270 Phylum Arthropoda 



a nymph, thereby destroying the evidence of the length of instars. 



From the 6th or 7th to the 9th or 10th instars, the nymphs were fed 

 Ceriodaphnia, and Daphnia pulex; and after the 9th or 10th, Daphnia 

 magna. The latter were also used to feed the full grown nymphs which 

 developed the breeding stock. Cultures of these Daphnia had to be main- 

 tained in the laboratory throughout the season. [For culture see pp. 207 

 to 220.] 



Diseases. This species is susceptible to a disease which may occur 

 under laboratory conditions (as well as in nature), if pond water is used. 

 The invading organism is a green protozoan which lives in the lumen 

 of the rectum, and is fatal to a large percentage of infected nymphs. A 

 heavy infection is detectable, even with the naked eye, for the rectum 

 appears green and may be seen in any but heavily pigmented nymphs. 

 Methods of preventing infection were not worked out, but it might be 

 effective to boil the water in which the insects are to live. 



The species is also subject, under natural conditions at least, to two 

 species of trematode parasites, which may or may not be fatal; to a 

 Gregarine infection ; and to external infestation by an aquatic mite.* 



Reference 

 For the rearing Sympetrum vicinum see p. 272. 



METHODS OF REARING ODONATA 



P. P. Calvert, University of Pennsylvania 



THE following methods were successful in rearing larvae of Nanno- 

 themis bella and Anax Junius from egg to adult, f 

 Eggs of N. bella were obtained in the field in July, 1925, by dipping 

 the abdomen of a female, caught in the act of oviposition, in a vial of 

 water. As the eggs hatched the resulting 1st instar larvae were removed 

 to various small dishes. After they made their first larval (nymphal) $ 

 molt they were isolated, each one being placed in a glass salt cellar 

 having a capacity of about 5 cc, covered with a sheet of glass, and num- 

 bered. In each dish a small quantity of an aquatic plant (Elodea in 



♦Editor's Note: Others have reared Odonata from egg to adult both in Europe and 

 America, but the preceding account appears to be the only one of maintenance of any spe- 

 cies through successive generations. W. H. Krull (Ann. Ent. Soc. Amer. 22:651, 1929) 

 reared Sympetrum obtrusum, finding 9 (in one case 10) nymphal instars. He fed the 

 very young nymphs on Paramecium and Tubifex. (For culture see pp. 119 and 142.) 



The larger nymphs will eat almost any small living animals that come in their way. 

 It is easy to rear them in, pillow cages of the sort shown in figure 42, and if the size of 

 wire mesh be just small enough to retain them and large enough to admit their prey, they 

 will feed themselves in any natural pond, protected by the cage from predatory enemies. 



J. G. N. 



t Abridged by the author from a paper in Proc. Amer. Philos. Soc. 68:227-274, 1929. 



+ Editor's Note: Equivalent terms; nymph is used in preference elsewhere in this book 

 to denote this type of larva. J. G. N. 



