110 MASS. EXPERIMENT STATION BULLETIN 160. 



{Phanerotoma) , not only because it is much less abundant, but also be- 

 cause it usually deposits its eggs in worms which have already been 

 parasitized by the Braconid. It is perhaps as much of a hindrance as 

 a help because of this interference with the Braconid. 



3. A Chalcidid {Trichogramma mimita Riley, ^ which is known to be 

 parasitic on the eggs of forty-six other species of insects, the codling 

 moth, the brown-tail moth, the pear-slug, the elm saw fly (American 

 Cimbex), the fall web-worm, the corn ear-worai and the cotton worm 

 being some of its important hosts). This, the most important parasite 

 of the fruit worm, was a new find this year. It undergoes all its develop- 

 ment and transformation in the fruit worm egg, causing the destruction 

 of the egg, as far as the development of the worm is concerned, and 

 emerging from it in July and August as a full-grown fiy-hke creature 

 of such small size as to be hardly visible to the naked eye. Its 

 presence in the eggs may be readily detected by their appearance, for 

 they turn black when infested with it. Moreover, when the fruit worm 

 itself hatches, the eggshell is left looking like a white flake, and the 

 worm's place of emergence is not readily seen because of its location 

 close to the surface of the berry. On the other hand, when the parasite 

 has emerged the eggshell looks black and the emergence hole is con- 

 spicuous. The writer has noticed these black eggs several seasons, and, 

 as he suspected parasitism in connection with them, he attempted to 

 rear the parasites last year, but failed to do so, probably because the 

 methods he employed were not suited to these very delicate creatures. 

 This year, however, different methods were tried, and the adult parasites 

 were obtained in considerable numbers without much trouble. This 

 parasite destroyed about 56 per cent, of the fruit worm eggs on dry bogs 

 near the station bog this year, about 700 eggs having been examined in 

 making this estim.ate. 



In last year's report (page 55), it was estimated that more than 50 per 

 cent, of the fruit worms on a dry bog near the station bog had been para- 

 sitized in 1912. As nothing definite was then known about the Chal- 

 cidid egg parasite and its importance, that estimate was much too low, 

 this year's investigations having shown that the natural enemies (para- 

 sitic and predacious) of the fruit worm took care of not less than 90 per 

 cent, of the infestation on dry bogs, and of fully 66 per cent, on flowed 

 ones, in the vicinity of the station during the season. 



The writer's findings concerning the natural enemies of the flowed- 

 bog fireworm and the bearing which flooding has on their effective activity 

 have been discussed fuUy in previous reports, but they must be briefly 

 brought to mind again here to show how they are supported by the results 

 of this year's study of the distribution of the principal fruit worm para- 

 sites. The fireworm seriously damages only flowed bogs, and it becomes 

 a pest because the flowage either drives out or destroys its natural enemies, 



1 Since this was written, this determination has been confirmed by Mr. A. A. Girault, the 

 authority on the Trichogrammatidm. 



