470 



Bulletin No. 116. [August, 



The method of the operations of this insect and the main facts 

 of its Hfe history have been worked out in my insectary during the 

 past two years by Mr. J. J. Davis and Mr. J. A. West from coccoons 

 and infested grubs sent in by Mr. Kelly from fields at Elliott, 111. 

 Thirty-three Tiphia cocoons were used in these observations, twenty- 

 one of which were obtained November 25, 1905, and twelve April 

 27, 1906. From those collected in fall the winged insect emerged 

 at thirteen dates between June 19 and July 28, 1906, and those ob- 

 tained in spring yielded the adult on eleven dates between June 26 

 and August 22. These collections consequently do not represent dif- 

 ferent broods. Only seven of the adults obtained were males, and 

 twenty-five were females, the sex of one being tmdetermined. 



A pair were seen in copula in one of the breeding-cages at 9 :30 

 p. m. July I, and eggs were laid on grubs in the insectary from June 

 "29 to August 21. One lot of young white-grubs brought in Sep- 

 tember 20, 1906, were already badly infested by very small Tiphia 

 larvas about one eighth of an inch in length. As insectary observa- 

 tions show that the eggs hatch in from seven to ten days, and that 

 the young larva reaches the length of an eighth of an inch in about a 

 week, it appears that the eggs for these larvae were laid a little later 

 than September i. The period of oviposition of this grub wasp is 

 thus something more than two months. 



In several cases a female Tiphia was induced to go through the 

 whole operation of preparing her victim and depositing her egg 

 upon it above ground in a breeding-cage, where she could be con- 

 tinuously watched, and the facts thus learned are unusually inter- 

 esting. Like others of its family — the digger-wasps, or Scoliida — 

 these insects sting their prey before attaching the egg to it, with the 

 effect to paralyze it more or less completely. Mounting the body of 

 the grub, which struggles violently against the attack, the Tiphia 

 seizes with her mandibles the skin of the back just behind the head, 

 curving her body downward around the side of the grub, with the tip 

 of her abdomen beneath and just behind the head, and then, after feel- 

 ing about with the abdomen for a time, finally stings her victim, with 

 the effect suddenly to quiet its struggles and reduce it to helpless- 

 ness. Then the Tiphia reverses her position and works the tip of her 

 abdomen backward and forward for several minutes in one of the 

 grooves or creases on the back of the larva, usually not far behind the 

 head, apparently smearing the surface there with a viscid fluid, after 

 which she deposits her egg on this sticky surface and goes away.* 



'^he above acconnt'is based on insectary observations and experiments. Several white- 

 grnbs parasitrzed by Ttpita larva? have been found in the field since this was written, and In 

 every case the larva was on the under side of the body between the thoracic legs. 



