14 IMPORTED PARASITES. 



older and larger caterpillars, and those which form still another 

 group reserve their attack until such time as the caterpillars 

 have spun up preparatory to their transformation into pupae, or 

 until after this transformation has taken place. It is confi- 

 dently believed that representatives of each of these three or 

 four groups will have to be established in America before any 

 marked results of a practical nature can be expected. 



There are two exceedingly good reasons for believing this, 

 which may be mentioned here besides others equally good, but 

 less easily expressed in non-technical language. One of these 

 is the fact that in not a single instance has one species of para- 

 site been found sufficiently abundant abroad to bring about the 

 percentage of destruction which will certainly be necessary in 

 order to offset the six-fold rate of increase of the gypsy moth, 

 which it is the consensus of opinion exists in newly infested 

 territory in America at the present time. The other is, that 

 there is not a single species of defoliating caterpillar, similar 

 in habit to the gypsy moth, of which the parasites have been 

 studied, and which is controlled by them to any extent, which 

 does not support a sequence of parasites similar to that which 

 it is proposed to establish for the gypsy moth. 



If the theory as to the necessity of a sequence of parasites be 

 accepted as a general rule, its importance cannot be overesti- 

 mated. Success in the work of parasite introduction will then 

 depend entirely on whether or not a sufficient variety of para- 

 sites can be established in America, and cannot obtain until all 

 of the species which go to make up a natural and effective se- 

 quence are established, and have increased to a sufficient abun- 

 dance to make each of the chain effective in its own particular 

 field. The predaceous beetles alone can never bring about the 

 desired end, neither can the egg parasites, nor those of the pupae, 

 nor, it is believed, can all these three groups together. The 

 parasites of the caterpillar, in addition to these others men- 

 tioned, ought to bring about the desired end. The Calosoma 

 beetles bid fair to assist the native predatory enemies materially 

 in the good work which they are doing, and their establishment 

 will make that which is expected of the parasites easier and 

 more certain of accomplishment. 



It ought to be stated, in this connection, that this principle. 



