236 MISS A. L. EMBLETOX OX THE AXATOMY 



remarked that " tlie creatures may be imjiorted on merchandise or by insects as -well as 

 on i^lants. Neither should it be forgotten, that if a pernicioiis scale be once introduced, 

 then the parasites that may be contained in the scales are excluded. To avoid this, a 

 knowledge of the marks by wbich parasitized scales can be distinguished from others, is 

 really essential in the carrying out of the quarantine regulations " ..." it is of utmost 

 importance that, previous to any attenijit to destroy the Coccidae, it should be 

 ascertained whether internal parasites are present or not. If they are found in large 

 ]n-oportion, then time should be allowed before any insecticide be used, so that the 

 parasites may emerge from all those individuals containing them, so as to allow the 

 beneficial creature to be perpetuated and increased. After the emergence of the flies, 

 then the Coccidie, if any such there be, may be killed by ixsing those insecticides which 

 are especially adapted to the j^^rt^icular case." There seems, however, to be some 

 difference of opinion on this subject of the importance of Hymenopterous parasites, but 

 I find myself moi'e and more convinced of the A^iews expressed in the preliminary 

 paper, because of the simple fact that having had this scale-insect under observation for 

 a long time I can testify to the well-nigh total destruction of it by Comijs infelix. I 

 can readily understand the reluctance of those who have not had this advantage to 

 admit the fact, when I recall tliat there may be a thousand scales on a plant, and that 

 though nearly every one may be really parasitized and consequently utterly destroyed, 

 there is nothing to reveal this. One must first understand the signs of parasitism in 

 the scale before being able to ajipreciate the work done by the fly. In economic 

 work of this description it is therefore of the utmost imi^ortance that the marks of 

 parasitism should be recognized. I have shown a plant covered with parasitized 

 Lecanium to j)eople used to making biological observations, and they could not believe 

 that the scales were parasitized and destroyed until they saw the fly actually emei^ge, 

 and that although the parasitism was nearly complete. 



It is necessary, in dealing with all insect pests, to use much vigilance and caution, but 

 at the same time to combat them whenever they appear ; but this can only effectually 

 1)6 thi'ough a proper knowledge of their habits and life-histories, for it is possible, as 

 already stated, to do harm by destroying some beneficial creatures which live upon the 

 pest. In countries wliicli have been under cultivation for centuries a balance between 

 the destructive and beneficial forces has been produced by adaptation, and in this way 

 the destructive species are kept in check ; it is therefore essential that care be taken not to 

 remove any of the factors Avhicli help to maintain this necessary and delicate equilibrium. 

 It is, at the same time, of utmost consequence that as soon as an injurious creature 

 makes its appearance, it should be watched carefully; in the event of a species coming 

 into the country, in the very early stages it may be dealt with successfully by resorting 

 to hand picking, giving it, if possible, no chance to become established. An added 

 danger to the introduction of an injurious species from another country, is the fact that 

 in its native land it is accompanied by some enemy which keeps it in check ; but when 

 it sets up in the new home, it is free from this restraint and spreads enormously in 

 consequence. In the case of parasites of injurious creatures it often happens that they 

 can also be introduced with ease, if, for example, they happen to be beetles, flies, birds, 



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