HEREDITY IN WASPS 



A Study of Heredity in a Parthenogenetic Insect, the Parasitic Wasp, 



Hadrobracon 



P. W. Whiting 



Child Welfare Research Station, State University of Iowa, Iowa City 



SEVERAL \arieties of honey bees 

 differing in color, habits, and tem- 

 perament have been developed by 

 apiarists. Crosses of these have giv'en 

 results of much interest both to bee 

 breeders and to students of genetics 

 and cytology. As is well known the 

 honey bee flies high in the air while 

 mating and consequently experimental 

 work with this form is seriously handi- 

 capped. Drones are supposed to arise 

 from unfertilized eggs and are haploid 

 having tiie reduced chromosome num- 

 ber. Workers and queens are the female 

 forms, the former with o\'aries unde- 

 veloped due to a difference in feeding. 

 Females are diploid and presumably 

 arise from fertilized eggs. This princi- 

 ple of se.x determination as applied to 

 the bee is known as Dzierzon's Law. 

 According to this principle drones 

 should always resemble the maternal 

 race while workers and queens should 

 be hybrid, either resembling the domi- 

 nant form or, in case of lack of domi- 

 nance, being intermediate. Results of 

 breeding tests have been conflicting. 

 Newell crossing Italian and C'arniolan 

 races obtained offspring according to 

 expectation, while earlier investigators 

 with German and Italian strains found 

 a variable number of more or less 

 "patroclinous" drones, that is drones 

 resembling the male parent. 



Mendelian heredity complicated by 

 parthenogenesis has been shown by 

 Nabours in a grouse locust, Apotcttix, 

 and by I'Vyer in a Phasmid, but the 

 bee is the only form in which hereditary 

 differences other than sex have been 

 studied in connection with haploid 

 parthenogenesis. If parthenogenesis is 

 haploid, the gametic series should be 

 given directly in the progeny from a 

 virgin female, in other words there 

 should be no complications due to 

 fertilization. This is inheritance ac- 



cording to Dzierzon's Law and is of a 

 "criss-cross" type resembling sex-link- 

 age superficially. It differs from the 

 latter, however, since males arise from 

 unfertilized eggs and the sex ratio is 

 consequently extremely variable. This 

 method of inheritance may be called 

 sex-linkoid. 



Sex-linkoid inheritance should occur 

 in bees, wasps, and ants, as well as in 

 many of the lower Hymenoptera, 

 white-flies, thrips etc. Several para- 

 sitic wasps, however, produce females 

 parthenogenetically and in this case we 

 may expect segregation if the reduc- 

 tional division of the egg nucleus is 

 not omitted. In the gall-wasps alterna- 

 tion of parthenogenetic and sexual 

 generations should show complicated 

 types of inheritance. Aphids should 

 also furnish material of much interest 

 if Mendelizing characters were studied. 



The writer has for some time been 

 working with a wasp, Hadrobracon 

 brevicornis (Wesmael), parasitic upon 

 the caterpillars of the Mediterranean 

 flour moth. The insect is easily manipu- 

 lated and passes through a generation 

 in ten days in the incubator. Three 

 hundred and fifty or four hundred 

 offspring are often produced from a 

 single female. Parthenogenesis is 

 strictly haploid or "male-producing." 

 Thousands of offspring reared from 

 virgin females include not a single 

 female. 



WlDIi COLOR V.\KIATIONS 



The insect's extreme \ariability in 

 color and size has caused nuich con- 

 fusion in taxonomy. The color ranges 

 from hon('>-\ellow to black, the darker 

 pigment being distributed in areas of 

 \ar>'ing size. This variation appears 

 to be due almost wholly to tempera- 

 ture, selection having no effect. Higher 

 temperatures produce relatively more 



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