STUDIES OF VARIATION IN INSECTS 



273 



Fig. 49. Frequency polygon of the variation in prothoracic pattern in 521 

 specimens of the convergent lady-bird, Hippodamia co}iverge7is, collected at one 

 time and one place. 



Thus the mode is one of the extremes of the series of classes 

 (= frequency curve strongly skew), according to the views of 

 Davenport, et al., indicating an evolution of this pattern from 

 the conditions shown in the other cases, or indicating, as held 

 possible by us, a tendency to vary (evolve) in the direction of 

 the other cases. 



Variation in Elytral Pattern of Diabrotica sorer (the flower-Dia- 

 brotica). — Diabrotica soroi' is a Chrysomelid beetle which is 

 abundant and a serious pest on the Pacific coast. In its larval 

 stage it lives underground feeding on the roots of alfalfa, chry- 

 santhemum and various other plants ; it pupates in a subter- 

 ranean cell near the surface and the adult beetle on issuance 

 from the pupal cuticle makes its way above ground, and feeds 

 on the buds and opened flowers of roses, chrysanthemums and 

 almost all other garden blossoms. The color pattern of the 

 beetle is definitive and fixed at the time of the first appearance 

 of the adult above ground. The ground color of the elytra is 



