COLLECTING AND PRESERVING INSECTS BANKS. 



119 



or Swiss netting over a stone or plant in the water on which arc the 

 larvae of the desired insects. 



Doctor Needham has used for rearing aquatic insects a wire cage 

 shown in figure 176. It is a cylinder of galvanized wire screen, open 

 at both ends, with a loose screen cover. The cylinder may be 

 pushed down over the plant or rock deeply enough into the bottom 

 so that the larvae or nymphs can not escape, sometimes 2 or 3 inches 

 into the mud. 



A water cage or aquarium can be made by cementing together 

 panes of glass. Make a bottom of one piece of wood, with a groove 

 around the edge. Set the panes of glass in the groove and bind 

 their edges where they come together with strips of muslin glued on 

 the outside, and place a narrow, oblong strip of glass inside across each 

 corner. Fill this space and also the bottom groove with a cement 

 made as follows : White sand, 1 part; plaster of Paris, 1 part; litharge, 

 1 part ; and powdered resin, one-third part. Make into a thick paste 

 with boiled linseed oil. Let the 

 cement harden for several days 

 before putting the water into the 

 aquarium. 



In rearing mosquitoes it has been 

 found necessary to isolate the larvae. 

 Doctor Dyar does this as follows: 

 When a batch of larvae is gathered 

 in a vessel from a pool a number of 

 flat-bottom vials (8-dram) are half 

 filled with, water from the same pool 

 and a little dirt or mud from the bottom of the pool placed in the bot- 

 tom of each vial. Then with a pipette each larva is transferred to a 

 vial, one larvae only in each vial, and the top plugged with cotton. 

 When the larva changes to a pupa the last larval skin is removed and 

 put into a tiny vial of alcohol with a little glycerin. This vial is then 

 inserted in the cotton, plugging the larger vial until the mosquito 

 emerges from the pupa. Then both mosquito and larval skin are 

 given the same number. One is thereby certain that the skin and 

 adult are of the same species. The adult mosquito should not be 

 killed as soon as it issues, but allowed a day or so to chitinize and 

 attain its colors. The vials with larval skins may be stored or canned 

 in larger bottles until one desires to study them, when they should 

 be mounted on slides. Anopheles mosquitoes need more surface than 

 is afforded by a small vial and can be reared in open saucers. 



In rearing caddiceflies, Vorhies has found that for those that 

 inhabit standing waters ordinary crystallization dishes, 6 or 8 inches 



Fig. 176.— The Needham aquatic cage. 



