496 STATE BOARD OF AGRICULTURE. 



solution were foiiiul to be less permeable to oxygen than before they 

 were treated with the solution. Thus lime-sulphur, in addition to its 

 effect as described in a former pai)er, would render the Avaxen covering 

 of a scale insect less permeable to oxygen. 



Pupa? of the Luna moth, and adults of Passalus coniutus in a dormant 

 condition from cold, absorbed much less gasoline-vapor or vapor of ether 

 in air than did the same insects when they were most active, at a warm 

 room temperature, in air charged with practically the same percentage 

 of vapor. This lowered absorption capacit}', which was found to accom- 

 pan}' the dormant condition, may furnish the chief explanation of the 

 fact that insects, dormant from cold, are harder to kill by ordinary 

 fumigants and by those contact sprays which depend partly upon vola- 

 tile insecticide ingredients for their effectiveness. 



It was found that certain non-volatile, powdered solids were able to 

 act as effective contact insecticides when used on certain insects. Such 

 dry, powdered insecticides stuck fast in exudations on portions of the 

 insect body, where they became partly dissolved, after Avhich they ap- 

 I)eared to be slowly absorbed through the body-integument. 



Both powdered borax and sodium fluoride may kill cockroaches in the 

 manner of purely contact agents, but normally they become stomach 

 poisons as well — since the roaches regularly lick and swallow some of 

 the powder in cleaning it from their bodies. 



In the case of powdered solid contact insecticides, the advantage 

 seemed to lie in having the powder so line and dry that it could sift 

 readily into all crevices and could adhere well. Similarly, other things 

 being equal, a weak surface tension gave a liquid contact insecticide an 

 advantage, enal)]ing it to thoroughly wet the liodies of insects and to flow 

 into all irregularities of the area treated. 



Among several substances which were found to increase the ''spread" 

 of lime-sulphur solution, saponin or extracts taken directly from the 

 stems and leaves of ^aponarki officinalis (bouncing bet) seemed to be 

 best. It is suggested that perhaps the use of extracts from "bouncing- 

 bet hay*' with lime sulphur solution might prove profitable in orchard 

 spray-practice. 



Exjjeriments with ammonia (derived from dry liquefied ammonia) as 

 a fumigant for mill insects were rather disappointing; but the liquified 

 ammonia Avas easy to apply and might prove to be a desirable fumigant 

 for insects in some instances. 



When carbon tetrachloride was compared with carbon disulphide as 

 to its action on grain insects in tight flasks, six times as much of the 

 former was lequired for effective fumigation. The carbon tetrachloiide 

 Avas vaporized with heat and satisfactorily used, at the rate of 3.55 lt)s. 

 for 100 cubic feet of air space, to insure furs against moths — fumigation 

 being repeated CAery five weeks during the summer months. The charge 

 as used killed adults of Tinea biselliclla. 



Evidence indicates that heat might be applied to advantage as an in- 

 secticide in many situations where it has neA'cr been the practice to use 

 it. 



