T02 N. J. Mosquito Extermination Association 



While, in the first case, the work necessary to control fresh-water 

 breeding is greatly increased, it consists for the most part in the 

 treatment of a larger number of pools, small swamp areas and 

 similar isolated breeding places that rapidly disappear on the cessa- 

 tion of the rains. If, as is the case in the Philadelphia district, the 

 rainfall over an, area of about 25 square miles is concentrated on 

 some 8,000 acres of diked marsh-land, an entirely dif¥erent situation 

 arises. The area becomes totally or partially submerged and the 

 control of breeding becomes an impossibility until the water levels 

 are reduced. Nor is it sufficient merely to unwater the marsh areas. 

 The ground water must be lowered before effective seepage occurs 

 and the isolated pools become dry. 



In the present instance, the latter part of July witnessed a precipi- 

 tation of over 9 inches in 11 days of constant rain with a total, at 

 the end of the month, of over 10 inches. In the records of the 

 local weather bureau for the past 47 years such a monthly total has 

 been equaled on only three other occasions. As was to be ex- 

 pected there was little, if any, play of the tide-gates and, with 

 virtually no evaporation, the entire burden was thrown upon the 

 pumps. With a combined capacity of over six and one-half million 

 gallons per hour and with 24-hour operation, they were unable to 

 handle the volume of water in time to prevent the flooding of the 

 lowlands. Pools, depressions and marsh areas that had been dry 

 since the spring of 1918 were filled with water and in a few days 

 with larvae of Aedes sylvestris hatched from eggs that had Iain 

 dormant a year or more. Even with the large capacity of the pump- 

 ing stations it was a matter of several weeks before the ground 

 water was reduced and the pools eliminated. 



To have prevented the appearance of any appreciable number of 

 adults was obviously out of the question. Nothing could be done 

 while the rains continued and the marshes were flooded. Later it 

 would have required a force of several hundred men for oiling and 

 mowing alone. Even had it been possible to organize the necessary 

 force in time, the fact that the war emergency no longer existed 

 would not justify the expenditures involved in such an undertaking. 

 The plan followed was to alleviate what would otherwise have be- 

 come an intolerable situation by making such an increase in the force 

 as available funds permitted, by transferring men from other opera- 

 tions to temporary work and by speeding up the work to the highest 

 possible pitch. In this way the situation was held within reasonable 



