THE GRASS GRUB.

Otago Witness, Issue 2428, 26 September 1900, Page 14

THE GRASS GRUB.

MR W. W. SMITH'S ADDEESS BEFORE THE ASHBURTON A. AND P. ASSOCIATION. (As-hbiirton Mail, August 23.) At the meeting of the Ashburton Agricultural and Pastoral Association on August 21, Mr W. W. Smith, FVE.S., curator of the Ashburton Domain, delivered the following address : — Mr President and Gentlemen,— ln accepting your invitation to address you on the gras>3 grub, I may tlate at the outset I do so with some diffidence, as 1 feel having set myself a somawhat difficult undertaking- to address a large assemblage of practical agriculturists on so important a subject. In doing so, however, my chief aim will be to state such facts and observations as I have collected and made personally on the life history and ' hiibits of this destructive pasture pest. This course seems to me the better one to adopt i in my remarks in order to enable you to fully ! discuss the various methods likely to be I employed for its destruction during each j stage of its existence. Tneie can be no q.uestios but that agriculturists in New Zealand are now confronted, with an insect pest more destructive than the rabbit or the sparrow, and no less formidable to deal with. You are probably aware that the 'brown beetle, whose' grub is now devastating'many thousands of acres of valuable pastures, also cereal and root crops, and attacks the roots and destroys _ innumerable species of non-pastoral plants, is indigenous to New Zealand. The inseot furnishes a remarkable illustration of the fitness of certain species of insects to adapt themselves to the wholly-changed conditions of a country, and increase and flourish at an immeasurably greater ratio on introduced than on indigenous plants. The breaking up and pulverising of the naturally solid virgin soil is conducive to their burrowing and root-feeding ho bits, while the roots of nearly all introduced agricultural plants are more nutritious, and more easily assimilated by these voracious grubs than the roots of native grasses. Haying thus briefly stated the cause of the rapid and prodigious increase of the pest, I will i • w proceed to elucidate its life history or cycle of existence, and habits from the egg to t le perfect or winged insect. The metamorphosis of the pest is completed when it attains the winged stage, which annually oocurs about the first or second week in November, when they emerge from the earth a small brown beetle, and swarm m millions ovei the country on calm, sultry nights. After jmiring they again take flight for several nights across the country, di.-.p-ping into the grass, young cereal crops, and on newly-ploughed lands, and depositing their eggs slightly below the surface of the &cz',. Each beetle lays from 11 to 21 eggs, which hatch in from 10 to 24- days, according to the condition of the soil. Although the newlyhatched grubs are very minute, they instinctively burrow into the pasture by aid of their powerful forelegs and horny head, and immediately attack and subsist on the more tcir'er roots of the various grasses. 'If they be numerous their presence may be detected in the paddocks in a few weeks, but the destruction they work increases more rapidly as they gradually attain maturity. For some weeks before they change into the chrysalis or third > stage of theii metamorphosis they becomo more voracious and very fat/jvliidi is a nafciv^

ral provision in their economy to enable them b) ppss through the pupa, or dormant stage. The grubs bogin to Irnipform into the chrysalis condition übout the end of September

or boginning of October, and remain in that , stage for about a month or ux weeks, when j they finally transform into the winged beetles. I woald here eiinpha^o the fact that all the grubs do not change into pups the first season, as I have occasionally found a few ;n; n I dividual* in the soil v/hils the beetles were j emerging;, and after they had oil Ji=appeiued ' for the iea«on. To the m-u.ira.lisl there is no- i thing reiaai kable in this apparent anomaly. The larvas and pupse uf buiiterfiies, moth/-, and beetled occasionally remain in those stages for several years v.ilhout transforming into the higher stage ju their proper time, while both larvae and pup:e may be observed in the nests of our native onts throughout the whole year. In the case of theae grubs, their continuance in that stage on to another season is probably due to the eggs being deposited late, or from an insufficient food supply. The latter remaik was exemplified to perfection during the prolonged drought of 18S6 to the autumn of 1899. The eggs laid by the beetles, which emerged from the moistei lands during these seasons of severe droughts were unable to feed up and pass through the uupal fctage; and, m consequence, remained in the grub stage, and increased in numbers in those seasons until the copious warm rains in the autumn of 1899 and the resulting great growth of pastures enabled them to fesci up, pass the pupal condition successfully, and appear in unprecedented swarms in November lost. The widespread devastation of pastures and the immense loss therefrom to agriculturists, at the present time, ib the result of these swarms. The fairly moist .summer and autumn, with the good growth of all vegetation that followed, and the late mild winter have been exceptionally favourable to the habits and development of these very destructive creatures. Ido not lemember, in any previous season, having observed the grubs to be in a fatter or more forward condition than at tlio present time. It therefore requires no piophclic vision to foretell that other great swarms will Ptsmedly appear earlier in November than in former year's, at least I would judge so from the early and mild season we arc now experiencing. There are sovsial' other important phases hi the natural economy of the insect to which 1 now refer. A remarkable feature is the greater preponderance of males over the female?. The ratio of the former is about four or five to one of the latter. The rule holds good in numerous other species of insects, r.nt\ readily explains the great fecundity of the parents of the gross grubs. The lntter can also subsist on decaying vegetation, though they do not then flourish so well as when they are consuming the soft, nutritious roots of living parturage. I mention this fact spacially in relation to the summer and autumn fallowing of land, which process is said to act as a check against the ravages of the grubs. The beetles, in winging their flight across the country, 'drop on to fallowed and imfallowed land alike, burrow into and deposit their eggs therein, which, when hatched, subsist on the decaying roots and other vegetation until the roots of the young crops strike into the soil, which they immediately assail. There must be many present who can corroborate this remark, as" the recent enormous destruction by these grubs of summer and autumn-sown crops of jfcmnips, oats, and wheat has shown. These grubs occasionally rise to the surface during the night, and change their quarters several feet away from where they rise. When thus engaged th&ir presence may easily be detected by the minute heaps of fine soil which they push out of the newlymade burrow/ It seems to me important to impress you with these combined facts in the life history of the insect, which, I hope, may cause a revulsion of feeling, and stimulate all agriculturists to some decisive and persistent action against the grass grub until it is effectively suppressed. Sufficient having been said on the habits and deptructiveness of the grubs, let us now proceed to discuss such methods as may prove to be more or less effective in checking- its increase and eradicating the pest. I, however, unhesitatingly confess my inability ~t6 suggest any clearly definable or workable method at present for its effective eradication. The question is one of community of interest, and must, "therefore, depend largely o» Jie collective and^ persistent efforts put forth by agriculturists and horticulturists for its rapid and ultimate suppression. For ten years I have endeavoured through the medium of the newspapers to urge the farmer* of, Canterbury to action by advising the adoption of stringently repressive measures against the pest, but with little good effect. Every possible means that are known to destroy it should, however, be put in force without delay. When the- beetles appeal in large flights on calm November nights they are easily attracted to largfe fires, into which they fly headlong and perish in millions. Agriculturists would, ! therefore, act wisely in preserving and accumulating heaps of old straw and hedge trimmings on suitable places on their land to be burned on the nights when the beetles "wheel their droning flight." Although fires can only rcciuoe their prodigious hosts in a small de-

green, it is obvious that the destruction of a thousand female b'eefcles in November" 1900 would probably (at the lowest computation) prevent 12 to" 20 thousand of their offspring appearing to continue the race in November 1 1901. In regard to the action of chemicals or strong chemical manure's in checking- or destroying the grubs, no perfectly satisfactory results have os yet been obtained by applying them to grub-infested land. Lime and strong; superphosphate applied to the surface of grubinfesfced patches before rain will sicken the grubs, and check their action for some time/ but they do not kill them outright. Irrigate ing the land causes the grubs to rise to the surface, or float about on the water for days} when they fall an easy prey to birds.' 'When the water subsides they again burrow; into the land. The grubs will also live in a ■^ e?sel of water for several days before dying. Excepting by the assistance of their natural enemies, and the careful use of appropiiata agricultural implements, specially constructed perhaps for destroying the grubs, in addition! to the ngencj' of fire, [ conceive no process at preseni effective in destroying (hem. Before referring to the use of implements, I would earnestly urge all agriculturists to protect Engiish starling; and the many thousands of sea birds Lhat annually migrate inland to breed j during the spring month.-!. Theses val-o.ah 1 © bird 1 ; follow, in large uuiabeis, the ploughs jvucl harrows eryso&ing tho grubs, and vora- | cicurily oomume and subsist oh- these for several weak?. " . v » I have, on -several occasions, advocated light h'arrov. ing and heavy i oiling to destroy ■th« grubs; and in the absence of' much, heavier, or perhaps specially constructed implements, there is certainly no known process '. nora convenient or effective for the jrurposo i tX tue pre s ent time. Possibly a roller "of fiva , or, fix tons' weight or more, faced or fitted j vvit.ii tenth two or three inches long, and eoni strutted in breadth according to weight, would I destroy the grubs lvicie effectively than cruch- | i2ig the land with a plain roller the iamo jv. e'i^lit. "Whatever process may bo devised or \ iiny'emeut invented to destroy the grubs, it ' must, I ilviuk, ultimately be constructed and 1 v/o/ked on some s-tteh lines as here suggested. The question, however, is open for tho-meet-i ing to deal with and subsequent experiments to te?t. In New Zealand there are numerous species of insects whose brvee are attacked by other I parasitic insect and fungoid pests. The rool- ! feeding grubs of native locusts are attacked i by diseases of the latter cla.-H. Up to the pre- | ?ent time, however, I have not observed a, tingle case of 'the grass grub being attacked by any of theae parasites. I would earnestly impress all agriculturists with the great importance and advantage of observing and ascertaining the life hWory_ of any new pest appearing on their properties, " which would enable them to assail and destroy it during its weaker stage of existence. The numerous leaflets dealing, with pests prepared by the Government biologist, and issued by the Agricultural department, if carefully perused and acted upon, would materially assist farmers and pa<=toralists in freeing their properties of insects and noxious weeds. « I have endeavoured in the foregoing remarks to avoid being prolix, and have coi:fined myself to facts, which will enable this meeting to discuss the question fully on broad andpractical lines. 1 regret sincerely that; owing to pressure of other* work at this busy season, of 'the year, I have not been able to deal witli the subject in a more exhaustive and interesting style. . I do not know, however, that much, more could or need be said by way of introducing the subject for discussiox^, The question of how to era-licatc the grass grub is an open one. and demands the careful and earnest consideration of all agriculturists who desire to improve and advance agriculture" in NewZealand.