510 THE MONTHLY BULLETIN. 



receive the germs chiefly from blight which enters their feeding grounds 

 through inoculation by other insects. As the twigs upon which they are 

 feeding beain to wither they naturally seek other quarters, carrying the 

 germs with them and readily inoculating them into fresh tissues. One 

 case became especially noticeable in our studies, where a colony of these 

 insects had vacated a blighted shoot, eacli individual descending to the 

 base and going upon fresh material. The colony thus became scattered 

 and seven surrounding fresh shoots were found to blight as a direct 

 result of their attacks. As these withered from blight the growing 

 colony from each again sought new quarters and thus became scattered 

 among the fresh growth. Summer cutting prevented me from carrying 

 out these observations, but the progression indicated and a knowledge 

 of the rapidity with which these insects multiply will readily indicate 

 the damage they are capable of doing. 



Blight Near Base of Tree Due to Insect Attacks. 



Many mysterious cases of blight at or beneath the ground are due to 

 the attacks of insects living in the ground, and among these are one or 

 two species of Elaterids or click beetles, and several others that were not 

 classified when these studies were made. In some cases the soil about 

 the trees is quite honeycombed with their burrows. They are very fond 

 of blight exudate. Like the root weevil, they feed upon the roots as 

 well as upon growth above the ground. They are often seen about 

 wounds caused by tlie tools or where sprouts have been removed from 

 the base of the trees. They have been found to cause inf«ction both 

 here and upon the roots themselves. 



Add to this list the cucumber beetle, an ubiquitous thing feeding over 

 a wide area and in a variety of places, deliberately taking exuding gum 

 and nectar from the flowers and attacking growing twigs and leaves; 

 include the canker worm, the codling moth larva\ numerous green fruit 

 worms, tussock moth larva and a number of Pentatomids, and other 

 true bugs, both large and small, and you have the chief insects carrying 

 this disease. It is a formidable list and sufficient to account for the 

 enormous virulence of pear blight and its appearance in every part of 

 the trees. 



There is one other agency worthy of mention, and this is contact blight, 

 a thing most common during a rainy spring. We found during our 

 studies that infection increased at a high rate following rains. This 

 was thought to be due to the dripping of blight virus from the upper 

 to the lower portions of the tree. Carrying this out with an atomizer, 

 we found that we could produce infection in as high as seventy-five per 

 cent of the cases tried, by spraying blight germs over tender growth, 

 flowers and even fruit. The abrasions through which the bacilli enter 

 may be caused by insects or by the rubbing. Blighted pears were cut 

 open and rubbed over the surface of healthy fruit, the pressure being 

 only sufficient to cause the gum to adhere. Infection following reached 

 nearly 100 per cent, and the disease did not enter at one point but over 

 the entire surface touched by the virus. 



