Download Insects and Packaging - A Review

International Biodeterioration 24 (1988) 175-187
Insects and Packaging - - A Review*
J. N e w t o n
Research and Development Division, Rentokil Ltd, Felcourt, East Grinstead, West Sussex,
RHI9 2JY, UK
ABSTRACT
This paper reviews the interactions of insects with food packaging, and
measures which may be taken to limit damage.
INTRODUCTION
Insects may deleteriously affect packaging in two main ways. First, and
by far the more important in practice, they may contaminate packaging
by their mere presence, and thus contaminate the materials to be
packaged. Second, they may physically damage packaging by boring
through it, generally when attempting to gain access to, or when
emigrating from, the packaged product.
Most complaints of insect contamination or damage associated with
packaged goods arise from consumers, who find insects or parts of
insects in or on the packaged goods, and complain to the local health
inspectorate or to the retailer. At the complaint stage it is generally
difficult to determine whether the infestation commenced in the
consumer's kitchen, at the retailer, the product manufacturer or at the
packaging manufacturer. The only stages at which it is possible to
determine whether the packaging itself is the source of an infestation are
*Paper presented at the Seventh International Biodeterioration Symposium, 7-11
September 1987, Cambridge, UK.
175
International Biodeterioration 0265-3036/88/$03.50 © 1988 Elsevier Science Publishers
Ltd, England. Printed in Great Britain
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J. Newton
manufacture and use, i.e. during fabrication and storage of packaging at
the manufacturer, or during transport to and storage at the packer.
Detection of any infestation further downstream may be attributable
to the packaging, the product being packed, or the conditions under
which the product is packed, stored or transported.
C O N T A M I N A T I O N D U R I N G T H E M A N U F A C T U R E OF
P A C K A G I N G MATERIALS
Packaging materials are generally rather inedible, so most of the insects
found in packaging manufacturing premises are either casual intruders
from outdoors, or general scavengers living indoors. The exceptions to
this are woodboring insects living in wooden packaging, and, in the
tropics or subtropics, termites (Isoptera) which will eat cellulose-based
packaging.
At the manufacturing stage the presence of insects is primarily a
problem of contamination rather than damage. Insects may be
accidentally incorporated into multilayer plastic films. This can happen
if insects alight on the single film, or are attracted by the electrostatic
charge which builds up on such film during manufacture. Trapped
insects may appear simply as non-descript blemishes on the film, but in a
transparent film insects show up very well, especially when wrapped
around a pale-coloured foodstuff! W h e n asked for advice in just such a
case, the author suggested that antistatic bars on film lines might help to
reduce the problem.
W h e n rigid plastic, glass or metal containers are stacked mouth
upwards they can function like arrays of'pitfall traps'. In a recent case,
for example, insects drawn in through a ventilation system were falling
into the upturned open ends of alloy toothpaste tubes. Not all insects
were able to crawl out, and there was an obvious risk of contamination of
toothpaste when the tubes were filled. Davis (1986) reports a similar
problem in the USA. Psocids living on pallets in an unheated warehouse
became trapped in empty sauce bottles, and subsequently contaminated
the sauce, despite caustic washing of the bottles. If containers cannot be
stacked mouth downwards, a turnover loop with an air blast should be
installed at the start of the filling line, so that insects and other foreign
bodies are expelled. This is particularly important if there is no pre-fill
washing.
The 'casual intruders' may include anything from cereal thrips to stag
beetles, and are basically outdoor-living insects which are attracted into
the premises, or just wander in. To some extent their numbers can be kept
down by keeping vegetation cut well back, grass short and the site clean
Insects and packaging
177
and well maintained. Blocked gutters, for example, may be breeding
grounds for midges and other small flies. The building should be kept in
good repair, so that insects find entry difficult. Gaps under doors can be
proofed with bristle strip; windows can be fitted with insect screens;
regularly used entrances can be fitted with strip curtain doors. Ideally
there should be positive-pressure ventilation with well-filtered air. The
episode referred to earlier of insects becoming trapped in plastic film was
due in part to the fact that the outer fabric of the building contained
many holes, and ventilation was by exhaust only. Added to this,
production continued into the night, so that night-flying insects, which
abounded in the rural location, were attracted to holes by light.
Several species of beetle and moth may be classed as general
scavengers as they feed on a wide variety of dry plant and animal
materials. Before pupation, mature larvae of the Australian spider beetle,
Ptinus tectus, tend to bore into and damage inedible materials such as
cardboard boxes, sacks and even plastic and wood. Larvae of the brown
house moth, Hofmannophila pseudospretella, and the white-shouldered
house moth, Endrosis sarcitrella, when mature may bite through soft
materials such as cardboard in search of pupation sites. Spider beetles
and house moths are often associated with birds' nests. Yet more closely
associated with birds' nests are the following insects (which prefer a diet
high in animal protein, which may include keratin):
clothes moths (Family Tineidae);
carpet beetles (Anthrenus spp.);
fur beetles (Attagenus pellio);
larder and hide beetles (Dermestes spp.).
Yellow mealworm beetles (Tenebrio molitor) usually feed on cereals but
will eat animal protein, and are associated particularly with pigeons'
nests.
These general scavengers are best controlled by thorough and regular
cleaning of premises. Removal of birds' nests and exclusion of birds is
essential. Disused areas and roof voids should be kept clean. Regular
spraying with residual insecticides will help to eliminate any insects
surviving the cleaning. Packaging manufacture and storage areas should
be considered to be food processing premises rather than engineering
works.
BOOKLICE u THEIR PRESENCE ON PACKAGING MATERIALS
The one group of insects which frequently lives on packaging itself is the
booklice or Psocids, Order Psocoptera. They are not infrequently found
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J. Newton
on paper and cardboard packaging; in books, they probably feed on
animal glues in bindings or on microfungi growing on the surface of
books. Booklice infest a wide range of materials, ranging from chocolate
to salami, bat guano to bagged nuts, birds' nests to milk powder (Dodd,
1981). It is assumed that on packaging they feed on microfungi or on
some other organic edible surface contaminant. They can breed
successfully on sterile foodstuffs, but do better when fungi such as
Saccharomyces, Mucor or Aspergillus are present. According to Pinniger
(1984), packaging infested with booklice may be fumigated either with
methyl bromide (150 to 300 mg h/litre depending on temperature) or
phosphine (dose at 10°C is 16 days at 0.1 mg/litre).
Not surprisingly, the food industry tends not to publish data on insect
contamination problems. However, when in 1984 a survey was carried
out in the U K under the auspices of the Society of Food Hygiene
Technology (SOFHT), of the 43 firms who replied and who might have
been considered to have the potential for booklouse problems, 31
reported a problem (Downing, 1984). Most of these were companies with
an annual turnover in excess of £10 million. For the majority of these
companies, the booklouse problems were in part or exclusively related to
consumer complaints. Manufacture was the next most important
problem area, Over one-third of the firms reported that the problem had
increased during the past five years, and all these firms reported
consumer complaints. Most complaints occurred during late summer
and early autumn. One firm reported up to 1700 complaints per a n n u m ,
another firm up to 30 complaints per million units sold. Booklice gave
rise to up to 52% of insect complaints, and up to 7% of all complaints.
Most companies reported consumer complaints of booklice on flour
products, sugar or packaging, and reported booklouse problems
elsewhere in the distribution chain with these, and with milk powder.
Turner (1987) classified 400 complaints of psocid infestation either
extracted from the British Museum (Natural History) files since about
1955 or sent to his laboratory. Over 30% of infestations were on flour. The
bulk of the remainder were from cereals, cereal products or sugar, and 5%
were on paper and books.
C o m m e n t i n g on the S O F H T survey, Downing (1984) postulated that
possible reasons for the susceptibility of some commodities might be
the presence of food dust on the outside of the package, or the presence of
mould (originating at any stage from point of manufacture) on the
package. C o n s u m e r complaints were ofbooklice both in the commodity
and on the packaging, but at this stage it is impossible to be certain about
the source of the insects. Where companies reported non-consumer
problems, booklice were most frequently reported to be associated with
Insects and packaging
179
the building fabric, pallets, packaging with product, and packaging
alone. Given the numbers of companies reporting infestation of
manufacturing premises and pallets, Downing expressed surprise at the
lower numbers reporting infestation in intermediate storage, transport
and shops. He considered it possible that cross-infestation from pallets
was largely prevented by the outer bulk packaging which encloses foods
when they are stacked on pallets at the factory and which is removed
when goods reach the retailer. The genera of booklice identified by
respondents to the survey were Liposcelis, Lepinotus and Trogium. The
only clear relationship that emerged between problems and particular
genera was that Liposcelis was always involved where only consumer
complaints were reported.
The relationship between genera ofbooklice and particular problems
had been discussed by Lilley (1981) at an earlier SOFHT symposium.
She reported that the company for which she worked experienced an
increase in consumer complaints in the mid 1970s, due to booklice in
packed semolina. The species found was Liposcelis bostrychophilus.
However, this species was not found on the company premises~ although
Lepinotus and Trogium were found on incoming goods and on pallet
boards, and Liposcelis subfuscus was found in non-semolina areas.
A report by the Pre-Packed Flour Association (Anon., 1982) came to
similar conclusions. The numbers of consumer complaints ofpsocids in
flour quadrupled between 1978 and 1981, and peaked in the autumn of
each year. L. bostrychophilus accounted for the vast majority of
complaints. The Association concluded however that there was no
evidence that infestation by this species arose from their manufacturing
and distribution systems.
Data based on insects sent in for identification to Rentokil UK, the
Danish Pest Infestation Laboratory and the Dutch Staatstoezicht op de
Volksgezondheid show similar patterns of increase in psocid-related
complaints over the 15-20 years up to 1984 (Turner, 1987). Again, the
autumn peak in numbers was seen, but with a levelling-offor decrease in
overall numbers over the last few years. UK companies responding in a
recent small, and as yet unpublished, follow-up survey to the main
SOFHT booklouse survey also reported a recent levelling-off or decline
in numbers of consumer complaints, as did the Pre-Packed Flour
Association. Whatever unknown factors are responsible for the variations
in numbers of complaints ofbooklice, they appear to operate in at least
three European countries!
Turner (1986) suggests that in the mid-1960s, when complaints started
to increase, houses were being equipped with 'fitted' kitchens, and central
heating was becoming more common. Food was being stored not in cold
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larders, but in kitchen units at kitchen temperatures. Draught-proofing
and double glazing have increased condensation problems. Psocids
generally grow and reproduce more rapidly at higher temperatures and
humidities (Dodd, 1981; Pinniger, 1984). However, Turner qualifies his
suggestion by remarking that it does not tie in well with the autumn peak
in complaints; central heating might be expected to cause a spring peak
following winter population growth.
In order to gather further information on the incidence of booklice in
domestic larders and factors which might encourage infestations, Turner
circulated members of staff of King's College, London, and personal
contacts with questionnaires and five booklouse 'pads' each (Turner &
Maude-Roxby, 1987). These 'pads' were small harbourages containing
yeast, and participants were asked to place the pads in their kitchens
amongst their dry foodstuffs for the month of October 1986. The returned
pads were examined for booklice, or incubated if apparently booklousefree. About 30% (541) of those households circulated returned questionnaires and pads. Most of the arthropods found were identified as either
non-predatory mites (15.3% of households), or the booklouse L.
bostrychophilus (14.4%). Very few booklice of other species were found.
Analysis of the replies to questionnaires showed no significant
correlation between the presence of booklice and the type of kitchen
(fitted or non-fitted), household conditions (condensation, central
heating), methods of storage of dry foods (original packaging or different
container), intervals at which various dried foods were purchased, retail
outlet, or brand of flour. Turner concluded that there was no compelling
evidence that differences in conditions in houses or kitchens affected
their suitability as booklouse habitats.
The results of the studies by the food manufacturers imply that L.
bostrychophilus is a common pest in domestic kitchens, and adventitiously
breeds on suitable packaged foods stored in kitchens. Turner (1986)
states that his survey does not support this hypothesis, and argues that
the lack of correlations in his data suggest that booklice appear in houses
on a random basis, such as might be expected if they were introduced
into houses in food products. However, the detection ofL. bostrychophilus
in 14-4% of responding households suggests that this species is a
common household pest.
PHYSICAL DAMAGE BY PENETRATING INSECTS
The second category of damage is penetration of food packaging by
insects, generally stored-product pests, gaining access to or emigrating
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181
from foodstuffs. This can occur at any point from packet closure to
c o n s u m e r kitchen storage. It is obviously desirable to deny insects access
to 'pest-free' packaged foodstuffs. If insects can be contained within an
infested package, spread to other packages will be prevented. An insect
which has found its way between the outer and inner packaging of an
uninfested product will still be cause for a c o n s u m e r complaint.
Ifa stored-product insect is simply placed on a piece of packaging film,
it will almost certainly fail to penetrate the film. Most insects cannot cling
to a smooth packaging film with sufficient strength for t h e m a n d i b l e s to
grip a n d damage the film. However, insects can bore into and out of
sealed packets by bracing themselves between the surface to be chewed
and any other nearby surface. Standard tests of the resistance of
packaging films to insect penetration take this into account, and provide
a tapered crevice between the packaging film and the frame in which the
film is held. A typical test set-up consists of an array of rings, bolted
together around the test film, which is exposed as a disc about 50 m m in
diameter (Fig. 1). The tapered crevice ensures that different species can
select the width of crevice ideal for their purposes (Wohlgemuth, 1979).
Some workers use a device with a series of flour-filled notches next to the
test film (Highland & Wilson, 1981).
The other main film-testing method employs small bags of test
material with foodstuff sealed inside. The bags are then exposed to
insects, either in a container or in an infested room. In a variant of this
technique insects are sealed inside the test bags, with or without a small
a m o u n t of foodstuff (Cline, 1978b). One disadvantage of the bag
technique is the long test period. It is also possible that some insects may
enter or leave through imperfect seams. The presence or absence of food
~
Insect
rr~etsaihnnig
\
.
.
.
.
.
B°sgp,°t°
Fig. 1. Diagrammatic section of apparatus for testing resistance of film to insect
penetration.
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J. Newton
can affect penetration; not surprisingly, starved insects may penetrate a
film which they fail to penetrate when fed. For example, larvae of
Tribolium castaneum (rust red flour beetle) penetrated cellophane and
polyethylene bags when sealed in without food, but not with food (Cline,
1978b). Such penetration may not result simply from a search for food;
larvae of many stored-product insects pupate preferentially amongst
edible or inedible debris, and chewing at a film creates debris. Despite
their limitations, the various bag methods are useful for quality control
of mass-produced packets, since they simulate the type of challenge to
which packets are exposed and test the entire packet (including strength
of seams and closures).
Highland 0984) has categorised films of the thickness commonly used
in food packaging in accordance with their resistance to insect
penetration (Table 1). According to Schmidt (1979) the insect resistance
of films is likely to be related to their smoothness, rigidity and
thickness.
Some species of insect are better penetrators than others. Rhizopertha
dominica (lesser grain borer), Tenebroides mauretanicus (cadelle beetle),
Lasioderma serricorne (tobacco beetle), Trogoderma variable (warehouse
beetle) and larvae of Corcyra cephalonica (rice moth) are particularly
efficient penetrators (Highland, 1984). However, Tribolium species (flour
beetles) and Oryzaephilus surinamensis (sawtoothed grain beetle) tend to
enter through existing openings in packages. Schmidt (1979) considered
that the gnawing ability of the insects might be influenced by the size and
shape of the mouthparts, and the position of the mandibles relative to the
axis of the body.
Folds and seams provide the major routes through which insects enter
packages, either by boring through or finding defects in seams. The
tendency to bore through along a fold or seam presumably results from
roughening of the packaging film by mechanical or thermal distortion at
this point, and the insect being better able to brace itself against an
adjoining surface when it is chewing. Cline (1978b) found, when testing
the resistance to penetration of films by confining stored-product larvae
in bags, that most beetle larvae made their penetrations in the bottom
half of bags, within 1 cm of a fold. The moth larvae, however, were able to
climb to the top of the pouch to penetrate. In previous work (Cline,
1978a), he examined the ability of last-instar larvae of stored-product
insects to cling to and climb packaging films and glass at various angles
to the horizontal. Larvae of the three species of moth tested (Ephestia
cautella, C. cephalonica, Plodia interpunctella) were able to climb all
surfaces at 90 °. Three of the species of beetle (Oryzaephilus mercator,
Insects and packaging
183
TABLE 1
The Relative Resistance to Insect Penetration of Commonly Used Food Packaging Films
(after Highland, 1984)
Packaging material a
Excellent
Good
Fair
Poor
Polyca rbonate
Polyester
Polyurethane
Cellulose diacetate
Nylon
Polyethylene (ca. 250/~m)
Polypropylene (biaxially oriented)
Polyvinyl chloride (unplasticised)
Acrylic
Ethylene-tetra fluoroethylene
Fluorinated ethylene-propylene
Polyethylene (ca. 125/am)
Cellophane
Cellulose propionate
Corrugated paperboard
Ethylene-vinyl acetate
Ehtylene-vinyl acetate/polyethylene (coextrusion)
Ionomer
Kraft paper
Paper/foil/polyethylene laminate (pouch material)
Polyethylene (ca. 25, 50, 75, 100~tm)
Polyvinyl chloride (plasticised)
Saran
Spunbonded polymers
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
"Where no film thickness is given, the resistance rating is based on thickness commonly
used in food packaging.
Cathartus quadricollis, Dermestes maculatus) were able to cling to all
surfaces at 90 °. Larvae o f beetle species were able to climb o n l y paper at
90 ° . S o m e species c o u l d not climb s o m e materials at 5 ° . Paper and glass
were generally easiest to cling to, a n d p o l y p r o p y l e n e m o s t difficult. The
order o f difficulty for clinging was not the same as that for climbing. For
example, glass was o n e o f the more difficult materials to climb, although
o n e o f the easiest to cling to. Referring to an earlier paper, Cline (1978a)
observed that the stored-product beetles investigated were generally
better climbers as adults than as larvae, but larvae tended to be better
than adults at clinging. It is possible that by tightly wrapping
c o m m o d i t i e s in materials such as p o l y p r o p y l e n e w h i c h are difficult to
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J. Newton
climb or cling to, infestation by invading insects might be reduced or
delayed.
It is often possible by close examination of holes made by insects to
determine whether the holes were made by insects entering a package
from outside (and therefore arguably not the manufacturer's responsibility),
or by insects escaping from within (Wohlgemuth, 1979; Highland, 1984).
The hole on the exit side of the penetrated material generally has a
smaller diameter than on the entry side, and has a clean-cut perimeter.
The perimeter on the entrance side is tapered or terraced, scratched or
roughened, and with plastics is usually upturned. However, even if the
direction of penetration may be unambiguous in a particular case, the
interpretation need not be. Only if it is certain that insects could not have
entered through minute defects in the packaging before despatch could
the manufacturer use the presence of entry holes and absence of exit
holes as a reasonable defence against liability.
Unfortunately, adult stored-product beetles can squeeze through
surprisingly narrow openings. By using stacks of sieves with circular
apertures, Cline & Highland (1981) determined that O. mercator
(merchant grain beetle) adults could pass through holes only 0.93 m m in
diameter. Adults of T. confusum (confused flour beetle) could pass
through apertures 1.35 m m in diameter.
The limiting factor in preventing entry by newly-hatched larvae of
stored-product insects is likely to be the size of the head capsule. The
head capsule diameter of a newly-hatched larva is about 260 p m for O.
surinamensis~ and 125pm for R. dominica (Khan, 1983a), so they can
probably enter packages through correspondingly small holes, down to
100pm for some species (Wohlgemuth, 1979). Last-instar Tribolium
larvae can easily pass through holes of less than 1 mm diameter
(unpublished work at Rentokil). K h a n (1983b) concluded that a
r h o d a m i n e test of packaging integrity was not a reliable substitute for an
insect bioassay.
If a packaging film is creased or crumpled it is more likely to be
penetrated by insects. Noack (1982) used a specially designed apparatus
to crease packaging films, which were then exposed to adults of T.
confusum. Cellophane became less resistant when creased several times,
but multilayer foils of polyester, polypropylene and polyamide with
aluminium, and biaxially stretched polyamide, remained resistant even
after being strongly creased.
Ironically, the integrity of a packaging film may be intentionally
damaged in a variety of ways. Embossing the date of manufacture or a
similar code onto a packet will distort and weaken the film, providing an
Insects and packaging
185
uneven area more readily accessible to insect mandibles. One solution is
simply to print the date instead. The perforations around the thumb tag
in a cardboard packet are another example of intentional damage.
Wohlgemuth (1979) cites an example of a manufacturer of tinned instant
chocolate drink who had frequent complaints of infestation by P.
interpunctella. The tin, the aluminium foil seal and the seal seam all
appeared to be resistant to larval entry. But the manufacturer was
punching two small holes in the foil to allow for pressure equalisation in
fluctuating temperatures. Even when these holes were made as small as
possible (about 0.25 mm), newly-hatched larvae could still enter.
Quite simple measures can improve the resistance of packaging to
insects. Highland (1984) reported that cases of raisins could be made
more insect-resistant by inverting prior to stacking, so that the weight of
the raisins pressed down on the folded closures of the polyethylene
liners, holding them tightly shut.
Incorporation of insecticides and repellents into packaging, generally
by surface application, has been used for many years to give increased
protection against insects. As this is an extensive subject in its own right,
it is here touched on only briefly. Egyptian papyrus scrolls dating from
about 1600 BC record the use of cat and bird fat applied to grain
containers to repel granary pests (Levinson & Levinson, 1985). Nigam et
al. (1969) cited investigations into the protection of packaging by use of a
variety of pesticides from silica-gel dust to carbaryl, and techniques
ranging from the application of DDT to jute sacking, to the use on
cardboard cartons of a varnish containing synergised pyrethrins. The
many recent studies on pesticides and packaging have included work on
chlorpyrifos-methyl and permethrin on jute and woven polypropylene
bags (Barakat et al., 1987); the same pesticides on film overwraps
(Highland et al., 1986); and etrimfos and malathion on jute bags (Rai et
al., 1985).
In the USA, the only pesticide currently approved by the Environmental
Protection Agency for use in insect-resistant packaging is synergised
pyrethrins, which may be used on cotton bags, multiwall paper bags, or
in the adhesive between the layers of a cellophane/polyethylene
laminate for dried-fruit packages (Highland, 1984). It is important that
packaging incorporating pesticides is designed to prevent migration of
significant quantities of pesticide into the foodstuff in contact with the
packaging.
In conclusion, it can be said that without doubt insects will continue to
cause problems for the food packaging business, but the risk of
contamination by insects can be minimised by manufacturing, handling
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J. Newton
a n d storing food p a c k a g i n g with the s a m e care a c c o r d e d to foodstuffs.
Careful selection o f p a c k a g i n g materials a n d choice o f package design
c a n m a x i m i s e the resistance o f packages to insect penetration.
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