69 



EXPERIMENTS WITH HYDROCYANIC-ACID GAS AS A MEANS OF 

 EXTERMINATING MEALY BUGS AND OTHER INSECT PESTS IN 

 GREENHOUSES. ' 



By H. D. Hemenway, Amherst, Mass. 

 THE USUAL METHOD. 



Hydrocyanic-acid gas has been known and used in the West for fumi- 

 gation of nursery stock and trees infested with scale since its introduc- 

 tion by the Division of Entomology of the United States Department 

 of Agriculture in 1886. We have no record of its being used in green- 

 houses until 1895, when, under the direction of Messrs. Woods and 

 Dorsett, of the Department, it was used successfully on ferns, coleus, 

 and in violet houses for the destruction of scales, mealy bugs, and 

 aphides or plant-lice. 2 It has been used to a limited extent since 

 that time, but not, as a rule, in fumigating greenhouse stock in general. 

 For many years in the large greenhouses connected with the Mas- 

 sachusetts Agricultural College, great expense has been incurred in 

 destroying mealy bugs and scale insects on the vines, palms, orange 

 trees, acacias, etc., and after a thorough trial of fir-tree oil, lemon oil, 

 and other insecticides, many of which proved of some value, but were 

 not wholly satisfactory, it was decided to try hydrocyanic-acid gas, the 

 most powerful insecticide kuown. As the common mealy bugs known 

 in every old greenhouse are very prolific breeders, each female averag- 

 ing 400 eggs, and with a prospect of a new generation every six weeks, 

 it became apparent that if we wished to keep plants in good condition 

 we must exercise constant vigilance or occasionally resort to some 

 heroic measure. 



After several i)reliminary experiments with some of the more deli- 

 cate plants in a wooden box the stove and cactus rooms were fumigated 

 at the same time, the connecting doors between the two rooms having 

 been opened. Many of the cacti were infested with the common cactus 

 scale (JHaspis cacti), while in the stove room all through the twining 

 vines was to be seen the flocculent network of white, waxy threads pro- 

 tecting the eggs and young mealy bugs. 



1 The manuscript of this paper was submitted to the Division of Vegetable Physi- 

 ology and Pathology of this Department and kindly examined by Messrs. Galloway, 

 Woods, and Dorsett, all practical violet growers and the perfecters of the hydrocy- 

 anic-acid gas method as far as it relates to the treatment of insects in greenhouses. 

 They point out that while the results obtained by Mr. Hemenway may hold good 

 for the conditions under which the trials were made, they will not necessarily do so 

 in a different environment, since it has been found in practice that a certain kind of 

 plant will be injured at one time in one section of the country and will show no 

 signs of injury at another time in the same section or in some other locality. In 

 other words, it would not be safe to use the gas on the same varieties of plants in 

 other sections on the evidence furnished by these experiments. — Ed. 



2 Circular No. 37, Division of Entomology, U. S. Department of Agriculture. 



