aphis body mainly consists, and there lock themselves together in a hold that is more rigid-than the bite ■of any bulldog. Whether or not ■ these mandibles possess minute sucking holes, as is the case in ■ some other insects, or whether tho sucking of the juice is done by the two other organs seen between thr-m, are matters that we have been unable to determine; it really doesn't matter which, but the. point is an interesting one,, and any of our', readers who care to. undertake tho task 1 of finding out will be rewarded in doing so by discovering a great many other interesting things at the same time. Tho utter coolness, the sublime impudence, the callous; leisurely indifference with which he picks up a startled aphis and makes an impromptu meal-on its precious, hard-earned juices; are surely not surpassed by any other creature 'in the insect world. A "beg pardon" has no place in his code of morals. •

He prefers a relatively small aphis—pro-1 bably because it is easier to lift tnan a big one —but he does not always say "No" to a largo, fat, and winged ' one. : Running along the branch till lie finds a morsel that takes his faucy, he stretches his neck ovor it, makes the grip, and then remains apparently motionless—though probably sucking all the time—until the aphis has withdrawn its tongue .-from the tissues of ; tho plant. Then ho lifts it into tile air, and holds it suspended until it is empty, finally pushing away the dry skin as useless. The favourite pose is on the other sido of a twig or leaf (as sketched in. Figs. 2 and 3), so > that the head may hang downwards. Possibly he has sufficient intelligence to know that if ho holds the wounded aphis up over his head, the exuding juices will flow down into his eyes and cause him some inconvenience. There must be many interesting thoughts in the minds of our little insect friends that wo.can never more than guess at. Take the suspended aphis ,by the lee and try to pull it away from tha larva, and ■ under a lons you will bo ablo to see clearly the rosentment glistening in his eyes. But he will never lot go. Pull harder.'His neck , will stretch as if on the point of snapping, 1 but still his foot ancl tail will cling tenac--1 iously to their foothold, and tho mandibles will not! open to release the prey. Pull ' harder yet, till something "gives," and thpn examine. You will find almost surely that j ' the larva is still on' tho twig, that his neck is not broken, nor his mandibles wrenched olf, but that the stomachwall, or whatever part of tho aphis he was attached ■ to, lias ' "carried'away." If you could only see into his mind you would probably find that ho is in a fury..

Thoso larvso are not always eating. They got their food so oasily that much loisure time falls to their lot. _ At suoh periods 1 thoy retire to sholtor, either in the apox of i a loaf or in a curled-up dead leaf lower J down, or on tho ground. Unlike the blind larva of tho syrphus-ily, which alio doyours aphides, our present friond has .prominent oyos, and, obviously, good sight. He will ofto:i dodge round a twig to escape tlia glaro of a lens, and, if disturbed whilo feeding, he will hurry away with his proy, tarrying a largo apliiß, twice as largo as him>olf, in his mandibles quite easily. How much more poworful arc insects, in comparison with their size, than we poor men. Our friond has a very bad temper. Socur- ® ing one that had boen resting, well gorged with food, and. failing to ma£o bm oat by we tried the effect of irritation.

> Holding ,m aphis by tlic logs, and concealing our fingers as much as possible beneath the twig, \v o poked him several times in the laco with tho body of tho aphis. At first he tried to evade it, but finally ho dashed at it savagely, gripped it. and started to suck it. Ho required 110 further help from us. In this respect be is superior to many other natural enemies, which usually will not proceed with thoir ordinary cannibalistic avocations if disturbed. Tho fly of this larva is a lace-wing fly} of which there aro some species which attach their eggs to twigs of plants by means of slender threads. The lame bear a great resomblanco to tho larvco of some ladybirds, and bunt their victims 'in the same bea-st-of-prey fashion. Tho larva appears to be very generally distributed in the districts itfrequents, but nearly always in small numbers, never in clusters. It has a great value ■ for growers of any crops subject to aphis attacks, and gardeners who possess choice rose or other bushes that they desire to guard against aphides could collcct, them from other plants and place them upon tho plants they desiro to protect. For observation .under a lens they aro among the most interesting small insects, to bo found. The chief enemy of the larva is a winged black ant, which alights upon it, thrusts a sharp ovipositor or sting into its back, and there leaves an egg to hatch later on and devour its vitals. Under the prick of the ovipositor tho larva plunges and runs, abo.ut in great agony, and finally reaches tho ground, where it hides in tho debris. Tho ant, unfortunately, exists in great numbers, and probably will always restrict the increases of the lace-wing fly. Its evil work, however, is balanced by tho destruction it works among the plant-eating caterpillars.-