WHITE BUTTERFLY PEST

Evening Star, Issue 22879, 10 February 1938, Page 14

WHITE BUTTERFLY PEST

HOT SERIOUS IN OTAGO DESTRUCTION CAUSED BY CATERPILLAR In recent weeks much concern appears to have arisen as the result of the reported presence of the white butterfly in Otago. However, steps are being taken to combat the pest, and the Fields Division of the Department of Agriculture has arranged for the liberation of parasites in various parts of the province. Although the white butterfly is wellknown in many other parts of the world, it made its first appearance in this country in 1930, when it was discovered at Napier. Since then it has multiplied, especially in the North Island. It has a wing spread of about Sin and is of an “ off ” white colour. The male has a single black spot on the middle of each front wing, while the female has two spots on each front wing. Further distinguishing marks characteristic of both sexes are a spot on each of the hind wings. The caterpillar is of an intense leaf-green colour and has a velvety appearance due to a large number of closely set hairs all over the body. Down the middle of the back there is also a slender orangecoloured stripe, while other broken stripes appear on the sides of the body. The pupa or chrysalis measures about fin in length and is usually to he found attached to buildings, trees, or fencing posts, from which it as a rule takes its colour, although it is often of a greyish appearance.

The only one of its three stages in life in which it causes damage is the caterpillar—the butterfly itself has no mouth parts suitable for damaging foliage. The caterpillar is essentially a pest of cruciferous crops, such as cabbage, radish, cauliflower, and rape, although there are known instances when it has attacked lettuces. The injury that it causes consists of the indiscriminate destruction of leaf tissues. In the case of cabbages and cauliflowers, which are its favourite object, the mere skeletons are left when the attack is severe. On the whole, the damage that the caterpillar does is very similar to that carried out by caterpillars of the common, hut seldom seen, diamond-hack variety.

So far as the damage caused by the white butterfly caterpillar in Dunedin is concerned, it is felt that it is negligible at the present time. The fact that the butterfly is conspicuous has no doubt given many people an exaggerated impression of its significance. There is little doubt that in Dunedin there are much more serious pests present in the aphis, slug, and wireworm, but, as these are not conspicuous, comparatively little notice is taken of them.

It is doubted whether any resident of this city has actually seen damage caused locally by the caterpillar of the white butterfly; that resulting from the work of the catterpillar of the diamondback moth is very similar to the butterfly caterpillar’s efforts, and may easily be mistaken if the caterpillar is not actually on the leaf when it is inspected. , Following the.discovery of the butterfly in Hawke’s Bay, the Department of Agriculture arranged for the importation of a parasite, which is somewhat like a miniature wasp. It lays its eggs in the caterpillar, and when these hatch the resulting grubs are seen when the chrysalis, which has been completely destroyed, is broken open. Before the parasite was liberated every care was taken to ensure that hyperparasitisation would not take place. That these parasites have done excellent work is shown by the fact that in one district where over 22,000 pupae were collected 96 per cent, were found to he parasitised. Although these parasites have done so well, it cannot he hoped that they will entirely eradicate the white butterfly.

The only factor that will influence the value of the parasites to he released in Otago will be the number of existing caterpillars. If the latter are in large numbers the parasites should have no difficulty in locating them, but if they remain in small numbers, as at present, the parasites may have trouble in finding them. At the present time there does not - seem to he any prospect of the white butterfly pest becoming serious in and about Dunedin. Experts are agreed that if the white butterfly were going to multiply in southern districts, it would have done so before now, considering that it has been in the Dominion for eight years.