50 



MASS. EXPERIMENT STATION BULLETIN 184. 



Co7nparative Efficiency of Lime-Sulfur and Miscible Oils against Apple 

 Aphid Eggs in the Late Dormant Period under Laboratory Condi- 

 tions. 



Discussion of Results. 



While these results can hardly be accepted as conclusive, for the reasons 

 given above, it seems evident that lime-sulfur thoroughly appUed at the 

 late dormant period is highly effective under favorable conditions in 

 destrojdng the aphid eggs, and is certainly more efficient against this 

 stage of the insect than miscible oils. Of course, in dipping the twigs it 

 is to be expected that better results would be obtained than in the ordinary 

 practice of orchard spraying, and it is also true that under field conditions, 

 as will be pointed out under the topic "Action of Lime-sulfur and Miscible 

 Oils upon the Aphid Eggs," discussed later, the intervention of rain 

 between the time of appHcation and the normal hatching period might 

 alter results to a marked degree. This may account to some extent for 

 the frequent ineffective control of apple aphids by the dormant or late 

 dormant season lime-sulfur treatment, with which absolute thoroughness 

 is practically impossible under field conditions, and which has also the 

 added element of uncertainty of results due to the meteorological factor 

 just mentioned. The hatching of a comparatively small number of eggs 

 that have survived treatment might result in quite a severe infestation 

 before the season is far advanced. There is also to be considered the 

 possibility of reinfestation from other sources by migrants in the case of 

 the green apple aphis. The destruction of the eggs or suppression of the 

 stem mothers in the spring does not always guarantee freedom from 

 these insects during midsummer, when supplementary treatments are 

 sometimes desirable or necessary. The miscible oils do not appear to be 

 very effective against the aphid eggs, even with absolute thoroughness of 

 appUcation; and it is probable that a sufficient number of eggs would 

 withstand the treatment, to produce a severe infestation later in the 

 season, unless other measures were taken for control. 



Action of Lime-sulfur and Miscible Oils upon the Aphid Eggs. — Obser- 

 vations as to the killing power of the lime-sulfur against the aphid eggs 

 indicate that the effectiveness of this material is due mainly to a me- 

 chanical action. On twigs examined after dipping, it was noticed that as 

 the lime-sulfur dried it tended to stick down the eggs and mat the twig 



