224 



KNOWLEDGE & SCIENTIFIC NEWS. 



[Sept., 1904. 



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



CoccidoLe. 



With Notes on Collecting a^nd 

 Preserving. 



By /Xlice L. Embleton, B.Sc. 



As greenhouse and garden pests, " scale insects " and 

 " mealy bugs " are only too well known to the florist 

 and horticulturist, for they abound in most climates, 

 particularly in the tropics. They are easily dis- 

 tinguished from other insects, being strikingly different 

 in many ways. The brown " currant scale " 

 (Leca7iium coryli) will serve as an example; or the brown 

 " peach scale " {Lecatmim persicum), both very serious 

 enemies to the fruit-grower in this country. The de- 

 scription applies almost as well to the dreaded vine 

 pest (P. I'iiis), which plays much havoc in wine-pro- 

 ducing countries, and equally truthfully to the common 

 brown scale on ferns and palms grown indoors 

 [Lccaiiiiim hanhphaericuni). These insects, and many 

 others, are very similar in appearance, and also agree 

 in .being of considerable economic importance. A 

 sketch of the scale found on the bark of currant bushes 

 will suffice to illustrate the general nature of these 

 creatures. In the adult stages they are firmly fixed to 

 the host plant, and appear as small brown convex 

 elevations, about one-eighth to one-sixth of an inch in 

 length; the convex dorsal shell still bears some trace of 

 a keel-like ridge running from back to front, sending 

 out transverse branches connecting this keel at right 

 angles to the limiting circumference. This description 

 is of the female, for the male is winged, is less common, 

 and has but a short life, so it may be left out of the 

 present description. To return to the adult female of 

 Lccanium coryli, it is found that under this hard, shining 

 brown carapace she lives and breeds. In the winter 

 her enveloping shell fits close to the surface to which it 

 is attached, and it needs care to remove the creature 

 uninjured; but in July one finds that the rounded 

 mother-shell is nothing but a tent covering a heap of 

 substance that looks like pink dust, but which is, 

 in reality, the mass of eggs of the coccid. In a short 

 time these eggs give rise to small yellow six-legged 

 larva?, which move about restlessly all over the parent 

 plant. It is interesting to note that the larvae of most 

 species seek to avoid light by creeping into crevices in 

 the plant. At the end of about ten to fourteen days 

 these active larvas stttle down, and become fixed to the 

 host plant by means of the long thread-like proboscis 

 vhich is then buried dreply into the vegetable tissues; 

 the nourishing sap being drawn up bv this apparatus. 

 The creatures have now assumed the characteristicallv 

 " scale " mode of life, the white waxy powder which 

 has until now coated them disappears, and gradually 

 the mature condition is reached, and the cvcle begins 

 once more. 



In different species there are, of course, minor dis- 



similarities, but in these characteristic features many 

 species are alike. Some species, such as the currant 

 brown Lecanium, produce at least three broods of young 

 in the year. 



Dactylopitis destructor or D. longiftUs will serve as an 

 example of mealy bugs. They are also easily 

 recognised, for they possess such distinctive charac- 

 teristics that there is no fear of ambiguity in identifica- 

 tion ; this is more particularly the case with 

 D. longiftlis, which is marked by the long white 

 posterior filaments in the female. The most common 

 species in our greenhouses is D. destructor. Though 

 they are such common and destructive insects, yet 

 there is very little literature to be found on the sub- 

 jects either of their life-history and habits, or morpho- 

 logy. However, it is known that they are very prolific, 

 the female of D. destructor laying usually from 400 to 

 600 eggs at a brood. They are embedded in a white 

 flocculose network of waxy threads, which cover the 

 eggs and quite effectually protect them from attacks of 

 other insects. The female feeds all the time she is 

 depositing her eggs, and the end finds her nothing more 

 than a little dry piece of dead skin, with the mass of 

 eggs behind her. Before egg-laying commences she 

 measures about 4mm. in length. In two or three 

 weeks the young hatch out of the eggs, and after a 

 day or two they leave the protection of the white floccu- 

 lent covering and begin to wander about actively. 

 They possess at this stage very conspicuous antennas 

 and legs, and are of a pale yellow colour. In one such 

 brood there may be a dozen males ; these soon separate 

 themselves from the rest to construct a special little 

 fluffy cocoon, from which, after two or three days, the 

 winged male emerges. It is provided with three pairs 

 of eyes, and lives but a very short time. D. longifilis 

 is not oviparous like D. destructor, but is viviparous. 

 It is a larger creature, but not so prolific, though it is 

 as general a feeder as the allied species. These pests 

 are very abundant in hothouses, where the artificial 

 conditions of relatively constant temperature, moisture, 

 and food supply give them a specially favourable en- 

 vironment, and their rate of production is consequently 

 very rapid. 



America suffers even more from the ravages of 

 Coccidae than we do in this country ; perhaps its most 

 destructive insect is the -San Jose, or Pernicious scale 

 (Aspidictus pcrnkiosus). It is so widely disseminated, 

 and has become so firmly established in the principal 

 deciduous fruit regions of the United .States, that its 

 extermination is now, in most cases, out of the ques- 

 tion ; it is looked upon as a permanent factor to be 

 regularly dealt with. There are, of course, the pre- 

 ventive ;md quarantine measures against introducing it 

 into new regions on nursery stock, but once it has a 

 foothold the only certain method of destroying it is 

 the hercjic measure of digging up and burning all in- 

 fested trees. But orchards can be made profitable 

 even if the scale be there, by controlling its spread by 

 means of insecticides. The San Jose scale is found in 

 Japan, being apparently of recent origin ; probably it 

 came on .Vmerican fruit trees, chieflv from California, 

 where it has been longest established, and where its 

 ravages are most serious. But it is interesting to note 

 that in Japan the San Jose has met its match, in the 

 person of the little twice-stabbed ladybird beetle 

 (Chilocoriis similis). This beneficent little creature is the 

 enemy of Japan's destructive scale, Diaspis pcntagona, 

 and, fortunately, it has taken just as readily to the 

 introduced species, and very materially checks its in- 

 crease. {To be continued.) 



