CONDITIONS FAVORABLE OR NECESSARY. 



13 



On several occasions it was observed that the tent felt somewhat 

 damp when being hantUed, although the humidity recorded by a 

 standard sling psychrometer had not reached complete saturation. 

 On other occasions, as shown by the above data, the foliage was 

 covered with a dew like a fuie mist when the sling psychrometer 

 indicated as much as 6 per cent below complete saturation. For 

 practical purposes, however, the moisture on the leaves may be 

 considered as indicating a condition of 100 per cent atmospheric 

 moisture. Blank spaces in the table indicate that no note was 

 made concerning this particular point, although the tent was evi- 

 dently "wet" in experiments 40.2 and 50.2 and the leaves were 

 evidently "dry" in experiments 45.21 and 45.22. In the experi- 

 ments summarized in Table I the possibihty of reducing the efficiency 

 of the gas through absorption by the moisture on the leaves and 

 tent had to be taken into consideration. To eliminate tliis feature 

 and to determine the effect of the gas on larvae and pupae of the 

 white fly when leaves are wet artificially, tests were made by wetting 

 the leaves both by dipping and by means of an atomizer. The 

 results are summarized in Table II. 



Table II. — Ejfect of art iJlnaUy VM'Umy leaves on cjjiciency of fumigation. 



In the above experiments — omitting the last one, in which all 

 insects were killed — 1,331 insects were under observation. Of these, 

 323 were on leaves wetted artificially. The weighted average of the 

 insects killed on these leaves is 92.5 per cent. Of the 1,008 insects 

 on the dry leaves 852, or 84 per cent, were killed. Tliis seems to 

 be of considerable significance in view of the fact that in every 

 instance where less than 100 per cent of the insects were killed, the 

 percentage of killed was greater on the artificially wetted leaves 

 than on the dry leaves. 



Taken as a whole the results summarized in the two foregoing 

 tables show conclusively that moisture on the leaves in the form of 

 dew does not reduce the efficacy of the gas in destro}dng the insects, 

 but possibly increases it. In the experiments in wliich moisture was 

 a factor no injury to the foliage followed, even when the dosage was 

 increased fully one-half above the amount called for by the table 

 in the appendix of this bulletin. The results give no justification to 



