White Butterfly is Doomed

Manawatu Times, Volume 63, Issue 59, 11 March 1938, Page 6

White Butterfly is Doomed

Parasites Increase Rapidly NOW 90 PER CENT. EFFECTIVE The silent warfare waged between the white butterfly and the parasite which was imported to counteract its activities has appeared throughout the latter part of the summer to have resulted in victory for the butterfly, but according to the observations carried out by Mr. C. J. Hainblyn, Fields Superintendent of the Department of Agriculture, the tide is rapidly being reverouu. About three weeks ago in the Mount Stewart district it was possible to col lect largo quantities of the butterfly chrysalids from posts and battens from fences around swede and rape crops said Mr. Hamblyn. If tho parasite had not been present these would, within a few' days, have hatched out as adult butterflies ready to play their part in multiplying the pest. The parasite was present and could bo seen at work lay i°g eggs in these chrysalids, but considerably over 50 per cent, of the chrysalids had not been attacked and would therefore produce the butterfly. An inspection made a few days ago revealed a vastly different state of affairs, lie continued. The parasite had apparently increased remarkably in numbers, and it was estimated that up to 90 per cent, of the chrysalids had been parasitised. This was forcibly demonstrated by a collection of some 500 chrysalids, which were removed and confined under glass. After three day's only five butterflies had emerged, whereas hundreds of parasites made their appearance. These active little insects about a-quarter of an inch long on coming out of the chrysalid, where they have developed bv making use of the carcase of the caterpillar in developing from the egg to the adult, immediately begin to lay their eggs in fresh adult caterpillars or chrysalids. “It is more than probable,’ said Mr. Hamblyn, “that throughout the southern half of the North Island, where the white butterfly is continually reported to be doing considerable damage tj crops of the turnip family, the parasite is present and the same state of affairs as was found in the Feilding district applies. This being so, it is not likely that further liberations of relatively small numbers of parasites would do any good at this stage. “Farmers interested are well ad vised to make a small collection of chrysalids, place them under glass and watch for the proportion % of parasites hatching out to butterflies." “The failure of the parasite to overtake tho butterfly in the early part of tno season cannot as yet be accounted for. The possibility of this parasite actually being reduced by a parasite o r its owu lias not been overlooked by Mr. J. Muggeridge, entomologist al Cawthron Institute, v here the work of breeding the paras cing done, but up to the jiresent i. of this nature lias been found. It \.oald appear that the exceptional weather conditions or last summer and autumn gave the parasite a greater check than the butterfly, and from very small numbers at the beginning of the season it has taken some time to increase to the extent ol overtaking the butterfly, which lias had everything in its favour for some months. “In all cases where control of an insect pest is maintained by a parasite," lie concluded, “there is a fluctuation in the efficiency of the control to the extent that occasionally the pest increusos enough to do considerable damage. ’ ’