10 circular 3 6 9, u. s. department of agriculture 



Effect of Light or Darkness 



Light and darkness have no appreciable effect upon the results of a 

 fumigation. Although insects are more quickly affected while they 

 are active, entirely satisfactory results follow the application of a 

 fumigant during the day when the insects, such as cockroaches and 

 bedbugs, are chiefly resting in hiding places. In general professional 

 fumigators work at times most convenient to the establishment to 

 be fumigated without thought of light or darkness. In the case of 

 an insect such as the cockroach that forages in the dark, more in- 

 dividuals may be killed by a night fumigation if the daytime hiding 

 places are in wall spaces difficult of gas penetration. Usually, how- 

 ever, hiding places of insects in commercial plants are easily pene- 

 trated by fumigants. and the time of day the fumigant is applied is 

 therefore unimportant . 



Choice of a Fumigant 



In choosing a fumigant several factors must be taken into con- 

 sideration. If the building is modern and very tight, several fumi- 

 gants can be used with success, and a choice can be governed by such 

 items as cost, efficiency, availability, safety, and effect upon the com- 

 modity to be fumigated. If the building is not particularly tight, 

 it will be impossible to maintain a strong concentration of any gas 

 for very long, and a quick-acting gas is the only kind that will be 

 effective. Hydrocyanic acid is the only gas available that will kill 

 quickly. 



Quantity of Fumigant Needed 



The quantity of fumigant to be used will vary according to the 

 length of exposure, the temperature, the tightness of the building, the 

 amount of absorption and adsorption by the commodities to be fumi- 

 gated and by the walls and floors of the building itself, and the insect 

 to be eradicated. The shorter the exposure, the lower the tempera- 

 ture, the looser the construction of the building, the greater the absorp- 

 tion and adsorption, and the more resistant the insect, the greater 

 must be the dosage. The fumigator must exercise his own judgment 

 in each case. 



Applying the Fumigant 



The fumigant should be applied in such a way that a maximum 

 concentration will be obtained as quickly as possible. Since most com- 

 mercial establishments are not airtight, the natural leakage from a 

 building is often great enough to prevent a killing concentration from 

 ever being attained, particularly if it takes considerable time to reach 

 that concentration. From some buildings fumigants escape so rapidly 

 that it is not practical to fumigate them. In buildings that can be 

 fumigated with reasonable expectation of success, the best results are 

 obtained by releasing the entire dosage at the beginning of the 

 fumigation. 



A uniform concentration will be obtained more rapidly if the fumi- 

 gant is distributed equally throughout the building. When using 

 lighter-than-air gases it is not necessary to place the heaviest dosage 



