HELPING THE FARMER

Evening Post, Volume CX, Issue 156, 30 December 1925, Page 9

HELPING THE FARMER

FIGHTING INSECT PESTS

NATURAL ENEMIES AND OTHER

METHODS

WOBK AT THE BIOLOGICAL

LABORATORY.

The life history of an insect, mite, or wolfm, seems a trivial matter, but it takes much labour to unravel. Yet it is upon the knowledge of such matters that we must rely if we Wish to mould to our advantage this wonderful nature which, too often through ignorance of it, does such incalculable mischief. The

complete understanding of the vagaries of this or that insect / pest may expose some vulnerable point where we can attack it with some' possible hope of success. Unimportant as insects may appear to the casual observer, they comprise' about four-fifths of terrestrial animal life, and often prove most destructive pests. No one suffers more from, these hosts than the agriculturist; it is there-' fore impossible that he ean remain an indiSerent spectator^ whilst it fiay be in his power to

palliate if not avert an evil.

As the prosperity of New Zealand depends almost wholly upon its primary products, it naturally follows that in the struggle to achieve success in the world's markets the farmer must not only adopt the best methods of agriculture'and of marketing but he naturally looks to the State, through its' Department of Agriculture, and its trained scientists to assist" him in combating insect pests already here ah3 in preventing the introduction of pests from pther countries. A brief review of the.work in which the entomological branch of the Biological Laboratory: is • engaged should be of general interest.. ..The Government Entomologist, Mr. David Miller, has had a:very busy time in studying the* life history of a number of insect pests affecting the crops and stock of the farmers, and in giving advice as to how best to deal with them.

DESTttTJOnVE INSECTS. ■

With regard to the general harm done in New. Zealand by insect pests, states Mr. Miller, #e are up against two tjrpea of destructive insects. One group of these are native to New Zealand, and the second group are those introduced from other countries. -The, greater proportion of these pests, about 70 per cent, are those of European origin, arid, then there are.those from Australia, comparatively. ,»iBaU: in number. Most of the Australian insects, as might be expeetad, infart the eucalyptus, . although there are amongst them a ?dw which attack' wchard trees and '; livestock.'" New Zealand native in' 'lect pests are practically all' plant ' feediers. About an equal proportion jf the in«»ets attack orchard trees. !°and fofesfteee?,- the Btipbetsef-those \;.attaf.king:;liTest6ek^are small.; •-.- „. It might be thought w^th regard to the insects introduced irom Europe tha't, there would be no need to itudythem in New Zealand, as their life histories must long ago have been known. Although that is true of some species, it is by no means true '■■'vt all; and even though the life history is well known elsewhere, it very often-.' presents. n6w characteristics uiidcr New Zealand conditions.^

ENEMIES OF OBOBABDB.

Take, for example, tie pear midge —a very destructive insect in some parts of New Zealand. The pear midge oeeurs in many parts of Europe, but it is not an important pest there, being held in check by natural agencies. Little Ss known of the habits of this I'insect in Europe, and it was not until it was studied in New Zealand that the vital points of its life history became known. Very Jittle attention has been given to.the midge in Europe. "One of the big problems we are working at in New Zealand now, said Mr. Miller, "is the eontrol of the midge by its natural enemies and insecticides. The Department has gone to a great deal of expense and trouble in securing the natural enemies of the midge from Europe. The first consignments of these parasites have already arrived in No# Zealand. The investigation of these beneficial insects is still in the experimental stagej and there is a great deal of preliminary work to be first accomplished; so little as yet is known concerning them; they are not even named. It is rather early to say what the outcome'.■will be. . ,

THE BEONZE BEETLE,

With regard to other orchard pests, although the method* of attacking the insects with insecticides is, generally •peaking, efficient, there are some pests which so far have not Been controlled. One of these is the bronze beetle, which apparently defies poisoning b.Y the poisons commonly used in orchards such as aTsenate of lead.

The bronze beetle attacks the young apple, eating the skin and causing the fruit as it grows to roal-fortn. The attacks.of this insect have a very direct bearing upon the export value of the crop. ■ ' "The work which has recently been flonc,?' eaid Mr. Miller, "seems to show that, we have now discovered a practicable method of controlling this pest. A-detailed description of the method adopted to destroy tho insect will be published shortly in the "Journal of Agriculture." ! „ THE MEALY .BUG. Although not such' a very serious pest a« the bronze beetle from the point of view of damage to the apple, the mealy bug also affeats the export value of the crop. The mealy bug has so far defied the ordinary means of spraying. We have attacked it by utilising a natural enemy, a ladybird. Both tie ladybird beetle and its gmb devour the mealy b\i,7. Large numbers'of ladybird beetles have been reared at the Biological Laboratory and distributed to orehaTdists. THE TTJBMTP FLT. As illustrations of the many problems with which the farmer haa to contend, the destruction eaused by the insecto- which attacVthe turnip and rape crops may be taken as examples*. Three of these species are of outstanding importance, namely, the so-called turnip fly, the diamond back moth, and the turnip aphis. These three insects .are responiible for a rcry heavy annual lose. The name

turnip fly is a misnomer. It is nothing but the beetle of the grass grub, and is not a fly.* This insect is one of the native species which has become injurious. Its activities are responsible for the wiping out of whole crops of rape and turnips, particularly during November and December, when the beetles are on the wing, and when tho young crops are just appearing above the ground. The attacks of this insect necessitate the re-sowing of crops, which iri itself means a considerable expense, apart from the loss of time in the growth of-the second crop.

In Southland, where turnip arid rape crops are extensively grown for the feeding of live-stock, it has been estimated that the logs amounts to about £50,000 a year.

The investigation of this trouble showed that the loss could be avoided simply by taking into account the tim« when the beetle emerges in November and December, and sowing the turnips either in October, before the beetles appear, or after they have finished their flight in December. Turnips sown in October are well advanced and in full leaf by the time the beetles appear, and the plants are quite capable of withstanding the »t----tack. It is in the .seed-leaf stage (when the young plant in just coming above the ground) that most of the damage is done. This case illustrates how simply some method? of control may be successfully adopted when the life history cf the "insect i» known. Vft GUIS'! TREE SCALE. The: insects which attack forest, trees present many important problems, although except in certain cases the forests I of New Zealand are so far remarkably free from very extensive insect depreda- | tions, such is have occurred in other ! countries. Amongst the exceptions, however, are the pests. which attack the eucalyptus trees. The gum tree scale or blight is perhaps the most outstanding example, siuce this insect attacks practically all forms of eucalypts. This insect is a native of Australia, and in order to combat it the ladybird was introduced. This pest first made its appearance in the South Island in 1900. The ladybird hag done very excellent work in tho South Island in controlling the pest. Whec thi scale made its appearance'in the North Island about, the year 1920, large supplies of ladybirds were secured .From the South Island, and were established in the blight-infested areas in the Nflrth Island. The blight had, however, got well established at 'he initial points of the outbreak before the ladybird could, prevent it doing extensive damage, - The present position is that the ladybird has got the blight well under control. A conspicuous example of the efficiency of' the ladybird is seen in Hawkes Bay. The blight spread ,to_ that district from the West Coast, but the ladybirds were available in sufficient numbers to establish rapidly in Hawkes Bay, so that' now there is hardly a sign of'injury to the trees from the blight in that diitrjct. This is a good illustration of the value of natural enemies in checking insect peita. ' The control of insects which attack forest trees, is a very difficult-prob-lem. The employment of natural enemies is of primary nse, for, of eours», spraying, ete H cannot be successfully adopted. Applications of insecticides to forest trees in the form of dnst are, however, given in Europe and North America by means of airplanes. I

SHEEP MAOOOT PLIES.

Another problem which we have had to face is the eontrol of sheep •maggot flies. There are three species pf fli** belonging to :the:i>lOff-iy group. ■. These flies are responsible for damage to sheep chiefly by means of the "blowing" of the wool on the animal.. The Australian species 'of this fly is th« chief culprit. As a rule,, the flies in hot, muggy weather lay their eggs on dirty wool, although they also blow clean wool on certain breeds of sheep. Qne species at least frequently lays live maggots, and not eggs, on the wool of the sheep. Tho maggots burrow down through the wool to the skin of the,animal, causing the skin to fester, and the wool to putrefy and slough off. In New Zealand the position is not nearly so serious as in Australia, where it is estimated that the loss due to the blow-fly amounts to two million sterling annually. In certain parts of New Zealand, however, the pest is a problem demanding constant, attention. Although the ordinary method of handling sheep in New Zealand, is sufficient as. a rule to control these pests there are occasions when special methods will,, have to be adopted fur dealing with the pest, since the ordinary methods do not serve in such cases, and a great deal of loss results. One prominent breeder of merino sheep estimates that it coats him over Is 6d per head during the fly season to control the pest This, of course, means a considerable outlay even in a small flock. By going to considerable trouble this breeder manages to keep his sheep comparatively fres from the.pest. To show what happens if, sheep are neglected: In on<j flock at a time when' sheep' were worth 30s a head, one-third of the flock were killed by fly attack, and about 25 per cent of the remainder were found to be "blown." This is probably an extreme case, but it'illustrates the possibility of serious loss.

"It is hoped," remarked Mr. Miller, "to solve in part at any rat* this problem by utilising natural enemies of the pest and by a modification of the. method of handling tho sheep.

■ "The primary object of solving all such problems as I have mentioned," stated Mr. Miller in conclusion, "is to.asist the producer to fully develop the resources under his control. This should be the main aim of all.Scientific research—the national saving of pounds, shillings; and pence either directly or indirectly."