EXPERIMENTS WITH CHRYSOMELID BEETLES. 1 



ROBERT \V. HEGXER. 



Results obtained by the writer within the last five years from 

 experiments upon Calligrapha bigsbyana and other chrysomelid 

 beetles have shown that the eggs, larvae, pupae and adults of these 

 insects are admirably suited for the study of many of the external 

 and internal factors of development. The eggs may be definitely 

 oriented with regard to the future position of the embryo quite 

 easily; they continue to develop when subjected to extremely 

 violent mechanical conditions; and various parts may be removed 

 without retarding their development(Hegner, 19080, 19086, 19090, 

 19096). The larvae are easily reared in the laboratory in an en- 

 vironment similar to that which they encounter in nature; they 

 usually thrive well under experimental conditions. The same 

 things may be said of the pupae and adults. 



It is the writer's intention to present in this paper, and those 

 that are to follow, the data and conclusions derived from experi- 

 ments dealing with the growth and external and internal factors 

 which influence the development of the various stages in the life 

 history of certain chrysomelid beetles. Thus far the willow 

 beetles, Calligrapha bigsbyanaand C. miiltipunctata, have received 

 the largest share of attention, but other species have also been 

 employed. 



I. THE NORMAL RATE OF GROWTH OF Calligrapha Bigsbyana. 



i . The Weight of Developing Eggs. 



Method and Data. Two series of weighings were made to de- 

 termine the loss of weight of developing eggs of C. bigsbyana. 

 Table I. shows the results for twelve eggs laid by four different 

 beetles at practically the same time. Two batches of two eggs 

 each, one of three, and one of five were taken at I P.M. on June 

 29, placed in a watch glass, and covered by another watch glass. 

 The loss in weight is quite striking. The pigmentation of ilu- 



'Contributions from the Zoblogical Laboratory of the I'nivcrsity of Michigan. 

 No. 128. 



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