THE MOSQUITOES OF THE SOUTHEASTERN STATES 21 
While the dilute pyrethrum is not toxic to fish, it is probably more 
injurious than an oil film or paris green to many of the aquatic insect 
predators. For anopheline control it is much more expensive than 
paris green (70). 
NATURAL ENEMIES OF LARVAE 
Various kinds of insects and other animals prey upon mosquito 
larvae and undoubtedly destroy large numbers. Of the many nat- 
ural enemies, however, in most cases only the small larva-eating fishes 
have been found of practical use in control. In the Southern States 
the most important of these is the top-water minnow (Gambusia 
affinis), which occurs in both fresh and brackish water. These fish 
are most effective against subsurface-feeding larvae and in places 
where the larvae are not protected by aquatic vegetation. They 
have been used to stock ornamental pools and other isolated bodies of 
water. They are highly useful in permanent ponds and in the salt 
marshes. The International Health Board of the Rockefeller Foun- 
dation (133) has prepared a review of the literature on the use of 
fish for mosquito control, and Hinman (75, 76) has given numerous 
references on other predators of mosquitoes. 
Different aquatic plants have been claimed to be of value in elim- 
inating mosquito breeding. One species of Chara (C. fragilis) ap- 
pears to exert a deterrent effect, although certain other species of 
this genus have been found to be innocuous. The bladderworts 
(Utricularia) capture and destroy small aquatic animals, including 
mosquito larvae. Duckweed (Zemna) and similar floating plants 
(Azolla and Wolffia) may form such dense mats on the water sur- 
face that they act as a mechanical barrier to mosquito breeding, al- 
though Anopheles and Culex larvae are found associated in abun- 
dance with them when the growth is scattered. Water hyacinths 
(Piaropus) may also act in somewhat the same way. Matheson (7/6) 
gives a review of the literature on this subject. 
ContTroL oF ADULT MOoSsQUuITOES 
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 atten- 
tion paid to the fitting of door and window frames, as 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 as 
a contact spray and is useful in destroying mosquitoes that have gained 
-entrance to screened houses. Most of the commercial fly sprays con- 
tain this extract. Home-made sprays may be prepared by soaking 
