ENTOMOLOGY

338 SANITARY ENTOMOLOGYpyrethrum. These are not recommended.control for such methods to be effective.Cattle lice are too difficult toTIME FOR THE APPLICATION OF CONTROL MEASURESThough cows are infested with the largest numbers of cattle liceduring the months of January and February, yet the measures for theircontrol should be applied long before that time; in fact, they should beused within a week after they have been brought into the barn for thefall and winter. A second ~pplication should follow twelve or thirteendays afterward. The purpose of these two applications is to rid thecows of the lice that are on them before they become numerous andspread to more susceptible animals. The lice may not be seen at thistime but the dairymen should not reason that the lice arc not present.This gives a proper length of time for all of the three species of cattle liceto hatch from eggs, but not long enough for them to lay eggs again and bein a resistant stage where the treatment will not reach them.Treatment should be repeated at intervals of a month from thesecond treatment. In case animals show any great number of lice,treatment should be given and repeated in twelve or thirteen days.Treatment with linseed oil can be made at the usual time when thecows are being groomed and cleaned.From five to six treatments during the fall' and winter should controlthe lice in the average herd.SKIN INJURmSOne of the most troublesome phases of the study of the control ofcattle lice was to determine the strength of insecticides that would killthe lice but would not injure the skin, thus causing the hair to come outbadly or making distinct burns.The skin of the cow is very susceptible to injury when comparedwith the skin of other animals. It is known that cows have been killed bythe application of certain insecticides recommended for the control ofcattle lice. This indicates that caution must be taken in the use of controlmeasures that have not been sufficiently tested. Caustic washes cannotbe used without danger of their doing considerable injury, unless theyare very accurately measured and applied very carefully to the skin ofthe animal.It is k'TIown that e:cposure to direct sunlight and active exercise afterapplication contributes to cause skin injury with 'TIearly every one of thecontrol measures for cattle lice.It is doubtful if there is any appliCD.tion that will kill lice on cows