New York Agricultural Experiment Station. 29 



Zinc arsenite as an insecticide. — Technical Bulletin No. 28 deals 

 with a series of experiments with zinc arsenite and lead arsenate 

 to determine their relative toxicity to insects and the safeness of 

 zinc arsenite for use on foliage. 



In field and laboratory tests one pound of zinc arsenite proved 

 equal in effectiveness to three pounds of lead arsenate. 



Zinc arsenite when added to calcium hydrate or bordeaux mixture 

 caused no injury to apple foliage; but more or less spotting of apple 

 leaves occurred when the poison was used singly or in combination 

 with lime-sulphur or glucose. Zinc arsenite alone or with glucose 

 caused severe burning of grape foliage. Laboratory tests indicate 

 that the injury to foliage by zinc arsenite may be due in part to the 

 solubility of the poison in carbonic acid. 



The contradictory results from the use of zinc arsenite on foliage 

 suggest that the poison as manufactured is not a stable or uniform 

 product. 



Zinc arsenite or lead arsenate with bordeaux, soap or glue continued 

 effective for twenty-five days. Either of the poisons alone or with 

 glucose gradually lost its poisonous properties on exposure to weather 

 and by the end of this period had ceased to protect the foliage. 



Incidental to the main problem it appears in these tests that the 

 lime-sulphur solution does not resist wet weather as well as bordeaux 

 mixture. 



The influence of temperature and moisture in fumigation. — Failure 

 to kill hibernating caterpillars of the browntail moth in importations 

 of foreign shipments of nursery stock led to a demand on the Station 

 to determine the conditions which rendered fumigation ineffective. 

 In Technical Bulletin No. 30, attention is called to a series of 

 fumigation tests in which the effectiveness of the treatments were 

 influenced by temperature and humidity. A greater number of 

 caterpillars survived the fumigations made at low temperatures 

 than at higher temperatures; also fumigations made under humid 

 conditions were uniformly more destructive to the larvae than tests 

 that were conducted in a relatively dry air. 



The bulletin closes with a general discussion on the resistance of 

 the caterpillars of the browntail moth to fumigation and the effects 

 of variations of temperature and moisture on this condition. It is 

 concluded that the unusual resistance of these caterpillars to fumi- 

 gation is due to a condition of hibernation in which the moisture 



