288 THE MOSQUITOES OF NEW JERSEY 



should be stocked with fish and the banks should be likewise sharpened 

 for the purpose of enabling these fish to reach all parts of the pools and 

 to consume the wrigglers as they hatch in the waters. 



For temporary destruction of mosquito larvae the use of oils or lar- 

 vicides is necessary. Oil has the disadvantage of injuring to a greater 

 or less extent the appearance of the pools treated with it, because that 

 fraction of petroleum oil known as fuel oil, which is the most practical 

 to use for this purpose, has a burning action upon plants with which 

 it comes into contact. There is also some danger of destroying fish 

 and water fowl inhabiting the waters thus treated. Within recent 

 years a larvicide consisting of pyrethrum extract dissolved in fuel 

 oil, emulsified with a sulphated higher alcohol, mixed with water and 

 sprayed upon the water surfaces has been developed. With this material 

 a total of about six gallons of actual oil is required to cover one acre 

 surface of water, as compared with about forty to fifty gallons of fuel 

 oil, yet the poisonous quality to mosquito larvae is practically equal to 

 that of oil. This is due to the toxic action of the pyrethrum extract 

 upon mosquito larvae. This type of pyrethrum larvicide has no delete- 

 rious effect upon fish, nor upon water fowl, nor upon aquatic vegetation. 

 The cost per gallon of the diluted larvicide is about one-half of the cost 

 of fuel oil per gallon. The pyrethrum larvicide has the disadvantage, 

 however, of lasting for a much shorter period than the fuel oil and can- 

 not always and everywhere be used as a substitute for it. It was de- 

 veloped by the New Jersey Agricultural Experiment Station for the 

 purpose of putting in the haAds of the mosquito fighter a material which 

 might be used on water surfaces where fish, aquatic plants or water 

 fowl are an important consideration. 



All species of mosquitoes are readily killed by these larvicidal appli- 

 cations except Mansonia perturbans which remains at the bottom of the 

 soft-bottomed pools attached to the roots of aquatic plants throughout 

 the larval stage. Surface larvicidal treatments cannot, therefore, be ef- 

 fective with this species. The larvicides that mix with water require 

 great volume and are usually suflSciently poisonous to do harm to the 

 aquatic plants and to fish. The only satisfactory way of handling the 

 problem of Mansonia perturbans is to dig out the water plants growing 

 in the infested pool or pond or section of the lake, so deepening the 

 water that no aquatic plants can grow through, piling the debris thus 

 obtained along the edge, building up the banks so that the descent from 

 the upland to the water surface will be sharp, or by so lowering the 

 water level that the breeding places of this species are uncovered and 

 dry out. 



