538 REPORT OP THE COMMISSIONER OF AGRICULTURE. 



ing on the barrel, was used. The flour was first placed in the funnel 

 and washed through the wire gauze with water. This caused it to 

 diffuse in the water without forming in lumps. The same process 

 was followed with the London purple or the Paris green, according 

 to which substance was to be used. 



London x)urple has tlie advantage over Paris green in cheapness, 

 better dilfusibility, and visibility upon the foliage, and experience 

 showed that the green seemed to injure the foliage more than the 

 purple. 



It was noticed with the Elm Leaf -beetle that the effect of a poison- 

 ing was slow in appearing; good effects are not expected before the 

 third or fourth day. Impatience which would lead to a repoisoning 

 on the second or third day would be apt to result in the burning and 

 fall of the leaves. 



Emulsions op Kerosene. — We have had occasion for the last few 

 years to many times recommend the use of emulsions of kerosene 

 against different injurious insects. We need not repeat the advan- 

 tages of these prejDarations here, but simply state that when the Web- 

 worms are abundant, a thorough spraying with a dilute emulsion 

 will doubtless destroy the majority of them. On account of our 

 absence last summer no experiments were made upon the effect of 

 applying such an emulsion upon the foliage of the commoner shade 

 trees, but the result of experiments detailed in Bulletin No. 11 of the 

 Division would augur the destruction of the worms. These experi- 

 ments (made by Mr. Webster at La Fayette, Ind. ) were not performed 

 upon this species, however, but upon the somevfhat similar larvae of 

 Pieris rapcE and Datana ministi^a. Colonel Bowles, as we shall 

 soon show, rejected the emulsion of soap and kerosene as not effective 

 against the worms when reduced so as not to injure the plants; but, 

 as he has not given us the details of the experiments, we still con- 

 sider the matter open to proof. The formula3 for several emulsions 

 are given in the article on the Cottony Cushion-scale {Icerya pur- 

 chasi). One of the most serviceable is that which we call the " Hub- 

 bard formula," and which was used most extensively by Mr. Hub- 

 bard in his work on the scale insects of the Orange, and which has 

 been repeatedly given in the publications of the Division. 



Naphtha. — Some experiments were undertaken in the height of 

 the Web-worm season by Col. John Bowles, of Washington, which pos- 

 sess a certain interest on account of the substance used and on account 

 of the manner of its application. It is, however, more expensive 

 than the arsenical poisons and the kerosene emulsions, and the spray 

 from the atomizer is not so far-reaching as from the force-pump and 

 cyclone nozzle. We append Colonel Bowles's condensed account of 

 his experiments, with the remark that the experiments with the oil 

 doubtless failed of satisfactory results because of imperfect emulsify- 

 ing and application: 



In accordance with your request I send herewith a concise statement of experi- 

 ments made by myself in exterminating caterpillars, web- worms, &c. , which destroy 

 the beautiful foliage of our shade trees. 



My experiment commenced with an effort to save the shrubbery of my yard and 

 garden from the rapacious caterpillars that seem almost to germinate in the poplar 

 trees, one of which stood in our front yard. After denuding this tree and literally 

 raising an army of conquest and invasion, they broke camp and set forth as a huge 

 foraging party, consuming everything in their way, save the rough bark of the trees 

 and the fences. 



I opposed them first with kerosene oil, which was equally fatal to the plants and 

 worms. 



