NATURE KNOWLEDGE THE DIAMOND-BACK MOTH

Press, Volume LXXI, Issue 21416, 7 March 1935, Page 2 (Supplement)

NATURE KNOWLEDGE THE DIAMOND-BACK MOTH

Goruori Bennett. Riverside, Ashbuiton, has submitted a larva which he correctly thought to be that of she Diamond-back Moth, Plutella rr.aculipenni.-i i-Plutella cruciferujuim».

The moth a a member of a small, but widely distributed family < Plutcllidao of small inoths, with narrow wings fringed with long hair; the larvae are leaf-feeders. The wings of this moth expand about 13 millimetres inch); the fcrowings are darkish grey, with 'af-e triangular whitish markings on the hind margin; the hind wings, a uniform grey, are fringed with very long hairs. When the moth is

»• rc-i the wings are held tent-wi.se arcsinit the sides and over the back, • ? 1 1- triangular marks thus coincide ■ form three diamond-shaped Miarkingo; the antennae are held, !• straight out in front. There is, however, a certain amount < f variation in the coloration of •!;<• species--in .some specimens the !< rewinds are decidedly blackish, :•/ others they are brownish; and :i:>r whitish markings are sometimes rather indistinct. 'Fig. A shows <h<, moth with the wings expanded, i B ;s a rough sketch showing -;tion of rest.) larva <Fjg. Di is green in rff.vur, and about 13 millimetres in :< '.h; ;t feeds from the under- • * .-face of the leaf, and often does great damage by extensively ri'i'Dh:? the foliage of such plants *'•> cabbages, rape, kale, swedes, tur- • and mustard * all these plants '•'•joujf to the family Cruciferae). '.Vneii di.tui'ijed it often drops to f' e grcur.d cr lianas .suspended by ■ tilkcn thread paid out from the •p:nrerc-t, which situated under the forward perl of the head (see ['• •; F ' r ' th»» Ic.r \ n ea>» regain the i'-; f b.mp.'y by cambir.g the thread. Pupation <i.e, the change from '-irva into pupa; occurs within a ■'lken cocoon of open white netting, which i:, attached to the undersurface of a leaf or some such similar convenient position. The Pupa 'i <'i. C), about 6 millimetres in length, is brown. This- cosmopolitan species has long been a pest of considerable •economic importance, but artificial control by means of spraying is ra il tte! ; of some difficulty cmuig to the larva's habit of feed&f- K« m i he und ersurface of the dmary methods of spraydefsurfaces of the leaves wea tail to get a thorough drench-

(By A.V.C.)

ing of spray and hence many larvae escape. Measurements—lt is generally considered preferable to use the metric system of measurement in dealing with small natural objects. Butterflies and Moths Probably many of you have been puzzled at times to distinguish between butterflies and moths; you have perhaps been told that certain characters at once distinguish the butterfly, and other characters immediately distinguish the moth, but. nevertheless, you may still experience difficulty. And such difficulty is quite understandable.

For the non-scientilic person there is 110 reliable method of differentiating between butterflies and moths; in dealing with even the limited number of New Zealand members of the order (Lepidoptera) to which the butterflies and moths belong, any person not closely acquainted with the beasties might easily reach conclusions differing greatly from those of the scientific investigators; in other regions of the world the possibility of such difference if much greater because there is a large number of species failing to conform to the set characteristics for either group. As for the

scientific persons—entomologists (bug-hunters) are divided in opinion; some retain the division, as a scientific one, of the order into the two great groups of moths and butterflies; others favour the omission of such division. So far as the characters at present in use are concerned, the division is a very artificial one, and each character employed is open

to many exceptions; the division really has very little, if anything, to commend it. It seems very probable that the entomologists who retain the division based as at present do so more in the spirit of conservatism than from any viewpoint of utility or convenience. If a scientific division of the order in place of the present artificial one be necessary, which is very doubtful, it is probable that such division could be based on characters more consistent and reliable than those at present in use for the purpose. So for the non-scientific person the matter virtually comes to this—it is really immaterial whether you call a member of this order (Lepidoptera) a moth or a butterfly, so long as you assign the creature to its correct order and to its proper place in the scheme of things; certainly the entomologists cannot supply you with an invariably workable means of distinction.