CONTENTS 



Chapter I. — Geographic ai, Distribution and Dispersion oe IvEpTinotarsa. 



Page 



The genus Leptinotarsa , i 



Data of the distribution 4 



Geographical distribution and dispersion of the genus 9 



The center of origin and dispersion 9 



The distribution and migrations of the lineata group, 14 



Distribution and oecology of the species 14 



Distribution of L. intermedia and decemlineata and probable movements 



within historic time 21 



Chronological history of dispersal of L. decemlineata^ 1859 to 1904 25 



Occurrence in Europe 39 



The highways of dispersal and rate of movement 39 



Other factors which have controlled the direction of movement 44 



Distribution of L. defeda and L. junda and retreat of L. junda 49 



Distribution of the other groups 50 



The relation of the distribution of the genus Leptinotarsa to natural environ- 

 mental complexes 52 



Chapter II.— Variation in Leptinotarsa. 



Introduction 59 



Individual variations , 62 



Observations and data of continuous variations 62 



Color characters -62 



Individual variation in the color pattern of the pronotum 62 



Individual variation in the color pattern of the epicranium 72 



Individual variation in the color pattern of the elytra 76 



Individual variation in the color pattern of the ventral surface 84 



Individual variation in the color pattern of the legs 86 



Individual variation in the color pattern of mature larvae 86 



Structural characters 87 



Individual variation in the punctation of the elytra . 87 



Individual variation in the punctation of the pronotum 90 



Individual variation in the glands of the elytra 90 



Individual variation in size and shape 90 



Observations and data concerning extreme variations 91 



The laws of variation in the genus Leptinotarsa 92 



Place variation 93 



Geographical variation 105 



Distribution and variation and the evidence they afford concerning evolution 113 



Chapter III.— Coloration in Leptinotarsa. 



Color phenomena in^ insects . 121 



Color classes 121 



Chemical or pigmental colors ". 121 



Physical or structural colors 123 



Chemico-physical or combination colors 123 



V 



