618 DIPTEBA. 



pupae within the onions, and come out as flies a fortnight 

 afterwards. 



We have a kind of fly corresponding almost exactly with 

 the description of the onion-fly. This strengthens my belief 

 that our onions suffer from the depredations of the maggots 

 of this or of a similar insect. The fly to which I allude is 

 often found on windows in the spring. It is ash-colored, 

 with black hairs sparingly scattered on its body. It has a 

 rust-colored forked spot on the top of its head, and three 

 rust-red lines on the thorax ; and the wings are tinged with 

 yellow near the shoulders. It measures one fourth of an 

 inch in length. It is stated that there are two or three 

 generations of the European onion-flies during the summer, 

 and that the late broods pass the winter in the pupa state, 

 and are ready to burst forth at the first warmth of the fol- 

 lowing spring. It is stated that the onion crop may be pre- 

 served from the attacks of this fly, by sowing the seed on 

 ground upon which a quantity of straw has been previously 

 burnt. 



The peculiar disease that has affected potatoes within the 

 last ten years has been attributed, by many persons, to the 

 depredations of insects. In the course of this work, several 

 of these insects have been described. Another is now to be 

 added to them, as will be seen by the following extract from 

 a letter, received from a correspondent in July, 1851. " A 

 new potato-rot theory has recently appeared in Brattlebor- 

 ough, Vermont. The mischief is referred to a fly, of which 

 an authentic specimen is enclosed. It is said that the species 

 first appeared simultaneously with the potato-rot; and the 

 flies are accused of hovering about the manure, and deposit- 

 ing their eggs, so that the larvae infect the potatoes." The 

 specimen proved to be a common dung-fly, which may be 

 found in abundance upon manure when carted into the field 

 in the spring. The male is easily distinguished from other 

 flies by its yellow and very hairy hind body and legs, and 

 by its long and narrow wings. It is about half as large as a 



