40 The Mechanism of Evolution in Leptinotarsa 



Source of Material. 



Materials utilized for experimentation were obtained at Pedro Miguel (stock 

 No. 1705, obtained August 1913), about 1 kilometer north of village ; at Corozal 

 (stock No. 1700, obtained August 1913), near railroad station; at Gatmi 

 (stock No. 1710, obtained August 1913; No. 1711, obtained September 1913), 

 and 3 kilometers south of the railroad station, and at Culebra (stock No. 1715, 

 obtained August 1913; No. 1716, obtained September 1913). Habitats fairly 

 uniform for all, but at the Gatun location, in the hills, it rains almost the 

 entire year, while at Corozal a fairly well-marked dry season occurs between 

 January and May. 



LEPTINOTARSA ANGUSTOVITTATA Jacoby. 



Leptinotarsa undecimlineata Stk\ var. Jacoby, 1883, Biol. Centr. Am., 



vol. VI, pt. 1, p. 234. Described as a variety. 

 Leptinotarsa angustovittata Jacoby, 1891. Biol. Centr. Am., vol. VI, pt. 1, 



suppl., p. 254, pi. XLI, fig. 15. 



This species, in its distribution, habitat, as well as its structural and color 

 characters, and in its juvenile stages, is clearly more closely related to L. diversa 

 than any other species in the group. Its occurrence in semidesert habitats, and 

 the fact that it is often closely approximated by the geographical variety of 

 L. diversa (rugosa nov. var.) lead me to suspect that it is either a desert habi- 

 tudinal variety of L. diversa or a modification thereof that has become perma- 

 nent in semidesert locations. The data is not available to reach a decision of the 

 relationship, and I have therefore allowed it to stand provisionally as an inde- 

 pendent species. It is possible also that this form may have arisen and is now 

 arising through hybridization, at any rate I have produced in experiment by 

 hybrid reactions a form that I am not able to differentiate from Jacoby's 

 L. augustoviUaia. Stock from nature at Guanojuato breeds genetically true, 

 even under changed environment. Jacoby's description (Biol. Centr. Am., 

 vol. VI, pt. 1) is as follows : 

 " Leptinotarsa undecimlineata, Huj. op. (partini). 



" Black : the head with two flavous spots ; the thorax and elytra flavous, the 

 former spotted with black, the latter with eight narrow black, strongly punc- 

 tured, longitudinal stripes. Length, 5-6 lines. Habitat : Mexico, Guanajuato 

 (Salle), Morelia, and Tacambaro in Michoacan (Hoge), Xucumanatlan in 

 Guerrero (H. H. Smith). 



" This insect was previously treated by me as a variety of L. undecimlineata, 

 but as we now have received twenty additional specimens, all alike, I am com- 

 pelled to treat it as a distinct species. It agrees in everything with L. undecim- 

 lineata, except that the elytra have eight very narrow black stripes, each of 

 which is abbreviated at a short distance before the apex ; these stripes are deeply 

 punctured in single, sometimes in double and very closely contiguous rows, this 

 character separating the species from L. undecimlineata, in which each elytron 

 has four much broader stripes, and the stripes singly or doubly punctured along 

 their margins." 



Description of Living Animals. 



Imago (plate 3, fig. 3).— Head: Pronotum, gTeenish ivory white, often 

 yellowish, marked with black spots ; eyes and mouthparts shiny black ; elytra 

 grayish white or grayish-gray white, with 4 pairs of closely placed parallel 

 black lines, strongly punctured. These are equivalent to the elytral stripes of 



