ENTOMOLOGY

MOSQUITO CONTROL !79squads to thoroughly flush the ditch below the gate and remove allmosquito larvm and algm.LarvicidesThe ditching, draining, and clearing of waterways insure a regularflow, carry off all surplus water, and reduce but do not prevent mosquitobreeding. It is necessary to use some additional means of control andfor this purpose various larvicides have been applied, but principallykerosene, c~de oils of paraffin and asphaltum base, as well ascreosote oils.The question of the effect of oils on mosquito larvre is most thoroughlydiscussed by Freeborn and Atsatt, who find that the t9xicity ofthe petroleum oils as mosquito larvicides increases with an increase involatility, the more volatile oils producing "the more marked lethaleffects. The volatile constituents of the oils contain the principlesthat produce the primary lethal effects. The lethal effects are producedby the penetration of the trach_l\al tissue by the volatile gases of the oils.In the heaviest and least volatile oils having a boiling point greater than!50 0 F., this action may be supplementary or apparently secondary tothe efFect of actual contact of the oil with the body tissue, or perhapsto mechanical means such as suffocation or plugging of the trachem.They found that oils which killed very quickly did so by means of thevolatile gases, whereas in the case of oils with slow effectiveness themechanical suffocation may be the cause of death.This paper is so recent that it has not been possible to obtain amass of evidence on the practical effectiveness of different grades of oilsused as larvicides. Kerosene and crude oil are the oils most commonlyused in general practice. Le Prince and Orenstein prefer crude oil tokerosene because of the film made by kerosene, its greater expense, inflammability,and liability to be wasted because of its transparency.These authors have set down a number of requirements for a goodlarvicide:1. It shall have a high toxic power, so that a small quantity maysuffice for a large volume of water.2. It shall kill rapidly in order that subsequent dilution and weakeningby rain have as little effect as possible .. S. It must be uniform in its toxic power and capable of standardization.4. It should mix freely with brackish and alkaline waters.5. It must be harmless to man and domestic animals, when in thedilution necessary for larvicidal action.6. It shall not be susceptible to rapid deterioration.7. It must be inexpensive.