84 variation in leptinotarsa. 



Individual Variation in the Color Pattern of the Ventral Surface. 



The ventral surface of these beetles presents variations of two kinds first, 

 modifications in the elements of a color pattern, and second, variation in the 

 color intensity of a unicolorous surface. The second is the predominating 

 one in the genus. The first, limited to a part only of the lineata group, is 

 more complicated than the others and of far greater interest. 



In the lineata group all the species present a highly variable color pattern 

 excepting undecimlincata, angustovittata, signaticollis, diversa, and melano- 

 tliorax. In these the ventral surface is unicolorous. The variation of the 

 color pattern of the abdominal segments is shown on plate 15, figs. 17 to 32, 

 and that on the thoracic segments in figs. 33 to 40. As may be seen, the color 

 pattern is made up of a series of spots arranged upon the abdominal and 

 thoracic segments. These spots, which are located over muscle attachments, 

 consist of three sets on either side of the median line. It is from these spots 

 as centers that coloration spreads out, or to which it contracts, as the case may 

 be that is, color appears here first in development, and disappears here last 

 in reduction. L. inultitcciiiata is the most variable species in the group, exhib- 

 iting the series of stages shown on plate 15, figs. 17 to 24, inclusive. An 

 examination of these figures makes plain the manner in which the color 

 spreads from these segmentally placed spots. Fusion moves first laterally, 

 extending until all the spots are united into bands on either side of the median 

 line ; next these bands begin to extend across the median line at the anterior 

 end of the series of abdominal segments until they finally fuse, first anteriorly, 

 and then posteriorly. The increasing pigmentation next extends between the 

 bands, first until the entire anterior border of the segments is covered, and 

 then posteriorly until the condition shown in fig. 24 is reached. In figs. 25 to 

 29 are given stages in the process of reduction, as observed in L.deccmlineata, 

 the series starting with a condition like that of fig. 17 in L. multitccniata. 

 First the middle rows of spots on each side are reduced (figs. 25 and 26), 

 then the median rows (fig. 27), and lastly the outer rows (fig. 28). In all 

 the pigment begins to disappear first on the segments at the posterior end and 

 remains longest at the anterior end. In figs. 30 to 32 (plate 15) are shown 

 stages in the reduction of the pigment of the ventral surface of L. undecim- 

 lincata from Panama, in which it is evident that the color disappears first pos- 

 teriorly and then anteriorly. On the thoracic segments is shown the same 

 processes at work in L. multitccniata (figs. 33 to 40) and /,. undecimlincata 

 (figs. 41 to 44). 



These variations in the color pattern of the ventral surface are found in 

 the genus only in multitccniata, rubicunda, oblongata, intermedia, undecim- 

 lincata, dejecta, and juncta, and all present the same strongly marked tendency 

 to modification along the definite lines designated above. Indeed, from the 

 variations figured on plate 15, conditions could be selected to illustrate the 



