234 



KNOWLEDGE & SCIENTiriC NEWS. 



[Sei't., 1905. 



Conducted by F. Shillington Scales, f.r.m.s. 



The Blacck CurroLnt 

 GaLlbmite. 



Bv Alice L. Lmbleton, B.Sc, F.L.S., &c. 



This disease is caused by a creature only one-half of ; 

 millimetre in length, yet it does enormous damage. 

 Its worm-like body has four short legs near the head, 

 and two long tail bristles. The disease is known to 

 gardeners as " knotting" or "knobbing," and growers 

 sre only too familiar with it; yet gardeners (especially 

 cottage gardeners) are often the worst ofTenders in 

 spreading the pest, for they propagate diseased cut- 

 tings on the ground that those particular trees produce 

 best " fruiting l)uds " — which buds are precisely those 

 that are swollen with the mites, and are wor.se than 

 useless. In reality there is no difficulty in recognising 

 infested bushes, for the buds arc swollen so that they 

 are at least three times as large as normal buds, and it 

 is exactly this that leads to the common error of believ- 

 ing these identical buds to be fine "fruiting buds." 

 While these buds are still green, with a strong magni- 

 fying ghiss, one can see them, when opened, to he 

 literrdly a mass of the parasites. Such buds usually 

 never open at all, but remain on the stems as brown, 

 dry knobs; if not so badly diseased, they occasionally 

 send out one or two feeble little leaves, but never any 

 more. .As the hold of the disease on the plant in- 

 creases, the effect becomes very striking ; the failure of 

 a large number of the buds forces into premature de- 

 velopment buds which normally would open the follow- 

 ing year, making overdrafts in this way on the plant's 

 vitality ; after some time it is incapable of responding 

 to these abnormal calls, for the provision for next 

 year's foliage is already exhausted, jmd the plant dies. 



All the winter the mites, in all stages, from the egg 

 up to adults, are tightly shut up in the buds, and they 

 only begin to come out in the spring — a few pioneers 

 may even be .seen as early as March, but the great host 

 get fret- in .May. In the severest frosts, they are un- 

 harmed in their protected quarters ; in fact, they seem 

 to revel in a hard frost, and it is indeed wonderful hov 

 their tiny bodies resist King Frost. 



During their migration perifxl, which is from the 

 middle of May to the middle of June, they exhibit 

 curif>us methods of locomotion ; the four short anterior 

 legs are ill-adapted for walking, and yet they continu- 

 ally crawl alxiut at a rale of twelve to fifteen times their 

 own length in a minute ; but this only lakes them from 

 bud to bud, at the farthest ; they get carried further 

 afield by passing insects and spiders, to which they 

 adhere first by the stickiness of their bodies, and then 

 by coiling round a hair or antenna in a worm-like 

 fashion, and holding on tenaciously. This can Ix; 

 shown by lightly touching an open, infested bud with a 

 fine camel's hair brush, when the little white creatures 



will be found wriggling among the bristles, yet holding 

 on in a determined manner. Their third method of 

 getting about the world is the most interesting. If 

 cne watches a community of these mites in a bud under 

 a microscope, one sees them continually standing up on 

 their tails, waving the front legs agitatedly ; then they 

 suddenly disappear, and at first it is hard to imagine 

 what has happened precisely. Tlie disappearance is 

 not so accidental as it seems ; the animals are, in fact 

 leaping ! The two tail bristles act as springs, and tne 

 mite covers about sixteen or twenty times its own 

 length at a jump. It is always seen that after standing 

 upright, waiting f( r a friendly insect to carry it off on 

 its unsuspecting body, the mite ceases to wave its legs, 

 remains rigid for a moment, and then launches itself 

 forth, torpedcv-like, into space. It is an entertaining 

 spectacle to watch, for occasionally, by retaining too 

 firm a hold on the bud, the leap is rendered abortive, 

 and the mite simply falls backwards with considerable 

 impetus, instead of making a clear jump. It is a sug- 

 gestive fact that while the mites remain upright for 

 minutes in the still air of a room, yet they can be in- 

 duced to leap at once by blowing upon them. It 

 seems, therefore, that they first try tO' get an obliging 

 insect to carry them away, and, failing this, take 

 advantage of a puff of air to make their blind leap. 

 Perhaps the mile succeeds in "boarding" :i passing in- 

 sect which hovers near enough to fan it by the heating 

 of its wings. 



Having vacated liuir winter home and cr.iwled. or 

 been carried, or Ic.ipt to fresh pastures, the mites 

 enter into the new young buds which are just formed, 

 and so set up the vicious circle again. Myriads are 

 lost, for tho.se which fall to the ground perish, but very 

 few are sufficient to carry on the species for the next 

 year, for they multiply, as soon as they get into the 

 new buds, at an amazing rate. They set up in the new 

 buds at the beginning of June, and by the middle of 

 the month they are all housed (or else they have 

 perished), and the migration period is over, and of the 

 hosts of mites which are turned loose into the world 

 in May, only an infinitesimal number has obtained a 

 footing in the now buds. Reproduction goes on at an 

 almost incredible rate through July and August, and 

 all the winter the tightly-folded buds arc crowded with 

 their unwelcome lodgers. 



The question, of course, is "hf)\v can we check the 

 ravages of these creatures?" and this c.in only be 

 answered by studying their life-cycle ;is given above, 

 and carefully considering at which points they arc most 

 open to successful attack. In very bad cases it cer- 

 tainly is best to cut down the bushes in the winter and 

 burn them on the spot, for the mites are then all safely 

 shut up in the buds, and the bushes can be dealt with 

 in this way without any fear of spreading the pest by 

 shaking them on to other trees, or by .scattering them 

 to the winds. Any treatment of the ground under 

 infested bushes is practicdly unnecessary, as the mites 

 do not live in the soil. ;Vs regards spraying, it is 

 manifestly useless during the winter, when the mites 

 are safe in the buds, and here I may call altcntion to a 

 misleading statement made hy the Board of Agriculture 

 (A 1-93 — I, I'"eb., 1893): — "Spraying. ... in the 

 autumn before the weather becomes cold, and just after 

 the leaves have f.illen, if possible, lliis will econo- 

 mise liquid and l,il)our, and will affect the mites before 

 they get into the buds." I simply quote this in case 

 it is doing damage by being so erroneous, for the mites, 

 as stated above, are already in the new buds in June. 



