54 The Mechanism of Evolution in Leptinotaksa 



Length of ontogeny: Twenty-one to thirty-seven days ; average 25 to 30 days. 

 The juvenile stages are variable in this geographical variety and some of the 

 larval colors may be isolated by proper breeding into line-cultures, breeding true. 



The range of this form has already been indicated and is shown on plate 5. 

 It has been observed in all stages at the following points : Toluca, Lerma, Sala- 

 zar, Ixtlahuaca, Malacatepec, Vale, Zitacuaro, Angangueo, Maravatio, in the 

 States of Mexico and Michoacan. 



Recitbbent Mutation, multit.«niata-melanothobax Stal. 



Identical with same mutant of L. multitceniata, except that stripes are often 

 broader upon the elytra. 



Color biotypes are present and easily isolated by selective purification in 

 cultures. These relate entirely to hypodermal color, and the following can be 

 easily established : L. variabilis h^, red elytral ground ; L. variabilis 6^ orange 

 elytral ground ; L. variabilis ¥, yellow elytral ground ; L. variabilis b*, white 

 elytral ground. 



The life-history is like L. multitceniata, excepting that the growing-season is 

 somewhat shorter and less favorable. Two generations per year are the general 

 rule. The last generation may be seriously retarded or nearly annihilated by 

 early autumn frosts, cold spells, or early advent of the dry season. 



Ecology of this variety differs only in trivial details from the ecological 

 relationship of multitceniata, excepting that it is in general compelled to meet 

 more rigorous conditions than L. multitceniata. 



Stocks for analysis and experiment have been obtained at the following 

 points: (a) Toluca, from the open plain west of Toluca, especially on the 

 northern side of Cerro de Zopilacalco and Cerro de Huitzila and from the banks 

 of a small rainy-season pool east of El Temple de El Eanchito ; ( & ) Lerma, on 

 open plain to south of town on shore of small lake; (c) Malacatepec, 3 miles 

 south of plaza, near an old ruined rancho; {d) Zitacuaro, near town, in waste 

 places, especially in corrals or pastures. 



LePTINOTABSA oblongata NOV. SP. 

 (Plate 4, fig. 12.) 



Leptinotarsa oblongata Tower, 1906. Inv. Evol. Chrys. Beetles genus Lept., 

 Carnegie Inst. Wash. Pub. No. 48, pp. 6, 20; Jacoby, as L. decemlineata 

 Say, etc., Biol. Centr. Am., vol. VI, pt. 1, p. 233, and suppl., p. 255. 



Jacoby refers specimens of this species from many Mexican localities to 

 L. decemlineata Say, on account of " fulvous legs, more or less marked or 

 spotted with black." The "fulvous" color of dead material is meaningless 

 and useless as a diagnostic character, and the highly variable black markings 

 are of service only when taken in conjunction with other characters. Some of 

 the localities recorded by Jacoby refer undoubtedly to this form (Cuernavaca 

 in Morelos) ; other localities are L. multitceniata Stal or its different geo- 

 graphical races. Jacoby's specimens now in the British Museum show clearly 

 much confusion with respect to this species and L. decemlineata Say. I have 

 been over this material and have given in tabular form below the determinations 

 reached. 



