2 CIRCULAR 6 00,, U. S. DEPT. OF AGRICULTURE 



This circular describes some of the possibilities of using cold storage for 

 this purpose. 



The senior author 2 has already presented evidence showing that all 

 apple maggot eggs and larvae will be killed within slightly more than 

 30 days when infested fruit is held in an air temperature of 32° F. The 

 two main objectives in the investigation reported here were (1) to 

 determine, more precisely, how many days' exposure at 32° are re- 

 quired to effect complete mortality and (2) to determine the efficiency 

 of higher temperatures, namely, 36° and 40°. 



MATERIALS AND PROCEDURE 



All the fruit used in the present study was of the Fameuse variety. 

 The test fruit came from 5 orchards, which varied greatly in degree of 

 infestation. Some lots averaged only 2 or 3 egg punctures per apple, 

 whereas others averaged 30 or more, extremes for individual fruits 

 ranging between 1 and 89 egg punctures. There were similar wide 

 differences among the lots in the stages of the insect present and in the 

 degree of fruit maturity. Classes under the latter category included 

 windfalls, ripe picked fruit, and slightly green picked fruit. With respect 

 to the insect stages, the length of time required for emergence of most 

 of the larvae in the controls (fig. 4) indicates that the pest was present 

 largely in the first and second instars. Some lots, however, contained 

 unhatched eggs and others — windfall fruit especially — included third 

 instars. 



The use of such diverse material has the advantage of giving results 

 representative of any class of fruit that might be submitted for disinf es- 

 tation. This experimental advantage, however, is contingent upon the 

 assembly of a homogeneous series of experimental units. That this 

 objective was gained in the present instance is shown by the uniformity 

 of the average number of egg punctures per fruit of the various lots 

 (table 1). 



Each experimental unit of fruit was put ina. standard unlined bushel 

 tub basket. The apples were not wrapped. In the refrigeration room 

 these baskets were arranged in a group 2 feet or more above the floor. 

 When a lot was removed from storage, each fruit was examined under 

 magnification to obtain a record of the infestation as indicated by the 

 egg punctures present. The lot was then placed in larval rearing 

 equipment of the type illustrated in an earlier report 2 and held at 

 temperatures ranging between 65° and 80° F. for a time sufficient to 

 allow any larvae present to complete development and emerge. Some 

 fruit was also kept in this equipment in each of the storage rooms to 

 ascertain whether or not emergence might occur at the temperatures 

 maintained. 



Experimental lots were placed in refrigeration rooms held at air 

 temperatures of approximately 32°, 36°, and 40° F. The cooling unit 

 in each case consisted of brine coils located at the ceiling, and air move- 

 ment was limited to that induced by gravity. A continuous record of 

 the air temperature in these rooms was taken by means of recording 

 thermographs installed centrally among the baskets. In general, 

 temperature fluctuations were minor, as is indicated by the mean tem- 

 peratures given for each treated lot in table 1. These are averages of 

 hourly readings as recorded on the thermograph charts. 



1 Chapman, Paul J. viability of eggs and larvae of the apple maggot (rhagoletis pomonella 

 walsh) at 32° f. N. Y. State Agr. Expt. Sta. Tech. Bui. 206, 19 pp., illus. 1933. 



