225 
plication of the insect-parasites. As previously stated, most probably 
nine-tenths of the young Hessian-flies are destroyed in the larva or 
pupa state by the parasites already described. For the most part 
these parasites live in the flaxseeds contained in the straw, and 
appear in spring. Now, to burn the stubble in the autumn or 
early spring is simply to destroy these useful parasites, the best 
friends of the farmer. We do not hesitate to urge that the straw 
be untouched. On the contrary, the parasites should be gathered 
and bred in numbers; and we believe that practical entomologists 
should bend all their energies towards clearing up the subject of 
rearing and multiplying these insect hosts. Much knowledge and 
practical skill is needed in this direction, as occasionally by dis¬ 
seminating the parasites their noxious hosts may increase and be 
distributed; but knowing, as we do, how many more of the para¬ 
sites are in many cases bred than the insects on which they prey, 
it seems safe and reasonable to advise not only not burning the stubble, 
but letting it stand, so that the parasites may finish their trans¬ 
formations, become fledged, and ready, when the eggs and larvae of 
the Hessian-fly are upon or in the young wheat, to destroy them. 
It is a matter of fact that in years when the Hessian-fly is spec¬ 
ially abundant and destructive, similar seasons are highly favorably 
to the corresponding increase in the number of their insects or 
ichneumon parasites; they do their work so effectively that the few 
following years the numbers of Hessian-flies are greatly reduced. 
It is, then, to these parasites that we are indebted for the years of 
immunity from the attacks of the Hessian-flv, as much as to favor¬ 
able or unfavorable weather, and this leads us to consider the 
apparent periodicity in the years of abundance and scarcity of the 
Hessian-fly. 
PERIODICITY IN THE ABUNDANCE AND SCARCITY OF THE HESSIAN-FLY. 
The following tabular view, though constructed from very scanty 
and often misleading data, may throw some light on this subject. 
All insects, especially the more noxious ones, those which fall under 
common observation, such as the Locust, Cotton-worm, Army-worm, 
Chinch-bug, and the like, have their years of undue numerical 
increase and of unusual scarcity. This periodicity is, without doubt, 
partly owing to the influence of the weather, of favorable and 
unfavorable seasons, and partly, in most cases, to the absence or 
abundance of the insect parasites, although the latter cause is largely 
influenced by climatic agencies. 
The table has been drawn up from the reports of Fitch, Hind, 
Cook, and the Agricultural Department at Washington, and from 
different newspapers, as well as from private correspondence. The 
record, as therein presented, is very imperfect, but still it is suffi¬ 
cient to show the periodicity in the return of periods when the Hes¬ 
sian-fly has been sufficiently abundant to ravage wheat fields and 
excite apprehension and alarm. Without much doubt, in the differ¬ 
ent States mentioned, especially in the Middle States, the insect is 
tolerably abundant nearly every year, but few seasons occurring 
when after a careful search by experts the fly would not be found. 
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