New York Agricultural Experiment Station. 339 



when caterpillars were on the foliage at the time of treatment or 

 placed on the tree when the leaves were still wet with the spray 

 mixture. In this case applications of zinc arsenite showed their 

 deadly effects upon the caterpillars much sooner than those con- 

 taining lead arsenate. 



As a rule the insects on freshly-sprayed foliage ate only one meal 

 and thereafter fed very little until death ensued or the experiment 

 was concluded. In all cases the amount consumed in the initial 

 meal was greater with the check than with any of the sprayed plants, 

 indicating that either there was a reaction by the insect to the poison 

 or that the spray possessed distasteful or repellent properties. In 

 the tests in which foliage that had been exposed to the weather 

 was fed to insects the period of feeding was more extended, depend- 

 ing on the interval between treatment and the feeding of the insects. 

 The caterpillars which were given foliage that had been exposed for 

 twenty-five days fed voraciously for three to six days before the 

 poison became effective. 1 



EFFECT OF WEATHERING ON EFFICIENCY OF SPRAYS. 



The effects of weather on the insecticidal properties of appli- 

 cations of the poisons are shown in Tests 3, 4, 5 and 6. The period 

 of exposure of the sprayed foliage was three hours, three days, 

 eight days and twenty-five days respectively. See Chart I, (p. 16). 



All sprays were practically equal in effectiveness when first ap- 

 plied, but exposure to weather tended to reduce their insecticidal 

 properties. In these experiments the preparations that contained 

 bordeaux, soap or glue in combination with either of the poisons 

 and the lime-sulphur combined with dry lead arsenate continued 

 effective as insecticides for twenty-five days. Zinc arsenite or 

 arsenate of lead alone or with glicose ceased to protect the foliage 

 from insects at the conclusion of this period. 



1 The effect of arsenic upon the higher animals and man depends upon the size and 

 form of the dose administered and the condition of the subject. According to Blyth 

 (Poisons: Effects and Detection, pp. 494-543. 1884) a large dose results in an acute 

 case. The symptoms usually appear within an hour and may be accompanied by 

 vomiting and diarrhoea, death following in from 3 to 24 hours. The symptoms 

 resulting from a milder dose are much the same, though death may not occur for a 

 longer period. Where the dose is very mild the ordinary vomiting and purging are 

 much suppressed and instead jaundice, narcotic sleep or partial paralysis may result. 

 These symptoms may be followed by death or the subject may recover after an illness 

 varying from a few days to several months. The behavior of poisoned animals 

 corresponds very well with that of the insects under observation. The caterpillars 

 which were supposed to have received a large dose were affected with a severe diarrhoea 

 and died within 20 to 30 hours. Some individuals were apparently affected more 

 than others, judging from the interval between feeding and death. In other tests 

 the insects became inactive, some ceased to feed, others would nibble here and there 

 until death ensued; while many of the larvae after one meal of poisoned foliage showed 

 symptoms of starvation, becoming less active, with an apparent drying of the body. 



