330 Annals Entomological Society oj America [Vol. X, 



generation, when continued into the second generation causes a 

 great diminution in the vigor of the individuals. Some of 

 these second generation individuals die in the larval stage; 

 some, as shown in my experiments, in the pupal stage; and 

 many of them in the adult stage inside of the earthen pupal 

 cases. 



Summary. 



1. The males of our common pear- or cherry-slug saw-fly 

 must be very rare in certain parts of our country. The exami- 

 nation, of several hundreds of individuals obtained at various 

 times during the late spring and summer for three seasons at 

 Ames, Iowa, and for two seasons at Corvallis, Oregon, failed to 

 reveal a single male. 



2. The species is parthenogenetic, and successfully so for 

 the offspring of the spring brood of females. 



3. The eggs deposited by spring-brood virgin females 

 hatch, and produce normal vigorous larvae. These feed nor- 

 mally, later pupate and finally produce adults. 



4. Unfertilized eggs produce females only. 



5. Parthenogenesis when continued for the offspring of 

 the second or summer brood of adults, gave larvas, a considerable 

 percentage of which failed to pupate, a considerable percentage 

 successfully pupated, but did not transform into the adult 

 stage, and a very large percentage transformed into adult 

 stage, but did not emerge from the enclosing earthen cells. 



6. Only a single adult was reared from 109 of the second 

 generation parthenogenetic larvae. 



7. An orchard which was heavily infested with spring- 

 brood females, and in which no males were observed, produced 

 an enormous number of second generation females, which 

 produced in turn an increasing number of second brood larvae, 

 causing injury so serious as to kill outright several cherry trees 

 of the orchard and to seriously injure all of the trees. From 

 this enormous second brood of larvae only a very few adults 

 emerged the following spring. 



8. I am unable to account for the failure of these second 

 brood larvae to produce active adults unless it be on account of a 

 lack of vigor due to the absence of fertilization for this brood, 

 yet it is possible that this failure was due to other causes. 



