18 MISC. PUBLICATION 336, U. S. DEPT. OF AGRICULTURE 
are very moist at the time of collection, drying in the air for a week 
or so may be necessary to induce hatching of the eggs. 
ENGINEERING SURVEYS 
During a mosquito survey much information will be accumulated 
which will be valuable in determining the feasibility of an anti- 
mosquito project and the best methods to be employed in handling 
specific problems. Where malaria or salt-marsh mosquitoes are to 
be controlled, an engineering survey is then undertaken to lay out 
the detailed plan of ditching and other operations, and to determine 
the approximate costs. Whether the local situation can be handled 
successfully within the means at hand, or at a cost commensurate 
with the probable benefits, is one of the first questions to be decided. 
Matters of the legality of the proposed work (including jurisdiction 
over the area involved), the probability of obtaining necessary ease- 
ments on private property, etc., must also be considered. 
Good maps are, of course, essential, and should be available both 
in smal] scale for use as key maps and in large scale for showing in 
detail the breeding places, ditching lay-outs, and natural topographic 
features. The different areas and the individual breeding places 
can then be given names or numbers for convenient reference to 
the mosquito-collection and engineering notes. Aerial photographic 
maps of rural or marsh areas are extremely valuable, as they show 
the bodies of water and the types of vegetation. A note-card system 
should be arranged and complete records kept of all inspection and 
survey data. 
For breeding-place or other preliminary surveys when elevations 
or exact locations are not required, the directions given by Hulse (84) 
for preparing field maps in public-health work based on methods 
employed in the military service are very useful. 
CoNTROL OF Mosquiro LARVAE 
Mosquito-control measures are usually directed against the larvae, 
since this seems to be the most vulnerable stage in their life cycle. 
ELIMINATION OF BREEDING PLACES 
Where at all feasible, efforts are made to eliminate the breeding 
places permanently by filling, drainage, or sanitation. 
Filling is frequently an economical method and gives permanent 
rehef when the fills are so graded as to leave no water-holding de- 
pressions. Large hydraulic fills, however, usually show shrinkage 
or surface cracks upon drying and may require one or more regrad- 
ings to prevent mosquito breeding. 
Drainage undoubtedly has the widest application of the various 
antilarval measures, especially in the control of the malaria carriers 
and the salt-marsh species. The drainage of swamplands in the 
United States has done much to reduce the malarious area and at the 
same time has made the land suitable for agriculture. Drainage or 
ditching purely for mosquito control, however, should be looked 
upon as distinct from agricultural drainage, since it is directed mainly 
toward the elimination of surface water during the time required 
