110 INSECTS AFFECTING THE ORANGE. 



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 4,568 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 maybe estimated as one-half that of 

 the upper face, or 25,000. Thus the number of Mites and their eggs, 

 upon a single leaf, is found to reach even in midwinter the enormous 

 sum of .75,000. 



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

 greatly exceeded. At times ail 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 

 light and heat of the sun, they also avoid dark shade. At midday they 

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

 they at all times show a marked preference for light, they desert those 

 parts of leaf or fruit upon which it falls brightest. On a leaf partially 

 exposed to the sun the Mites congregate near one edge in the morning, 

 and in the afternoon cross to the opposite side of the same surface, fol- 

 lowing the shifting shade, which, by reason of its curvature, the edges 

 of the leaf throw upon one side or the other.t 



Rings of Rust on Fruit. On the fruit, this preference of the Mites for 

 half shade causes a phenomenon which will be recognized as verycom- 



*The number of eggs exceeded that of the Mites, a phenomenon not often observed, 

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

 of the examination and for several weeks previous. 



tThe conditions most favorable to their increase are afforded by luxuriant foliage 

 when thoroughly penetrated by light, but dense shade effectually bars their progress. 

 Vigorous young trees on which the foliage is illuminated from beneath by radiation 

 from the surrounding soil are especially subject to attack, the succulence of their 

 leaves serving only to increase enormously the numbers of the invading host. The 

 same luxuriance in older trees, whose branches interlock in the grove and shade the 

 ground, acts unfavorably upon the productiveness of the Mites and checks their in- 

 crease. These are facts of importance, as will be seen when we come to consider the 

 means of combating the pest. 



