Ll. Lloyd 



25 



lOth days respectively. In one case where an exact count was made after a fumigation 

 lasting 9 hours on six tomato plants holding scales from 9 days old to mature pupae 

 the mortality was yi per cent. (2900 out of 3184). 



The fact that the small numbers surviving these fumigations were 

 apparently young for the most part at the time of treatment is difficult 

 to explain as, when smaller doses of cyanide were used, it was found, as 

 other workers have stated, that the jjupae, which would give rise to 

 adults in two or three days' time, were the most resistant forms. Series 

 of plants were prepared as described above so that in each series one 

 plant held scales representing one day's development from egg to adult ; 



100 

 90 

 80 

 70 

 60 

 50 

 40 

 30 

 20 

 10 



Emergence 

 just begun 



J L 



J L 



J I L 



A 



Eggs 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 

 Age of Scales in Days 



Diagram II. Showing percentage mortalities of scales of A. vajmrariorum of various ages 

 obtained with small doses of cyanide, long exposures. Compare with Diagram I. 

 The gaps on the lower curve ai-e due to the death of three plants. J oz. cyanide per 

 1000 eft. 1 oz. cyanide per 1000 eft. 



i.e. at one end of the series was a plant holding only eggs, due to begin 

 hatching, and at the other end was one holding mature scales from which 

 emergence of flies had just commenced. Two series were cyanided as 

 follows: (1) 18 tomato plants representing complete development except 

 that three plants died from stem rot and caused gaps; fumigated with 

 I oz. cyanide per 1000 eft., 9 hours' duration; (2) 19 bean plants repre- 

 senting complete development, fumigated with ^ oz. of cyanide per 

 1000 eft.; 9-| hours' duration. After the treatment the plants were kept 

 for a week and a count was then made of the living or emerged scales 

 and the dead ones, which had by this time turned brown and dried up. 



