NATURE NOTES.

New Zealand Herald, Volume LXVIII, Issue 20762, 3 January 1931, Page 1 (Supplement)

NATURE NOTES.

UNDESIRABLE VISITOR.

BY J. DRUMMOND, F.L.S., F.Z.S

A report by Mr. E. S. West that he caught two individuals of the English small garden white butterfly in Napier is important, in view of the fact that this insect is not only one of the commonest butterflies in the Old Country, but also is very destructive. It lays its eggs on cabbages and allied plants. Tho bluish-green downy caterpillars, ornamented with yellow stripes, destroy vegetables and attack nasturtiums and other plants in flc(wer gardens, becoming a pest and creating a problem that takes a good deal of solving. In a new environment, with the conditions in the Dominion, it is feared this butterfly may become more troublesome in New Zea-

land than even ill Europe, North America and Hawaii. A hope has been expressed that the two individuals are merely odd specimens from a batch acciderttally introduced in the egg stage, possibly -in vegetables in cold store on a steamer that came from Honolulu or North America. The species was established in Hawaii about thirty years ago. This is the first time it has been reported in New Zealand. It has not been reported from any part of Australia.

The male " small while," as it is usually called in England, wears a white costume, with dark clouding at the tips of the fore-wings, and a black spot in the centre of each fore : wing. The female has the dark cloudings, but does not seem to have the black spots. The markings, however, are variable. In this stage, and with this simple colourscheme, the small white is known to every butterfly man in England As if England failed to produce sufficient members of the species, largo reinforcements sometimes swarm into the country from the Continent. Officially, this black and white butterfly, so innocent in appearance, so disastrous in habits, is Pieris rapae.

This butterfly is described as almost a domestic insect, as it is more plentiful in gardens and allotments than in fields, except where the fields grow crops of cabbages and allied plants. As a matter of fact, it is believed that man, by extensive cultivation, is responsible for the small white's plentifulness. An English entomologist has pointed out that man produces the small white's food abundantly. He has taken pains, by selection and cultivation, to make it tenderer and more luxuriant. Taking full advantage of this, the small white thrives on his industry, " and there are times when the voracity of its teeming caterpillars threatens to extinguish that industry by making it non-productive.

The small white butterfly probably has almost the same habits as its close connection tho large white, Pieris brassicae, except that the large white lays its eggs in batches, while the small white lays its eggs singly. In any case, the species are equally destructive and equally undesirable additions to the butterfly fauna of a new, country. The pernicious presence of the large white's caterpillars is evidenced by a cabbage patch reduced to skeletons, only the thicker and tougher ribs being left. The caterpillars finish off one leaf and then migrate to another. One leaf is sufficiently large to feed a whole family of caterpillars for a time. They continue in company until they shed their skins for the third time. Then they separate-, each wandering off to find a leaf for itself.

A fact in the caterpillars' favour and unfavourable to using birds against them is that they are uneatable. Their green coats, with yellow stripes, may be warning colours. In addition, they give off an odour that is very unpleasant from a single caterpillar. From scores of them it is intolerable. Fully fed, the caterpillars migrate to the nearest wall, fence or post, on which they settle, to go through the inertia of the chrysalis stage. To do this, they sometimes have to travel far. They often are seen on door frames and window frames. Mr. E. Step has described the little pieces of silk they spin in which to cast the final caterpillar skin and to become greenish-white or greenish-grey chrysalids, dotted with black and streaked with yellow.

In spite of protective colours and defensive smell, many caterpillars never reach the chrysalis stage, and many chrysalids never produce perfect butterflies. This is the result of attacks by small parasitic ichneumon wasps. These lay many eggs in some of the caterpillars' bodies, undeterred by colours or smells. The parasites, grubs feed on a caterpillar's soft flesh. When a grub is ready to be transformed into a chrysalis, it makes its way out through the skin of the caterpillar, which dies. On reaching the chrysalis stage, the butterfly is not safe. It may be attacked by another parasite of tho same order aa the other one. This deadly enemy lays more than a hundred eggs in tho chrysalis. When these hatch, they consume the material that otherwise would have developed into a perfect butterfly.

Fewer butterflies havo come to New Zealand from the Old Country than might be expected, in view of the facilities for unintentionally bringing their eggs in vegetation and in other ways. English Rod Admirals, related to the New Zealand Red Admiral, have been caught in Wellington and in other places, and there is a single record of the English small tortoiseshell butterfly in New Zealand. A few years ago a writer suggested that, as New Zealand is poor in gaudy butterflies. some of the brightest should be introduced from other countries, to enliven the landscapes and supply a deficiency in this Dominion's insect, life. The danger of experiments in this direction is so obvious that iu hardly needs mentioning. The English small white certainly is not wanted here, and in view of the report from Napier, steps probably will be taken to discover if it, is established, and, if bo, how it may be checked.

The whites, that is, members of the family Pieridae, not necessarily white, are not represented in New Zealand's native fauna, which is just as well, seeing the evil reputation possessed by some of them. Australia has about thirty species, all bearing evidence of a tropical origin, and all with strong migratory instincts. Among them is the travelling butterfly, whoso caterpillars travel steadily across hundreds of miles of country, " sometimes like a veritable snowstorm,'""Dr. R. J. Tillvard states. Another Australian wears a narrow 6carlet sash, and is the most brilliant member of the family. The Painted Lady in New Zealand is the same flighty Painted Lady that flies in vast numbers in the Old Country and in Europe. The Wanderer is another butterfly that includes New Zealand in its far-flung kingdom.