NATITKAL ENEMIES. 



55 



The diagram (fig. 25) shows the relation of the three generations of 

 parasites as observed in the breeding cages to the time of oviposition 

 and the time of hatching of the host eggs. With the data in hand it 

 is not possible to determine the period covered by each generation. 

 The records only show the appearance of the first adults for the three 

 generations. A few conclusions can, however, be drawn from the above 

 diagram. Adult parasites must have existed in vineyards at the 

 time of earliest oviposition of the grape root-worm. Adults producing 

 the second generation appeared before the greater portion of the root- 

 worm eggs had hatched, and since eggs could become parasitized 

 within two days of hatching, the second generation is apt to infest 

 more eggs than either the first or the third generation. In fact, the 

 third generation appeared so late that it only reached a very few 

 belated eggs. 



Fidiohia jlavipes is an important factor in the control of the grape 

 root-worm. Professor Webster, who for several years studied the 



plllipi i ^pSgliM:^^ 



Fig. 25. — Diagram showing the relation between the three generations of the Fidiobia parasite and 

 the relative occurrence of eggs of the grape root- worm at North East, Pa., during 1909. (Original.) 



grape root- worm in Ohio, reported in 1896 that the decrease in num- 

 bers of the beetle was largely due to this and other parasites. Though 

 the data on hand for North East, Pa., for the years 1907, 1908, and 

 1909 are not sufficient to show any increase in occurrence, it is our 

 impression, from extensive observations, that the insect is becoming 

 more and more numerous. 



A DIPTEROUS PARASITE. 



Along with Fidiohia Jlavipes there occurs another grape root- worm 

 egg parasite (fig. 26), which is at present only known in the larval 

 stage. It is supposed to be a dipterous insect, in view of the resem- 

 blance of the larva to dipterous forms. It was first observed by the 

 senior author and Mr. P. R. Jones, of the Bureau of Entomology, who 

 in 1907, at North East, Pa., collected several parasitized egg clusters. 



