10 MASS. EXPERIMENT STATION BULLETIN 201. 



For instance, a relatively high temperature, low humidity and a good 

 circulation of air at the time of application, followed by warm, dry weather 

 should tend toward a minimum of arsenical injury. On the other hand, 

 factors conducive to solubility of the arsenic and its passage by osmosis 

 into the substance of the leaf are detrimental, as, for example, warm, 

 "muggy" weather, or warm weather accompanied by fogs or heavy dews. 

 Rains are not necessarily injurious if of sufficient quantity to wash off the 

 soluble arsenic as soon as it is formed. 



2. Hellebore. 



White hellebore is the powdered rhizome (root) of Veratnim album, 

 and green or American hellebore that of V. viride. Both are sold as insecti- 

 cides in the form of a gray powder containing about 1 per cent of alkaloids 

 (usuallj^ guaranteed from 0.30 to 0.42 per cent) and a varying amount of 

 ash. Though known to possess poisonous properties, hellebore received 

 little attention until about 1842 in England (17), and 1865 in this country 

 (18). 



The chief insecticidal action of hellebore is as a stomach poison. It 

 appears to possess also a certain value as a repellent. The active principles 

 which give hellebore its insecticidal value are certain alkaloids which are 

 poisonous to insects, but in amounts usually recommended for use do not 

 seriously affect man. These alkaloids are so volatile that the material soon 

 loses its strength and efficiency, particularly if exposed to the air. Con- 

 sequently a fresh product should always be demanded. Its non-poisonous 

 effect on man renders hellebore a suitable material for the protection against 

 chewing insects of fruits or vegetables that are about to ripen or are soon 

 to be eaten. It is, however, limited to rather small-scale applications, 

 the cost of the material prohibiting its use on large areas. The material 

 may be applied either dry or as a spray. In dry form it is used either 

 undiluted or mixed with five times its volume of flour or finely divided 

 air-slaked lime. For liquid application its use at the rate of \ ounce to 

 1 gallon of water is recommended. 



II. CONTACT POISONS FOR SUCKING INSECTS. 



Contact poisons include a large number of diversified compounds 

 (solid, liquid and gaseous), and their effectiveness may depend upon more 

 than one property. The compound may act in any of the following 

 ways : — 



1. Glue the insect down. 



2. Attack the body, dissolving fat and even muscle, precipitating proteids, etc. 



3. Act as a narcotic, paralyzant or ana;sthetic. 



4. Asphyxiate the insect by closing the breathing pores (spiracles or trachea;), 

 or, by saturating the body, prevent necessary aeration. 



