96 BULLETIN 536, U. S. DEPARTMENT OF AGRICULTURE. 



the procedure so that the parasites were given an opportunity to 

 oviposit in the larvae within host fruits under more normal conditions. 

 The methods previously used permitted much moisture to gather on 

 the sides of the glass jars in which the host fruits and parasites were 

 placed. The method now recommended by Mr. Bridwell consists in 

 the use of two ordinary nursery flats, the boxes being 16 by 12 by 3 

 inches. Into one of these is placed a layer of dry sand and a wire 

 container so arranged that it will hold the infested host fruits exposed 

 within it clear of the sand. The second tray, the bottom of which 

 has been replaced by fine-mesh copper wire, is used as a cover and 

 is made sufficiently small so that it can be inverted and thrust down 

 into the tray containing the sand and fruits as soon as vials containing 

 the adult parasites have been unstoppered and placed upon the fruits. 

 By pressing the edges of the covering tray well into the sand the adult 

 parasites are prevented from escaping and ants are, temporarily at 

 least, prevented from interfering with the experiment. When the 

 covering tray is in place, the wire-screen top is not far from the ex- 

 posed fruits; hence the parasites are forced to confine their activities 

 where they net the best results. The Bridwell method has not only 

 made it possible to rear large numbers of opiines quickly and without 

 skilled labor but is largely responsible for the success of the Fullaway- 

 Bridwell parasite expedition to Africa. 



The writers have been able to rear both sexes of the opiine parasites 

 in large numbers very easily since the summer of 1914 by merely 

 placing in test tubes about 2 inches in diameter a number of infested 

 host fruits and parasites. This method requires greater care and 

 produces much sweating of the sides of the containers, but parasitic 

 material of both sexes can be very quickly secured for experimental 

 work, and the investigator has the advantage of being able to observe 

 the activities of the adult parasites. The objectionable feature of 

 excessive moisture was overcome by the use, in the summer of 1914, 

 of a wooden box, the top and bottom of which was of fine-mesh 

 copper wire which contained a sliding shelf made of coarse-mesh 

 wire supported midway between the top and bottom of the box and 

 which could be easily removed through one end of the box which 

 was hinged. This device possessed the advantage, demonstrated by 

 Bridwell, in that it prevented accumulations of excessive moisture 

 and confined the parasites closely to their hosts, but was not so well 

 adapted to the purposes of parasite work since the host larvae which 

 pupated on the bottom of the box could not be so readily secured. 

 After the host larvae have emerged from the exposed fruits the pupae 

 may be easily sifted from the sand beneath the fruits and held in 

 glass jars until the adult parasites have emerged. 



It was not necessary to expose adult opiine parasites to strong 

 sunlight for a few minutes each day to hasten mating, as recommended 



