5S4 STATE BOARD OF AGRICULTURE. 



In the lusectary, an orange tree whicli was covered witli Aspidiotus 

 (ChrysompMlus) fiais afforded excellent opportunity for studying the 

 action of the wash on scale insects. First, it was found that when home- 

 made wash (Lime 20 lbs., sulphur 15 lbs. and water 50 gals.) was ap- 

 plied to these scales it rendered many of them partly dormant after 

 a few hours. That is, when the scale coverings were lifted up from 

 insects, a few hours after they had been treated, many of the little in- 

 sects were unable to move until after three or four minutes exposure 

 to the air. When untreated scale-coverings were lifted, the muscles of 

 the delicate walled insects contracted, usually, so as to telescope the 

 abdomen and pucker the body up into a shapeless little lump. If the 

 contraction had not occurred upon lifting the scale, a touch with a 

 needle point would cause the body to contract as described. But many 

 of the insects beneath treated scales would not respond, even to the 

 needle prick, until after they had been exposed to the fresh air (i. e., 

 after the scale-covering had been lifted) for a few minutes; and then the 

 response, when it came, was sluggish or slow. 



Similar results were observed when home-made concentrate diluted to 

 the strength of a winter wash was used. 



It had been suggested by some that the odor often noted on sunny 

 days in orchards freshly sprayed with lime-sulphur was similar to that 

 of sulphur dioxide. Knowing that small amounts of that gas can readily 

 bring about torpor and death in insects, tests were arranged to deter- 

 mine whether the gas is actually given off from a surface sprayed with 

 the wash. Lime-sulphur on paper and on twigs (both moist and dry) 

 was placed above mercury in the respiration chambers already described, 

 and allowed to stand confined with the air for various periods of time 

 up to ten days. For about five hours each day the containers were 

 exposed to strong sunlight. The air thus confined was tested for sul- 

 phur dioxide by passing it into a solution .of iodic acid with starch 

 paste. No trace of sulphur dioxide was found in any case. Other ex- 

 periments went to show that sulphur dioxide would not be formed in 

 appreciable amounts from the sulphur deposited by lime-sulphur ex- 

 cept at temperatures much above those found under spraying conditions 

 in the orchard. 



It was noticed, however, in these experiments in which lime-sulphur 

 was confined with air, that the volume of the air was decreased. The 

 decreased volume was found to be due to a loss of oxygen. This was 

 not strange, since Haywood* ('07) and others have shown that lime- 

 sulphur wash is composed largely of polysulphids of calcium which ox- 

 idize on exposure to the air, forming calcium thiosulphate and free sul- 

 phur — the thiosulphate oxidizing further to the sulphite and this, per- 

 haps, finally to the sulphate. The surprising thing was this — the loss in 

 volume, as noticed, indicated that very considerable quantities of oxygen 

 had been used. When a scale was covered with the wash, could it be 

 possible that oxygen was used in such amounts as to partially or wholly 

 deprive the insect beneath the scale-covering of that gas? 



A study was next made to discover whether the bodies of the little 

 insects rendered comatose beneath scales treated with lime-sulphur had 

 really all been wet with the spray. From observations already made it 

 had seemed that some of them at least had not been wet at all. It was 



*J. K. Haywood, Feb. 1907, Bulletin 101, Bureau of Chemistry. 



