August, '14] GOODWIN: HEAT CONTROL FOR MILL INSECTS 319 



near the surface of infested material, especially ground cereals, and 

 also of pupating in similar places or near the confining walls, makes 

 heat an especially effective means for destroying these insects. Dry 

 heat was more effective than the moist heated atmosphere, as some 

 of the individuals would recover after being subjected to a moist heated 

 atmosphere; the heat and lack of moisture seemingly fixing the tissues 

 more readily than when moisture was present. 



Ephestia kuehniella was readily killed by either a moist or dry 

 heated atmosphere. The eggs and young larvse were destroA'ed if 

 actually subjected to 4o°C. to 46°C. for 15 to 20 minutes. The 

 other stages were killed if subjected to 47.5°C. to 48°C. for a similar 

 period of time. In many respects it resembled P. interpundella in the 

 effects of heat treatment. Its habits of living in the machines, eleva- 

 tors, spouts and conveyors in the center of the mill, make the dry 

 atmosphere high temperature a very effective means for its control. 



Conclusions and Practical Applications 



The practical value of high temperature at 48°C. to 50°C. for the 

 destruction of pests affecting cereal products is much lessened when 

 the heated atmosphere contains moisture in proportions greater than 

 40 per cent to 50 per cent. In practical work, if the moisture content 

 of the heated atmosphere remains constant, or is greatly increased as 

 the temperature rises, an increase, proportionally, in the amount of 

 radiating surface will be necessary in order to maintain and raise the 

 temperature to the fatal or killing point. Throughout the series of 

 experiments, the extreme difference in the quantity of gas required 

 to heat the oven during a dry heat test and to heat it during a moist 

 heat test was especially noticeable. The most careful estimates, based 

 upon the pressure of gas and the rapidity of its flow through a known 

 diameter opening, indicated that the extremely moist atmosphere 

 tests sometimes require almost twice as much gas as the extremel}^ 

 dry atmosphere tests. Careful measurements with adequate instru- 

 ments may discredit these estimates in part, but that an extra amount 

 of radiating surface is required, or that an excess of fuel is required to 

 heat the moist chamber, cannot be doubted. The latent heat absorbed 

 in vaporizing water accounts for these results. A fairly moist atmos- 

 phere at 47 °C. to 50°C. will prove fully as effective as the dry heated 

 atmosphere, but is not practical for use because of the difficulty in 

 obtaining 50°C. under moist conditions. The excess of radiating 

 surface required to heat the buildings to the killing temperature, in- 

 creases the cost of the heating plant, but sometimes it may be neces- 

 sary. All leaks in the heating system allowing water or steam to 

 escape into the rooms being heated should be repaired, especially if 



