U THE EEPOET OF THE No. 36 



by trees of other varieties apparently untouched. Nevertheless, it seems to be 

 true that in most cases the bug vi^ill gradually enlarge its field of operation from the 

 more to the less susceptible sorts. Fruit-growers tell of numberless instances 

 where the trouble began in their Nonpareil and gradually spread to their other 

 trees. The following varieties show susceptibility in the order named: — Ribston, 

 Gravenstein, Golden Eusset, Blenheim, Baldwin and Greening. 



Among the varieties of pears attacked the Bartlett shows the highest degree 

 of susceptibility. So much is this the case, that some have regarded the trouble as 

 a disease of this variety. Other susceptible varieties are Clapps' Favorite, Bur- 

 bridge, Maria and Flemish Beauty. Varieties not so susceptible are Louis Bonne, 

 Bosc, Lawrence, Duchess and D'Anjou. 



Conditions Fayoring Increase. 



It is difficult to state definitely under what condition this insect flourishes 

 best, since it is found in orchards treated in every conceivable way. Sprayed and 

 unsprayed, clean cultivated and sod, well cared for and neglected orchards are all 

 attacked. It is a notable fact that some of the very Avorst infestations are in 

 orchards that have received the best of treatment in the way of spraying, fertiliz- 

 ation and tilth. In most cases, however, such orchards were unduly shaded, in- 

 sufficiently pruned, or too thickly planted. In two very bad cases the orchard was 

 cultivated on the strip system, i.e., a strip of clover sod alternated with a clean 

 cultivated strip. In another case the orchard was part cultivated, part in sod. 

 Here the trees in sod seemed to show the greatest evidence of injury, but the differ- 

 ence was not readily detected. On the whole orchards with a thrifty, succulent 

 growth seemed to suffer most. 



As a result of all our observations throughout the infested area, it appears 

 that the most suitable conditions for the undue increase of this pest are shady 

 orchards with closely planted, thick growing trees, with a certain amount of herb- 

 age at their base, but for the most part thrifty and vigorous in other respects. 

 Nevertheless, these factors are not essential, as the insect is capable of doing in- 

 jury under a wide range of conditions. 



Natural Enemies. 



Ants seem to be the only natural enemies that exert any appreciable influence 

 on the control of this pest. These have been frequently noticed carrying away 

 nymphs on their jaws. On one occasion, when a number of nymphs were liberated 

 at the base of the tree, four of them were seized by as many ants and carried off 

 through the grass to the ant hill, which was distant fifteen feet from the tree. 

 Spiders also destroy a certain number of nymphs, but it is questionable whether 

 ants or spiders ever kill enough nymphs to noticeably reduce their numbers. The 

 ant responsible for this work was determined by Dr. Wheeler as Formica fusca. 



Control Experiments. 



Control experiments were carried on under most unfavorable conditions this 

 spring, the weather being almost continuously wet. This made it very difficult to 

 apply the spray at the proper time or to observe its effect upon the insect. Two 

 orchards were chosen, containing a large number of mature apple and pear trees 

 of the susceptible varieties. 



