188 
F. M. CAMPBELL-THE HESSIAN FLY. 
of the Cecidomyice were viviparous, and multiplied agamogenetically 
in autumn, winter, and spring. This was fully corroborated by 
Meinert,* * * § Pagenstecher,f and Leuckart.J It seems that this 
process may extend largely amongst that genus, and should it 
occur with C. destructor , the hybernating larvae found by B. 
Wagner may have been the descendants of the larvae which pro¬ 
ceeded from the eggs laid in the spring. H. Hagen thinks that 
the perfect insect may he capable of parthenogenetic reproduction, 
for one of this species, which was hatched out from a solitary 
pupa in a glass tube, laid about 100 eggs, and these u showed the 
unmistakable development and transversal segmentation of the 
embryo.” § They were, however, non-productive, owing, it is 
supposed, to external conditions, hut K. Lindeman’s opinion, after 
experiments, is that the perfect insect is not parthenogenetic. || 
Parasites. 
I have already stated that the apparent absence of the Hessian 
fly which immediately succeeds its superabundance is supposed to 
he largely due to parasites. Curtis similarly accounts for the 
same phenomenon in the case of the wheat-midge. Meteorological 
conditions must, of course, exert a powerful influence on all insects, 
hut there is little to guide us as to the way the Hessian fly may he 
affected, except indeed the knowledge that in America the chinch- 
hug, which requires dry weather, is abundant when the Hessian 
fly is scarce. We are thus led to think that these gnats, in some 
stage of development, require a certain degree of moisture, and 
this is confirmed by K. Lindeman’s experiments.^ But whether 
this he the fact or not, all observers are agreed as to their great 
destruction by parasites; and B. Wagnerff found on dissection 
sixty to seventy per cent, of the puparia to be thus attacked. 
These friends to the agriculturist are hymenopterous insects. 
The female places an egg in the egg (?), larva, or pupa of the 
Hessian fly. The resulting larval parasite consumes the substance 
of its host, whose puparium furnishes it with a pupal protection. 
The importance to he attached to such parasites, from an economic 
point of view, cannot he over-rated. [Since this paper was read 
I have had ample opportunity of examining the puparia of this 
summer’s brood. Only about 10 per cent, contained parasites, 
which were on the 20th July almost fully developed, and two 
emerged on the 23rd. In a few days they would have laid eggs 
in the larvae of the Hessian flies, which, though in puparia, had 
* ‘ Zeitschrift fur wissenschaftliche Zoologie,’ vol. xiv, p. 392. 
t lb. vol. xiv, p. 400. 
+ ‘ Archiv fiir Naturgeschichte,’ I 860 , p. 286. 
§ ‘ North American Entomologist,’ vol. i, p. 65. 
|| ‘ Bull. Soc. Imp. Moscou,’ 1887, p. 400. 
U ‘Farm Insects,’ p. 270. ** Op. cit. p. 414. ft Op. cit. p. 33. 
++ It must be borne in mind, however, that it by no means follows that a parasite 
which emerges from a pupa is parasitic on the species to which the pupa belongs. 
It may he a parasite of the original parasite, or, in other words, a secondary 
parasite. 
