APPLICATIONS TO PREVENT OVIPOSITION. 143 
The pyrethrum and water mixture is prepared by stirring up as 
much of the powder as the water will hoid in suspension, or a little 
milk may be added to increase the holding power of the water. The 
results obtained with pyrethrum in water against the transformed 
insects are as satisfactory as with the dry powder, with the additional 
advantage of its being possible to throw the water by force pumps to 
parts of the plant where it would be difficult to place the powder. 
Against the pup, the water solution is more effective than the 
powder, but is less so than kerosene emulsion. 
Kerosene emulsion, as an application for destroying the emerged 
pupe and adults, is used in very strong solution, or at a strength 
ranging from one part of the emulsion to one of water up to a dilution 
of the emulsion with eight parts of water. The greater strengths were 
more immediate in their effects, but even with the more diluted washes 
very satisfactory results have been obtained. The emulsion at once 
stops all molting or transformation. Applied to the partly trans- 
formed insects, the soft wings harden into shapeless masses, and while 
occasional individuals may survive the treatment for two days or 
more, the application is usually fatal in the end. The treated pupz 
are unable to transform to the adult stage and they eventually die or 
are devoured by their natural enemies. The death of the mature and 
hardened insect is caused by closing its breathing pores with the oily 
mixture, and in the case of the partly expanded or soft, immature 
individuals by the caustic effect it has on the forming wings and soft 
body. 
The experiments with acids demonstrated also that exuviation may 
be prevented by spraying the newly emerged pupa with a 2 per cent 
solution of carbolic acid or a 15 per cent solution of acetic acid. 
APPLICATIONS TO PREVENT OVIPOSITION. 
All the early experiments with washes or other applications to 
prevent oviposition proved unavailing except such protections as 
could be applied to small trees or shrubs, such as covering them with 
netting. Professor Riley in 1868, and later, at his instance, Dr. 
W. S. Barnard, tested a number of repellent substances, such as 
kerosene emulsion, vartous oils, and carbolic-acid solutions, all pun- 
gent and disagreeably smelling substances, with results either unsat- 
isfactory or of negative value. 
In the occurrence in 1902 of Brood X some indications were obtained 
showing the possible* protective value of lime washes. Mr. Slinger- 
land reports that spraying a heavy coat of whitewash on the trees 
will keep the locusts away to some extent when there are other 
trees in the neighborhood. He states that the reason for this seems 
to be that the insects do not like to sit on a white surface. The 
