508 THE MONTHLY BULLETIN. 



Ants will also carry much blight back to the trees from cuttings left 

 on the ground. This is made possible by a sweating process which takes 

 place from the under side of these cuttings, as a result of dew or artificial 

 moisture that settles upon them. Under the influence of this moisture 

 the hard fihn that has formed over the outside of the gum readily dis- 

 solves and exposes the soft materials underneath, that is full of live 

 germs. This is the chief danger in all cuttings that are not destroyed. 

 The glassy surface of the gum protects the germs beneath for many days, 

 and even weeks, making them a constant menace. The affinity between 

 ants and aphids is well known. Add to this the fact that ants have 

 actually carried blighted sap into their underground nests to help feed 

 their precious milk cows during the winter, and you have a situation not 

 easy to reckon with. Both ants and aphids will emerge in the spring 

 thoroughly contaminated and ready to start infection. Carbon bisulfid 

 is cheap at any price where ants are living in or near a pear orchard. 



The Pear Thrips as a Disease Disseminator. 



Pear thrips are very fond of the pear bloom and upon their appear- 

 ance in the spring are chiefly confined to the flowers which are then very 

 general. Going from the bloom their first attacks are largely upon the 

 leaf buds in the tops of the trees. Later, as these begin to harden, they 

 tire found in greater abundance in the lower growth, which comes on 

 later and remains soft and succulent much longer. They may be found 

 in all parts of the trees, however, where there is any material available 

 to them as food. Within the developing leaf buds, and enclosed within 

 the rolls of the growing leaves of these buds, are their favorite haunts. 

 They also infest freely the lateral buds, and much blight which enters 

 at the sides of twigs and suckers is due to their attacks at these points. 

 Even buds on second year wood are freely invaded and contaminated by 

 these pests. Leaves, petals of the flowers, stamens, pistils and even the 

 tender first year wood itself are all' included in their diet. Dangerous 

 as these insects are in orchards containing blight, they must, like most 

 of those which follow, be distinguished from the preceding by the fact 

 that they do not deliberately spread the disease through a fondness for 

 the gum of blight exudate. Like the aphids and many other forms, they 

 extract their food from the tissues of the host plants and are not fond 

 of these when blighted, though they may occasionally be found upon 

 tissues quite blackened with the disease. Blight germs which they 

 receive from any feeding grounds except the flowers, must be inoculated 

 into the tissues by other insects or by thrips which have already received 

 the virus from other sources, and are extracted by them from the plant 

 cells into which the blight is spreading. They have frequently been 

 found in flower cups containing milky exudate and, as has been stated, 

 are probably not able to distinguish this from the nectar of the flowers. 

 When the virus is once secured from either flowers or shoots they are 

 perpetually supplied with it and prepared to leave infection in their 

 wake. 



Mr. Moulton, in his bulletin on this insect, points out that the beak 

 is used in making an incision for the deposition of the egg beneath the 

 epidermis of the stems of the blossoms, the petioles, midribs and veins 

 and even the tissues of the leaves, and this, of course, is a prolific source 

 of infection from the contaminated mouths of the females. 



