WHITE BUTTERFLY PEST

New Zealand Herald, Volume LXXII, Issue 22197, 26 August 1935, Page 13

WHITE BUTTERFLY PEST

CONTROL BY PARASITES LARGE NUMBERS RELEASED GOOD RESULTS EXPECTED The appearance of the white butterfly in several parts of the country at an unusually early stage of the season is giving concern to many market gardeners and Horticulturists who are setting out plants for the main crop. The loss from the ravages of the pest during the past few years has been beyond computation, but it has been estimated at thousands of pounds. Many acres of ground planted with cabbages and allied plants have been abortive in production, on account of the ravages by caterpillars, which are an evolutionary life-stage of the white butterfly cycle of propagation. However, according to observations and reports collected by the Department of Agriculture at its research centres, both in the North Island and South Island, there is reason to believe that the alarming increase in the number of white butterflies has been definitely checked by the cultivation and liberation of thousands of insect parasites.

Dr. W. S. Hill, the agricultural instructor at the Otahuhu Technical High School, where a special house and equipment for the cultivation of insect parasites were constructed about 18 months ago, stated at the week-end that the pest was being successfully combated. Referring to the chance introduction of the white butterfly to New Zealand Dr. Hill said the climate and the abundance of the cabbage family plants grown in the Dominion were favourable to the rapid breeding and spread of the pest. With the exception of birds the white butterfly had no natural enemy in New.Zealand to check its development, and the consequent ravages. Parasites From England

Dr. Hill said Mr. J. Muggeridge, the Government entomologist, had arranged for suitable insect to be forwarded from England. Two types of parasite were received and bred at the Plant Research Station at Palmerston North. One parasite, Apanteles Glomeratus, laid its eggs in the caterpillar of the white butterfly and the maggots lived on the caterpillar, which died. This larval parasite had been very effective in England, where up to 95 per cent parasitism had been observed. It was, however, more difficult to breed under controlled conditions than the other parasite, Pteromalus Puparum. The latter insect laid its eggs in the pupae, or chrysalids, of the white butterfly, continued Dr. Hill. The insects devoured the contents of the chrysalids and emerged when full-grown as minute flies, slightly larger than the ordinary sandfly. This was the parasite which had been bred and liberated in •large numbers at Palmerston North and which had successfully reduced the numbers of white butterflies in the Hawke's Bay and Manawatu districts. In the South Island the Cawthron Institute had carried out similar good work. Auckland District Operations Dr. Hill said that with a view to extending the work in the Auckland district and to give beneficial instruction to tho boys in the agricultural classes at the Otahuhu Technical High School, a special glasshouse had been constructed by the students. _ The school committee and local bodies in the district V.-kI co-operated in raising funds for the work and the installation of the essential equipment. About 10,000 of the second type of parasites were reared and liberated through the school activities last year. The liberation was conducted at various points between Auckland and Clevedon, including tho large market gardening areas around Panmure. The tiny flics had become established at many points, and would increase under natural conditions during the coming year. Further batches of the parasite insects were being reared at tho school, whero there were facilities for rearing up to one million parasites each year. The opinion was expressed by Dr. Hill that the damage done to cabbages and, allied plants by the caterpillar cf the diainond-back moth was freqnentlv as great as that done by tho white butterfly, and the ravages of the moth pest were often erroneously attributed to the white butterfly. He said the introduction of a parasite which would control the diamond-back moth would be most welcome and of inestimable value to tho Dominion.