BOOK REVIEW
Retracing the Long Journey of the Insects
George Poinar, Jr.
Evolution of the Insects. David Grimaldi and Michael S.
Engel. xvi + 755 pp. Cambridge University Press, 2005. $80.
History of Insects. Edited by Alexandr P. Rasnitsyn and
Donald L. J. Quicke. xii + 517 pp. Kluwer Academic Publishers, 2002. $359.
The humble beginnings and evolution of insects are wrapped in a
shroud of mystery and controversy, owing in part to their great
diversity. Because many of the crucial fossils that could answer
significant questions are fragmentary or are of doubtful age, some
people might claim that their designation is more a philosophical
exercise than a scientific study. Indeed, one
paleoentomologist—Robin John Tillyard (1881-1937)—is
reported to have taken his specimens to a clairvoyant in hopes of
receiving some message about their true nature. Although fossil
insects have been collected and studied for some time, a comparison
of two recent books dealing with their appearance, phylogeny and
status makes it obvious that opinions still vary as to just what
begat what.
Evolution of the Insects (2005), by David Grimaldi and
Michael S. Engel, and History of Insects (2002), edited by
Alexandr Rasnitsyn and Donald Quicke, contain facts about fossil
insects that will be useful to general biologists. However, both
works will be appreciated chiefly by systematists attempting to
decipher the evolutionary pathways of a given insect group and by
fossil collectors endeavoring to identify specimens. Each of the
books presents a synthesis of phylogeny, biogeography, ecology and
the fossil record, supporting the presentation with a wide selection
of detailed photographs and drawings. Evolution of the
Insects is filled with lavish color photographs of both fossil
and recent insects, thanks to a generous donation that defrayed
publication costs. However, it remains a puzzle why Grimaldi and
Engel selected particular photos of modern insects, because many
seem to have no direct bearing on evolution. Their book's most
striking portrayals of insects in Dominican amber come from a
private collection in Italy, making the point that individual
collectors can assist scientists by loaning their specimens for study.
Dealing with such a complex subject is an arduous task. Grimaldi
(Curator of Invertebrate Zoology at the American Museum of Natural
History) and Engel (a paleoentomologist at the University of Kansas)
take on the challenge themselves, but Rasnitsyn (a professor at the
Paleontological Institute, Russian Academy of Sciences, Moscow) and
Quicke (reader in systematics, Division of Biology, Imperial College
London) enlist the assistance of 21 well-respected experts from the
Russian paleoentomological community to cover many of the insect
orders, an approach that results in a more enlightened and in-depth
overview of the topic. Also, the contributors to History of
Insects follow a basic outline for each insect order.
Unfortunately, such a presentation was not used in Evolution of
the Insects; it is therefore time-consuming to locate
specific categories within that volume's often verbose discussions
of the various insect taxa.
Because the books employ different nomenclatorial systems for fossil
and extant insects, it can be difficult to compare their respective
treatments of a particular insect group. For instance, Rasnitsyn and
Quicke place silverfish in the order Lepismatida, bristletails in
Machilida, mayflies in Ephemerida and termites in Termitida, whereas
Grimaldi and Engel use Zygentoma, Archaeognatha, Ephemeroptera and
Isoptera, respectively, for the same groups. And why Grimaldi and
Engel use "citizen roaches" as a common name for termites
is a mystery.
The authors of the two books take opposing views on a number of
matters, as becomes clear if we use information they supply to
attempt to answer three questions of general interest to biologists:
1) When did the first insects appear? 2) What is the earliest known
bee? and 3) What is the fossil record of mosquitoes?
So, just when did insects first appear? Grimaldi and Engel reanalyze
an enigmatic fossil from the Devonian epoch (roughly 416 million to
359 million years ago) that was originally described in 1928 as
Rhyniognatha hirsti. They claim to show that it is
definitely an insect, probably a winged one, and on that basis they
establish a phylogenic scheme for the subsequent evolution of all
winged insects. They base their conclusions on their personal
interpretation of a pair of "mandible-like structures"
located at one end of the fragmented fossil, neglecting to mention
that other scientists had previously interpreted the
"mandibles" as belonging to a springtail, an insect larva
and an early orthopteroid.
In History of Insects, Vladimir V. Zherikhin gives reasons
to doubt that these fragmentary fossilized remains belonged to an
insect; in his view, fossils from the Carboniferous (about 359
million to 299 million years ago) probably represent the earliest
insects. But if these "mandibles" don't belong to an
insect, what could they be? Analogous structures in diverse groups
appear throughout geologic time. Mites in the order Opilioacarida
possess rutella that resemble the fossil "mandibles" in
size and shape. As the most primitive extant mite group,
opilioacarids are opportunistic predators, scavengers and mycophages
that consume particulate food and would fit comfortably into the
stratigraphic range of Devonian terrestrial acarines.
What is the earliest known bee? Everyone knows the important role
bees play in pollinating plants. The origin and subsequent adaptive
radiation of bees was extremely significant, possibly crucial, for
angiosperm diversification in the Early Cretaceous (roughly from 145
million to 98 million years ago). In 1988, Charles D. Michener and
Grimaldi described in American Museum Novitates what they
claimed was the first Cretaceous bee, found in New Jersey amber that
is 96 million to 74 million years old, characterizing it as
Trigona prisca. However, doubts about the age of the
bee were raised first in 1991 by Rasnitsyn and Michener in
Annals of the Entomological Society of America, again
in 1994 by Vladimir G. Radchenko and Yuriy A. Pesenko in their book
Biology of Bees and finally by Zherikhin in History
of Insects. In addition, Michener discusses the
"cloud" surrounding the fossil, in The Bees of the
World (2000). The age became suspect when the bee turned out to
belong to a modern species group, something that is almost unheard
of for a fossil 96 million to 74 million years old. Also in 2000, in
American Museum Novitates, Engel redescribed the bee,
placed it in a new genus (Cretotrigona) and agreed that it
belonged to a relatively modern group, indicating that the
diversification of bees had occurred much earlier than had
previously been believed. Curiously, he lowered the age down to 65
million years, which according to the latest authority—A
Geologic Time Scale 2004, edited by Felix M. Gradstein,
James G. Ogg and Alan G. Smith—would place it in the Tertiary period.
Doubting the bee's age is a valid criticism, because as early as
1968, Jean H. Langenheim and Curt W. Beck had reported in
Harvard University Botanical Museum Leaflets that
chemical tests showed that New Jersey amber is a mixed bag, with
material younger than Cretaceous age occurring in at least six
different localities.
Medical entomologists and parasitologists should find the question
concerning the fossil record of mosquitoes (Culicidae) interesting,
considering the important role these insects play as vectors of
pathogens that cause disease in humans and domestic animals. Indeed,
culicid-transmitted diseases, especially malaria, kill more than one
million people each year. The recent discoveries of a mosquito in
Dominican amber carrying the developmental stages of
Plasmodium malaria in its tissues and of a triatomid bug in
Dominican amber with evidence of Trypanosoma in its fecal
droplets show how fossils can be used to trace the origin and past
distribution of pathogens.
Grimaldi and Engel present a partial fly specimen in mid-Cretaceous
amber (about 100 million years old) from Burma and state that it is
the oldest mosquito. However, this specimen has a short proboscis
and lacks scales on the wing veins, which by today's definition
would exclude it from any known group of mosquitoes. And it is
curious that Grimaldi and Engel not only neglect to cite Grimaldi's
2004 publication officially describing this fossil (with Art Borkent
as first author) in Annals of the Entomological Society of
America but also ignore the article inActa Geologica
Hispanica that I wrote in 2000 with Tom J. Zavortink, Ted Pike
and Paul A. Johnston about the only uncontested Cretaceous mosquito.
The latter oversight is surprising, because Grimaldi and Engel
mention the fossil—Paleoculicis minutus—in
their book. In History of Insects, Zherikhin refers to
Paleoculicis minutus as "the oldest fossil mosquito."
The failure of Grimaldi and Engel to discuss the controversy
surrounding the age, interpretation and identification of fossils
that were initially announced with much fanfare and bravado is
certainly not a service to the reader.
Like most books covering subjects in fields of active research,
Evolution of the Insects was already out of date when
it was published. However, its relatively low price, thanks to the
aforementioned generous donation, certainly makes it more affordable
than History of Insects, whose cost unfortunately limits
its accessibility. In the future, we can expect to read other
accounts, with different interpretations, of the mysteries of the
insects' journey through time. But one thing we can be certain
about: Insects have spent a tremendously long period on the planet,
and chances are excellent that they will still be around to witness
our disappearance.