24 BULLETIN 842, U. S. DEPARTMENT OF AGRICULTURE. 



all larvae in these experiments at 50° and 52° C, namely, 15 and 

 10 minutes, respectively, is exactly half that consumed in accom- 

 plishing an identical result with the nematodes inclosed in galls 

 which were soaked in water previous to treatment. Thus, the data 

 as a whole in Table III show conclusively that the active parasites 

 are much more sensitive to high temperatures outside of the pro- 

 tective galls than inside of them.' 



EFFECT OF CHEMICALS ON THE LARViE. 



As adequate and dependable data regarding the response of larvae 

 to some of the chemicals more commonly used as sterilizing and dis- 

 infecting agents were not available, the writer has carried out a large 

 number of experiments which were planned to obtain such data. 

 In these experiments, as in those with hot water, both the free larva? 

 removed from galls and the protected larva? inclosed in galls were 

 treated. Experiments with the protected larva? will be discussed 

 first. 



LARVAE IN GALLS. 



The method of procedure followed in subjecting the nematode 

 galls to the chemicals and in determining the effect of the latter 

 on the larva? was essentially the same as that used in the hot-water 

 investigations; that is, water-soaked galls were submerged in the 

 solution for the desired length of time, then washed in water sev- 

 eral times, and each opened in distilled water in a Syracuse watch 

 glass. The larval contents were subsequently examined microscop- 

 ically daily for several days to determine the effect of the treatment. 

 The average number of larvae from each lot of galls surviving the 

 treatment, as well as other data, is recorded in Table IV. 



By a study of Table IV it will be seen that unheated formalde- 

 hyde at strengths of 1 : 640, 1 : 320, 1 : 160, 1 : 100, and 1 : 80 produced no 

 marked effect on the larva? within two or four hours. Submerged 

 in a 1 : 50 solution, however, for two hours only 2 per cent of the 

 larva? in the galls remained alive, and when kept in this same 

 strength of the chemical for four hours none survived. Likewise, 

 all larva? were killed Avhen the galls were treated in 4 per cent for- 

 maldehyde for two and four hours, respectively. A 1 : 320 strength 

 of the chemical at a temperature of 50° and 52° C. killed less than 

 half the larva? when the galls were treated for one, two, and four 

 minutes. It was thought that these hot solutions might be effective 

 in eliminating the nematode, since Melhus (23) controlled oat smut 

 by applying a 1:320 strength at temperatures of 45°, 50°, and 55° 

 C. for one minute. In the galls kept in tap water for four days 

 and used as a check on those treated with formaldehyde, 95 per cent 

 of the nematodes were alive. 



