NEW ZEALAND FLAX.

Manawatu Herald, Volume XXXIX, Issue 1738, 17 July 1917, Page 4

NEW ZEALAND FLAX.

PESTS AND DISEASES. [Continued from Page I.] gether. They do not frequent those leaf-tubes lying on the ground, since the latter as a rule are damp, the larvae certainly preferring the dry shelters. Immediately after flax lias been cut the larvae may also be found in the axils of the outer dead leaves where dry. It is usually found that where there are practically no accumulations of leaftubes —which is usually correlated with the presence of moisture the larval attacks are comparatively absent. When Xanthorhoe is present and the leaf is considerably older than usual the accumulated attacks of the previous years give a very badly damaged appearance lo the’leaf—more so than if the flax had been cut earlier. This is seen at Pallia and on the mountain-flax of Arthur’s Pass. If during a flood the water does not completely cover the flax-bush-es or completely immerse the loaftubes, the larvae will still shelter in the unsubmerged portions of the later, or hang suspended by threads amongst the denser foliage. An experiment carried out in' the laboratory showed that the larvae do not usually become agitated until (he water has touched or covered the head, so that if the larvae arc resting perpendicularly, -head uppermost, the whole body may become immersed before they attempt to crawl out of the reach of the Avater. When resting head downwards the tendency is, when the water reaches them, to crawl downwards to some opening in the loaf-tube before attempting to reach safety. As the water rises the larvae move higher up the leaf, eventually holding on to the apex when it becomes immersed, and, standing more or less erect, feel round for some further support, such as a floating leaf, twig, or even a bit of grass, which, if present, is immediately grasped. A larva will live tor a considerable time upon such a float, but not in the direct sunlight. K no such support is to be had, the larva will eventually float oil on the surface of the water, where, if it continues struggling, it will soon sink and perish within ten minutes. A shorter immersion of less than two minutes docs not, as a rule, seem to ailed the vitality of the larvae. A specimen was placed upon a flax- leaf surrounded at the base by water. This larva made immediately for the least, shelter afforded |,y the slightest (urn of the leaf, and if turned to the sunlight would promptly move to the opposite side. It remained thus for seven days without feeding, and practically inactive, after which it dropped off and w.is drowned. By the morning of the sixth day this specimen had become much darker in colour’, and, as was expected, underwent an eedysis in the evening, the old skin remaining fast to the loaf; the larva was of the normal reddish colour. On the following day it perished as stated above. Another specimen when disturbed by lamp-light while feeding looped off to shelter, where it was content (e remain with just its head hidden while its body was exposed. Specimens sheltering in this manner have not yet been found under natural conditions. Larvae when alarmed usually drop to the ground or amongst the (tax-leaves; at times they will fall by means of a silken thread. Colonies of this species will migrate from place to place. In the case of a badly attacked patch of llax about four years’ growth which had just been cut, and where accumulations of leaf-tubes abounded, the larvae moved into an adjoining block and commenced their depredations, In a block which had been cut two months previously, and where there was a fresh growth of flax, several fresh and narrow incisions wer-e observed. On examination a number of small emerald-green larvae about .}-in. in length were discovered. Some of these were kept under observation, and it was found that about four days they had assumed the characteristic reddish colour of the larvae of Xanthorhoe praefectata. Generally in the daytime (hey were found sheltering between the outer dead leaves at the butt of the plant. When about j-in. long the larvae will burrow into the dry or very slightly moistened ground and pupate. The greatest depth any were observed to burrow in the laboratory was about 2A -in. Sometimes where (he conditions arc favourable a larva may pupate between two dead leaves on the ground, where it can gather together nodules of earth which it builds around itself, forming an earthen cocoon; but this is also done in the ground. The cocoon measures less than if-in. in length and nut quite as broad. The head of the larva blocks the only opening. In these shelters the pupae are invisible on account of their close resemblance to nodules of earth. Dampness to any extent is fatal to (ho pupae. Several were kept in a sheltered place but exposed to the rain, and were frequently soaked;

the pupae came to nothing, and eventually bore a shrivelled appearance. The larvae of Xanthorhoe first appear during the beginning of August, and in increasing numbers in the following months till about the end of December. Those feeding during March, April and May are the larvae which hibernate in the leaf-tubes and the offspring of the moths which appeared in the summer. Apparently the individuals hatch at different periods, as young and old are found attacking in the same patch of ilax. This would he less so in those colder localities where the seasons are more sharply defined. In tlie immediate vicinity of bush areas, particularly whereThcre is a dense undergrowth or scrub with the flax, the larval attacks are less marked. This may be partly due to the presence of a greater number of insectivorous birds and parasitic insects which arc found in those bush areas, and not deeper in the swamp, where there are no such shelters and where these birds and insects arc not nearly so abundant, and partly to the increased moisture caused by the presence of such bush areas. Two cages for birds were erected in the Makerna Swamp, but owing to the exceptional rarity of the larvae during the past season extensive experiments and observations could not bo carried out. The reason of the larvae being so scarce was probably due to the heavy floods during August, when the larvae were first appearing. A patch at Tokomaru which was the most severely attacked and had been kept under observation was unfortunately destroyed by fire. Xanthorhoe pm elect a has a distribution throughout New Zealand, and is found not only at sea-level bat at an elevation of ■1,500 ft. Tim imagines may be found from November to May. ME LA NCH R A AST ER ()PASTIS. The larva of Melanchra stcropaslis is most abundant upon the hillllax of Southland, but is found 1 hronghoul New Zealand. Its manner of attacking too leaf dittoes from that of Xanthorhoe; instead of removing the lower epidermis this larva cuts notches from (lie edge of I lie leaf, removing the fibre as well as the epidermis. The prevalent idea was that those notches were caused by I lie wind rubbing (wo leaves together along . (he edges, saw-fashion. The general habits of Melanchra larvae resemble (hose of Xanlhoritoe in (lie maliner of seeking shelter in leaf-lubes, but the former are less sensitive to tight than the latter, and are found in both moist and dry localities practically throughout the year. They sometimes pupate in the ieaf-tnbcs, but (hough (hey also burrow in the ground they have not yet been observed to impute there. Those larvae when full grown arc larger than those of Xanthorhoe, and have a pinkish colour. The larvae of Xanthorhoe and Melanchra may be distinguished not only by colour and manner of attacking the leaf, but also by tho presence on the latter of four pairs of pro-legs just beyond the middle, as compared with the single pair on the former towards the posterior end. In dry flax areas where the larvae exist it will be found that though the ground will be soaked by heavy rain-showers there is usually a, dry bolt surrounding the bushes under (he shelter of the leaves, Imti not in immediate contact with the base of tbe plant; the soil adjoining the base is sodden owing to the rain water running down the leaves. The dry leaf-tubes, which are usually hard and firmly-rolled, remain perfectly dry within. (ECETIC US OMNI VO 11OUS. The larva of (Eeelicus omnivorous is found throughout New Zealand, and is active most of the year. As yet it docs no serious damage to the flax, and is never found in any numbers in those areas. The larva varies considerably in length, and lives in a case which it carries with it. It feeds during the day. 'Phis species removes the lower epidermis of-the flax-leaf in circular patches, varying from small to very large areas. Sometimes not only the lower epidermis, but also the fibre and upper side are devoured, thus leaving small to very large holes in the leaf. In one instance a specimen measuring fully 2 A in. in length had cut a large circular hole some 3 in. in diameter. [To be continued in Thursday’s issue.]