Entomological Department. 327 



The mites instinctively migrate from the leaves as soon as the latter 

 become dry. Whenever branches were brought into the insectary, as 

 soon as the leaves began to dry, the mites left them and gathered in 

 great numbers in the buds. It is impossible to accurately estimate the 

 number of mites that may live iu the galls on a single leaf. Sections 

 of galls made while in their red stage would seldom cut through more 

 than two or three mites; but sections of the brown galls often showed 

 four or five times as many. Thus on a badly infested leaf there is 

 without doubt at least a thousand of the mites. 



Methods of Destroying the Mites.— Owing to the fact that the mites 

 live within the tissues of the leaves during the giowing season, they 

 are then beyond the reach of ordinary insectides. It is obvious that 

 they would not be affected by any poison dusted or sprayed upon the 

 surface of the leaves. In 1890 we demonstrated that the mites could 

 not be reached by an application of kerosene emulsion to the leaves. 

 It was hoped that a sufficient quantity of the liquid would pass into 

 the galls through their open mouths to injuriously affect the mites, but 



it did not. 



Thus the only practicable method of combating the pest while 

 in the galls is to gather the infested leaves, either by picking or 

 pruning, and burn them. This method is a sure one, and is practicable 

 where the pest is just starting in an orchard, or where the trees are 

 small or when but a few large trees are attacked. It can be done at 

 any time before the leaves dry and fall iu the autumn, but the earlier 

 in the season the better. In May, while the galls are red, would be 

 the best time to do it. 



The most vulnerable point at which the disease can be attacked on a 

 large scale is when the mite is in its winter quarters in the terminal 

 winter buds. Doubtless the pest receives a considerable check in many 

 orchards at the annual pruning to which the trees are subjected. In 

 this manner many of the winter buds containing the mites are removed 

 and the burning of the brush soon after destroys the pest. 



The methods just discussed are sure means and are practicable within 

 certain limits. But a method which is cheaper, easier, more practicable, 

 and one that is effective and applicable to large orchards, has resulted 

 from our experiments during the last two years. One winter while 

 experimenting to learn the effects of kerosene oil on dormant wood, it 

 was noticed that the oil penetrated every crevice of the wood with 

 surprising thoroughness; and it was at once siispected that kerosene 

 might be used with effectiveness against this mite while in its winter 

 quarters under the bud scales. 



In the fall of 1891, before the leaves fell, several badly infested trees 

 were labeled; and in Februry, 1892, two trees were treated with undi- 



