April, '16] DAVIS: WHITE GRUB INVESTIGATIONS 271 



Natural Enemies 



Insect Enemies of Grubs.— Of the several insect enemies of white 

 grubs, the Tiphias and Asilids are the most effective checks, according 

 to our observations. In the genus Tiphia are several species attacking 

 grubs, and of these we have worked out the life-history of two, neither 

 of which has yet been specifically determined. Both have a one-year 

 life cycle, passing the winter as larvae within the cocoons, are partheno- 

 genetic and paralyze the grub only temporarily, that is, only about 

 long enough to deposit an egg. One of the species lays its egg on the 

 dorsum of the thoracic segments of the grub while the other lays its 

 egg on the underside of the abdominal segments. 



Elis 5-cincta^ and probably several other species of the genus are 

 important enemies of the grub in some localities. The wasp has a 

 one-year life cycle, it is not parthenogenetic according to our obser- 

 vations, and differs noticeably from Tiphia in that it paralyzes the 

 grub completely, a paralyzed grub never coming back to active life 

 although it remains inertly alive for several weeks to a month or more. 



Three tachinids are parasitic on the grubs, all attacking it in a 

 similar manner. These are Microphthalma disjunda^ which is common 

 in the central western states, M. pruinosa^ in the New England states, 

 and Ptilodexia tibialis^ in Texas. 



Of the asilid enemies we have reared but one species, Promachus 

 vertebratus, from larvse actually observed feeding on grubs, and in 

 certain parts of Wisconsin this is a prominent grub enemy. In the East 

 the analogue of this species, according to Doctor Felt's observations, 

 is Promachus fitchii. Both of these species appear to have a three- 

 year life cycle, thus following the cycle of the grub. We have reared 

 other asilids from grub infested fields but we have no absolute proof 

 as to their predaceous habits excepting circumstantial evidence. 



Several species of carabid beetles and their larvss are predaceous 

 on white grubs and the role they play in the control of grubs is probably 

 greater than has heretofore been supposed. 



Three insect enemies of minor importance have been previously 

 reported, namely, Pelecinus polyturator, Ophion bifoveolatum, and 

 Sparnopolius fulvus, thus bringing the total number of insect enemies 

 of the grub to more than twelve species. 



Insect Enemies of Beetles. — We have reared five dipterous para- 

 sites of the adult May-beetles, all of which have been previously re- 

 ported as parasitic on May-beetles, and are Pyrgota undata, P. valida, 

 Cryptomeigenia theutis,'^ Euirixa exile,^ and Biomyia lachnosterncB.^ 



1 Gahaia and Rohwer det. 



2 Walton det. 



