218 



THE AGRICULTLiUAL NEWS. 



July 9, 1910. 



INSECT NOTES. 



THE 



ACARINA 

 PART 



OR 



II. 



MITES. 



Among the sp-cies included in the order Acarina are 

 many forms which are of great importance in connexion with 

 agriculture, on account of their depredations on both plants 

 and animals. With the exceptiou of the ticks, the members 

 of this order are small, so small, in fact, that in man}' cases 

 the organism is not .seen until after the effect of its pre.sence 

 is demonstrated. Such pests as red spider, bete rouge, poultry 

 mite, scab and mange mites, the leaf-blister mite and the 

 ticks, are examples of this group of animals. 



As the reader can judge from the few- 

 common names just given, the Acarina have 

 very diverse habits. There is also a consider- 

 able variation in structure and habit. In the 

 mites, generally, the body forms one closely ' 

 connected structure, without division into 

 regions such as the head, thorax, and abdomen 

 of insects, or the cephalothorax and abdomen 

 of the Scorpionida. 



The adult mit^s usually have four pairs 

 of walking legs, while the newly-hatched have 

 only three pairs. The eyes are often small, and 

 may be absent; the stigmata are generally 

 wanting, and the mouth parts are adapted 

 for piercing or biting, and sometimes for both 

 biting and sucking. Certain species are entire- 

 ly free-living and plant-feeding; others are 

 parasitic on plants, forming galls on them; 

 and others again are parasitic on, or in, animals 

 of various sorts, from man to certain in.sects. 



The Acarina may be divided, for con- 

 venience, into several families, which are as 

 follows: — 



Via. 



The spinning mites. 

 The snouted mites. 

 The poultry mitts 

 The ticks. " 

 The beetle mites. 

 The scavenger mites. 

 The itch mites. 

 The gall mites. 



I. Tronibididae — 



II. Bdellidae— 



III. Gamasidae — 



IV. Ixodidae — 



V. Orobatidae — 

 YI. Tyroglyphidae- 

 YII. Sarcoptidae — 

 VIII. Phytoptidae— 



The red spiders may be taken as good examples of the 

 first family of mites. Although called red spiders, they are 

 variable in colour; the older and more fully fed individuals 

 seem to have a deeper colour than the younger ones. They 

 are so small as to be practically invisible. Attention is 

 generally attracted to them only when the injury which they 

 do to the plants has progressed far enough to be noticeable. 



The red spiders spin a web of very delicate silken threads, 

 underneath which they live. The females lay rather large eggs, 

 from which the young hatch in from six to eight days. The 

 young mite is practically colourless, and has only three pairs 

 of legs. The metamorphosis is gradual, the most marked 

 change in appearance being the increase in the number of the 

 leg.s, the adult mite having four pairs. 



The red spider most common in the West Indies is 

 'Tetranychus telarius, which is often to be seen attacking 

 sweet potatos. The mites live on the under side of the leaves, 

 where they spin their webs. The drying and yellowing of the 

 sweet potato leaves is often an indication of the presence of 

 this pest, and when this condition is observed, examination 



reveals the presence of tiiese mites, in all stages of develop- 

 ment, under and iu their webs. 



Ked spiders tiouri^h be.st in dry, hot weather, and the 

 advent of rain often checks an attack of the pest. Sulphur 

 is a remedy int mites of all kinds, and may be applied for the 

 control of red spider as a dust, or as a spray. The more 

 practical way for field application would probably be the 

 dry one, for which purpose, the sulphur would best be 

 mixed with its own weight of slaked lime. Sulphur may be 

 used as a spray, mixed with water at the rate of loz. to 

 each gallon. 



Cotton is' often attacked bj- a red spider, probably not 

 the same as that of the potato, but a related species. Roses 

 also are attacked by red spider. 



The Bryobia mite which, in many countries, is a serious 

 pest on fruit trees, clover and other plants, 

 belongs to this family. When these mites are 

 very abundant, they .sometimes swarm into 

 houses, and cause considerable discomfort to 

 the inmates. 



Another pest well known in the West 

 Indies for its irritating eflect on man is the 

 larva of a mite, belonging to this family, which 

 is there called bete rouge. In England, this 

 mite is called the harvest bug, and in the 

 .southern part of the United States it is often 

 called chigger. In the AVest Indies, however, 

 the term jigger, or chigoe, is applied to one 

 of the true insects, which is really a flea 

 {Sarcopsi/Ua jM'netraiis). 



The parent or adult form of the bete 

 rouge does not seem to be definitely known, 

 although it is said to be Tromf/idium holoseri- 

 cemn. The harvest mite has been described 

 as Lepl-i^x irritans, birt it is now generally 

 believed that Trombidium and Leptus have 

 been applied to different stages of the same insect. 



The ver}' small, bright-red mites which are often found 

 on the bodies of grasshoppers and beetles, belong to the 

 genus Trombidium, and are either the adult form of the bete 

 rouge, or closely related to it. 



In many islands of the West Indies, bete rouge, at certain 

 seasons of the year, causes very serious inconvenience. The 

 regular dwellers in a locality where this mite is abundant 

 seem to become accustomed to its attacks, or at least less 

 susceptible to them, and to suffer but little, while strangers, 

 especially visitors from northern climates, may undergo an 

 extremely di.sagreeable experience at their first acquaintance 

 with this pest. Bete rouge is very minute in size, reddish in 

 colour; it inhabits grass and weeds in open fields, and may 

 be found often in tennis lawns and other well kei)t grass. 

 The animal attacks the ankles and lower limbs of the 

 victims, and burrows into the skin, where it completely buries 

 itself, if it is not removed in time. Different persons 

 recommend different remedits; the favourite applications for 

 the West Indies seem to be oily or greasy substances, rum, bay 

 rum and lime juice. Any ointment containing sul[ihur would 

 also be useful. It must be remembered, however, that to be 

 really efficacious, these remedies should be applied as soon as 

 possible after the attack begins, for if the mites once become 

 embedded in the skin, the remedies do not reach them, and 

 the irritation and annoyance caused by the presence of these 

 foreign bodies is extreme. 



3.3. A Red Spidek. 

 (Magnified.) 



