1906.] PUBLIC DOCUMENT No. 73. 133 



during certain seasons is capable of exerting quite a repressive in- 

 fluence on the brown-tail moth caterpillars and pupae, and thus 

 renders them more susceptible to fungi. 



Dr. A. Y. Grevillius ' mentions several caterpillars of the brown- 

 tail moth being killed by Empusa, during very warm and rainy 

 weather. In one place he states : " The caterpillars were deci- 

 mated in an important degree again about the middle of June, 

 especially by an epidemic outbreak of Empusa aulicce, Reich., and 

 there were correspondingly few of them to pupate. Their feeding 

 in the following autumn was not very noticeable in this part of the 

 country." And further: "In the feeding time of 1902, on the 

 contrary, notwithstanding the special destruction of the caterpil- 

 lars by Empusa aulicce, Reich., a tolerably large number of moths 

 emerged from the cocoons, and these laid their egg clusters not 

 only on orchard trees and oaks, but also on a few other trees and 

 shrubs." Occasionally epidemics of more or less severity occur in 

 this State from this fungus in connection with grasshoppers and 

 moth larvae. 



POSSIBLE HELP FROM PARASITES. 



Insect parasitism is one of the most interesting subjects 

 in the whole field of entomology. Nearly every insect has 

 enemies of its own kind, remote relatives, they may be 

 called, which prey upon it and attempt to destroy it. Their 

 work is shown in the relative abundance or scarcity of their 

 unwilling hosts. The farmer notices that certain years are 

 " caterpillar years," and that others are not so characterized. 

 The abundance or scarcity of any caterpillar pest depends in 

 large measure upon the presence or absence of the parasites 

 which attack that particular insect. Of course the work of 

 birds is an important factor, but the influence of parasites in 

 the long run controls the situation. 



Take the case of the army worm, a pest of grass and 

 grain fields at comparatively long intervals. This insect is 

 notably attacked by a certain fly which lays its eggs on the 

 " worms," the eggs hatching into grubs which kill their hosts. 

 When the "worms" are abundant, there is offered a wealth 

 of food for the parasite. The}' multiply prodigiously, de- 

 stroy their hosts, and in a season the army worm outbreak 

 becomes a thing of the past. The following year there is a 



1 Zur Kenntniss der Biologie des Goldafters. Kempen, 1905. 



