192 



SCIENCE 



[N. S. Vol. XLVI. No. 1182 



NOTES ON MITES ATTACKING ORCHARD AND 

 FIELD CROPS IN UTAH i 



During the summers of 1915 and 1916 while 

 making investigations for the laboratory of 

 the American Smelting & Eefining Company, 

 Department of Agricultural Investigations, I 

 found certain mites to be particularly abun- 

 dant and destructive to grains in Utah. 



The most important of these was the com- 

 mon Tetranychus himaculatus Harvey, which 

 Ewing believes is the same as T. telarius Linn. 

 The host list for this species, as Ewing has 

 pointed out, is a long one, and it is an impor- 

 tant pest on a surprisingly large number of 

 crops. In 1916 it was so abundant in orchards 

 that many cherry trees were completely de- 

 foliated before the end of August, and apricot, 

 pear, plum and apple trees were only a little 

 less seriously affected. Easpberry and currant 

 bushes suffered severely, some of them losing 

 all of their leaves. Peas, beans, tomatoes and 

 other kinds of garden truck showed more or 

 less injury in all stages of their development, 

 and in one field of sugar beets, I found many 

 leaves drying and turning brown on account of 

 the attacks of this mite. The loss of the 

 foliage of many ornamental plants, while not 

 of so much economic importance, was, of 

 course, a very annoying thing. 



Corn probably suffered more than any other 

 field crop. In many fields practically every 

 plant suffered the loss of some of its leaves, 

 and in other places all of the leaves turned 

 brown and became thoroughly dry because of 

 the presence of the myriads of mites that 

 covered the undersides of the leaves. The 

 parts of the fields where the soil was lighter 

 and dryer usually suffered most, but no parts 

 seemed to be immune from the attacks of this 

 pest. The suckers and lower leaves were the 

 first to be attacked and to show the brown 

 spots or streaks where colonies of the mites 

 were feeding. When the trouble went no fur- 

 ther it was of but little economic importance, 

 but when the upper leaves were attacked and 

 practically all destroyed the plant withered and 

 was not even good for fodder. 



1 Contribution from the laboratories of the 

 American Smelting and Refining Co., Department 

 of Agricultural Investigations. 



Many wheat fields also sustained consider- 

 able losses due to the attacks of the same mite. 

 The wheat plants would usually be attacked a 

 short time before the head burst from the 

 sheath and when the infestation was bad the 

 leaves would become dry and brovm at the 

 point of attack and the portion of the leaf 

 beyond this would droop down and dry out. 

 Often all of the leaves would be affected in 

 this way and the heads, if they developed at 

 all, would be small and poorly filled. 



Earlier in the season, while the wheat plants 

 were much smaller, they were often attacked 

 by two other species of mites. One of these 

 is the well-known clover mite, Bryohia pra- 

 tensis. The other has been called the jumping 

 mite on account of its habit of quickly fold- 

 ing its legs and dropping from the plant when 

 disturbed. Banks in Proc. Ent. 8oc. Wash., 

 Vol. 14, p. 97, named this species Tetranychus 

 longipes. A letter dated June 29, 1915, says 

 that he now places it with two others in a new 

 genus, Teiranobia. He refers to this genus 

 again in his bulletin on " The Acarina or 

 Mites" (Kept. No. 108, U. S. Dept. Agric. 

 Office of Sec, pp. 33 and 38) but the formal 

 description of the genus has not yet been pub- 

 lished. The common name, jumping mite, is 

 somewhat misleading, for the mite does not 

 actually jump, but, when alarmed, it folds its 

 legs quickly and may thus be thrown a short 

 distance from the spot where it was feeding. 

 In fields where the mite is abundant the 

 leaves turn distinctly gray and many of them 

 become so dry that the growth of the plant is 

 seriously affected. Both B. pratensis and 

 Tetranoiia longipes were found destructively 

 abundant not only on wheat, but on barley, 

 oats and many wild grasses. 



E. "W. DOANE 



STANrORD TJnivebsity 



THE OCCURRENCE OF MANNITE IN SILAGE 



AND ITS POSSIBLE UTILIZATION IN THE 



MANUFACTURE OF EXPLOSIVES 



During the course of our investigations ou 

 the fermentation processes that occur immedi- 

 ately after the ensiling of corn, and the chem- 

 ical products resulting therefrom, it was found 



