266 



THE AGRICULTUKAL NEWS. 



AouusT 20, 1910. 



INSECT NOTES. 



THE ACARINA OR MITES. 

 PART V. 



SAECOPTiDAE. lu this family are included all those 

 parasitic mites which cause the diseases known as itch, mange 

 and scab, each species being specially adapted to some par- 

 ticular host. They live on the surface of the skin, or burrow 

 into its tissues, and in :iome ca.ses even infest the quills of feath- 

 ers. The various forms of itch and mange in the human species 

 and in horses, dogs and cats, are due to the attacks of these 

 mites, as are also the scaly leg of fowls, and the very impor- 

 tant disease known as scab in sheep. Sheep scab (Pgoroptes 

 communis, var. ovis) is perhaps the most important of all the 

 mites of this family. Its distribution is practically world- 

 wide, and its control in infected areas requires constant effort. 

 The mite and its egg.'* are easily to be seen in the scab of 

 infected sheep. The adult mites have a rounded body, and 

 the legs are provided with long hairs or bristles. The eggs 

 are very minute, glistening, white bodies, which may serve 

 for the identification of the pest, even though the mite.s 

 themselves are not found. 



Another form of parasitic mite is to 

 be found in the follicle mites. Demode'' 

 folliculorum, which live on man and cer- 

 tain domestic animals. These mites are 

 ■worm-like in appearance, and in this they 

 differ from all those so far considered. 

 One occurring on pigs gives rise to 

 a peculiar appearance of the skin, which, 

 if not recognized as being due to a para- 

 site of this kind, may cause suspicion as 

 to the suitability of the flesh for eating 

 purposes. Except in cases of extreme in- 

 festation, they are not of great importance; 

 but those that attack cattle sometimes 

 become sufficiently abundant to damage 

 .seriously the hides in relation to leather- 

 making. The entire life-history of these 

 mites is pas.sed in the hair follicle, but 

 but the adult probably migrates over the 

 surface of the skin for the purpose of 

 egg-laying. 



ERioPHYiDAE. The Eriophyidae differ m appearance from 

 the mite.< of all the other families. They are elongated in 

 shape, microscopic in .size, and present the appearance of 

 having a cephalothorax and an abdomen, the division being 

 indicated by a distinct suture. They are provided with two 

 pairs of legs, the other two pairs normally present in the mites 

 being represented bj' stiff' hairs or bristles. The general shape 

 of the body is similar to that of Demodex, from which they 

 are distinguished by the number of pairs of legs, and their 

 plant-infesting habits. 



The member.s of this family are parasitic on plants, and 

 are known as gall mites, or leaf-blister mites, on account of 

 the peculiar distortions of plant tissues which they produce. 

 Each species of mite seems to favour some particular host 

 plant, and to produce its characteristic gall or deformity, by 

 which it may generally be recognized. In the West Indies, 

 the most important of these mites is Eriophyef. gossypii 

 (Fig. 3.5) which attacks cotton. It occurs in all the islands of 

 the Lesser Antilles, except Barbados, attacking both wild and 

 «ultivated cotton. It has sometimes been such a serious 

 pest of Sea Island cotton as to destroy entire fields of this 

 crop. 



Fig, 3.5. Erio- 

 phyes gossypii. 



The adult mite enters the leaf bud of the young cotton- 

 plant, and when these develop, and the leaves are unfolded, 

 the characteristic galls ( Fig. 36) are seen. These galls are 

 produced by the irritation caused by the feeding of the mites 

 on the ventral surface of the leaf. This irritation also 

 induces a growth of fine hairs within the gall, among which 

 the mites live. 



When the mites are fully developed, they leave the galls 

 and wander about in search of leaf buds in which to establish 

 new colonies. 



The remedial measures at present in use for the control 

 of the leaf-blister mite are entirely cultural, and consist in 

 the thorough destruction of all the old cotton two or three 

 months before planting the new crop. This method, com- 

 bined with the picking-off of infested leaves as they appear 

 on the young cotton, has been found to reduce the numbers 

 of the mite to such an extent as to render it practically 

 harmless. Sulphur and lime in equal parts, dusted on the 

 plants at the time when the mites are migrating from one 

 part to another, will be found very useful in checking the 

 increase of this pest. 



Other species occurimg in the West Indies are Erioj^hyes 

 hucidae which causes the bright-red, felt-like growths on the 

 leaves of Terminalia Buceras; Eriophyes morrisi which 

 causes the spheroidal .swellings on the leaves of Acacia 

 farnesiana and other species; and Eriophyes striafiis which 

 occurs on Eupato^-ium odoratum. 



This article completes the series dealing with the Acarina, 

 or Mites, which was commenced in No. 213 of the Agricul- 

 tural Keu's. As was stated in ihe introduction to Part I, the 

 object of these articles has been to give definite information 

 concerning form.? of lifi that are popularly regarded as insects, 

 but which cannot be strictly included among them. 



It was necessary, in Part I, to recap- 

 itulate the fact that the arthropods, or 

 animals with jointed legs, contain four 

 classes, of which the crabs, the spiders, 

 the centipedes and the insects form the 

 ^""-'^1 broad types; and as the Acarina, or 

 ^^•^"~^^ mites, belong to the second of these — the 

 one containing the spiders — this was 

 described under its usual name, Arach- 

 nida; a short account of the different 

 orders being given. 



This cleared the way for the conside- 

 ration of the Acarina, commenced in 

 II of the series, and after a general description of the 

 order had been presented, its ditterent families were enumer- 

 ated, the remainder of the article being taken up by an 

 account of the Trorabididae, or spinning mites, of which 

 the most interesting are the red spiders, the jigger (or chigoe) 

 and the bete rouge. 



Part III dealt with the Gamasidae and the Ixodidae, 

 the former of which include the poultry mites, while 

 the latter family is especially interesting, as it includes 

 the ticks — the largest among the mites. Special attention has 

 been given to finding cheap and effective means of getting rid 

 of ticks. Some of these are indicated in Parts III and IV; and 

 it may also be stated that particular information relating to 

 freeing pastures from ticks is given on page 157 of the current 

 volume of the Ayficultural Ketrs. 



Parts IV and V, the latter of which deals with the im- 

 portant family Eriophyidae (leaf-blister mites), conclude 

 a series of articles which, it is hoped, will be found useful in 

 giving information concerning several groups of pests that 

 cannot be classed properly as insects. 



Fig. 36. Section 

 theough gall 

 MADE BY Erio- 

 phyes GO.SSVPII. 



Part 



