FARM TOPICS.

Colonist, Volume LIII, Issue 13169, 27 July 1911, Page 4

FARM TOPICS.

THE GRASS GRtIB

Dr. Hilgendorf, biologist of Canter-.' bury Agricultural College, in an interesting interview with the Christchurch "Press," gives.'a brief outline of the life history of the grass grub. The grub, he says, is the larva of a beetle i which is a native ofNew Zealand, its ' scientific appellation being ' 'odontria Zealaiidica" ; 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 very busy laying eggs which" will provide for the next generation. A fortnight or so before Christmas all the beetles .* have finished their egglaying, and by the time Christmas is passed most of them are dead. Tho eggs they have laid usually hatch out in December, but the grubs are very small, and the damage they do ia hardly noticeable until about May, by which time they have grown a good deal and^ cat proportionately more food. If the season is a mild and genial one, the grubs live about two inches below x the surface of tho soil, but, if the season is wot and the temperature low, the grubs burrow down- | wards to escape the rigours of the climate, and they < consequently get below their food region. If the food supply is rTocd, and the j grubs have been enabled to. lay up a sufficient store of nutriment in their bodies to act as a reserve to take them through their.resting stage, they will pupate, that is, turn into a chrysalis about October, aiid emerge as a beetle 'in November, thus completing their t life cycle. But if the food supply has ; boon poor, and if they have had to burrow deep to esdapo the cold and wet and bo have got below that portion of the soil that contains their food suppl, then they do not pupate in October, but will hang on until a second season has passed, and some-

times 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 1 as tho beetles, by laying eggs, provide the increase, the fact that few, if any, beetles emerge after a severe season is a great check to tho 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. .- -,' ■'