Whiting: Heredity in Wasps 



263 



WINGS OF WASPS SHOWING HEREDITARY VENATION 



The parasitic wasp Hadrobracon brevicornis furnishes excellent material for studies in heredity. 

 There has been found a variation in the venation of the wings, and the character has proved to be 

 hereditary and also correlated, as is color, with the size of the insect and the temperature in which it 

 is bred. In wing a the vein r4 is complete in the normal wasp. It shows a slight break in the speci- 

 men figured here. Breaks in this vein are hereditary. Wings b, c, d, e, and / are non-genetic 

 abnormalities of wings which include omission and addition of veins and remarkable reduplica- 

 tions, (about x8) (Fig. 21.) 



yellow, so that insects bred at 32° C. 

 or over are almost entirely yellow, 

 except for compound eyes, ocelli, and 

 antennae, which remain black. The 

 correlation of lighter color with higher 

 temperature may be due to a differen- 

 tial effect of the latter upon formation 

 of integument and pigment. 



In size the insect ranges from three 

 and one-half millimeters in well fed 

 wasps, to one and one-half millimeters 

 in those that are less fortunate in 

 obtaining their food supply during 

 growth. Small females lay fertile 

 eggs which develop into adults of 

 normal size. At constant temperature 

 the smaller individuals show relatively 

 more black. Starvation may therefore, 

 like temperature, have a differential 

 effect. 



A HEREDITARY DEFECT IN VENATION 



In progenies bred from wild stock 

 there was found to be a variation in 



the venation of the wings. The typical 

 wing shows the fourth branch of the 

 radius, n, extending completely across 

 from the third branch of the radius in 

 front to the first branch of the media 

 behind. 



In some of the wasps, however, there 

 was a break in this vein of greater or 

 less extent, appearing on one or both 

 wings. The character proved to be 

 hereditary but very irregular in appear- 

 ance. It was soon noticed that this 

 variation also, as in the case of color, 

 was correlated with temperature and 

 with size. Either at low temperatures 

 or in small specimens the defect is not 

 as likely to appear as at higher tempera- 

 tures or in larger specimens. Conditions 

 favoring development therefore have a 

 differential effect upon the formation of 

 the wing as a whole and the fourth 

 branch of the radius. When bred at 30° 

 C. the temperature at which the wasps 

 are reared, different inbred stocks 



