208 



meus of The same scale on BlackbeiTT collected by Mr. T. C. Chamber- 

 lin at Santa Barbara. Cal. In Bnlletin Xo. 5 of this Division (p. 25) 

 other specimens of this species are recorded as having been reared from 

 a Mvtilaspis upon an undetermined species of Dycaste from Japan* 

 which we received in 1874 from the late Dr. George Thnrber, of the 

 American Agriculturist. The fact that this species is now found to 

 attack the Bed Scale (and we consider Mr. Coqnillett's observations to 

 indicate more than a mere probability is interesting and important, 

 since but one trne parasite has previously been recorded from this in- 

 sect, viz. the so-called CoccopJiagus citrinus Craw, which does not seem 

 to be mnltiplying rapidly. 



PAPvASlTIS:^! IX BEES OF THE G-EXI'S STELIS. 



That the Apid genus Stelis develops in the cells of the allied genus 

 Osmia has been known for some time, but the exact nattire of the par* 

 asitism. and more especially when and how the Osmia larva is destroyed 

 by the Stelis larva, have hitherto not been explained. In a recent 

 number of the Zoologischer Anzeiger (vol. XT. Xo. 3S3. February 1. 

 1892. pp. 11-4.3 . ^Ir. C. Terhoeff. of Bonn. Germany, stimmarizes the 

 results of a series of carefnl observations which throw a flood of light 

 on the subject. The species observed are Osmia Uucomelaena K. and 

 SteJis minuta yyl. 



The species of Osmia construct cells in the interior of hollowed twigs 

 in the manner of Megachile and similar bees. At the bottom of the 

 ceU the female Osmia first puts a layer of i^oUen which is to serve as 

 food for the nearly fall-gTown larva. Above this pollen, the bee com- 

 mences to store the cell with prepared bee-bread. At this moment the 

 female Stelis watches her opportunity to lay an egg in the Osmia ceU, 

 the egg thus beiag always near the bottom posterior end of the food 

 mass. Unaware of the presence of the parasite egg. the Osmia female 

 continues her work. and. after nearly filling the ceU. deposits her own 

 egg on the top i anterior end) of the food-mass. The cell is then closed 

 wirh a layer of macerated particles of plants and a second cell pre- 

 pared above the first. The Stelis larva hatches but little earlier than 

 that of the Osmia. and both larva? feed on the food-mass, the parasite 

 larva at the bottom, the host larva at the top. The latter remams sta- 

 tionary at the top and grows very slowly: the parasite larva gTOws 

 more rapidly, and gTadiially works its way upward through the food- 

 mass, thus gradually approaching the Osmia larva. The crisis finally 

 comes: the Stelis larva encounters the Osmia larva — a short but deadly 

 combat ensues — the Osmia larva is easily overpowered and killed by 

 the much larger and sn^onger parasite, and its body is devoured by the 

 latter within one or two days. 



It is thus evident that Stelis furnishes another Illustration of that 

 partial parasitism which I have shown to be the rule with the Meloidne, 

 but differs in that the parent introduces her egg into the host cell in- 



