HEAT 221 



species. On the other hand, these same observers ascertained 

 that five minutes' subjection to a temperature of 62-8° was required 

 to kill Rhizopertha dominica, also a grain-infesting beetle, but one 

 which appears to be especially resistant to a high temperature. 

 Clothes moth larvae are killed after thirty-one minutes at 53-3° 

 (Back), and the beetle Silvanus surinamensis in all its stages 

 succumbs at a temperature of 51 -T" (Back and Cotton). Pediculus 

 humanus, according to Nuttall, is killed in dry heat at 55° after 

 five minutes' exposure, while its eggs require ten minutes at 

 55° to 61°. 



The practical application of fatal high temperatures, with 

 reference to insects infesting stored grain and analogous products, 

 has come very much to the fore in recent years, and there is a 

 considerable literature on the subject. Under such conditions it 

 is obviously essential to ensure that every part of the material 

 is heated to the temperature known to be lethal to the insects 

 concerned. Much depends, therefore, upon the nature of the 

 stored product that it is desired to sterilise, its moisture content 

 and its bulk. Recent experiments by Barber (1929), with 

 reference to the killing of caterpillars of the corn borer (Pyrausta 

 nubilalis) within the ears of maize, will serve to illustrate this 

 point. It appears that fifteen minutes' exposure to a temperature 

 of 54° is necessary to kill these larvae. On the other hand, to 

 attain this temperature within the corn cobs the latter require to 

 be subjected to a temperature of at least 60° for a period of eight 

 hours, or for a shorter time at higher temperatures. It is probable 

 that if stored food-products be heated uniformly to a temperature 

 of 62-8°, and maintained at that temperature for five minutes, they 

 will be completely sterilised as regards all insect life (Dendy and 

 Elkington). The same result, however, would be achieved by more 

 prolonged exposure at lower temperatures, and it appears from a 

 recent bulletin by Dean, Cotton and Wagner (1936) that a tempera- 

 ture of 49° to 52°, applied for a period of ten to twelve hours, is 

 sufficient to kill the various insect inhabitants of flour mills. 

 • Fatal Temperatures. B. Cold.^ When insects are subjected to 



^ The greater part of this section is taken from a paper by A. D. Imms in 

 Annals App. Biol., XIX., 1932, p. 125. 



