The Mosquitoes of New Jersey 8i 



are usually where the marsh, which has been diked, sluiced and cul- 

 tivated, has been allowed to fall into neglect. The dikes have been 

 breached and the sluices have rotted away, and ordinary tide covers 

 the land regularly. In such places no breeding occurs except along 

 the edges of the highland where the water is screened away from the 

 fish. 



When dikes have been erected to keep the sea out, sluices and 

 tide-gates will be found useful to remove cheaply the surplus water 

 lowering the water level to about i foot above mean low tide. Pumps 

 must be installed to remove the balance because the surface is likely 

 to be covered more or less with pools after the utmost low water 

 reached by gravity has been attained. 



Pumps of various types have been used and thus far the low- 

 head centrifugal kind has been most satisfactory. One 12-inch pump 

 of this type when contributory ditching has been so arranged as to 

 permit it to work at its limit of efficiency seems quite sufficient to re- 

 move the surplus water from 1000 acres. Such a pump cannot do 

 this, however, unless the water is removed and a reservoir of sur- 

 face soil from 8 to 12 inches thick has been dried out before the 

 mosquito season starts, for with water at the marsh surface an ex- 

 tra heavy rainfall would so fill up the marsh that mosquitoes would 

 probably escape before the water could be drawn ofif. This would 

 be especially likely to occur when the rainy period is followed by 

 cloudy weather, reducing evaporation to the minimum. 



In dealing with marshes of this type either provision must be 

 made to bring in brackish water with its supply of killifish, to be 

 circulated through the ditches, or the ditches must be pumped dry 

 and kept so. The former alternative is probably the better plan, 

 because the adoption of the latter is likely to be followed by the ap- 

 pearance of growth in the bottom of the drains creating blockages 

 and eventually breeding places. 



The enclosed, shrunken and polluted salt marsh. The third 

 type of enclosed marsh (enclosed, shrunken and polluted) must 

 be enclosed to keep the sea out and must be pumped dry 

 and kept pumped dry throughout the mosquito-breeding sea- 

 son. Much greater pumping capacity will be required than in the 

 second type because not only rainfall but constant sewage discharge 

 must be removed. The size of the pump depends not only on the 

 acreage to be cared for but upon the volume of sewage being dis- 

 charged. 



The introduction of brackish water into such a marsh is usually 



