6 U. S. BUREAU OF FISHERIES. 



methods of relative precision. The solution of many existing aspects 

 of the mosquito problem must be sought through the methods of 

 ecology. 



In applying these methods to an existing mosquito nuisance ^ the 

 first step toward mitigation is to ascertain the species involved, 

 whence they come, and the ecological associations to which they be- 

 long. When the latter come to be studied, it will probably be learned 

 that a condition or conditions exist peculiarly favorable to the de- 

 velopment and survival of the young stages of mosquitoes or, what 

 amounts to the same thing, that are unfavorable to the action of 

 natural repressive influences. Such may be the absence or paucity 

 of enemies or their ineffectiveness through the existence of physical 

 or physiological barriers. It may be that the productive breeding 

 places are newly established water areas, into which the more im- 

 portant inhibitory elements of the association have not yet pene- 

 trated or where they have not yet reached their normal numbers. 

 It may be that some specific change in the physical or organic en- 

 vironment has taken place which acts as a check to the multiplica- 

 tion of an important enemy but remains neutral to the mosquitoes ; 

 or it may be that a barrier has arisen which prevents these enemies, 

 although present in sufficient numbers, from reaching the mosquitoes 

 and which serves, therefore, as an added means of defense for the 

 latter. It may be simply that food for the larvae is unusually abun- 

 dant and nutritious, and this again may arise from conditions of 

 water, temperature, etc., favoring the growth of minute organisms; 

 or it may be due to the absence or scarcity of animals which ordi- 

 narily compete for the same food supply. All of these and other 

 conditions were met with in the course of this investigation. 



When the factor or factors which (from the viewpoint of mosquito 

 control) are at fault in any particular case have been ascertained, 

 it remains to neutralize or remove it or them with as little disturb- 

 ance of the remaining factors as is consistent with attaining the 

 desired end of reduction of the mosquito element to a very subor- 

 dinate place in the complex. In many cases it has been found easily 

 possible to effect this without seriouslj^ jeopardizing any of the other 

 living elements or other human interests. Looking upon the rela- 

 tionship as a struggle between the mosquitoes and their enemies and 

 competitors and on man as a powerful ally of the latter, the general 

 strategic policy should be whenever possible to weaken the defenses 

 and protective adaptations of the mosquitoes and to strengthen the 

 offensive of their enemies. The tactics suitable to particular con- 

 flicts readily follow. 



The theory of natural control has been discussed at some length 

 not because the writer considers that he has anything particularly 

 novel to offer on the subject — for doubtless all biologists and cer- 

 tainly all biologists of ecological training view it from much the 

 same standpoint — but because conversations with a number of per- 

 sons engaged in antimosquito work have shown a prevalence of the 

 so-called practical attitude of demanding quick results and a single 

 purpose, which is the attitude that has stripped our country of its 

 forests, lowered the fertihty of much of our agricultural land, con- 



=^ These principles l^^ive no application to small, artificial containers of water, temporary 

 pools, waters badly polluted by sewage, reclaimed swamps, etc., which produce vast num- 

 bers of mosquitoes and which are best dealt with by mechanical or chemical means. 



