THE GRASS GRUB.

Waipa Post, Volume I, Issue 31, 1 August 1911, Page 4

THE GRASS GRUB.

TPIE INSECT AND ITS HABITS

The depredations of the dreaded grass grub have been very severely felt, particularly in South and Mid-Canterbury, during the past season. Huge areas of pastures have been rendered practically valueless owing to the ravages of the insect in question, and in addition to attacking grass the grub has in some cases almost completely destroyed considerable areas of autumn-sown grain crops. The loss in Canterbury alone is said to have already amounted to some thousands of pounds, and it is not ended yet. Dr Hilgendorf, biologist of Canterbury Agricultural College, in an interesting interview ' with

the Christchurch “ Press,” gives a brief outline of the life history of the grub. The grub, he says, is the larva of a beetle, which is a native of New Zealand, its scientific appellation being “odontria Zealandica”; it is a cockchafer and belongs to . the same species as the European cockchafer, though our insect is a smaller one. The beetles emerge generally about the first week in November, and for the next six weeks or so are busy laying eggs which will provide for the next generation. A fortnight or so before Christmas all the beetles have finished their egg-laying, and by the time Christmas is passed most of them are dead. The eggs they have laid usually hatch out in December, but the grubs are very small, and the damage they do is hardly noticeable until about May, by which time they have grown a good deal and eat proportionately more food. If the season is a mild and genial one, the grubs live about two inches below the surface of the soil, but if the season is wet and the temperature low, the grubs burrow downwards to escape the rigours of the climate, and they consequently get below their food region. If the food supply is good, and the grubs have been enabled to lay up sufficient store of nutriment in tfieir bodies to act as a reserve to take them through their resting stage, they wili pupate, that is turn into a chrysalis about October, and emerge as a beetle in November, thus completing their life cycle. But if the food supply has been poor, and if they have had to burrow deep to escape the cold and wet and so have got below that portion of the soil that contains their food supply, then they do not pupate in October, but will hang on until a second season has passed, and sometimes even until a third. Thus it will be seen that a severe winter, while not perhaps killing many grubs, will prevent them turning into beetles, and as the beetles, by laying eggs, provide the increase, the fact that few, if any, beetles emerge after a severe season is a great check to the pest for a time, as it prevents the multiplication of the species. The fact that few beetles emerge after a cold, wet season does not mean that the grubs have been killed.