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 ET-155 February 1940 
 
 United States Department of Agriculture 
 Bureau of Entomology and Plant Quarantine 
 
 A LABORATORY METHOD FOR THE STUDY OF INSECTS IN THEIR COCOONS 
 
 By L. Courtney Fife. 
 Division of Cotton Insect Investigations 
 
 In many studies of insects it is essential to make daily ob- 
 servations on the development of larvae and pupae in their cocoons 
 without disturbing them. A cocooning rack for this purpose was 
 devised by E. R. Van Leeuwen, ^ and later a similar rack was devised 
 by Rodney Cecil. 2 However, these racks are rather large and could 
 not be used in desiccators for studying the effect of humidity on 
 larvae and pupae of the pink bollworm ( Pecti n ophora Rossypiella 
 (Saund.)) in their cocoons. The method devised to overcome this 
 difficulty may be useful to other workers in the study of insects 
 that spin cocoons during their development. 
 
 Method and Procedure 
 
 As shown in figure 1, larvae are permitted to spin up between 
 the bottom surface of a petri dish and a thin disc of absorbent 
 cotton. This cotton disc can be easily made by stripping a thin 
 layer from a roll of absorbent cotton obtained in a drug store. 
 A disc of toilet tissue is placed over the cotton disc. These 
 discs are cut to fit the inner surface of the dish. 
 
 From 30 to 50 larvae are placed in the dish and given a few 
 shakes tc distribute them somewhat evenly over the surface. The 
 disc of absorbent cotton is quickly placed over the larvae, and then 
 the disc of toilet tissue is placed over the cotton disc. A heavy 
 cardboard disc is placed over the other two discs, and a light 
 weight is placed on top. The cardboard and weight act as a thig- 
 motropic stimulus to the larvae in spinning their cocoons. Soon 
 after the larvae start to spin their cocoons, the weight and disc 
 of cardboard are removed. 
 
 1 Siegler, E. H. , and Plank, H. K. Life history of the 
 codling moth in the Grand Valley of Colorado. U. S. Dept . Agr. 
 Bull. 932, 119 pp. Sept. 1921. 
 
 2 Cecil, Rodney. A cocooning rack. Bur. Ent. and PI . Quar. , 
 ET-94 (multigraphed) . March 1937. 
 
 i^ 
 
- 2 - 
 
 In the studies made by the writer very few larvae left their 
 cocoons when exposed to various high or low temperatures or a wide 
 range in humidity. 
 
 If individual records are desired, each insect can be num- 
 bered by the use of India ink on the outside bottom surface of the 
 petri dish. A tight-fitting lid of copper screen can be substituted 
 for the glass cover of the petri dish, if desired. 
 
 From figure 1 it will be noted that the various stages of 
 the insect can be easily recognized without disturbing them when 
 the dish is held up to the light. 
 
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 Figure 1. — Spin-ups of the pink bollwonu between the bottom 
 surface of a petri dish and a thin disc of absorbent cotton. 
 
UNIVERSITY OF FLORIDA 
 
 3 1262 08537 1069 
 
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