REPORT ON MOSQUITOES. 129 



ing is better. Used wherever there are any fish, these will be 

 killed with the wrigglers that may be at the edges, and after the 

 material has disappeared the mosquito development will be 

 greater than ever, because even the open areas will then be safe 

 to them, for lack of fish to keep them down. Nevertheless, the 

 Phinotas oil is a valuable auxiliary in a mosquito campaign, and 

 its cost, about 40 cents per gallon, is not excessive in proportion 

 to the effects obtained. In my notes I had detennined the mini- 

 mum amount that was certainly effective; but as these are lost, 

 my recollection that it was i part in 100,000 parts of water must 

 be accepted subject to revision after further tests. 



It has the advantage of being fatal to pupae at the same 

 strength that it kills larv?e, but it is not soluble in salt or dis- 

 tinctly brackish water. It is therefore of no value along shore 

 except in rain pools or where there is only a mere trace of salt 

 in the water. 



The simplest and cheapest larvicide is common kerosene of low 

 grade, or, better, the material known as fuel oil. It costs from 

 10 to 13 cents a gallon, or even less, and an ounce of it applied as 

 a spray will cover about fifteen square feet of water area with 

 a film sufficient to kill all mosquito larvae or pupae that rise to 

 the surface to breathe. Young and mature larvae are equally 

 affected, and pupae resist very little more. Fish and insects that 

 do not come to the surface tO' breathe are not affected, and those 

 diving beetles that must get their supply of oxygen from the 

 air will fly from the pools as soon as they discover the presence 

 of the oil. So' long as the film remains, any adult mosquito that 

 attempts to oviposit on the surface will be caught and killed. It 

 acts almost equally well on salt water, and the only drawback 

 is that the film is easily broken and may be driven by even a 

 slight wind to one shore, where it is absorbed by the soil or in 

 the vegetation, leaving- a free field for a new infestation. In 

 sheltered pools or in barrels the film lasts a long time, and even 

 after the oily gloss has disappeared there is a remnant that is 

 effective. It may be used in rain barrels or cisterns where the 

 water is drawn from the bottom ; but unless the film is very thin, 

 a slight taste of oil will be detected after a few days. If the 

 water is used for washing or other purposes than personal con- 

 sumption this will not matter. 



The oil has no disinfecting qualities and is offensive in gut- 

 ters and ' lainage ditches, hence I prefer tO' use the chloronap- 

 tholeum tiiere. That there is a difficulty in reaching Anopheles 

 and other larvae that seek shelter among dense vegetation is no 

 fault of the oil. It is a matter of application, referred to only 

 to indicate that the subject is elsewhere discussed. 

 9 MO 



