PROCEEDINGS, 1916. 



63 



Table No. XI is a composite of tables 2 to 10, and shows the general points brought 

 out by the individual tables, with the errors greatly diminished, if not eliminated. 



TABLE NO. XI. 



AVERAGE PERCENTAGE OF LARVAE KILLED WHEN THE DIFFERENCE 

 IN THE POISONING QUALITIES OF THE COMBINATIONS OF POI- 

 SONS AND FUNGICIDES, UPON WHICH THEY WERE FEEDING, 

 WAS MOST CONSPICUOUS. AVERAGE TAKEN FROM NINE 

 SEPARATE LOTS OF LARVAE. 



© Unsafe on apple foliage. 

 + Unsafe on apple foliage under certain conditions. 



From a study of these tables we find that the carrier of the poison, i.e. the fungicide 

 to which it is added, has a very marked effect on its efficiency. The effect of each, cal- 

 culated from the average total, may be summarized as follows: 



The four poisons used in this experiment, when employed in combination with 

 sodium sulphide (soluble sulphur) were 13.1 per cent more efficient than when used a- 

 lone. When the poisons were added to a mixture of barium tetrasulphide and sodium 

 sulphide their efficiency was reduced by 6.4 per cent, while, added to lime sulphur, the 

 reduction in efficiency amounted to 19.2 per cent. Barium tetrasulphide reduced their 

 toxic value 41.3 per cent and Bordeaux mixture 43.5 per cent. 



It would thus appear that with one exception, fungicides inhibit the action of ar- 

 senical poisons used in combination with them, the exception being sodium sulphide, 

 which noticeably increases their killing power. This very marked effect of the fungi- 

 cides on the action of the poisons is difficult to explain fully. The effect of the sodium 

 sulphide in increasing the toxicity of the various poisons is apparently due to the pres- 

 ence of the element sodium. A portion, at least, of its action consists we believe in its 

 effect in increasing the palatability of the leaves, resulting in the larvae eating ravenous- 

 ly for a few days. They thus get a large amount of poison into their system in a short 

 time, resulting in their more rapid death. The sodium sulphide also has the effect of 

 rendering the metallic arsenates, such as lead arsenate, more active, (and more danger- 



