MUSEUM NOTES

Southland Times, Issue 23499, 4 May 1938, Page 12

MUSEUM NOTES

HABITS OF WHITE BUTTERFLY

No. 7

The very dry summer which Southland has just enjoyed has not been without its drawbacks. Towns not supplied with a good service have been short of water, and even Lake Monowai has been unequal to the draw-off for power purposes. However, this week s article is not to discuss these matters, but to give some information on certain forms of insect life that have been affected also by the good season. The white butterfly (Pieris rapae) has been reported in increasing numbers from many parts of the province, and as there seems to exist a good deal of misunderstanding about this latest imported pest, some facts are given. The butterfly in itself, is incapable of doing any direct damage to plants. It is the caterpillar, the only stage of the insect in which any growth takes place, that is responsible for all the damage. The butterfly lays the eggs on various plants, passing over many which to it are unattractive, and generally choosing a cabbage or cauliflower, or perhaps ever a wallflower which is closely allied botanically. The eggs quickly hatch into caterpillars and then the trouble begins. At intervals during the caterpillar’s growth the skin is shea, and finally when fully grown and having done all the damage of which it is capable it turns into a chrysalis. From this stage, if the weather is suitable, it soon becomes a butterfly. With winter coming on the chrysalis remains unchanged until the spring, and is proof against bad weather and a fair amount of frost. The white butterfly is one of the most abundant of British insects, ana also occurs in Europe, North Africa, Central and Western Asia, and North America. The species did not exist in New Zealand before 1930 when it was intro- < duced, probably accidentally, into Hawke’s Bay. An ichneumon fly (Pteromalus puparum) has been introduced to combat the white butterfly pest in New Zealand. It is about the size of a sandfly, and seeks out the caterpillar and lays its eggs in it. The eggs in turn hatch out into maggots, which feed on the internal organs of their host, ultimately destroying it. DIAMOND-BACK MOTH Another serious destroyer of cabbage and turnip crops is the Diamond-back moth, and it has been reported from many parts of the province. Cabbages, in particular, have been badly attacked, so much so, that, many people will have no winter cabbages at all. As with the white butterfly, it is the caterpillar that causes the damage. The caterpillars drop to the ground quickly if disturbed, are voracious feeders, and change from the chrysalis to the adult form in a few days. Some' reared in the Southland Museum hatched out in 24 hours. Thus it will be seen that they multiply very quickly. Perhaps the most alarming feature is that a crop of turnips having become debilitated by the activities of these caterpillars, becomes a ready prey to more serious diseases, and large areas can thus be ruined. As turnips are generally fed off in New Zealand it will at once be apparent that there will be a large amount of affected turnip material left on the various affected paddocks. The driving of sheep from an infected paddock to a healthy turnip crop will also disseminate vast quantities of spores, and the healthy crop will soon become mfected also. Care would need to be taken in the next season to sow turnips in perfectly clean ground, otherwise spores in the ground will rapidly infect the young crop. The most serious disease caused through the debilitation by. Diamond-back moth larvae is known as tumip-phoma rot.

EUCALYPTUS TORTOISE BEETLE A single specimen of the Eucalyptus Tortoise beetle was sent into the Southland Museum for identification from the Winton district. Its scientific name is Paropsis dilatata and it is a native of Australia which was introduced into New Zealand many years ago. Along with its larvae, it is found on the foliage of eucalyptus trees throughout Canterbury and Otago. The larvae are very destructive on eucalyptus and wattles. The great genus Paropsis contains hundreds of Australian species all of which do considerable damage. Plantations about Dunedin show the ravages of this beetle and its larvae but more evidence is needed before it can be definitely stated that they are on the increase in Southland. The eucalyptus in the city reserves show no sign of being affected.