EXPERIMENT STATION BULLETINS. 59] 



Seven respiration experiments, in all, were carried out with this 

 dormant apple tree. The range of temperature, and of light and dark 

 conditions is represented in the table. In every case oxygen was used 

 by the tree and carbon dioxide given off. 



It is certain that the scale insects themselves respire, taking up 

 oxygen and giving off carbon dioxide, but no determinations of the rate 

 of respiration for these delicate bodied insects was obtained. Ke>pira- 

 tion experiments with plant lice, however, were carried out which 

 showed that (per unit of body weight; their respiratory activity was 

 much greater than for larger insects tried (see Xo. 5,' Table TV, for 

 example). Furthermore, it was found that respiration (per unit of 

 body weight) in young plant lice, was nearly twice as active as in the 

 case of adults of the same species. It seems very probable, therefore, 

 that the comparative respiratory rate for minute scale insects is rather 

 high. 



On a dormant apple tree, then, the limited air space about a scale 

 insect (the scale covering of which has been treated with lime-sulphur) 

 must tend to become deficient in oxygen from three causes: — 



The tree on one side is using oxygen and giving off carbon dioxide. 

 On all other sides is the waxy scale covering coated with lime-sulphur 

 which uses oxygen more or less rapidly, depending upon moisture condi- 

 tions, and which tends at first to seal the scale to the tree. Finally, 

 the enclosed insect itself uses oxygen and gives off carbon dioxide. 



All this is not absohite proof that the scale insect, which becomes 

 comatose (i. e., unable to move until after being exposed to fresh air) 

 beneath a treated scale-covering, suffers from lack of sufficient oxygen; 

 but it is much good evidence that such may be the case. 



One other possibility should be suggested. It is now well known, and 

 may be easily shown, that carbon dioxide in considerable amounts, 

 when confined with lime-sulphur gives rise to hydrogen sulphide. This 

 is a poisonous gas to insects; and with a solution of lime-sulphur pres- 

 ent, all the conditions Avould exist for the formation of a small amount 

 of that gas beneath the scale-covering of a living scale insect. But no 

 means could be found to prove the presence of hydrogen sulphide, satis- 

 factorily, beneath a treated scale-covering. 



Two properties — strong reducing power (i e., great affinity to take up 

 large amounts of oxygen) together with the ability to. at first, soften 

 or partiall}^ dissolve the newly secreted wax at the margin of the scale 

 — appear to be the most important in making lime-sulphur an efficient 

 scalecide. If this is true, then that chemical combination of lime and 

 sulphur which will make the strongest, most persistent redticing agent, 

 and whose solution will at the same time be able to soften the wax 

 about the margins of the scale-covering best. Avould seem to be the 

 most desirable combination for a wash against scale insects. 



Laboratory tests have shown that anything which tended to increase 

 the alkalinitv of the wash, enabled it to more readilv attack the wax 

 of the scale. Ammonia, potassium hydrate, and whitewash made from 

 slaked lime were tried. The latter would, of course, be cheapest and 

 it wotiild seem most likely to prove practical. 



When a solution of potassium hydrate was added to lime-sulphur- 

 the potassium replaced some of the calcium, throwing it down as a 

 precipitate. Ammonia seemed to affect no combination with the sul- 



