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ADULT CONIFER SAWFL Y,
or
Neodiprion ,
is
a
serious pest ot coniterous trees.
A medium-sized insect, it is common throughout most ot North America.
éxcept in the Midwest.
From the German weekly .
Die Zeit,
No. 33. August 9, 1974. Translated
by
Werner G. Gerlach.
O
n the surface. few people
would s us pec t that one
small insect co uld have an
unsettling e lfect on the basic tene ts
of the theory o f evo lutio n . But the
larva o f the commo n sawfl y doe
jus t tha t.
The sawfly la rva . a ra ther ordi–
nary loo king crea ture as ca terpillars
go . has managed to ca rve o ut an
ecologica l n iche on the frag rant nee–
dles of the pine tree. At first gla nce
this may not seem like a pa rticula rly
noteworth y accomplishment. But in
th e sma ll wo rld of insects it repre–
se nts a rad ical depa rture from ac–
ce p ted environmenta l no rms.
T o ma ny sma ll insects the pin e
tree is a virtua l no- ma n's land. lts
res ins a nd o ils. which may sme ll
swee t to us huma ns. a re hi ghly toxic
su bs tance as fa r as the six legge rs
a re conce rned .
But not to the sawOy la rva !
Thi s littl e critter not o nl y can tol–
erat e pine oil and resi ns. but it even
" knows how" to chew them up with –
o ut be ing poisoned .
Wh ilc munchi ng on its s tap le di et
of p ine need les, the larva omehow
se para tes the poisonou!> o ils a nd re–
sins from the diges tibl e pulp and
~lo res
thcm in two go ite r-li ke sack
loca ted a t t he sides o f its o ra l cavity.
l f provoked. it ins ta ntly turns its
18
head toward its aggressor and se–
cretes a drop of its s tored liquid.
T his foul- smelling brew is usually
enough to discourage would-be
predators such as spiders. ants, and
birds.
Thi s neat trick could be compared
to a pe rso n who ea ts a sandwich
conta in ing poisoned sausage. but
who swall ows jus t th e bread whi le
s to r in g th e sau sage in a chee k
pouch .
But just how does th e sawfly larva
accomplish this phenomena l feat?
Forestallíng a Major Case
of lndigestíon
Firs t of a ll, fo r the sawfly to do this.
the edibl e parts mus t somehow be
se parated from the inedibl e parts:
secondly, each mus t go the right d i–
rection o that the resins and o ils
will not ge t into the diges tive tract ;
a nd thirdly. th e tissue o f its s to rage
sacks must be insensit ive to th e resin
ac ids.
The la rva o f the sawfl y is a b le to
pe rfo rm these. functio ns qui te we ll.
lts sto rage sacks a re covercd with a
chitinous membrane and are thus
elfectively protected. Th e muscle tis–
sue o f the sacks is so ext raordina rily
tro ng that o ne sawfl y expe rt be–
lieves it hc lps in the sepa ration of
the d iges ti b le a nd indiges tibl e ing re–
di ents. Exactly how the scpara tion
ta kes place - how th e la rva is able
Lo le t a ll resino us bits disappea r in
th e sack d uring th e chewing pro-
cess a nd eat only edibl e parts - is
s till a puzzle.
Ouestions Evolution Can 't Answer
T he sawfly's unique diges ti ve sys–
tem is more than just an oddity.
It
presents a number of t horny ques–
tions as far as the theory of evolu–
tion is concerned. First of a ll , try to
imagine the difficulties sorne ancient
variety of sawfly larva wo uld have
encountered had it tri ed to switch
from a normal leafy diet to o ne of
pine needles. According to evolu–
tionary theory, the cha nges neces–
sary to enable it to diges t the pine
needles cou ld only have occurred
through small mutatio ns in a step–
by-s tep fashion. But in the case of
the sawfly larva , such pi ecemeal
transitions become tota lly impracti–
cal. and one is immedia tely con–
fro nted with one of evolution's basic
problems of logic.
The sawfly la rva could
not
live on
pin e needles until a comple te ly devel–
o ped mechanism which sepa ra ted
wholesome food from poisonous pine
resin was wo rking with perfect re–
liability. But such a mechanism, if it
ca rne gradua lly into exis tence by
sma ll muta ti ons, wo uld have deve l–
o ped only if the food
a/ready
con–
sis ted o f pine needles. Ye t a ll the
sawfly's
inte rmediate
tra nsition
fo rms (which evolution requires)
would clea rly have been unsati sfac–
to ry because th ey would have been
un abl e to ad eq uate ly cope with the
poisonous e lfects of the pine needl es.
In tha t case the sawfly's evolution a ry
progress wou ld have been bro ught to
a s tands ti ll.
On the o the r hand if there wcre
no pine need les a round fo r the la rva
to feed on , the re would a lso have
been no s timulus for it to develo p
any mechanism for digestive epa ra–
tio n and pro tection .
No ma tter how inte ll igib ly the
theory o f evolu tion may presen t the
reasons fo r the s tep- by-s tep d eve l–
o pment o f
a/ready existing
o rgans or
parts o f the body. the difficulties in
try ing to expla in how ce rtai n ind e–
pendent ana tomical-phys iologica l
ystems could or igi na te by evolution
seem insurmountable. Science is still
fa r from unde rs ta nd ing how differ–
ent organisms carne in to be ing, even
tho ug h it somet imes secm · tha t we
unders tand '·i n pr incipie."
O
The
PLAIN TRUTH September 1976