632 



NATURE 



[October 26, 1905 



EXPERIMENTS ON VARIATIONS OF LEPI- 

 D OPT ERA BY ENVIRONMENT. 



A N important addition to the numerous papers of 

 ■^~*- recent years recording experiments as to the 

 influence upon the forms of living beings of their 

 environment has lately been published.' In this 

 paper the inquiry is concerned only or chiefly with 

 varieties in the pigmentation of Lepidoptera. The 

 author enumerates as among the agents to which 

 change in this pigmentation is to be ascribed " in- 

 tensity of light, temperature, nutrition, humidity, 

 dryness, electricity, and other meteorological pheno- 

 mena." His references to the 

 literature on these subjects are 

 very useful. The suggestion that 

 mechanical movement, jarring, of 

 pupae, might cause effects analo- 

 gous to those of temperature is 

 mentioned, but this has long since 

 been abandoned. M. Pictet divides 

 the variation of pigmentation into 

 two opposite types, the one 

 " albinism," by which red can 

 pass into yellow and even into 

 white, the other "melanism," bv 

 which red passes into brown and', 

 as an extreme, into black ; and 

 this classification is kept in view 

 all through the description of his 

 experiments and their results. 

 So is a theory which he puts for- 

 ward, though with diflidence, that 

 caterpillars in general were 

 originally adapted to live only on 

 certain special plants or trees, and 

 afterwards, owing to finding them- 

 selves, as the result of migration 

 or otherwise, where these were 

 not to be had, adapted themselves 

 to many other kinds, so as to be- 

 come more or less polyphagous, 

 still, however, in nature attaching 

 themselves by preference to special 

 food plants, called in this paper 

 their normal or ancestral ones. 



M. Pictet 's treatment of this 

 subject can be best illustrated 

 by an extract : — " Lasiocampa 

 quercus, known from the time of 

 Linnaeus as feeding almost ex- 

 clusively on the oak, as indeed 

 its name indicates, and the leaves 

 of some trees and hedge shrubs, 

 is now found frequently on ivy, 

 poplar, sallow, birch, heath arid 

 arbutus." He does not always 

 say what the normal food plant is, 

 as in the case of Phalera buce- 

 phala, of which he states that it 

 absolutely refuses to eat anv but 



its normal food. In England it i. , 



elm, willow, and many other forest trees at least as 

 freely as on oak, and there is a record of a companv 

 found on laurel. Oak is given as the normal food 

 of Biston hirtarius (found in England on a great 

 variety of forest trees), gooseberry and spindle tree 

 (Euonymus europaeiis) as those of Abraxas grossii- 

 lariata. In England this species is found in" abun- 

 dance also on blackthorn, &c., and it has of late 

 years addicted itself to the Euonymus japonicus, an 



1 ''Influence de I'Alimentation et de I'Humidite sur la Variation des 

 I'apillons. By Arnold P.ctet. (Memoires de In Sociite de Physlgiie et 

 ■ 'tt-Z'f, vol. XXXV., fascicule t, June, 1905, 



evergreen which became widely distributed in Europe 

 during the last century. Though, as stated, it is left 

 uncertain in some cases what M. Pictet considers the 

 normal food plants to be, that creates little or no 

 difficulty in appreciating most of his experiments, as 

 the kinds of food plants which in these experiments 

 were substituted for the foods well known to be usual 

 were so diflerent that they may certainly be dis- 

 tinguished as abnormal ; for example, when walnut or 

 laurel, or low plants such as sainfoin (Onobrychis 

 sativa), dandelion, lettuce, or salad burnet (Poteriurn 

 sangnisorba) are substituted for any of the ordinary 

 forest trees. 





found on lime. 



tVHisloirc tmturelli 

 pp. 46-127 ) 



NO. 1878, VOL. 72] 



.\mong the principal conclusions arrived at by M. 

 Pictet are the following : — (i) Change of ancestral 

 food plant is often a factor of variability. (2) In 

 general, a food difficult to absorb and digest prevents 

 the larva from developing within its usual period, 

 and this longer larval period is associated with the 

 shortening of the pupal period, and consequently with 

 insufficient pigmentation. (3) Normal food plant in 

 insufficient quantitv has the same effects. {4) A food 

 easy to take in (ingcrer) and rich in nutritious 

 elements accelerates the larval development, and thus 

 reacts on the duration of the pupal period, which, 

 being thus lengthened, a more intense pigmentation 



