50 The Mechanism of Evolution in Leptinotaesa 



BlOTYPE L. MULTIT^NIATA-OBSCURA NOV. VAB. 



This form occurs in nature, especially in the populations of multitaniata, in 

 the valley of Mexico, and in the region of Puebla, often with considerable fre- 

 quency, and is aai extracted homozygous recessive of P^ or Fg that comes out in 

 the crossing of the typical muUitwniata and melanothorax. It has been the 

 experience that the majority of the specimens found in nature were homozygous 

 when isolated in cultures, and continued to maintain their type, but not infre- 

 quently individuals are found that are heterozygous, often of great complexity. 

 The typical aspect of the pure-breeding recessive from nature is shown in 

 figure 8, plate 14. I have seen it in nature only in that form, where it has the 

 form and aspect of the modal L. muUitceniata Stal, but with the head and pro- 

 notum entirely black, excepting for the edges of the pronotum, which are 

 brownish or yellow, but with the pronotal markings entirely obscure. The 

 ventral side and the legs are entirely black. 



This form does not, as far as I am aware, maintain itself in continued genetic 

 lines anywhere in nature, but is constantly breeding back into the general 

 population. Its habits, juvenile stages, and ecological relations are in every 

 respect like those of L. multitcBniata Stal. 



This form has been produced many times in crossing experiments between 

 muUitceniata and melanothorax, and as far as experience goes is always a 

 recessive. 



Habitudinal Variety Intermedia nov. var. 



Leptinotarsa muUitwniatOrintermedia nov. var. nov. sp., Tower, 1906, I. c. 



This form, a variety of L. muUitceniata Stal, is found in the main in the north 

 plateau of Mexico, and is distinguished from the southern variety by its smaller, 

 less robust form, lower variability, conspicuous absence of minor divisions, 

 uniform pale yellow-white color, and its freedom from extensive fusions of the 

 elements of the color-pattern. It differs also in the larval stages, which are 

 yellow, yellow-red, or pale red in color, with the same system of ornamentation, 

 but more pronounced. As known from museum material, it might well be 

 confused with the varieties of muUitceniata or decemlineata, but the fact that it 

 is a stable, genetically perpetuated type, distributed over a wide geographical 

 range, and tiiat it is alternative in its attributes to corresponding attributes of 

 muUitceniata in crosses, and its distribution leaves no choice but to class it as a 

 habitudinal variety of the same species, or perhaps to raise it to specific rank. 

 (Plate 4, fig. 9.) 



Description of Living Animals. 



Imago. — Above : Oval, convex, head and pronotum light yellow-brown, orna- 

 mented with black spots. Elytra pale yellow-white, with five longitudinal black 

 stripes, second, third, and fourth often fused ; edged with irregular double row 

 of punctations, interspaces arched, polished; costal edge inflexed, grooved, 

 smooth brownish or yellow-white. Head : Eyes black, mouthparts dark brown, 

 anterior basal parts brownish, last six joints black, faintly pubescent, eleventh 

 joint broader than long, twelfth conical, truncate, last six joints forming an 

 elongated cone-shaped club. Epicranium faintly irregularly punctate, spots all 

 present, variable. Pronotum smooth, polished, few faint punctures in posterior 

 outer angle. Spots all present and not extensively fused, central V-spot 



am 

 a'— + —a is a common condition, often also include V — lj spots d', e', /', and 



pm 



