84 Indian Economic Entomology. [Vol. I. 



and 3 k khaons respectively. In this case, however, the loss does not 

 appear to have been caused by fly alone, for muscardine was also pre- 

 sent. 



On the other hand, Mukerji states that the regular cocoon bunds in 

 the villages do not suffer much from flies ; and if this is the case some of 

 the preceding estimates must be excessive. Where so many causes are 

 at work to affect the outturn of a crop, exact estimates of the actual loss 

 occasioned by the fly are no doubt difficult to obtain, and estimates, based 

 on the amount of injury, done by the fly to small experimental reariugs 

 are likely to be excessive, as it is just the small rearings which suffer most. 

 Taking everything into consideration, however, we may conclude that the 

 pest is a real and serious evil, though perhaps not such a deadly one as 

 some have been inclined to suppose. 



The Bengal silk-worm fly is much like a big house-fly, but its great 

 wing power makes its capture particularly difficult. 

 In Rajshahye it is found about rearing rooms and 

 silk stores all the year round, but it greatly increases in number during 

 the months of July, August, and September. It attacks the common 

 Bengal mulberry worm (Bombyx), the eri worm (Altacus ricini), and is 

 also supposed to be the species which was found to be parasitic upon 

 the caterpillar Dasychira thioaitesii, a pest which has been known to do 

 much injury in the Doarsby defoliating lea and soil (see Indian Museum 

 Notes, I (1), page 31). 



Copulation takes place in the air, one male fertilizing several females. 

 The impregnated female is very active and persistent in her efforts to get 

 at the worms, and once having reached a rearing tray, she will wander 

 all over it, depositing an egg here and an egg there indiscriminately on 

 the worms. The act of oviposition is rapid, and the fly simply glues 

 her minute egg into the worm's skin with her ovipositor without making 

 an incision. She moves under and about the leaves and stems on the 

 tray, sometimes even ovipositing from below on to the ventral surface of 

 a worm. When she suspects danger she conceals herself amongst the 

 leaves and escapes from one part of the tray to another, so that an hour 

 may sometimes be spent in endeavouring to dislodge her from a single 

 tray. According to Louis two or three dozen flies are sufficient to de- 

 stroy a whole roomful of worms. A silk-worm is only capable of 

 nourishing about four maggots, but if there is a scarcity of worms the 

 flies will lay many more than this number of eggs upon one caterpillar. 

 Cleghorn found that the fly survived for about four or five days in confine- 

 ment, but he is of opinion that it usually lives about eight days. 



When freshly laid, the egg has a hard white shell that can just be 

 seen with the naked eye. About fifteen hours after the egg is deposited, 

 it hatches, and the maggot penetrates the skin of the worm. Cleghorn 

 found that worms, which moulted within fourteen hours of having eggs 



