Carpenter et al.: Mosquitoes of Southern U. S. 19 



need for larval control; (3) the effectiveness of the larvicidal program; and 

 (4) any changes in breeding conditions that may occur. 



Larval Stations. — The individual lakes, ponds, sections of streams, ditches, 

 tree holes, groups of small adjacent pools and other specific larval habitats 

 may be designated as larval stations from which regular collections are made, 

 preferably at weekly intervals. In addition to the collections obtained from 

 regular larval stations, frequent miscellaneous collections from other places 

 should be made in order to obtain a more complete picture of the problem. 



Equipment. — Larvae are usually collected with a white-enameled dipper 

 having a hollow handle into which a round stick or cane may be inserted for 

 convenience. Shallow, white-enameled rectangular pans are preferred by some 

 collectors. A rubber suction bulb attached to 3 or 4 feet of rubber hose is 

 a convenient device for collecting larvae from tree holes, crab holes, and 

 similar inaccessible places. Other apparatus for collecting larvae include nets 

 of various types and sizes, soup ladles, small dishes, spoons, and large glass 

 pipettes with rubber bulbs attached. 



Collecting Technique. — Dipping should be dore in a systematic and uni- 

 form manner in order to provide data as to the comparative abundance of 

 larvae at different seasons or in different areas. For Anopheles, the dips are 

 made by skimming the surface of the water in places where aquatic vegetation 

 or floating debris offer protection for the larvae. As it is usually desired to 

 obtain a fair sample of the larvae present in a breeding place, the dips should 

 be adequately distributed over the station: the tendency to make most of the 

 dips in a few spots should be avoided. The number of dips made when search- 

 ing for larvae should mainly depend upon the size and type of breeding 

 place and the abundance of larvae. 



Larvae of some species sink to the bottom rapidly when disturbed and 

 remain there for several minutes. If the collector will remain quiet near pools 

 in which these mosquitoes breed, the larvae and pupae may be picked up 

 singly with a dipper or pipette as they come to the surface. When collecting 

 Anopheles larvae from small pools, it is often advisable to remove the vege- 

 tation from a small area; then stir up the water, making it muddy. Larvae 

 and pupae are very conspicuous against the muddy background anrl can be 

 collected with a pipette or spoon as they appear on the surface. When col- 

 lections are taken from tree holes, crab holes, and other specialized breeding 

 places by means of a suction bulb and hose, the water should be emptied 

 into a white-enameled pan to be examined for larvae. The suction bulb 

 should be thoroughly rinsed after each collection, as specimens may cling 

 inside it and appear to come from the next breeding place inspected. 



Fourth instar larvae should be selected for identification, as immature 

 specimens of most species cannot be accurately identified. It is often advisable 

 to preserve the larvae in small vials at the time of collection, but if they are 

 to be taken alive to a laboratory for studv, they may be transferred bv means 

 of a pipette from, the dipper or other collecting device to a wide-mouth bottle 

 or jar. Such containers should never be left in open sunlight, and during warm 



