WHITE BUTTERFLY

Manawatu Standard, Volume LVII, Issue 181, 2 July 1937, Page 6

WHITE BUTTERFLY

PARASITE’S GOOD WORK. VALUE TO CRUCIFEROUS CROPS. “The parasite has unquestionably played a oig part in the control ot the white butterfly. Its monetary vaiue cannot be estimated, but 1 am inclined to tinnk tnat without it cruciferous crops (turnips, rape, etc.), of wincli there are 060,000 acres in New Zealand, could not be grown now at all "ere it not for the work of the parasite. In the foregoing statement Mr J. W. Muggeridge, Government entomologist attached to the Plant Research Bureau at Palmerston North, to-day reviewed in brief the results of the introduction and propagation practically right throughout New Zealand ot the Pteromalus puparum, an insect native to England and the Continent, as a means of combating the white butterfly which some years ago wrought devastation among some farm crops. „ “The butterfly seemed to be increasing toward the latter part of last season,” said Mr Muggeridge, “and it appears that that was largely due to weather conditions. In my opinion the butterfly is better able to survive the wet conditions than the parasite. In dry years 90 to 95 per cent, of the butterfly chrysalids, whether collected from posts, grass or other . vegetation, have been found to be parasitised, but in the wet years, while the parasitisation of chrysalids from dry spots has been substantially the same as formerly, the parasitisation in wet localities (such as damp grass and undergrowth) has dropped down as low as 50 per cent. As soon as dry conditions are encountered, however, the parasitisation immediately goes up again. One would imagine that at the beginning of this coming season the butterfly may be a bit more numerous than formerly, but if it is a drv season there should not be much to fear from the butterfly, as the parasite seems to do particularly well under dry conditions. “The spread of the parasite is now practically Dominion-wide,” said Mr Muggeridge in referring to a map ot the two islands showing where the parasite has been liberated and how it lias spread. “We think it might still be necessary to liberate other supplies where it is not so well established, but apart from that it is now just about general. We do not know how it will respond to cold conditions in the southern end of the South Island, where it has not touched to as great an extent as in other parts, but it should be just as- effective there as it is in other districts.” Questioned as to whether the parasite had been noticed attacking anyliing else, Mr Muggeridge said that it had not been rearea on any other host hut the butterfly. “Unless we were very sure of our grounds we would not have brought it into the country, ’ he said “Anything that it might attack would be of the same order in butterflies and moths. In that order are some of the most injurious to the crops of mankind, so if the parasite did attack anything else but the white butterfly it would be all to the good. “We are not breeding the parasite to the same extent a-s formerly, but we are breeding a fair number for this year, although I do not think the same numbers as we have been liberating m the past will be necessary this season> “The parasite is considered to be oi more importance from the point of view of the control of field crops, rather than household gardens. The degree ot control required for field crops is not nearly as high as that needed m a garden. A few caterpillars of the white butterfly will ruin a garden crop as far as the housewife is concerned, but that same crop will be eminently suitable for farming purposes. The cheapest method of controlling the w.iite butterfly in the garden is the use of the dust-gun with a suitable powder, of which there are a number of proprietary lines on the market,” Mr Muggeridge concluded.