February, '17] MERRILL: aphids and blight 45 



PURTHER DATA ON THE RELATION BETWEEN APHIDS 



AND FIRE BLIGHT (BACILLUS AMYLOVORUS 



BUR. TREV.)^ 



By J. H. Merrill, Assistant Entomologist, Kansas Agricultural Experiment Station 



In the Journal of Economic Entomology, Vol. 8, No. 4, 1915, a 

 report was given of field observations made on the relation of aphids 

 to fire-bhght in Doniphan County, Kansas, for the years 1913, 1914 

 and 1915. In 1915 and 1916, observations were carried on in Atchison 

 as well as in Doniphan County, and in both counties a direct relation 

 was found to exist between the severity of the aphid infestation and 

 the amount of fire-blight infection. 



It was planned to carry on experiments during the spring and sum- 

 mer of 1916 to determine two points — (1) how it was possible for the 

 aphids to come in contact with the blight bacteria, and (2), whether 

 or not the aphids could inoculate trees with fire-blight. 



To determine the first point, a large number of hold-over cankers 

 were examined and it was found that the aphids deposited their eggs 

 in blight cankers (PL 2, Fig. 1) as readily as in any rough places on the 

 bark. In the spring, the live cankers resume activity, giving forth 

 gummy exudations filled with bacteria. The aphids, which hatch 

 from eggs laid in the cankers, crawl through these exudations in 

 passing to the terminal growth of the twigs and, in so doing, become 

 contaminated with blight bacteria. 



To determine the second point, it was planned to secure a large 

 number of aphids, allow them to pass over pure cultures of blight bac- 

 teria, and then transfer them to the twigs of apple trees. Owing to 

 the fact that aphids were very scarce in Kansas during the summer of 

 1916, none were obtained for this work until August. 



During the month of August, the average maximum temperature 

 at the field insectary at Manhattan, where these experiments were 

 being conducted, was 96.5 degrees and the total rainfall for the month 

 was .71 of an inch. Naturally, the trees put forth but very little 

 new growth during this period. 



Despite these adverse weather conditions, aphids, which had pre- 

 viously passed over pure cultures of blight bacteria, were placed on the 

 twigs of four Yellow Transparent trees and these twigs covered with 

 cheesecloth bags (PL 2, Fig. 2) to prevent other insects gaining access to 



1 Contribution from the Entomological Laboratory, Kansas State Agricultural 

 College, No. 21. This paper embodies the results of the investigations undertaken 

 by the author in the prosecution of project No. 13. Kansas Agricultural Experiment 

 .Station. 



