86 ENTOMOLOGICAL SOCIETY OF ONTARIO. 



own exertions to save his crop. There are however, many insects which are very 

 commonly parasitized, and among them may be mentioned the various species of cut- 

 worms. It is nothing uncommon to find in an infested field that fully one-half, and 

 sometimes as many as three-quarters, of the specimens will have eggs of the Tachina flies 

 attached to the skin, and probably others have parasites which are not externally visible. 

 Yet the fact that these cutworms are infested by parasites is of absolutely no value to 

 the farmer. They eat just as much as if they were not parasitized, and it is really a 

 matter of little importance to the agriculturist whether the food that is stolen from him 

 makes a moth or a fly. The caterpillar feeds all the same until it is full grown. Next 

 year in the same field there will just as many cutworms as there were in the previous 

 year. The parasites have kept the number within the same limit, and the farmer has not 

 been benefitted. If he desires to save his crop he must himself adopt measures for the 

 destruction of these insects; parasites will not help him in the least. Let us take another 

 instance : One of the species of Tortricids infesting the Cranberries is very subject to the 

 attacks of parasites, two species being abundant and a third rare ; yet every year the bogs 

 sufier equally from this species. If we collect a large lot of larvte in the early spring, we 

 will find that very few of them will give out parasites. From the second brood we will 

 breed a great many more, while of the third and last brood, probably seventy-five per 

 cent, will prove to be infested by parasites. This sounds very pretty, indeed, and we say 

 that the insect has been controlled by its parasites, and so it has ; but not until it has 

 ravaged the bogs, and has done all the injury that it could do. It has destroyed the crop, 

 and seeing the enormous increase of the parasites during the year, the natural conclusion 

 is, that they will next spring still further reduce the number of their host and bring 

 matters to such a state that little or no further injury is to be apprehended. Yet, as a 

 matter of fact, nothing of the kind occurs. We find that somehow during the winter the 

 mortality among the parasites has been very much greater than it has been among the 

 moths, and that just as in the previous year the first brood of moths will be almost 

 exempt from the attacks of the parasites. We will have on the bogs exactly the same 

 history that we found in the previous year. Of what practical benefit is this parasite to 

 the farmer 1 It does not do anything in the world to prevent the destruction of his crop, 

 nor does it any way lessen the damage, for where these insects occur and are allowed to 

 increase without check, except by their natural enemies, they appear in sufficient numbers 

 each year to take the entire crop. This is not a solitary instance. It can be matched 

 with case in all our common insects. The Codling Moth, for instance, has parasites, and 

 is doubtless kept in some check by them ; yet every one present knows that if parasites 

 and natural enemies alone were depended upon, farmers oukl not count on a single 

 perfect apple. They do check the excessive increase of the insect, but they do not lessen 

 in the least the number that can be supported by the food plants. All the parasites that 

 have been described from the Codling Moth, from the Plum Curculio, and any others of 

 our injurious insects do not benefit the farmer one dollar in the value of his cro])S, and I 

 think it is well that this should be generally understood, because of the tendency that I 

 have already mentioned to expect too much from the parasites It must be remembered 

 also that in the operation of preserving the proper balance between life of all descriptions, 

 nature itself has intervened to prevent the undue increase of the parasites, either by 

 making them less fertile than the hosts upon which they prey, by giving them a smaller 

 number of broods, or by supplying them in turn with parasites which keep them in check. 

 This secondary parasitism is well known and it is as eSective in preventing the excessive 

 increase of the primary parasites as these are in preventing the excessive increase of the 

 original host. There is really almost as much danger, and that is very little, that the 

 secondary parasites will destroy the primary parasite as that the primaries will exter- 

 minate their host. Predaceous insects are in much the same case, they never entirely 

 destroy the species they feed upon, and in 99 cases out of 100 they conquer their prey 

 after all the injury has been done to the growing crops. Let us take the case of the 

 Melon Louse for example. This makes its appearance in June or July, and increases 

 with marvellous rapidity. Very soon after various species of Coccinellids make their 

 appearance and begin preying upon the plant louse ; but in the number in which they 

 first appear they are incapable of eating up the lice as fast as they multiply. By Sep- 



