Ll. Lloyd 



89 



prices and is more trouble to mix. It should therefore not be used when 

 saponin can be obtained. 



Table VI. Comparing the death date of the larvae on tomato plants sprayed 

 with suspensions of lead arsenate paste (20 per cent. As 2 5 ) of various 

 strengths. 



The larvae die off gradually when the lead arsenate is used at a 

 strength of 2 lbs. to 100 gallons, or stronger. Some are found dead the 

 day after the spraying but others survive a week or more. This is 

 probably because they find the poison distasteful and the majority cease 

 feeding before they have taken a fatal dose. After a time hunger forces 

 them to recommence feeding, until finally a fatal dose is taken. In 

 order to discover what concentration should be employed, small bushy 

 plants in pots were sprayed with various strengths, from 2 to 10 lbs. of 

 the paste to 100 gallons. When the spray was dry the plants were 

 infested with a large number of larvae collected in the tomato houses. 

 Half grown to mature ones were employed and they were kept from 

 wandering either by enclosing the plants in muslin sleeves, or by placing 

 them in large vessels covered with cloth. They were examined daily 

 and the dead larvae were counted and removed. In each case a few of 

 the larvae pupated but the varying numbers of these have little signifi- 

 cance, as they were probably fully fed when placed on the sprayed 

 plants. Two tests were made for each strength from 3 to 6 lbs. to 

 100 gallons and one test at strengths of 2 and 10 lbs. respectively. The 

 results are given in Table VI, which shows under each strength the 

 number of larvae employed and the percentages of these which survived 



