32 CIRCULAR 9 7 7, U. S. DEPARTMENT OF AGRICULTURE 



insecticide. The sawdust is either broadcast by hand or placed in 

 bags and thrown into the breeding places, sometimes before flooding 

 occurs. However, these methods have limited practical use, as the 

 duration of effectiveness is uncertain and they are not always so eco- 

 nomical as they may seem. Drip cans require frequent servicing, and 

 an excessive amount of larvicide is expended to maintain an effective 

 dosage. A much smaller quantity poured at the same points every 

 7 to 10 days will prevent the emergence of adults and require no more 

 labor. 



CONTROL OF ADULT MOSQUITOES 



In many respects the destruction of adult mosquitoes is even more 

 important in time of war than in peacetime. Troops entering an area 

 where malaria and other mosquito-borne diseases are prevalent may 

 be exposed for weeks to infected vectors even though operations for 

 control of larvae are initiated at once. On the other hand, rapid de- 

 struction of adult mosquitoes will prevent transmission of these dis- 

 eases. Ways of destroying adult mosquitoes have therefore been 

 given much attention, and effective methods are now in use that were 

 never employed before World War II. 



The work on adult mosquito control has been along three major 

 lines: (1) The development of sprays and equipment for destroying 

 them on a large scale out of doors, (2) the development of residual 

 treatments for buildings and other places where mosquitoes congre- 

 gate or alight, and (3) the use of aerosols and concentrated sprays for 

 indoor use. 



Outdoor Space Sprays 



Before DDT was available, pyrethrum sprays were frequently 

 used for the temporary protection of outdoor gatherings, such as pic- 

 nic parties and baseball crowds. In recent years DDT and other 

 synthetic organic compounds have been employed for destroying 

 mosquitoes over large areas. Airplane spraying is particularly well 

 adapted to this purpose (see pp. 42-55). Spraying with ground equip- 

 ment has also proved useful for reducing mosquitoes in small areas. It 

 is an economical and practical means of protecting troops in temporary 

 campsites or in small isolated installations. Some of the larger ma- 

 chines are also useful for treatment of larger camps when the main- 

 tenance of spray planes is not feasible or where spot spraying to meet 

 localized infestation is needed frequently. 



Many species of mosquitoes do not fly far from their resting places 

 during the day. Then destruction in small areas may therefore pro- 

 vide excellent protection even when others are numerous in surround- 

 ing untreated areas. At dusk the treated areas may be reinvaded so 

 that additional treatment is required. 



Hand-operated equipment. — Finely atomized sprays containing 5 per- 

 cent of DDT in kerosene have given excellent control of anopheline 

 and various kinds of pest mosquitoes. One means of dispersal over a 

 small area is a DeVilbiss-type paint sprayer operated from a hand- 

 pumped or other type of pressure tank (fig. 4). In nearly still air the 

 spray is dispersed in 20-foot swaths at the rate of % to 1 pint per acre. 

 The 2-gallon compression cylinder with a fine nozzle may be used in a 



