Journal of Agricultural Research vol. xii, NO. 7 



On May 25, 1917, large numbers of gipsy-moth larvae were found in 

 and around ruptured blisters, and several days later some of the blisters 

 where the presence of larvae had been previously noted were empty, and 

 spore production was apparently arrested. Subsequent observation on 

 these blisters showed that no further spore production took place, while 

 on the same cankers blisters which were artificially protected from larvae 

 continued to produce spores in abundance until June 25. To determine 

 the rate of blister destruction on June 9 a number of larvae were placed 

 on a twig infection which had 38 sporulating pustules. Many of the 

 larvae crawled away or dropped off, but a sufficient number remained to 

 destroy the fruiting layer in practically every blister by noon of the 

 following day, with the result that no subsequent spore production took 

 place. 



Cessation of spore production in injured blisters was caused by the 

 destruction of fruiting hyphae. Usually the spores and hyphae were eaten 

 away first and then the larvae very often ate through the base of the 

 fruiting layer to a depth of several millimeters. Apparently, after blis- 

 ters no longer furnished suitable food for the larvae, they began feeding 

 on the areas of the yellowish, discolored, infected bark outside the fruit- 

 ing region and in some cases a large per cent of the outer bark of next 

 year's sporulating zone was destroyed. Careful observations on many 

 larva-infested cankers showed that spore production was prematurely 

 arrested in 25 to 100 per cent of the pustules, the percentage usually aver- 

 aging highest on small twigs. 



SPORES ON LARV# 



Larvae working in blisters collected so many aeciospores on their hairy 

 bodies that they appeared nearly the color of spores in mass. On differ- 

 ent dates larvae were taken from blisters and placed in separate capsules, 

 precautions being taken against including spores not on the bodies. 

 These were taken into the temporary laboratory and spore counts made 

 of the bodies and the alimentary tracts. Spores for counting were re- 

 moved from larvae by washing the bodies in series of water, and alcohol 

 mounts on slides followed by final examinations to assure thoroughness 

 in the method used. This procedure proved quite effective, and, where 

 carried through 5 to 10 washings, practically all spores were removed 

 from the outside of the bodies. Counts were made on the spores adher- 

 ing to the inside of the capsule and added to the total found in the wash- 

 ings. After bodies of the larvae had been thoroughly washed, they were 

 dissected and counts made of spores in the alimentary tracts. On May 26, 

 June 4, and June 1 1 fifteen small larvae were collected. Spore counts on 

 the bodies of these 15 gave a minimum of 1,120, a maximum of 28,320, 

 and an average of 18,100. Counts of spores in the alimentary tract gave 

 a minimum of 1,740, a maximum of 48,570, and an average of 26,022 



