REPORT OF THE ENTOMOLOGIST. 



365 



tinge of green, but a clear yellow, unmistakably indicating the source 

 from which it came. 



Wandering Habits. — While engaged iu feeding, the mites remain qui- 

 escent for a length of time varying from a few minutes to half an hour. 

 They then move on a short distance and agaiu become motionless. If 

 disturbed they have a habit of erecting themselves upon the leaf, cling- 

 ing to its surface only by the anal proleg. 



When dissatisfied' with their surroundings, or when food becomes 

 scarce, the}' wander restlessly about, and undoubtedly travel to consid- 

 erable distances. Their rate of progress on a smooth surface is quite 

 rapid, and amounts to 10 or 12 feet per hour. It is therefore not sur- 

 prising to find them changing their position frequently; disappearing 

 suddenly from one portion of a tree, and appearing as suddenly in great 

 numbers upon another and distaut part of the same tree. 



It is not to be understood that the mites show any concert of action 

 iu moving their colonies, or that they are iu any other sense gregarious 

 than that they are usually found very thickly scattered over those parts 

 of an infested plant which offer favorable conditions for their support. 

 Thus the new growth of many orange trees becomes occupied or in- 

 fested by them as rapidly as the leaves fully mature, and the number 

 upon a single leaf may be estimated by many thousands. 



Numerical abundance. — The following examination made in January 

 will give an idea of the extent of the brood during the coldest part of 

 the Florida winter. 



From a large number of leaves of late autumn growth, one was se- 

 lected, which showed an even distribution of mites upon its surface. 

 An area of one square inch was accurately marked out with a needle, 

 and subdivided into sixteen equal squares. The number of mites and 

 their eggs upon four of the small squares, taken at random, was counted, 

 and found to aggregate 1,142.* This gives for the square inch under 

 observation 4,508 mites. The leaf was then cut into squares and tri- 

 angles, and was found to cover 15 square inches upon a sheet of paper. 



On the supposition that the experimental square inch gives a fair 

 average, the number of mites upon the upper surface of this leaf was 

 68,520. Certain portions, not exceeding one-quarter of the whole, were 

 however more or less thinly populated. Deducting, therefore, 27 per 

 cent, from the above, we have 50,020 mites, the approximate popula- 

 tion of the upper surface. The under side of the leaf was less thickly 

 infested, but the number of mites may be estimated as one-half that of 

 the ripper face, or 25,000. Thus the number of mites and their eggs, 

 upon a single leaf, is found to reach even in mid-winter the enormous 

 sum of 75,000. 



[n early summer, when the breeding is active, these estimates will be 

 greatly exceeded. At times an orange tree may be so completely in- 

 fested with the mites that, of its thousands of leaves, very few can be 

 found free from their presence. If then, we attempt to calculate the 

 number that may exist contemporaneously upon a bearing tree, we find 

 it represented, not by millions but by billions, and the figures obtained 

 convey no definite impressions to the mind. 



Preference shown for half Shade. — An examination made on a bright, 

 sunny day shows that, while the mites cannot long endure the direct 

 li^ht and heat of the sun, they aiso avoid dark shade. At midday they 

 are more abundant upon the under side of exposed leaves, and although 



*The Dumber of egg\s exceeded that of the mites, a phenomenon not often observed, 

 and which may be attributed to unusually cold and unfavorable ^ eather at the time 

 of the examination and for several weeks previous. 



