22 MISC. PUBLICATION 336, U. S. DEPT. OF AGRICULTURE 



face that they act as a mechanical barrier to mosquito breeding, al- 

 though Anopheles and Gulex larvae are found associated in abund- 

 ance with them when the growth is scattered. Water hyacinths 

 (Piaropus) may also act in somewhat the same way. Matheson (91) 

 gives a review of the literature on this subject. 



CONTROL OF ADULT MOSQUITOES 



Screens, bed nets, repellents, contact sprays, smudges, and fumi- 

 gants are all employed for protection against mosquito annoyance. 



In the screening of houses galvanized or copper screens are usually 

 employed, and the 16-mesh screen has come to be a standard size 

 for this purpose. Copper (or bronze) screens, although higher in 

 first cost, are the more durable, especially in the vicinity of salt 

 water. Monel-metal screens have also been recommended in such 

 situations. To be effective the screening must be carefully done 

 and special attention paid to the fitting of door and window frames, 

 a's mosquitoes will find entrance through very small openings. Bed 

 nets made of open-mesh cloth are used extensively in some localities 

 in the absence of, or to supplement, screening. They are frequently 

 employed for protection of individuals, especially in malarious or 

 salt-marsh areas. To be of value they should be in good repair and 

 carefully adjusted. 



Kerosene extract of pyrethrum (insect powder) is very effective 

 a's a contact spray and is useful in destroying mosquitoes that have 

 gained entrance to screened houses. Most of the commercial fly 

 sprays contain this extract. Home-made sprays may be prepared by 

 soaking 1 pound of the ground pyrethrum flowers in a gallon of 

 kerosene for 24 hours or longer, and then pouring off the super- 

 natant fluid for use. "Water-white kerosene is generally used for this 

 purpose to avoid staining of the clothing or walls. The pyrethrum 

 spray is also effective temporarily as a mosquito repellent when 

 sprayed on the ankles or the clothing. For application on the skin, 

 a mixture of a concentrated extract with a nonirritating oil such as 

 petrolatum or liquid vaseline may be used. Oil of citronella and 

 other essential oils have long been used as temporary repellents. One 

 formula, recommended by Howard and Bishopp (67), consists of 1 

 part of oil of cedar, 2 parts of citronella, and 2 parts of spirits of 

 camphor. 



The dry pyrethrum powder is sometimes burned as a fumigant 

 for destroying mosquitoes in closed rooms. It is also used as a repel- 

 lent smudge, and the writers have seen it employed with good results 

 in a large screened camp into which swarms of salt-marsh mos- 

 quitoes gained entrance with each opening of the door. In the open 

 room the fumes were not strong enough to be objectionable to the 

 persons present but were sufficiently toxic to incapacitate the insects. 

 To make the smudge the powder is mounded on a plate or other flat 

 dish and ignited at the top with the aid of a little alcohol. One or 

 more dishes may be used, depending on the size of the room. Grass 

 or wood smudges provide some relief to livestock in open fields and 

 stables during severe outbreaks of mosquitoes. It seems probable 

 that the pyrethrum smudge would be much more effective than the 

 wood smoke for use in the stables. 



