2H Control of t lie Grecnhoni^c White Fhj 



The smallest count made on any one plant was 140 and the highest 970. 

 while the average number dealt with was 460. The mortalities on the 

 several days reduced to percentages are shown in Diagram II. The 

 mortality on a tomato plant uncyanided but otherwise similarly treated 

 was 29 dead out of a total of 900 scales, or 3 per cent., while the natural 

 mortality on uncyanided beans was also negligible. If these two curves, 

 and especially the lower one given by | oz., are examined in relation to 

 Diagram I which shows the proportion of the scales which would be in 

 the different stages on each day, it will be seen that there are very sug- 

 gestive drops in the mortality which correspond roughly with (1) the 

 first moult on the sixth day after hatching; (2) the second moult on the 

 eighth day, seen only in the upper curve; (3) the third moult on the 

 tenth to twelfth days, and (4) the time of true pupation just before 

 emergence begins. The mortality of the adults given by these small doses 

 varied with 4 oz. from 95-100 per cent, (average of five tests 98 per cent.), 

 and in 10 tests with \ oz. from 88 per cent, to nearly 100 per cent., but 

 was never total with the weaker charge. 



After these experiments it appeared possible that a very good result 

 could be obtained with two fumigations with a small charge on successive 

 nights, and two heavily infested tomato plants were tfeated with \ oz. 

 cyanide per 1000 eft. On the following morning one of them was re- 

 moved from the fumigation greenhouse while the other was treated 

 again the next night with the same charge. The mortality of the scales 

 in all stages, on the first plant was 75-8 per cent, (805 out of 1045) and on 

 the plant treated twice 91-8 per cent. (903 out of 1013). The combined 

 effect of the two thus gave a less satisfactory result than would have 

 been obtained with \ oz. in one fumigation. 



The very small charges will clearly give a moderately good check to 

 the pest, though they will not exterminate it, and it is at times advisable 

 to use them on soft sappy tomato plants which for one reason or another 

 cannot be brought into a proper condition to withstand the normal dosage. 



Dosage. From these experiments and tests made in commercial 

 houses it was concluded that in an isolated greenhouse in a moderate 

 state of repair \ oz. of cyanide per 1000 eft. could be relied on to give 

 practically total mortality for all stages except the eggs, if the fumigation 

 lasted through the night. In a block of greenhouses in decent repair 

 which communicate with one another a dose of this size is not required 

 as the proportional leakage is less and \ oz. per 1000 eft. is a sufficient 

 quantity, or when the houses are new and in very good repair even 

 g oz. gives almost total mortality. 



