Table Of ContentLEPIDOPTERA
GENETICS
BY
ROY ROBINSON
PERGAMON PRESS
Oxford · New York · Toronto
Sydney · Braunschweig
Pergamon Press Ltd., Headington Hill Hall, Oxford
Pergamon Press Inc., Maxwell House, Fairview Park, Elmsford, New York 10523
Pergamon of Canada Ltd., 207 Queen's Quay West, Toronto 1
Pergamon Press (Aust.) Pty. Ltd., 19A Boundary Street, Rushcutters Bay,
N.S.W. 2011, Australia.
Vieweg & Sohn GmbH, Burgplatz 1, Braunschweig
Copyright © 1971
Pergamon Press Ltd.
All Rights Reserved. No part of this publication may be reproduced, stored
in a retrieval system, or transmitted, in any form or by any means, electronic,
mechanical, photocopying, recording or otherwise, without the prior permission
of Pergamon Press Ltd.
First edition 1971
Library of Congress Catalog Card No. 74-112613
Printed in Hungary
08 006659 3
PREFACE
THIS book is an attempt to provide a systematic account of genetic and karyological
studies with Lepidoptera species. So far as I am aware, this task has not been attempted
hitherto on a worldwide basis. In particular, no endeavour has been made to collate the
extremely scattered literature. This latter aspect, alone, is something eminently desirable
and should fill an important gap in the entomological literature.
Every effort is made to make the literature survey complete to 1966, although it is
realized that even so some papers may have been overlooked. I would appreciate to have
my attention drawn to any omissions or to research which perhaps should have been
included. Similarly, it is difficult in a work of this kind not to have committed some errors,
either textual or bibliographical, and I would appreciate to be notified of these.
It should not be thought that the subject matter of this opus is only the concern of the
specialist. This is far from being the case. Any person who is interested in the variation
or breeding of butterflies and moths should take notice of research in this field. There is
much to intrigue and much more to be discovered in almost any species which can be
named. It is the purpose of this book to encourage people to take up the breeding of
Lepidoptera as part of their entomological interests. This injuncture applies as much to
the amateur as to the professional, if not more so, since as a body their opportunities are
so much greater.
Only a few species have been studied to any depth and the opportunities for new work
are boundless. In a number of instances the liberty is taken of pointing out seemingly
profitable openings for investigation. It may be mentioned that genetics is still one of the
sciences to which the amateur can contribute. In fact, among the Lepidoptera much ex
cellent work is currently being done by amateur naturalists and the potential scope is
considerable. If this account is able to assist and extend their endeavours, I, for one, will
feel well satisfied.
ROY ROBINSON
ACKNOWLEDGEMENTS
I SHOULD like to record my appreciation to the many people who have assisted me in
numerous ways in the writing of this book, especially for their general encouragement
and stimulation. I am particularly grateful to Messrs. S. R. Bowden and C. E. Dyte,
and Drs. H. B. D. Kettlewell, H. de Lesse and Z. Lorkovic for various forms of assistance.
I am also obliged to many other investigators who generously sent me reprints of their
published research. I am indebted to the Literary Executor of the late Sir Ronald A.
Fisher, F.R.S., to Dr. Frank Yates, F.R.S., and to Oliver & Boyd Ltd., Edinburgh, for
permission to abridge tables III and IV from their book Statistical Tables for Biological,
Agricultural and Medical Research.
INTRODUCTION
AMONG the insect orders, the Lepidoptera have always been popular subjects, probably
as a result of yielding to the enchanting coloration of the more showy species. This is
undoubtedly so among the amateur entomologist, if not among the professional re
searcher who is perhaps governed a little more by practical commitments.
The insects present interesting material in one respect. Their life cycle can be conveniently
divided into four stages: egg, larva, pupa and imago. Each stage is sharply differentiated
from the previous, yet ontogenically dependent upon it. This fact suggests a remarkable
degree of genetic control which can engender such transformations. The implications are
that the individual carries genes which govern development throughout all the successive
stages and others which come into play at each stage. Mutant genes are known which
produce characteristic effects in all or several stages and others whose activity seems to
be confined to one particular stage. The difference is mediated by the feature affected;
the last category of mutants are usually those which modify a character for which no
counterpart exists in other stages. This sort of argument, of course, is partially dependent
upon the level of experimental sophistication; upon the ability to recognize manifold
effects of a mutant gene.
It is feasible that most genes may have some function at all stages, but that the mani
festation has been modified by natural selection. Unless the effects of a gene are bene
ficial for all stages, natural selection will tend to minimize or suppress the disadvantages
but maximize the advantageous aspects. This differential action could operate between
the various developmental stages so that the manifestation of a given gene may appear to
be restricted to a single stage. This shaping of gene expression need not apply to mutant
genes, so a detailed study of the effects of a mutant allele should disclose if the corre
sponding type gene is potentially capable of having some expression for more than one
stage. It is of interest that one very broad category of genes which are of special interest
to naturalists, namely those affecting colour and pattern of the wing, are restricted in
expression to the imago stage simply because comparable structures do not exist in the
larva and only in an immature form in the pupa.
It is probably a truism to remark that every organism has some special virtue for
research, perhaps not always uniquely but very often in a most useful manner. The
Lepidoptera, as a whole, are no different in this respect. All of the vast range of species
are doubtless capable of contributing to the sum of genetic knowledge and some probably
have idiosyncrasies which could make them particularly valuable for tackling certain
problems. Indeed, a number of species have already emerged as eminently favourable
subjects for certain work. All of this research is pertinent for Lepidoptera genetics, of
course, but some is of greater import and significance. The reason is that certain phenom
ena have long intrigued biologists in general, particularly those interested in ecology
and evolution. Two of these, namely the occurrence of industrial melanism and that of
1
2 LEPIDOPTERA GENETICS
mimicry, have yielded to a determined onslaught which combined patient observation,
field studies and genetic analysis. It seems that the processes underlying these phenomena
are now understood in principle, though not in all of their ramifications. Now that the
first truly analytical steps have been taken, it is likely that work on these topics will
steadily progress and who can foretell what surprises may be in store?
People able to visit the Zoological Museum at Tring (Hertfordshire, England) can
consult the splendid collection of British Lepidoptera which is housed there (Riley,
1948, 1950; Cockayne and Kettlewell, 1953). This collection, known as the Rothschild-
Cockayne-Kettlewell, is remarkable for the emphasis which is placed upon variation
and genetics. Apart from type forms, many varieties and named aberrations are displayed,
together with notes on heredity and references to the published literature. From a genetic
point of view, this makes the arrangement of specimens rather unique and certainly
interesting. Additional material is constantly being added and integrated in a systematic
manner with that already existing. For a few species, it has been possible to exhibit
representatives of the actual material used in genetic experiments. The inclusion of
this sort of material cannot be too highly praised since it allows of direct appraisal by
generations of future workers. The spirit in which this collection was founded would
be extended and perpetuated if further donations of this nature can be made. It behoves
all students of Lepidoptera genetics to support the collection with gifts representing the
highlights of their research. The value of type specimens is beyond dispute and it is just
as essential to have standard specimens of phenotypes of known mutant genes. Even
if obligations demand that certain material be deposited elsewhere, it would still be
desirable for duplicate material (paratypes, so to speak) to be lodged at Tring. The more
complete the collection, the more valuable it will progressively become.
The literature on Lepidoptera genetics seems to be extraordinarily scattered. Relevant
papers may be uncovered in the most diverse, and sometimes unlikely, journals. In some
respect this reflects the different backgrounds of the people who have undertaken, and
are still undertaking, work in this exciting field. In some respects, Lepidoptera genetics
has been well served with the occasional review article and general textbook. The publi
cations of Ford (1937, 1953a, 1955c, 1957a, 1964) deserve special citation in this regard,
as also the labours of Remington (1954a, 1958a) and Sheppard (1961a). The reviews of
Kikkawa (1953), Tanaka (1953) and Tazima (1964), dealing with the extensive work on
Bombyx mori, the domestic silkworm, are particularly welcomed since these allow the
Western mind to transcend the language barrier. Sericulture is an important industry
in Japan, and so much of the published literature on the silkworm is published in Japa
nese. Tazima's book provides a very admirable insight into the extent and the progress
being made with the genetics of this species.
COLOUR AND PIGMENTATION
The phenomenon of colour is due to two causes, either to a physical or optical effect
of the surface upon which light is falling or to the presence of pigment. Quite often the
two causes may be combined to produce some exceedingly beautiful effects. A fascinating
and well-written account of the interaction of the two processes and their distribution
throughout the animal kingdom is that of Fox and Vevers (1960).
Although it is important to have a working concept of the production of colour in the
INTRODUCTION 3
Lepidoptera, this section is not meant to be exhaustive. The vast majority of mutant
genes discussed in later chapters involve colour changes and it is advisable to have some
idea of the processes by which the genes produce their effects. It is regrettable that in
most cases little effort is made to ascertain if a colour change is due to an optical effect
or to pigment.
Those colours which arise from physical effects are known as "structural colours" and
can be produced by one of three mechanisms: (1) interference, (2) diffraction and (3)
Tyndall scattering. Not all of these optical effects are of equal importance for any one
group of animals. The first two are associated with iridescence, giving the illusion of a
brilliant range of colours, depending upon the angle by which the object is viewed.
The presence of iridescence is a means of distinguishing structural coloration from that
due to pigment, since the colour of pigments remains the same whatever angle the vision.
This is not to deny that pigment may underly the iridescence and contribute towards
the total effect.
Interference occurs when very thin layers of transparent material are separated by
minute air spaces, or a fluid with a different reflective index, which causes ordinary white
light to separate out into its component colours. The vivid iridescence displayed by the
wings of many butterflies and moths lies in the fine structure of the scales, particularly
that of the reflective upper surface, in which up to six laminar separated by air spaces
have been observed (Onslow, 1920c, d, e, 1923; Süffert, 1924a; Baylis, 1924,1926; Mason,
1927a; Anderson and Richards, 1942; Gentil, 1942). The soft velvety sheen of Apatura iris
(Purple Emperor) and similar butterflies is attributed to interference interacting with a
dark underlay of pigment (which could be melanin), as well as the spectacular blueness
of the Morpho species, which derive their intense vividness from successive refractive
layers. The blue of most Lycaenids and the green of Callophrys rubi and Procris statice
all come into the same category. The magnificent range of multiple iridescence of the
moth Urania rhiphoeus owes it colour largely to interference (photo; Fox and Vevers,
1960).
Three fundamentally different types of scales engendering the interference are recog
nized (Süffert, 1924a; Mason, 1926, 1927a, b; Gentil, 1942): the Morpho, Urania and
Entimus types. Interference colours disappear when the insect is held with its back to the
light or change colour in a definite sequence when a drop of either chloroform or ether
is placed on the wings to fill the air spaces within the scales. The colour returns as these
substances evaporate. This test fails with the various Emerald moths, and seemingly
with Bena fagana and Daphnis neriU suggesting that a pigment is involved in these
cases.
Diffraction coloration occurs when a beam of light falls across, for example, a striated
surface. Such colours probably do not occur in Lepidoptera, but a brilliant example is
provided by the beetle, Serica sericea. The effect is due to the presence of fine striae on
the epicuticle of the elytra, as shown by Anderson and Richards (1942). Iridescence of
this nature is dependent upon parallel rays of light, such as sunlight, and is scarcely ev
ident or absent in diffused illumination. It can only be seen by an observer standing at an
angle to the path of light and this fact differs diffraction iridescence, from that of inter
ference, since the latter is apparent from all angles.
The third mechanism, Tyndall scattering, arises from the scattering of the shorter
waves of white light by excessively small particles. If these particles are below the wave
length of red and yellow light, they will reflect a high proportion of the shorter blue com-
4 LEPIDOPTERA GENETICS
ponents. The "blueness" of the sky is due to this phenomenon and it is responsible for a
wide variety of blue coloration in the animal world. The blue iris of the eye of many
animals, blue mammalian skin (mandrill's face and buttocks) and the blue colour of
many bird feathers are well-known examples. The green skin of some lizards and frogs
is due to the same effect, the colour resulting from Tyndall scattering over a base of yellow
pigment. Apparently this phenomenon is unknown in Lepidoptera. In fact, it may be
rather rare among the Insecta in general, for Fox and Vevers only mention the effect
for the dragonfly. The bright metallic blue of some species is ascribed to the scattering
of light by the epidermal cells over a base of brownish-violet. The green colour of the
female Aeschna cyanea is due to a similar effect, combined with a yellow pigment in the
cells, again over an underlying dark pigment.
Whiteness is usually due to the random reflection of light of all wavelengths by innu
merable surfaces. The white of many Lepidoptera species results from this, especially
when the surface of the scales are reticulated and have air-filled cavities within them
(Mason, 1926). When the scattering of light is not fully at random but has a certain
regularity, a pearly or silvery lustre is produced. Süffert (1924) indicates that the bright
glittering areas on the under side of the wings of Argynnis lathomia are effected in this
manner.
Somewhat akin to the above is the production of a colour due to a mixture of two
other colours. Various shades of grey may result from the admixture of dark and light
scales to produce the often complex patterns of the innumerable grey or brownish-grey
moths. According to Wigglesworth (1928), the olive-greenish colouring on the under
surface of the wings of Euchloe cardamines and Pontia daplidice is caused by an inter
mingling of dark brown and yellow scales, the admixture producing an illusion of green.
A similar deception is reported by Watt and Bowden (1966) for the greenish tinge apparent
on the underside of the posteriors oiPieris bryoniae.
Independent of, but supplementing, the structural colours are the "real" colours, those
due to actual presence of colouring substances or pigments. It is difficult to judge the
relative importance of physical colouring versus that of pigment for the Lepidoptera,
as some writers have speculated. Few species of butterflies or moths are totally devoid
of pigment, while certain genera, or even as high as sub-families, owe their gorgeous
colouring largely to optical effects. Often the two interact, a fact which ought to offer a
warning against the basic futility of this sort of discussion. The important pigments for
the integument (larvae skin, pupal case or body and wings of the imago) are melanin
and pterins, together with anthoxanthins derived from the food. The dark coloured eyes
of some species are pigmented partly by pterins and partly by ommochromes. Carotenoids
and bilins, such as mesobiliverdin, appear to be important colouring pigments of the
haemolymph.
Melanin is exceedingly common in the animal world. It occurs as granules of various
sizes and forms, and seems to be characterized by complete insolubility to the usual
solvents. Among mammals, for instance, melanin is entirely responsible for the coat
and skin colour. The colours produced by melanin are black (or its variations, grey,
blue, brown) when it is termed eumelanin and yellow (or its variations red, ginger, fawn,
beige) when it is known as phaeomelanin. Eumelanin features among Lepidoptera, but
apparently not phaeomelanin. Onslow's (1916) experiments with the immature (pupal)
wings of Pieris brassicae strongly indicate that the black pattern of this species is due to
eumelanin. Melanin is usually depicted as being formed from the chemical reaction of
INTRODUCTION 5
the amino-acid tyrosine ("colourless chromogen") and the enzyme tyrosinase. When the
pupal wings are immersed in tyrosine, these blacken all over, but when placed in tyro
sinase, only the typical Pierid black pattern appears. This implies that the whole wing
contains tyrosinase, but that the presence of tyrosine is confined to those areas which
produce the normal pattern. However, for some reason, Fox and Vevers (1960) remark
that this work needs confirmation. It is generally assumed that the black, grey or brown
markings of the Lepidoptera is due to eumelanin and there is no evidence to indicate
otherwise. On the other hand, it seems curious that this generality has not been checked
by direct chemical tests.
The pterin pigmentation of the wings seems to occur to a significant extent only for
the Pieridae. This restricted distribution was first suggested by Hopkins (1889a, b, 1891,
1892, 1895, 1942) and since confirmed by Ford (1947a, b). Hopkins isolated at least
two substances from various Pierids. A white pigment is extracted from Pieris brassicae
and JP. rapae and a yellow substance from Gonepteryx rhamni, Colias croceus and several
other yellow species, together with a red pigment which behaves similarly to the yellow.
He considered the first to be uric acid and the second to be an allied compound. Appar
ently, Hopkins was mistaken in referring to the white pigment as uric acid (Gates, 1947)
although this acid has been detected in the wings of some Pieridae species (Tartter, 1940;
Good and Johnson, 1949). There the matter rested for several decades, when the problem
of the pterins has been tackled by several people. Useful review articles on the pterins
are those of Purrmann (1945), Gates (1947), Albert (1954), Ziegler-Günder (1956),
Cromartie (1959) and Ziegler (1961).
Hopkins's white pigment emerged as leucopterin, indeed similar to uric acid in some
respects, but nevertheless distinct from it (Schöpf and Wieland, 1926). Leucopterin
abounds in the wings of Pieris brassicae and in the white or pale yellow areas of many
other species. The yellow pigment seems to be xanthopterin and is found in the rich
yellow Brimstone butterfly, Gonepteryx rhamni (Wieland and Schöpf, 1925; Schöpf and
Becker, 1933). The red discoidal spot of Gonepteryx rhamni, the red wing tips of Euchloe
cardamines and the red wings of Appias new are coloured by another pigment of this
group, erythropterin (Becker and Schöpf, 1936; Schöpf and Becker, 1936). Yet other
pterins are known and described under various names, of which isoxanthopterin (Wie
land, Metzger, Schöpf and Bülow, 1933) deserves special mention. Further details of
these and other pterins and their derivatives may be found in the not inconsiderable
literature. In addition to the review articles cited earlier, the following papers are among
the more pertinent: Albert (1952), Albert and Wood (1952, 1953a, b), Becker (1937),
Busnel and Drilhorn (1949), Purrmann and Eulitz (1948), Purrmann and Maas (1944),
Schöpf (1940), Tschesche and Körte (1951), Umebachi (1954), Watt (1964), Weygand,
Simon, Dahms, Waldschmidt, Schliep and Wacker (1961), Wieland and Decker (1941),
Wieland and Liebig (1944), Wieland and Purrmann (1939, 1940), Wieland and Tartter
(1940b) and Wieland, Tartter and Purrmann (1940).
Of special significance are those reports which describe differences in the estimated
quantities of the various pigments between various genotypes. There are two of these on
wing pigmentation. The first deals with gene-controlled variation in Pieris brassicae.
Harmsen (1964) examines the erythropterin and xanthopterin content of the wings of
the aberrations coerulea (whitish), jauni (orange-yellow) and albinensis (absence of me-
lanic pattern) in comparison with type. Both pterin pigments are either absent or are
reduced to infinitesimal amounts in coerulea but are present in increased amounts in
6 LEPIDOPTERA GENETICS
jauni. The pterins in albinensis did not differ from those of type, indicating that only
the synthesis of melanin is disrupted. All three aberrations are due to recessive genes.
The second report is that of Watt and Bowden (1966) on aberrations of Pieris napi.
The pterin content of three aberrations and the wild type are investigated. Genetically,
the four forms are inherited as a series of alleles, the aberrations and the order of domi
nance being as follows: subtalba (white), type (yellow in certain areas), Thompson's
yellow (pale yellow in most areas) and citronea (bright yellow). Out of the various pterins
isolated by the Chromatographie analysis, those estimates for the amount of sepiapterin
show a correlation with the phenotype. No sepiapterin could be detected for subtalba,
but a small increase for the pale yellow form and a marked increase for the bright yellow
form over the amount normally present for the type is clearly evident. The increase in
yellow pigmentation, therefore, is due to enhanced production of sepiapterin. The ana
lysis also indicates a decrease in the quantities of the colourless leucopterin and iso-
xanthopterin in the bright yellow citronea form, as if there is interference in the produc
tion of these pterins. This could arise, for example, if the increase of sepiapterin could
only occur at the metabolic expense of the other two pterins.
An interesting contribution by Yagi and Saitoh (1955) shows that a distinct difference
exists in the pterin content, as assessed chromatographically, of the wings of type and
the dominant white form of Colias erate poliographus. The main difference revealed by
this method is an absence of xanthopterin from the wings of the white form. An exami
nation of the normal and white wings of a bilateral yellow/white gynandromorph indi
cates clearly that the pterin composition of the normal wing corresponds with that of
the type insect while that of the white wing corresponds with the white form. The corre
spondence is remarkably close and demonstrates the independent action of the W gene
in contiguous tissue of the same individual. Genetically, the W is carried by an autosome
but has sex-limited expression. It can only find expression in female tissue. In terms of
the gynandromorph, this means that the wings of the male half are type while those of
the female half are white.
The vivid red pigments shown by many species are far from being fully understood,
certainly not on the chemical level. Ford (1940a, 1942a, 1944a) defines a series of red
pigments, each of which may be distinguished by routine chemical tests. At least five
types are recognized, with the likelihood of a sixth (in the Riodinidae: Ford, 1944a).
The five main pigments are denoted by letters. Pigment A seems to be responsible for
the reds of the Arctiidae and Zygaenidae, and certain of the Papilionidae, for example
the Graphium and Polydores species (but excluding the Battus group). Pigment B occurs
in the Battus species and in most of the Papilios. Pigment C seems to be characteristic
of the red colouring of the Vanessids. The last two are found in the Pierid genus Delias.
They are indistinguishable macroscopically but give different chemical reactions. Type
D occurs in many Delias species, except for the Pasithoe group, which possesses type E.
In all probability some of these red pigments, particularly D and E, may be pterins
or related compounds. However, not every one would seem to be, since the A, B and C
types are negative in the murexide test for uric acid. None of these are soluble in a fat
solvent, hence it is improbable that they are carotenoids. Fox and Vevers (1960) comment
that some of the red or brown pigments of the Vanessa could be ommatins since the
red moulting fluid of these species is rich in these compounds (cf. Cromartie, 1959, for a
review of the literature; also Linden, 1903, 1904). The type D is so insoluble (resisting
hot water and dilute alkalis) that Ford speculates that it might be a melanin. The existence
