F. M. CAMPBELL—THE HESSIAN FLY. 
185 
Life-Histoey. 
The general life-history of the Hessian fly in the United 
Kingdom does not differ from that observed in other parts of 
Europe and in America. There are two broods—one is due in 
spring, and the second in autumn. The first lays eggs late in 
April or May, some of which develope into perfect insects by 
August or September, whilst others are retarded until the follow¬ 
ing spring, as I show later on. The eggs in spring are laid on 
wheat, barley, or rye, in the grooves of the upper surface of 
the leaves growing above the first, second, or third joint of the 
stalk. Oats are not attacked. The female appears careful in the 
selection of plants on which to lay her eggs, giving preference 
to those which are not too far advanced, and Mr. Palmer informs 
me that though his barley was infested, yet his wheat was almost 
free. This may he explained by the barley in that season being less 
forward than wheat, and therefore offering to the parent a more 
suitable plant for rearing its offspring. In the act of oviposition 
the fly stands with her head towards the point of the leaf, and in 
less than half a minute lays two or three eggs; she visits leaf 
after leaf until she has parted with about eighty eggs. The 
number found on each leaf varies from one to thirty or more. 
The larvae hatch out in four days in warm weather; making their 
way very slowly down the leaf, they enter the sheath, and proceed to 
the joint below, where they cast their skins (according to Lindeman), 
and undergo their other developmental changes.*' They do not 
burrow into nor gnaw the stalk, for their mouth-organs are far 
too weak for this. With the aid possibly of their anchor-process, 
they bruise the stalk and remain lengthwise living upon the sap. 
In four or five weeks, varying with the season, the larvae begin to 
turn brown, and then take a chestnut colour, when they look like 
flax-seeds. The growing plant presses them firmly on all sides, and 
the irregularities of the stalk and sheath produce the longitudinal 
lines and depressions referred to (p. 184) in the description of the 
puparium. The pupal stage is however not yet reached. The 
body having slightly contracted, has separated from the external 
skin, which has now no vital function, and only acts as a protective 
covering. Thus sealed in, the larvae cannot feed, and remain 
dormant for a varying period until they enter the pupal stage.f 
Meanwhile the ear of the plant is ripening, and the injured stalk, 
too weak to hear the weight, bends over just above the joint where 
the larvae are situated, as shown at A in Eig. 3. 
The appearance is characteristic. The duration of the pupal stage 
has been observed by B. Wagner (op. eit.) to extend from 12 to 
14 days. The time for the full development of the imago having 
arrived, the insect breaks its chestnut-coloured outer protective 
covering, or puparium, by bending the body, and works its way 
* I have found the puparia in a few cases attached to the sheath some distance 
from a joint. 
f Such a pupa is termed coarctate, i.e. protected by the skin of the larva. 
