16 



BULLETIN 265, U. S. DEPARTMENT OF AGRICULTURE. 



genesis may take one of several forms. Unfertilized females will de- 

 posit eggs which either will not hatch or will hatch and the resulting 

 larvse will die before attaining maturity, or the larvse from such eggs 

 will produce only male adults. The dock false-worm belongs to the 

 latter class, the unfertilized females ovipositing normally and the 

 eggs hatching and ultimately producing males. 



Great care was taken in rearing the dock false-worm to ascertain 

 the status of parthenogenesis in this species. Single pupae were kept 

 separate in glass vials, and females emerging from them were confined 

 alone with the larval food plant. They appeared as eager to oviposit 

 as those confined with males, and the average number of eggs deposited 



Fig. 5.— The dock false- worm: a, Superior saw blade of the ovipositor of adult female; 

 6, inferior blade of ovipositor. Highly magnified. (Original.) 



by them was greater than that deposited by mated females. The 

 period of development of all stages, as a rule, averaged somewhat 

 shorter than that of normal individuals, comparison, of course, being 

 made only with normal males developing under identical conditions. 

 The figures for parthenogenetic individuals of the various broods are 

 given below, under the heading "Life-history studies," where they 

 are kept separate from the figures for normal individuals. Table I 

 compares the period of development of normal males and partheno- 

 genetic males of the first, second, and fourth generations. No 

 parthenogenetic individuals of the third generation were reared. 



Table. I. — Comparison of life cycle of normal and parthenogenetic males of the dock 

 false-worm, Wenatchee, Wash., 1915. 



Generation. 



Origin of males. 



Average number of days in— 



Egg 



Larval 

 stage. 



Pupal 



Total 



life 



cycle. 



First . . 

 Second 

 Fourth 



Normal 



Parthenogenetic 



Normal 



Parthenogenetic 



Normal 



Parthenogenetic 



11.5 

 11.2 

 6.0 

 4.2 

 4.8 

 5.8 



33.6 

 29.7 

 20.9 

 20.6 

 27.8 

 26.8 



5.5 

 5.2 

 5.4 

 6.3 



50.7 

 46.1 

 32.3 

 31.1 

 32.6 

 32.6 



