EMPUSA MUSCAE versus MUSCA DOME STIC A L. 



By H. T. GUSSOW, 

 Dominion Botanist, Department of Agriculture, Ottawa, Canada. 



(With Plate XXI.) 



The biological control of insect pests has received considerable 

 attention for some years past, and success has without doubt accom- 

 panied research work along these Unes. The common house fly 

 {Musca domestica, L.) is more than ever now, because of additional 

 proof furnished by more recent investigations into their responsibihty 

 as carriers of wound infections, recognised as an important source of 

 danger to public health. 



The most destructive disease, to which the house fly is subject, is 

 that caused by the fungus Empusa Muscae. The question whether 

 this fungus may be used in the control of this pest is of decided interest, 

 and has received more or less careful attention from writers, as well 

 as from investigators. 



It has already been pointed out in an earher paper^ that it is an 

 easy matter experimentally to spread the disease among flies in 

 captivity. That is to say material from flies recently dead from the 

 disease produced infection in others brought into contact -with the 

 spores of Empusa. Yet, fatal as the disease is among flies, it was for 

 long a matter of conjecture whether it really constituted an important 

 factor in the death of flies. No doubt the very fact of its being fatal, 

 coupled with the number of dead flies to be seen every year towards 

 autumn, helped to attach an importance to this disease, which a close 

 study failed to confirm. Close observations made in places, where 

 flies are present by thousands throughout the season, indicate that 

 perhaps one in a thousand flies is killed naturally by the disease, — 

 in some instances even a smaller proportion. The determination of 

 the mortality among flies from this disease is comparatively simple, 

 since, as a rule, the fly killed by Empusa is and remains attached to 



^ Giissow, H. T., "Empusa Muscae and the Extermination of the house fly." Rep. Loc. 

 Govt. Board, on Publ. Health and Medical Subjects. New Series, No. 85, p. 10. 



