GYPSY AND BROWN-TAIL MOTHS. 9 



cannot develop upon, more than a very limited number of hosts. 

 The great majority are thus closely restricted in their host rela- 

 tions, and the parasites which are most effective in controlling 

 the increase of plant-feeding insects are generally of this char- 

 acter. It is on account of this that the many hundreds of dif- 

 ferent parasites of native caterpillars do not, and cannot, attack 

 and control an insect like the gypsy moth, which is different in 

 many respects from any native American insect. 



NATURAL CONTROL OF THE GYPSY MOTH. 



With the exception of the parasites, nearly every, and prob- 

 ably every, controlling agency which works to keep the gypsy 

 moth within bounds in Europe and Japan is present in America. 

 Mortality through catastrophic causes, such as storms and cli- 

 matic changes, is heavy here, as it is abroad. It is probable that 

 the birds, which destroy so many of the caterpillars, pupae and 

 moths, are equally effective in both Europe and America. Dis- 

 ease, induced through overpopulation, is more prevalent in some 

 parts of Massachusetts than in those countries where overpopu- 

 lation is not so apt to occur; and a multitude of predatory in- 

 sects, notably, the bugs described by Mr. Kirkland in the report 

 on " The Gypsy Moth," by Forbush and Eernald, render great 

 assistance. So effective are these various agencies, that, taking 

 the older infested section as a whole, the. gypsy moth is prac- 

 tically at a standstill so far as permanent increase in numbers 

 is concerned. Its numbers cannot be said to decrease to a notice- 

 able extent, except as the immediate result of artificial repres- 

 sion, and it has reached its maximum possible abundance. If it 

 had continued to increase at a rate of only twofold annually, it 

 would by 1909 have been thirty-two times as common as it was 

 in 1904 in tracts of woodland where artificial suppression could 

 not be economically employed. This is obviously not the case. 



Even in newly infested territory, where the controlling ef- 

 fect of starvation and disease is hardly or not at all apparent, 

 an increase of six-fold annually' during the first few years is 

 about all that is expected; and when it is considered that the 

 number of eggs deposited by one female is frequently in excess 

 of 500, it is at once evident that natural causes are responsible 



' Forbush and Fernald: " The Gypsy Moth," p. 94. 



