August, 1944 



Ross: Caddis Flies of Illinois 



17 



Where conveniently situated they may be cut lowed the operator to take off the lid, see 

 away from both sides with the sharp ends what adults had emerged and grasp them 

 of a pair of forceps. with fingers or forceps through the muslin. 



Rearing Methods 



Association by Pupal Dissection. — In 



almost all caddis fly groups the larval scle- 

 rites are packed into the posterior end of the 

 pupal chamber after the pupa is formed. 

 Later in the pupal life the adult structures 

 take definite form within the pupal skin, 

 and, just before actual escape of the pupa, 

 the complete adult may be teased out of the 

 pupal skin. Such pre-adult specimens show 

 all adult characters except those of wing 

 venation, which does not develop until the 

 wings have expanded and dried by natural 

 emergence. Of greatest importance is the 

 fact that the genitalia of both sexes become 

 completely formed, hardened and colored 

 before emergence of the adult. 



If, then, a cocoon or case is collected 

 which has a mature pupa in it, the larval 

 sclerites and fully formed genitalia are 

 associated, and it is possible thus to link 

 the adult and larval forms of the species. 

 This type of association was fully explained 

 by Vorhies (1909) in his report on the 

 Wisconsin caddis flies. It was described 

 again by M. Milne (1938). We have used 

 this method for many years as a means of 

 linking the various developmental stages. 

 It is frequently necessary to collect in the 

 same locality several times before certain 

 species can be associated, but we have found 

 it more satisfactory than cage rearing be- 

 cause of extreme cannibalism developed by 

 caged larvae. 



Cage Rearing. — A few caddis fly groups 

 have pupal cases with a slit at one end, in- 

 stead of the conventional mesh used by most 

 groups. In these species the larval sclerites 

 are kicked out of the case by the respira- 

 tory movements of the pupa. This is true 

 throughout the family Leptoceridae and to 

 a limited extent in the genus Parapsyche. 

 For these species we used cages for rear- 

 ing numbers of specimens. The type of 

 cage used was square and suspended by side 

 flanges from a raft constructed to form 

 square openings, as described and used for 

 stonefly rearing by Frison (1935, p. 303). 

 The caddis fly adults were so fast in their 

 movements, however, that a layer of muslin 

 had to be tied over the cage and the lid 

 placed over this; such an arrangement al- 



Preservation 



As mentioned before, for study purposes 

 it is most practical to preserve all stages 

 of caddis flies in liquid, preferably 80 per 

 cent grain alcohol. This allows study of 

 different structures from various angles, 

 since the material is flexible. Furthermore, 

 the muscle tissue of caddis flies does not 

 become coagulated as in some other insect 

 groups and can be cleared readily in caustic 

 soda or potash solution. 



One genus, Leptocella, must be collected 

 dry, as mentioned on p. 213. Specimens of 

 this genus should be killed a few at a time 

 in a strong cyanide bottle and handled and 

 pinned with great care to avoid rubbing the 

 delicate hair which makes up the pattern. 



For display purposes or for color study, it 

 is sometimes necessary to pin material of 

 other genera. The pin should be inserted 

 with care to avoid piercing the scutellum 

 and middle line. These areas may be diag- 

 nostic for family or genus. 



Clearing Technique 



Accurate identification for almost every 

 caddis fly species must be based on charac- 

 ters of the genitalia, not only in the males 

 but also in the females of those groups in 

 which specific characters are known for this 

 sex. It is usually necessary to clear the 

 genitalia to see the diagnostic characters, 

 and for this operation we have found the 

 following procedure entirely satisfactory. 



Remove the apical half or third of the 

 abdomen from the specimen and place this 

 portion in cold 10 to 15 per cent caustic 

 potash or caustic soda solution. Allow it 

 to soak 6 to 12 hours, depending on its size 

 and color; then remove it to a dish of dis- 

 tilled water. If the specimen softens up in 

 a minute or two, gently squeeze, prod and 

 press until the dissolved mass of viscera has 

 been worked out of the shell. If the speci- 

 men does not soften, resoak it in hot 5 per 

 cent caustic solution for 5 or 10 minutes; 

 then squeeze out the viscera. The follow- 

 ing procedure is recommended for hot treat- 

 ment: Put the caustic solution in a vial, 

 which should be placed in a beaker of water; 

 a little twisted wire should be placed in the 



