NO. 16.

New Zealand Mail, Issue 1202, 15 March 1895, Page 7

NO. 16.

Potato-moth, Potato Tuber-moth, Potato-grub (Lita solanella). By T. W. Kirk, F.L S., &c , London. The grub, of this very destructive moth has long been knowu in many ' parts of the world, ami for a very long period has caused mioi im >u - loss in some district's an Australia. N .»• is it a stranger in New Zealand— sjme of the North island growers have had bitter experience of its destructive powers. The caterpillar, Or “ grub,” is from £in to |j-in in length. The colour is dirtywhite, with a pinkish, or sometimes greenish, tinge. The head is dark, occasionally almost black. On reaching the tuber it eats galleries in all directions, and so induces putrefaction, It attacks potatoes both in field and store. Arrived at maturity, the grub takes up a position.on the outside of a potato, piece of earth, or other convenient object, but usually near the mouth of its gallery, and spins a covering like, a roof merely not a true cocoon —of dirty-white silk. The chrysalis measures about three tenths of ah inch ; and the time spent in this stage varies from eighteen to twentyS«syeh days. The moths usually pair within twenty-four hours after emerging, ■ arid eggs are laid within the next forty‘eight hours; but it is probable that A. '

other layings take place, for the moths live for several weeks; and in one case, at least, the moth took the male three times in eight days, and fresh eggs were deposited after each time \ within twenty-four hours of the event. I am unable, at present, to say whether this is common with the species. I isolated two females, after impregnation, in order to ascertain how many eggs were.laid. The first deposited 117, and the other 123. The first were all deposited in the eyes of a potato lying on the floor of the breeding-cage ; in the second case the potato had been carefully covered with earth, and young shoots had developed to the length of about 2|- in., and the moth, being unable to get at the tuber, deposited her eggs on these shoots, quite close to the ground. These and other results, obtained from examinations of specimens reared in confinement, agree well with the description given by Mr Tepper, Mr French, and other writers on the subject. The moth is very active both on foot and wing, taking short, quick flights, and running rapidly ; it is a night-flier, and is attracted by light; this 1 know to my cost, as opening the breedingcages one night to try the effect of a strong light, some of my best specimens flew straight at the lamp, and were spoilt. The markings of the moths vavy, and I believe that the on those that pupate in the stalks are darker than on ..those that come from the tubers. Further experiments are, howesrer, necessary before this can be * stated positively. The tobacco crop in some parts of New South Wales, and I am informed in Queensland also, has been attacked

by this pest. The fact, that it feeds on other plants besides those of the Solanacese cultivated for food, will increase the difficulty of dealing with it. The measures adopted must be preventive rather than curative. In infested districts it will be well, if possible, to abstain from growing potatoes for a season or two ; failing this take care that all sets are sound and free from eggs, and the ground thoroughly clear of all weeds; plant, rather deeper than usual, keep well earthed up, and bag as soon as possible after digging Stow in a moth-proof room, and examine from time to time to ascertain if any grubs have been gathered 'ahum with the crop ; if so, remove the affected tubers, otherwise the potatoes will soon become a mass of putrefaction.

As stated above, the moth is a nightflier, and attracted by light; 'therefore, cheap forms of lamps or fires may be used with advantage, and will destroy hundreds. A good ' plan is to place' a light canvas screen of convenient size on either side of the lamp. This screen should be smeared with grease, treacle, or other sticky substance. The number of moths thus captured will be surprising. The lamp and screens may easily be removed from place to place, i The lamps should also be used in the stores or pits. Never throw infested potatoes on the rubbish heap. This is only increasing and spreading the pest—providing the very conditions it rejoices in. Always destroy all grubs' by soaking the potatoes in water foF some days before giving to the pigs, or, if not J required for the pig?, soak in the same, way,

before burying ; or, better still, burn the lot. Mr Allan Wight has observed that grubs hatching in the stalk are frequently slow in eating their way to the tubers, and has proved that harrowing off the tops somewhat early and burning them in heaps is very beneficial —always providing that the potatoes have been kept well earthed up Mr French states that air-slaked lime, well harrowed in before planting, has been found of great advantage. He also suggests that potatoes should be so planted as to allow of the use of the strawsonizer to distribute tar- water pr other fluid obnoxious to insects, .and so largely prevent the laying of ejfgs. Mr Allan Wight, of Paei’ba, the well-known entomologist, considers Lita solanella a native of this country, and states that it formerly fed largely on the bulrush or raupp ( Typha angustifolia), and that as this was used for thatching potato houses, the insect soon discovered that the tubers were more to its liking. It is quite pertain, however, that the species have been known for many years as a potato-pest, even in this hemisphere, being reportel from Tasmania in 1854, just**about the date when Mr Wight first observed it on .the raupo. Is it not likely that it was brought to New Zealand in some of the earliest importations of tubers, and took to other plants in consequence of the scarcity of potato ? I have proved by experiment that it will feed on So lanam aviculave , a native of this colony. Tar water is prepared as follows : —|4b coal-tar, boiled in 1 gallon of waters and, after boiling for some time, diluted with 50 gallons fresh water. This must be stirred till well . mixed ; it is then ready for use.