BUZZWORDS
Chance the Wrapper
MAY R. BERENBAUM
I
have mixed feelings about
plastic. Used as an adjective, the word means “easily shaped or molded,” but as
a noun, it refers to polymeric,
primarily synthetic substances
that can be molded (especially
when heated), yet can undergo
irreversible changes in shape
without breaking; they are also
the substances of which most
of our contemporary world
appears to be made. On one
hand, my father was a polymer chemist over the course
of his entire adult life, so I have
a family affiliation for all manner of long-chain compounds,
both natural and unnatural. On
the other hand, I’m an ecologist, and one of plastic’s initially
attractive features has turned ugly of late
from an environmental perspective. Synthetic plastics seem to last forever, and
as such, they are wreaking havoc with
the natural world, most components of
which, by contrast, conveniently die and
decompose after a decent interval. Plastic
waste fills garbage dumps, clogs lakes,
rivers, and streams, and contaminates
air and soil on a global scale. The North
Pacific gyre, the world’s largest ecosystem,
encompasses 20 million square miles of
open ocean now filled with a floating,
swirling mass of plastic debris and chemical waste that is otherwise known as the
“Great Pacific Garbage Patch.” News stories now appear with depressing regularity of baby dolphins helplessly ensnared
in plastic netting, dead albatrosses with
intestines jam-packed with plastic grocery bags, and endangered sea turtles
asphyxiated by plastic drinking straws
(for heat-sealed films, shrink
wrap, and dry-cleaning bags)
in 1933; polymethyl methacrylate (PMMA) in 1936; and polystyrene (PS, the stuff of which
takeout containers are made)
in 1938.
World War II ramped up the
demand for material to insectproof food, as explained by
Essig et al. (1943):
The importance of a thorough understanding of the
biology and control of stored
products insects in connection with the food situation
in the war effort, with regard
to the supplies for the armed
forces and civilian population in our own country and
those of our allies, has been evident
for some time. However, the situation now has become critical for at
least five distinct reasons: viz., (1) the
necessity for storing dried, dehydrated, and cured foods in great quantities for considerable periods of time:
(2) the difficulty of obtaining suitable
packaging materials that will endure
rough handling and remain vapor
tight, and also completely resist the
attacks of insects; (3) irregularities
in cleaning and disinfecting storage
warehouses and transportation facilities, particularly freight cars, barges,
and cargo ships; (4) the hazards of
insect infestation and contamination
on shipboard during transit, which
requires weeks and even months of
temperature and moisture conditions
extremely favorable to the development of insects; and (5) the tropical
“I’m pretty sure that plastic bag is safe for you to eat.
The ‘Best if Used By’ date stamp says
‘December 31, a million years from now.’”
American Entomologist • Volume 62, Number 4
lodged deep in their nostrils.
When it’s not blocking chelonian nasal
packages or otherwise entangling food
webs, about one-third of the developed
world’s plastic goes into packaging, and
that’s where it typically encounters the
insect world. The invention of plastic
offered the promise, for the first time
in human history, of effectively keeping food intended for humans out of the
mouths of stored-product insect pests.
Plastic for packaging didn’t really take off
until after World War I, when methods of
mass production of polymers were developed (Teegarden 2004). Commercial production of polyvinyl chloride (PVC), still
used today for shrink-wrap and deli wrap,
began in the late 1920s. The 1930s saw a
veritable explosion in plastic acronyms:
among others, polyvinylidene chloride
(PDVC, the precursor to Saran Wrap)
and low-density polyethylene (LDPE)
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climates with their large numbers of
insect pests which attack all kinds of
edible products. Frequently these
materials must be dumped in areas
where exposure to high temperatures,
and rain make them even more susceptible to infestation.
Thus it was that, in early 1942, new
packaging materials designed to replace
metal containers underwent testing at the
U.S. Dept. of Agriculture Western Regional
Laboratory in Albany, California, to meet
the “ever increasing” demand for testing
packing materials designed to foil insects
(“foil” in the sense of “thwart,” not “wrap
in aluminum”).
In the context of today’s sensibilities,
plastics were among the least terrifying
materials being considered as appropriate for storing human food. Among the
products tested by Essig et al. (1943) were
“super calendered unbleached sulfite” and
the “Reynolds Metal Bag (type A 10),” comprising “dense Kraft, asphaltic compound,
solid sheet alloy, moisture-proof adhesive,
cellophane, special heat sealing coating.”
Sometimes a fungicide (e.g., Dowicide G,
pentachlorophenol) was mixed in with
the laminated materials for good measure. (If you’re interested, according to the
Material Safety Data Sheet for this product,
even short-term exposure to pentachlorophenol can cause, among other things,
“elevated temperature, profuse sweating,
uncoordinated movement, muscle twitching, and coma” (T3DB, 2009). The “Kraft
paper laminated with asphalt” was made
with a bone glue/petroleum asphalt emulsion in 15% w/w dialdehyde and chrome
alum solution. Then there was the “Bemis
bag,” with an outer wall made from “0.001
inch leadfoil laminated with 15 pounds
asphalt”—and, yes, lead foil is indeed made
out of lead. The Material Safety Data Sheet
(MSDS) for lead foil mentions “gastrointestinal irritation, abdominal pain or cramps
(lead cholic [sic]), spasms, nausea, vomiting, bloody diarrhoea, constipation, headache, muscle weakness, aching bones and
muscles, hallucinations, anorexia, malaise,
and convulsions…encephalopathy, permanent brain damage and reversible renal
injury, distorted perceptions…weight loss,
weakness, lassitude, insomnia, dizziness
and other symptoms” as potential hazards (ChemSafe 2012). These are not the
ideal attributes for a material to be used
for carrying your lunch or wrapping your
sandwich in.
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Although the lead-lined bags might
have been impervious to X-rays, they
were easily penetrated by many insects.
Essig et al. (1943) found that larvae of
the cadelle, Tenebroides mauritanicus,
could penetrate just about any package
(although, by contrast, Oryzaephilus surinamensis, the sawtoothed grain beetle,
literally didn’t seem capable of eating its
way out of a paper bag). In addition to
testing the packaging materials, Essig et
al. (1943) also tested repellents that, again,
by today’s standards, are horrifying to contemplate; they include, but are not limited
to, dry lime-sulfur, thiourea, O-ethyl sym
methallyl xanthate, diamino-diphenyl sulfide, tetramethyl thiuram-disulfide, zinc
dimethyl dithiocarbamate, lauryl thiocyanate, tert butyl-thiocyanate, barium,
lead, copper, and cerium naphthenates,
1,2,3-trichloropropane, 1,1,1,2,3-pentachloropropane, diamyl amine, chloramine
B, and sodium benzene sulfon-chloramine. Other investigators were similarly
unsuccessful in identifying insect-proof
packaging; Linsley (1944) lamented the
fact that “No commercially available glassor metal-substitute packages are known
to be insect-proof against all pests.” What
must have been particularly galling—the
insult to the injury—was the finding that
the adhesive asphalt-glue used to laminate the Kraft paper was actually attractive to roaches and silverfish (Sweetman
and Bourne 1944).
By mid-century, then, plastics were
looking like the last best hope for insectproof packaging material. The need
seemed only to increase with each passing year; by 1951, insect damage to stored
cereals cost an estimated $600 million
(Parkin 1956). Entomologists redoubled
their efforts to find the ultimate penetration-proof packing film.
The level of concern was reflected by
the fact that the very first issue of Annual
Review of Entomology dedicated a chapter
to the subject, with author Parkin (1956)
calling for more research and concluding, yet again, “All the commonly used
packaging materials can be penetrated
by insects…The inability of the closures
to exclude insects is clearly a major weakness of present package construction.”
For the next 20 years, entomologists
tested materials as fast as they were patented and produced by polymer chemists
(Gerhardt and Lindgren 1954; Gerhardt
and Lindgren 1955; Sreenathan et al. 1960;
Highland et al. 1965, 1969; Cline 1976).
All manner of stored product pests were
confined individually, with or without
food, in small pouches made of polyethylene, polyvinylchloride, polyester,
polypropylene and just about every other
poly-product available. Efficacy depended
on species (with the cadelle being particularly tough to stop), but no material
could stop them all. The frustration that
these investigators experienced is palpable
in the accounts of their research. Murata
et al. (2006), for example, described how
Plodia interpunctella caterpillars “invaded
instant noodles packaged in a heat-shrunk
sealed foam polystyrene cup,” literally
worming their way between the lid and
the cup, enlarging the vent holes, and
boring through the polypropylene film on
the side and bottom of the cup and the
polypropylene film of the lid flange. The
authors somewhat understatedly concluded that “there was room for improvement
of the heat-shrunk packaging and the cup
surface of the instant noodle product.”
Modern science hasn’t given up on
plastics for protection against pests. The
full measure of advanced technology is
being deployed to keep insects out of the
world’s stored food, instant and otherwise.
Kim et al. (2016), for example, is incorporating halloysite nanotube technology into
plastic film production to thwart stored
product pests. If you’re wondering, as I
did, what a halloysite nanotube is, I looked
it up to find that
Halloysite (Al2Si2O5(OH)4_ nH2O)
is a two-layered (1:1) aluminosilicate chemically similar to kaolin
which exhibits a range of morphologies. One predominant form is a hollow tubular structure in the submicrometer range. The size of halloysite
tubules varies from 500-1000 nm in
length and 15-100 nm in inner diameter depending on the deposit…The
neighboring alumina and silica layers, and their water of hydration, create a packing disorder causing them
to curve and roll up, forming multilayer tubes. The reason flat kaolinite
rolls into halloysite tubules remains
unclear” (Lvov et al. 2008).
Frankly, it’s all pretty unclear to me.
I can report, though, that acronyms
are alive and well; Kim et al. conclude
their abstract with their finding that
“Gravure-printed LDPE film containing
HNTs/CO/LBL displayed the greatest
American Entomologist • Winter 2016
preventive effect on insect penetration.”
At least 36 of the 187 words in the abstract
are acronyms.
Although some progress has been
made, insects have evolution on their side,
and it’s looking like plastics may soon be
going the way of adhesive asphalt-glue in
the context of protecting food from stored
product pests. Insects, ever adaptable, are
actually developing new uses of plastic to
replace natural materials, much in the
manner that we humans have done. In
the open ocean, the pelagic ocean-skater Halobates sobrinus is a marine water
strider that was once reproductively constrained by a dearth of oviposition substrates far from shore, historically depending on occasional bits of natural flotsam
and jetsam (including driftwood and dead
birds) for oviposition. In 2002, Cheng and
Pitman were surprised to find 70,000 eggs
of this species (along with 833 adults)
on a single floating plastic gallon jug. A
decade later, Goldstein et al (2012) noted
that the “microplastic concentrations in
the North Pacific Subtropical Gyre (NPSG)
have…released the pelagic insect Halobates sericeus from substrate limitation for
oviposition.” The virtually inexhaustible
supply of microplastic pellets (less than
5 mm in diameter) in the Great Pacific
Garbage Patch has been a bonanza for
H. sericeus, increasing egg densities and
possibly reconfiguring food webs in the
new “plastisphere” (Goldstein et al 2012,
Majer et al. 2012, Reisser et al. 2014).
In terrestrial environments, plastic is
also being embraced by insects. MacIvor and Moore (2013) documented the
use by two megachilid leafcutter bees
of plastics in place of natural materials
to line their nests. Instead of using cut
leaves, Megachile rotundata makes brood
cells out of pieces cut out of polyethylene
plastic bags. Its congener Megachile campanulae eschews tree resins for constructing brood cells, opting to use polyurethane-based exterior building sealant
instead. In what may be the ultimate
challenge to finding pest-resistant plastic packaging, the yellow mealworm, Tenebrio molitor, can actually eat the stuff
(Yang et al 2015). Styrofoam in the gut
of the larvae is digested in less than 24
hours; the larvae live as well on Styrofoam
as do conspecifics on bran for at least a
month. Radiolabel studies confirm that
the carbon in the polystyrene ends up
as carbon dioxide or incorporated into
lipids. And Plodia interpunctella larvae
American Entomologist • Volume 62, Number 4
can digest polyethylene (or at least their
endosymbionts can) (Yang et al. 2014).
It’s unlikely that mealworms can make
much of a dent in the 33 million tons of
plastic that end up in U.S. landfills every
year; even if they could, the journalists
and bloggers breathlessly touting the
mealworm as the “solution to our growing garbage problem” (e.g., Mountain
2015) probably haven’t considered the
downside of converting 33 million tons
of plastic into mealworm biomass. Even
with a relatively low efficiency of conversion of ingested food of 20%, that’s still 6.6
million tons of mealworms, which may
create some waste management challenges of their own. Say what you will about
Styrofoam—at least it can’t eat its way
out of a plastic recycling bin.
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May Berenbaum is a professor
and head of the Department of
Entomology, University of Illinois,
320 Morrill Hall, 505 South
Goodwin Avenue, Urbana, IL 61801.
Currently, she is studying the
chemical aspects of interaction between
herbivorous insects and their hosts.
DOI:
10.1093/ae/tmw075
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