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Psyche 7:170-174, 1894.

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PSYCHE.
CONVERGENCE AND POECILOGONY AMONG INSECTS. BY ALFRED GIARD, PARIS, FRANCE.
[Professor Alfred Giard in the An-
nals of the Entomological Society of
F ~ ~ ~ ~ ~ * presents a careful discussion of convergence and poecilogony among
insects and ;I resumi in- the form of a
ratlicr free translation may be of interest to some who do not have access to this
publication. HERBI~RT OSBOKX.]
It is a well known fact to entomolo-
gists that certain insects which are
the earlier stages, we should attach
more importance to the early dissimil-
arity than to thc similarities of the
adults. The question would be
answered immediately in the affirma-
tive if the principal of Fritz Mueller,
the fundaiiieiital biugenelic law of
Series and Haeckel, were applicable
in its exactitude. That is to say, if
the various ontogenetic states of an
very similar to each other in the adult animal repeated exactly the pliylogcny state have larvae which are quite
different. Many examples of this
peculiarity have bccn indicated, princi- pally m-long the Lepidopteni, the
larvae of which are better known than
those of other groups. But all insects
with complete mctamorphoses may
present the same phenomena, and, if
it is more rare among the ametabola,
it is because, among these, the passage
from the larval to the adult stage is
gradual, by insensible steps, and the
larvae and imago are subject to much
the same conditions. One of the ques-
tions of much importance and at the
=me time a problem of much difficulty
to solve is to detcrmine if, in the recog- or the successive ancestral forms.
Were this so, embryology would indi-
cate the true relation of the parents.
The more or less perfect rcscmblance
of the adults in certain cases would be
interpreted as the result of convergence due to similar ethology of these adult
forms. But, among ammats with
metamorphosis, ctnbryonic forms are
subject during a long period to the
modifying action of the surroundings
and often, also, their evolution depends in a large measure upon the ethology
of the adult. Accordingly, the prin-
ciple of Fritz Mueller is applied with
difficulty and singularly though actually the determination of the relation of the nition of the agreement between similar parents becomes more arduous the animals which present differences in bctter we know the different phases of - development. If it lie true that partial *Yo]. 63, pp. 128-135. knowledge happens thus to.complicate



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172 F ' s K ~ . [December 1804.
the problem, we may hope that a more
complete knowledge, that is a lmowl-
edge of the dynamic embryology of
a largc number of species, will give
us the solution.
At present we may distinguish two
principal categories of insects which
arc similar in adult stages and differ in earlier stages of development.
First : certain insects pertaining to
the same genus or to distinct genera,
sometimes even widely separated,
which present in sill cases larval stages which are quite different aid in each
case adult forms similar by conver-
gence, a convergence due to the sur-
rounding conditions (protective resem-
blance, mimicry direct and indirect,
isotypy, etc.) .
Second: among other insects the
different generations of the same spe-
cies considered at different points of
their geographical distribution, at dif- ferent seasons of the year, or in different conditions of nutrition, have larvae
which are dissimilar while the adults
are very similar to each other and
present very slight modifications. It
is to this form that we apply the tenn
Poecilogony.^ In this case the larvae
have become divergent in adapting
themselves to different ethological sur- roundings. Tlic final result is the
same in all cases but from the point
of view of consanguinity and therefore
of natiirai classification the two cate- gories arc far Srom having the same
signification.
The related species of poecilogonic
origin have between them direct parent-
age and approach each other notwith-
standing their embryonic divergencies.
The species which resemble each othcr
by convergence can on the contrary
have only phylogenic separation and
must be considered as naturally distinct. From a practical point of view it is not always easy to decide if two similar
forms are poecilogenic or convergent
species. In certain cases, however, the
distinction is easy and no doubt is per- missable. When, for example, the
species which by selection have become
convergcnt, belong to genera sufficiently separated, the profound anatomic char-
acters and the embryonic characters arc
not altered by convergence to the point
of being' unrecognizable. The resem-
blance is only superficial and if the older naturalists have been deceived by a
similar aspect of the adults the error is not possible today. Mimicry, so perfect
in Leptalis and Ithornla, of Papilio
$aradoxa and Elfplaea &damns,
imitation of Danaides or of the Acracides by different species of Papilio or of
Diadenaa do not impose upon any en-
ton~ologist.
The resemblance although less exact
in other respects of Dichonia afrilina
and Moma orion is, nevertheless, an
example of the same kind. Even when
convergence of the adults takes place




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December I&++] PSW2T.E. I73
among congeneric species, that which
deprives us in great part of the advan-
tage of indications of comparative
anatomy, we can in most cases still
recognize the origin as entirely distinct for the two species and establish the
resemblance as due to the effect of the
sun'oundings upon the imago.
It is this which occurs, for example,
in the case of isotypy. Some related
forms such as Pieris hrassicae and
Pieris ra-pae, the numerous Euplaeae,
etc. The fact tliat these species frequent the same localities without mixing and
without crossing indicates that the
larval differences which they present in the midst of identical conditions are
differences of ancestry. This is still
' more evident when it is applied to
Hymenopterous parasites (Isotypes) of
which the larvae have the same hosts or
of parasites of plants of which the larvae feed side by side npon the same plant.
ffomomyia capraeae Bremi is distin-
guished with difficulty in the adult state from another Cecidomyian living also
very often upon the willow (SaZix ca-
paen),
Thc gall has been described by
Scl~lecl~tendahl under No. 332." But
the larvae of these two Diptera remain
distinct and produce very different galls upon the leaves of the same tree. ~h&e
is here no doubt tliat the resemblance
of the adults is simple convergence and
does not indicate a closely related
ancestry.
* Schlectendahl, Die Gallbildungen (Zoocecidien) 1891, p. 40.
When, in the place of living in the
same surroundings the larvae have a
different habitat the question becomes
more difficult to solve.
Guh4e in a remarkable memoir npon
some European bomhycesf has con-
sidered as distinct species two types,
Bornbyx sfartii Hb. and Bombyx
caZZznae Palen, which represent one
the southern and the other the northern
form of B. quercus L.
If one examines an extensive collec-
tion of B. que7,cus such as that of our
collcague M. }. Fallou he will easily
see that it is almost impossible to
separate the adults of these three
species. Certain forms of B. percus
passing manifestly, as GuMe and
Bellies de la Chavignerie already have
recognized, in part to B. sftartii, in
part to B. caZZunae.
Gn6n6e had discovered that the
young catcrpillar of B. caZZznae differs from that of B. quercq but that the
divergence diminishes after the first
moult and finally disappears. One
may attempt to see in this dissimilarity of the larvae in the early state a proof of the primitive separation of the two
species. But the habitat differs suffi-
ciently to explain this divergence. One
of the two forms, without doubt B.
caZZunae, represents the first ancestral larva which is modified in B, percus
and B. s-partii and this species may
truly be considered as a poecilogonic
form slightly modified in the adult
stage.
å´I Annales Soc. ent. Fr. 1858,435-442.




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174 PSmE. [December 1894.
We have elsewhere direct proof of
the existence of poecilogony among
insects. In two very important memoirs
published in Russian and of which we
have a translation by our learned
colleague C. R. von Osten Sacken, the
Russian entomologist Portchinslcy has
demonstrated that the common Mziscu
corvinu presents two distinct forms in
different parts of its wide habitat. In
the north of Russia this coprophagous
fly generally deposits 24 eggs of medium size from which ariselarvae that present two very distinct phases of evolution.
In the Crimea where coprophagous
insects are more abundant and con-
sequently the struggle for life more
intense, the same Dipteron deposits
only one large egg in which the
metamorphosis is very rapid and con-
densed and recalls that of the Pupipara, the larva arriving almost immediately
at its last phase of development.
Analogous cases are known among
different Lepidoptera and notably in
the mulberry silk-worms (Sericu~ia
mori). In the south of Europe this
species furnishes an interesting race
called TreuoZtini which not only pro-
duces several generations annually but
is distinguished from the type in that
the caterpillars have only three moults
in place of four. Cultivated in the
north this race regains the ordinary
characters of the species (the sec-
ond or third year) as shown by Robi-
net.*
As the caterpillar of Sericaria mori
varies more or less the pl~ysiological
peculiarity of the suppression of one
moult attracts the eye, hut in other
cases struct~iral morli'Rcatious are more apparent.
Th. Goossens has indicated several
very interesting examples of geographic
poecilogony. DeilefhiZu eU-phorbiae
does not present in Ardache and in
Var the ordinary yellow points and the
rosy spots are replaced by spots of a
pale yellow. The caterpillar of Helio-
this marginata, light or green in tlie
North is more often of an almost black
brown in Provence. In the south of
France the dorsal part of the caterpillar of Zygaena fuusta is almost always
tawny. At Paris this part is water
grecn.t
When in cases of this kind the adults
of two poecilogonic varieties come to
differ hut little at the two extremities of its habitat, we do not err if we establish two species, saying : Without doubt
the perfect insects differ but little, but the larvae present differences so great
as not to permit us to unite the two
forms. This is certainly what occurs
for a large number of species called
representative for the old and the new
world, Triuena psi and T. occiden-
falls, for example. Comparison of the
monographs of Gu6n6e and Abbot is
very instructive in this respect.
Sometimes even the variation of the
adults rests exclusively upon the ana-
toinical characters of the genital
apparatus of such a kind that the
Robinet, Art d'filever les vers a sole; traduction du comte Dandolo, 1825, p. 317,
t Th. Goossens, Des variations sur les chenilles (Ann.Soc. ent. Fr., 1871, p. 118).




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December iSo4.1 PSYCHE. 175
poecilogonic forms, while preserving a
great resemblance in the adult state,
cannot be crossed and this inability to
cross facilitates the divergence of the
two species even if they come in
contact in some point of their habitat.
It is thus, that, according to Grote and Smith, Ag-rotisharusjdica and A. rubi-
fern are the American representatives
of the European A. auger and A. nih4
from which they differ only in the
genital armature of the male; but that
these modifications may be effective
they should perhaps recede and deter-
nine the poecilogony instead of being
caused by it or produced by it. This
question is hard to solve at present and stands with the numerous problems
that Romanes has stated in his work on
pl~ysiological selection. In other cir-
- ~
cumstances poecilogony seeins to be
due to the varying nourishment of the
larvae. If certain caterpillars are
modified directly by' the supporting
plant as is known to be the case among
a great number of species, we know
also that some are adapted definitely to a determined plant and are protected
by a permanent form, a different livery. Poulton has stated, as well as other
authors, that many caterpillars die of
hunger rather than touch nourishment
for which their race has lost the habit. Perhaps it is to poecilogony of nourish- ment that we should attribute the
differences found in the caterpillars
of Cuculia 'uerbasci and C. scrofula-
riae, moths, the similarity of which in
the adult state is not easily explained
by convergeme. Further, certain cases
of resemblance among insects, in which
the larvae differ but live in the same
localities, sometimes upon the same
plants, are difficult to interpret under one or the other of these alternatives
which we have indicated (convergence
or poecilogony) . We cite for example
Liihosia complanana and L. Zuri-
deoZa, Deilephila euiihorbiae and D.
ntcaea.
Finally the only purpose in this short
note is to state a very important
problem of general biology, touching
at once embryology, ethology and
taxonomy. Perhaps on certain sides
the problem is capable of experimental
solution. In any case the question
ought to receive light from our spe-
cialist friends, if they will study into the