120 AGRICULTURE OF MAINE. 



PARASITES OF THE GYPSY AND BROWN-TAIL 

 MOTHS IN MAINE. 



Before considering the parasites of the gypsy and brown- 

 tail moths which have been introduced into the State of Maine, 

 it is necessary to explain briefly the subject of parasitic con- 

 trol of injurious insects in order that the difficulties encoun- 

 tered in controlling insects by this means may be understood. 



The control of injurious insects by their enemies is a subject 

 which needs some light thrown on it to remove certain errone- 

 ous ideas which appear to be common. The impression seems 

 to be current that these enemies are miracle workers capable of 

 performing astounding feats of destruction and that it is only 

 necessary to liberate a few of them in ^ locality suffering from 

 the work of some injurious form, to have this latter disappear 

 at once. Unfortunately such immediate destruction is not pos- 

 sible in the majority of cases, and we have to be content with a 

 more gradual removal. These enemies only increase at a cer- 

 tain rate and under the most favorable conditions ; considera- 

 ble time is required for them to become numerous enough to 

 make their efforts noticeable, especially if the injurious forms 

 they attack have been present for a number of years and have 

 increased unmolested. 



Insects in their native homes are usually kept quite effec- 

 tively under control by their enemies, but if any factor favora- 

 ble to them is introduced to disturb this arrangement they are 

 apt to increase enormously. Such disturbance takes place 

 when they are accidentally taken from one country to another 

 and if the conditions in the new home are favorable they are 

 very apt to increase by leaps and bounds until they become 

 serious pests, the amount of damage depending on the value of 

 the crop attacked. If such an insect becomes established it is 

 necessary to introduce those forms which were responsible for 

 the control in its native country. These beneficial forms after 

 introduction must first become acclimated ; they must increase 



