THE HESSIAN FLY.

Wairarapa Daily Times, Volume XV, Issue 4328, 27 January 1893, Page 2

THE HESSIAN FLY.

Notes by a Scientist

Mr G. V. Hudson, the well-known etomologist, sends tho following inte» resting letter to the Evening Post:— In view of tbe recent occurrences of

the Hessian fly (cecidomyk deslrudor) in the Masterton diotriot at several placeß in tbe south of New Zeax land, a few facts relating to the life, bistory, and meanß of iktroyMk the pest may perhaps be of some ihte- ' rest. It should be borne in mind that tbe presence of the Hessian fly in New Zealand is no new thing. When, investigating an attack in Uarton in 1888, under instructions from 'Government, I was informed by several farmers whose grain had been more or less affected, that they had observed tho fly, or rather its effects, for seven or eight years previously. This faot would seem to indicate that the climate of New Zealand is not congenial to its ready propagation, or else that the thousands of parasites which were swarming in its locality, to which I shall refer later on, effectually hold it in check. In a paper entitled, "The Life-history of tbe Hessian Fly," read by Mr .Frederick Enook, F.E.S., bef.Wrffyomological Society of Londoner February, 1891, that gentleman gives a most exhaustive aocount of the iuaeeb's habits, from the egg stage onwards. As his observations are entirely original, and as they are certainly some of the most recent that have been mado, I have taken a few notes lrom his paper, supplementing tbem by my own observations on the insect, made at Marton in 1888. Like most inseots, the Hessian fly is very prolific From the investigation of a large number of females in the aot of egg-layir.gj£?jMflHfl Knock concludes that the from 100 to 150 eggs, distributing them over many plants. Thlß is a much greater number than was formerly supposed, 80or OO.being the usual number stated by previoußwriters. The female fly, iib a rule, lays her eggs with the head end pointing downwards towards tbe main stem, so that when the tiny larva emerges it is started from its infancy in the right direction on its journey downwards. Guided by the longitudinal riba of tun leaves, it reaches tho stem, round which the leaf ebeatb is olosely [ wrapped, but not too tightly to prevent the larva forcing its way to the base of tbe sheath, which is generally : that of the second joint above the ground. The injury to the plant then ' commences, the young larva bringing , its head and mouth up to the soft I stem, and imbibing tho life-juice for _ its maintenance. The numhor of larva) present in each stem varies according to the severity of tbe attack. At Marton in 1888, there were often ! bb many as 8 or 9 inßects feeding on each blade, This ince3sant drain on the plant generally causes tho stem io fall over through weakness, and it is t at this stage the attack of the Hesßian _ fly arrests the attention of the farmer. An examinationof the "fallen wheat," < as it is usually termed, reveals the presenco of a number of minute brown objects, almost exactly resting a flax seeds, closely stowed away»je.- ' tween tho stalk and the shoathing leaf. Thcso are the pupa? of the Hessian fly, and their remarkable resemblance to flaxseeds, which has _ been observed and suggested as a « means of identification, by all writers on the subject, rendors themextremely t easy of recognition. It is m this stage - t that tbe insect is best known, the in- . jury to the crop at an earlier date not » being noticeable, - whilst the conspionn ous and characteristic nature of the "flax seeds "on the bent cornstalk at once causes them to be as- , sociated with tho damage. Tho flax seed or pupa state is ■as- ' siimed about three weeks after the * eggs aro deposited. The duration of •' the pupa state appears to be very r variable. Some of the flies emerge a Jj fortnight after their change into the flax-seed condition, whilst others r under less favourable circumstances '' remain quite two years in the pupa stale. This power of resisting adverse conditions must not be lost sight of in any efforts to cope with the pest, As P a rule, two broods occur in tho year, but it is thought that in a damp soason there may occasionally be a third ' one. With regard to remedies, one of the simplest was that which I believe I first suggested during the attack of 1888, w. to abstain from growing till cereals on the infested areas for somo 7 time, in order that tho insect may bo starved out. To bo of service this should be continued for at least three ' years, as the Hessian fly has been , proved to exist in a dormant condi- ' tkra,.as a pupa, for moro than twe^"' years. If not successful in aotuslr)* a exterminating the inseot, this methorl . x would undoubtedly very muoh dimin« ish the pest for a long time afterwards. Damp weather is favourablo to the development of this inseot, and it may be that the damp and mild ,' winter has had something to do with l ' the present visitation. That tho olimate ol New Zealand as a rule is not ' very congenial to tho Hessian fly may perhaps bo assumed from tho fact that I although stated, to have been present ( in the Kangitikei for upwards of twelve years, no very serious attack has yet been experienced. , During my observations on the f Hessian fly at Marton, I noticed large numbers of a small hymenopterous ' insect frying about among the infested j wheat, and specimens of this insect j were subsequently reared by both Mr J Maekell and myself. Tbese paiasitcß j have probably been the most powerful agents in keeping down the numbers ofthe Hessian fly> As tajjiirning the crop or stubble of course, ' in the case of the ' and expensive remedy, whilst colleot- ' ing and burning the stubblo and _ screenings involves a good deal of ' labour. It also kills any parasites ' that may bo present in the pupie of tho Hessian fly at the time. Dr. ! Packard, a well known economio en» , tomtlogist, condemns this method on ' these grounds, and advocates the ' preservation, distribution, and artifi*. j cial breeding ot these parasites as the best remedy for the ravages of this insect. These hymenopterous para- | sites, of which there are several speoies, can easily bo distinguished from tbe . Hessian fly. The latter is a two* , winged gnat, with a considerable reI semblance to a small mosquito, except ( thfit it has no visible proboscis, whilst , the parasites aro very much smaller ; four.winged flies, with short BtoutV"' 10/?s and hard shining black or bronzilL | tidies, They take dioit qniok flights 7 ?— , aDOU t the wheat, appearing to hop I ratbor than fly from stem to stem. It ( is probable that they are still abun* . (lant in tho Marton district, and are | very likely present wherever the Hes- ' sian fly occurs. If not, they could , easily be introduced to the infested areas.—l am, etc, (J. 7. Hudson,