A NEW SPECIES OF GRASS-GRUB.

New Zealand Journal of Agriculture, Volume VI, Issue 3, 15 March 1913, Page 295

A NEW SPECIES OF GRASS-GRUB.

A SERIOUS PEST OF SEEDLING FOREST-TREES.

A. H. Cockayne.

A considerable loss is annually sustained in the seedling-beds at the State Forestry nurseries through the roots of the young trees being destroyed by the larvae of certain species of grass-grubs. I was under the impression that the damage was occasioned by the ordinary grassgrub (Odontria zealandica), so well known in New Zealand on account of its very serious effect on pastures. A visit to the Whakarewarewa State Nursery in the second week of last December showed conclusively that the insect damaging the seedling trees at that nursery was not 0. zealandica, as full-grown larvae were abundant in the larch-beds at that date. If the damage had been due to 0. zealandica there would have been very few larvae present, as normally the majority would have pupated and emerged during the latter part of November.

No method for distinguishing the various species of grass-grubs while in the larvae or grub stage has yet been worked out, so it was necessary to wait till the beetles emerged before the species could be ascertained. From the size of the grubs they were thought to belong to one of the larger species, such as 0. sandageri or 0. striata. On the 27th and 31st January a fine series of the beetles collected in the ground before they had taken to the wing was received by me from Mr. H. A. Goudie, Superintending Nurseryman of the Forestry Branch of the Lands and Survey Department. Being unable to determine the species, I sent specimens to Major Thomas Broun, the well-known Coleopterist, who decided they belonged to a new species, and named it .Odontria puncticollis. He very kindly drew up a diagnosis of this species, and this is appended.

The following notes supplied by Mr. Goudie give some interesting information with regard to this insect: —

On the 23rd January a blank portion of one of the larch-beds, where all the trees had been killed, was selected : If ft. by the full width of the bed— 6 ft. All the soil to a depth of 9 in. in this space was put through a sieve. Ten grubs were obtained. in this way, most of them from 6 in. to 9 in. from the surface. Below this the subsoil to a depth of 6 in. was taken out and screened, with the result that I secured twenty fully developed beetles, and eleven in the pupa stage, or forty-one in all. If this is representative of the whole of the beds, then there are about five thousand grubs in each bed, or about one grub to three trees. Probably the grubs have been going down into the subsoil since about the beginning of November. They apparently

burrow into the hard subsoil, where they pupate. The beetles will probably emerge from the ground about the beginning of February. The larch-beds are in a frightful state, there being huge patches in which every tree is dead. I propose laying scrim over these places in order to catch the beetles as they emerge from the ground. There is no doubt that tillage is the best means of eradicating this pest. I have tried to get grubs and beetles in various other places without any great success. Breaks Nos. 5 and 6 were sown in larch in October, 1910. From July, 1911, to July, 1912—when the crop was lifted—the; grubs were very bad. The soil was top-dressed with apterite in August, 1912,. and was well harrowed and ploughed deeply. Cow-peas and Soya beans were sown in November, 1912. I have since failed to find a grub or beetle. A horsepaddock has been in grass for ten years. Here the land is very hard and consolidated, with, the turf 4 in. thick. A few grubs were near the surface. Block 1 was sown with Corsican pine (Pinus laricio) in October, 1910. The crop was lifted in July, 1912, no grubs or beetles being discovered. It was sown in prairie-grass in October, 1912, and no grubs or betties are now present.

On the 6th February a large flight of Odontria puncticollis occurred, over one hundred beetles being collected by hand in a few minutes. This shows that the time of the main emergence differs very considerably from that of Odontria zealandica, and, in consequence, the control measures for 0. puncticollis will be different to those that would be effective against 0. zealandica. A small flight of the Rotorua grassgrub occurred in September, and I am inclined to think this is due to a small proportion of the grubs not completing their life-history in the twelve months.

It is a matter of great importance to determine what are the species that are causing damage in the southern nurseries, as until that is known and their life-histories are worked out it is useless to endeavour to formulate control measures. .

Data required.

The following data are urgently required with regard to Odontria puncticollis: — (1.) Dates of emergence' of the beetles. (2.) Crops in which egg-laying takes place. (3.) Length of time the grubs remain in the larvae condition. (4.) Food-plants of the adult beetles. (5.) Food-plants of the grubs. (6.) Effect of fires in destroying the beetles. (7.) Effect of spraying and application of soil-fumigants (ci) poison sprays, (5) deterrent sprays, (c) soil-fumigation. When reliable data under these headings have been secured a . satisfactory method of control should be able to be devised so far as protecting the young trees is concerned. This is extremely important, because this insect is greatly increasing the cost of the production of certain trees, notably the larch. Any reduction in the cost of the raising of trees is of fundamental- importance in forestry, and this is especially true of species with a long rotation.

Suggested Methods of' Control.

One of the most suggestive methods of control would be the covering of the beds each evening with beetle-proof frames during the short period the beetles are on the wing. The present seed-frames employed could easily be adapted for this purpose. It is more than probable that the main flights will occur at approximately the same date each year, and if the beetles are stopped from laying in the beds during that period the damage should be reduced to a minimum. The important fact that 0. puncticollis does not damage Corsican pine is a most suggestive, one. It would appear as if the beetles do not lay any eggs in soil occupied by seedlings of this pine. This appears to be correct, as larch-trees that come up accidentally in the Corsican-pine breaks are not affected. It might prove feasible to combine the sowing of a certain amount of larch with the Corsican pine, and this is a matter that can easily be determined. The Corsican pine is an extremely aromatic one, and the question of experimenting with deterrent sprays may probably yield valuable results. If any specially favourite food-plants for the beetles are found, the growing

and spraying of these with arsenical washes might prove a valuable method of control. The following is Major Broun’s description of Odontria puncticollis : Group MELOLONTHID2E. Odontria, white, Man. N.Z. Coleopt., p. 265. Odontria puncticollis, sp. nov. Subovate, broadest near the hind thighs, moderately convex, somewhat nitid ; head and thorax reddish-chestnut, elytra and legs rather paler, the latter often testaceous; sparingly covered with distinct, decumbent, moderately'short, yellowish hairs, but also with longer erect ones along the sides, the base of elytra thickly clothed, in the middle, with elongate pubescence. Head coarsely and moderately closely punctured, except at its extreme base, the forehead with reflexed, well-developed margins, broadly rounded in front, the upper surface nearly nude. Eyes large, only slightly convex, hyaline. Thorax almost twice as broad as long, its sides finely margined, nearly straight, and only slightly narrowed behind the middle, gently curvedly narrowed towards the front; anterior angles acute, the posterior somewhat rounded; base widely sinuate towards the sides, rounded in the middle, the apex widely emarginate ; its surface very distinctly, moderately closely and evenly punctured, frequently with a smooth linear space along the middle. Scutellum punctate, cordate or suboblong. Elytra thrice the length of the thorax, of the same width as it is at the base, gradually dilated posteriorly, the apices rounded at the sides, much less so, sometimes subtruncate, towards the suture ; on each elytron there are nine fine striae, the outer ones indistinct, the central ones obsolete near the shoulder; interstices plane, their punctation distinct, slightly finer than that of the thorax. Pygidium broad, with distant subgranular sculpture. Under-side more or less finely punctate, fusco-testaceoiis, the abdomen a little shining and often fuscous in mature individuals; the sternum with numerous elongate, slender, fulvescent setae, those, on the femora erect. ■ Male. Antennae rather short, basal joint elongate, oblique and thickened at the extremity, the second as stout but only half as long, third more slender, fourth stout, angulate, and generally slightly produced in front; club minutely and densely pubescent, composed of four nearly equal leaflets. Female. Fifth antennal joint short, usually somewhat prolonged in front, but only a third, or less, of the length of the club, which is triarticulate and shorter than that of the male. Length, 12-14 ; breadth, 7-8 mm. This species can be distinguished from almost all the others by the very distinct, though not coarse, thoracic punctation, which is quite perceptible to the unaided eye, whereas in many other cases the punctures, either very fine or obsolete, can only be detected by means of a powerful lens. As a further aid to identification, it may be stated that, with the exception of White’s Rhizotrogus zealandicus, 474, and one or two others, the surface is. opaque and often maculate, and the elytra in some instances broadly sulcate. In the more closely allied, but larger, much paler, and. rather more glossy, O. nitidula, 3233, the hind angles of the thorax, though obtuse,- are more rectangular, and only those striae that are near the suture are well marked. Specimens collected by H. A. Goudie, in larch nursery-beds, Whakarewarewa, 6th February, 1913. The illustration is drawn from nature by Mr. E. H. Atkinson.

A very striking demonstration of the success of dry farming when aided by green-manuring may be seen in No. 40 paddock (lately reclaimed, and naturally -very poor) at the Ruakura Farm of Instruction. A crop of crimson clover was recently ploughed under, and is now growing a splendid crop of tares and barley which is. quite unaffected by the dry weather. The land was thoroughly worked, and when the crop'was sown was left unrolled so as to ensure a deep, loose surface mulch.