42 The Mechanism of Evolution in Leptinotarsa 



There is no diflBculty in the recognition of this species, even in badly pre- 

 served museum material, but the variety nigropunctata Sturm, is a, biotype, 

 breeding true in its distinctive character, and behaves as an alternative domi- 

 nant character in heredity. Stal's description of L. signaticollis (Monog. 

 Chrys. Am., p. 163), is as follows : 



" Nigra, supra sordide flavescens ; maculis prothoraeis capiteque nigris, hujus 

 vittis duabus flavis; elytris subvage nigro-punctatis, vitta angusta suturali 

 margineque inflexo aeneo-nigris. Long. 12, Lat. 7 millim. 



" Patria : Mexico. (Mus. Holm., Coll. Dohrn) . Ovalis, sat convexa, nigra, 

 nitida. Caput parce punctulatum, vittis duabus obliquis maculisque duabus 

 minutis ante medium sordide flavis. Antennae articulis quinque ultimus leviter 

 transversis, clavam minus distinctam formantibus. Prothorax sordide flaves- 

 cens, elytris nonnihil, angustior, lateribus parallelis, antice angustatus, disco 

 parce, subtiliter, utrimque pauUo densius et distincte punctatus, litura media 

 ut littera V f ormata maculisque lateralibus pluribus, plus minus confluentibus, 

 nigris. Scutellum laeve, nigrum. Elytra lateribus parallelis, dilute sordide 

 flavescentia, vage distincte nigro-punctulata, pimctis hie illic in series dispositis, 

 vitta angusta suturali margineque inflexo seneo-nigris." 



This description applies very well to the dead dried specimens of collections. 

 The following description is from living material in all stages : 



Imago (plate 2, fig. 1). — Above: Hypodermal color of head and pronotum 

 pale grayish white, often pale yellowish ivory-white, becoming darkened with 

 age; elytra, pale gray or pale gray-green. Head, mouthparts black; antennae 

 black, terminal joint truncate, eighth to eleventh thickened, broader than long. 

 Epicranium with anterior lateral epicranial spots fused medianward to form 

 heart-shaped spot, and prolonged caudad to fuse with posterior lateral epicranial 

 spots, which are united mediad. Posterior border and lateral portions of epi- 

 cranium behind eyes irregularly punctate with fairly well marked pits. Eyes 



am 

 black. Pronotum with variable pattern of black spots. b'+a'+ + +a+b 



pm 

 are always fused to form widely open V-shaped median spot, c' and c always 

 free, and d, e, f groups somewhat variable. Margins, especially anterior lateral 

 portions, punctate, with well-defined pits ; central portion with few minute pits 

 irregularly distributed. Elytra with black anal edge giving median black stripe 

 when closed. Each elytron with ten irregularly placed double rows of pimcta- 

 tions, marking position of chitinous columns between elytral lamellae, and with 

 slightly variable amount of black pigment in bottom of each pit. These rows 

 are arranged in a definite pattern shown in plate 2, figs. 1 and 2. Under wings, 

 pale yellowish brown, transparent, darker towards the base. The adult colora- 

 tion is not attained until about the third day after emergence. 



Size: Male 7 to 13 mm. long, 6 to 7.5 mm. broad; female 7.5 to 14.5 mm. 

 long, 7 to 9 mm. broad. 



Sexes: Female with sternal sclerite of last abdominal segment rounded ; male, 

 same sclerite sharply punctate, with median groove reaching nearly to anterior 

 border. 



Food: At Cuernavaca, Solanum hertmgi Bereth., S. diversifoUum Schlecht. 

 At Atlixco and Matamoros, S. diversifolium and 8. lanceolatum Cuv. Will also 

 feed upon ^S'. chrysotrichum Schl., but will not eat S. torvum from the Antilles. 

 Identification of food-plants by Dr. Greenman. 



