PRACTICAL VALUE OF EMPUSA 165 



example, Bivfeld believes that the Empusa is continued over the 

 winter in warmer regions, migrating northwards with the flies on 

 the return of the summer ! In the case of EntomophtJiora cal- 

 liphora, Giard believes that the cycle is completed by the corpses 

 of the blow-flies falling to the ground, when the spores might 

 germinate in the spring and give rise to conidia which infect the 

 larvae. Olive (1906) studied the species of Empusa which attacks 

 a species of Sciara (Diptera) and found the larvae infected. He 

 accordingly thinks that the disease may be carried over the winter 

 by those individuals which breed during that period in stables 

 and other favourable places. As I have shown, M. domestica, 

 under such favourable conditions as warmth and supply of suitable 

 larval food, is able to breed during the winter months, although it 

 is not a normal occurrence so far as I have been able to discover. 

 If, then, these winter-produced larvae could become infected they 

 might assist in carrying over the fungus from one year to the 

 next, and thus carry on the infection to the early summer broods 

 of flies. This suggestion and the possible occurrence of a resting- 

 spore stage or the infection by conidiospores surviving from the 

 previous year, appear to me to be the probable means by which 

 the disease may be carried over from one " fly-season " to the next. 

 Until this gap in the life-history is filled it will not be possible 

 to determine experimentally the practical value of this fungus 

 as a means of destroying the house-fly. No one, so far as I am 

 aware, has yet succeeded in rearing the fungus on artificial media 

 although many attempts have been made. Nor has it been pos- 

 sible in my own experience to infect flies from flies of a previous 

 year which have been killed by the fungus. Investigations are 

 now being conducted, according to Bernstein (1910), on this 

 parasitic fungus in connection with the enquiry of the Local 

 Government Board and the results will be awaited with interests 



^ Since the above was written two interesting papers on this subject have 

 appeared. 



Giissow (1913) has given the results of a careful investigation on the life-history 

 of E. muscae. He did not succeed, however, in carrying cultures of the fungus 

 from spore to spore outside the fly and failed to find resting-spores. His observa- 

 tions indicate that flies may become infected by ingesting the spores into the 

 alimentary tract. 



Buchanan (1913) studied chiefly the possibility of bacterial dissemination by 

 the spores of E. muscae and found that the spores were able to take up, and to carry 



