34 PEOCEEDINGS ENTOMOLOGICAL SOCIETY 



with a female and immediately mated. Next day he was placed 

 with another female and immediately mated. Both females de- 

 posited eggs, and the young began feeding in the wood, but the fe- 

 male parents at no time displayed a desire for a migration flight. 

 It is believed the colony was originally from a single set of eggs 

 and that more than two generations would have been passed 

 within the log in nature. 



In the second group the "provisions" against, or obstacles to in- 

 breeding assume varied forms. Usually the ratio chance of unions 

 between brothers and sisters to unions between unrelated individ- 

 uals, is so low that the offspring would be quickly reabsorbecl 

 into the normal form, but the details of habit that control this low 

 percentage may be varied. Chief of these is the instinct for mi- 

 gration, which appears to precede sexual maturity in many social 

 insects, but there appears to be also a remarkable difference in 

 time of development of the opposite sexes among the progeny of 

 a single parent of some species. The writer believes from prelimi- 

 nary experiments, that in Phengodes the males develop after two 

 years in the larval stage, while their sisters must spend three or 

 more years as larvaB. In this genus the males are strong migrants 

 while the females must lay their eggs where they have transformed. 

 The writer has shown that in Micromalthus the males issue about 

 two weeks after their sisters are out, but subsequent observations 

 indicate that males issue abnormally or irregularlj r at times. At- 

 tempts to mate specimens from different colonies in the breeding 

 cells all failed, and as both males and females manifested only 

 a desire to migrate from the time of their issuance almost until 

 death, it is believed sexual maturity will develop only after such 

 migratory flight. 



ON THE PROPER GENERIC NAMES FOR CERTAIN THYSAN-' 

 OPTERA OF ECONOMIC IMPORTANCE. 



BY J. DOUGLAS HOOD, United States Biologiml Purvey. 



The tobacco thrips, the pear thrips, and the orange thrips 

 species responsible in the United States for damage amounting 

 to many thousands of dollars every year and each the subject of 

 several published accounts are at present wrongly placed in the 

 genus Euthrips Targioni-Tozzetti by all North American workers. 

 The purpose of this paper is to correct the generic positions of these 

 and other allied species and to direct attention to several papers 

 which have been overlooked in America, that the proper names for 

 these insects may be used in the rapidly-growing economic litera- 

 ture. 



