Pest Control for Food Safety - III

Stored Product Insects

This group includes large number of insects which attack foodstuffs of raw materials in storage, transport and manufacture. The group includes beetles, weevils, moths and their larvae which attack dried products, cereals, flour, beans, and nuts. It has been estimated that approximately ¼ to 1/3 of the world grain production is lost in the storage mostly due to pest attacks each year.  In addition, grain which is not lost is severely reduced in quality by insect damage and many grain pests preferentially eat out grain embryos, thereby reducing the protein content of feed grain and lowering the percentage of seeds which germinate. Stored food product pests are found in almost every home at some time or most of the food storage. Yet few people recognize why stored product pests occur, or how to identify them. Many are transported into the home from a store or warehouse, since most of the storage act as their buffer stocks. In last article we discuss the beetles ad here rest of the most common storage food pest are given here. But this is not a comprehensive list since there many different storage pests in different parts of the world and we only try to discuss most common types here.

Granary Weevil – Sitophilus granarius

The Granary Weevil is among the most destructive of all stored grain insects, because of their larvae develop inside kernels of whole grain in storage, which makes an infestation difficult to remove in the milling process. Most of their life is spent within the grain kernel and both larvae and adults feed on grain where they also attack hard cereal products such as macaroni and spaghetti.

The adult insect is about 2.5 - 5 mm in length and dark brown-black in colour, which possess a long slender snout and cannot fly. Females drill a tiny hole in the grain kernel and deposit an egg in the cavity, then plug the hole with a gelatinous secretion. The egg, larva, and pupa stages of these weevils occur in the grain kernels and are rarely seen, where larval stage of the weevils are legless, humpbacked, with white to creamy white colour, with a small, tan head. Weevils in the pupa stage have snouts like in the adults. Emergence holes of the granary weevil are fairly large and tend to be more ragged than smooth and round. The life cycle is about 30 to 40 days during the summer, and 123 to 148 days during the winter, depending on temperature.

Maize Weevil - Sitophilus zaemais

Also known as the Greater Rice Weevil which are frequently regarded as primary pests of grain since they are able to infest otherwise undamaged grain as well as they are observed to be infesting buckwheat, peas, acorns, chestnuts and cottonseed. The weevil damaged grain can be readily recognized by the presence of large holes which are the exit holes of the emerging adults, where both larvae and adults will feed upon grain.

Adult insect is about 2.5 - 4 mm long and the head has a long slender snout, which resembles to rice weevil, as differences only bigger and the red-brown spots on wing covers are more clearly marked and it is a stronger flier than the rice weevil. Females drill a tiny hole in the grain kernel, deposit an egg in the cavity, then plug the hole with a gelatinous secretion. The egg, larva, and pupa stages of these weevils occur in the grain kernels and are rarely seen, hence egg hatches into a young larva which bores toward the center of the kernel, feeds, grows, and pupates there. New adults bore emergence holes from the inside, then leave to mate and begin a new generation.

Rice Weevil – Sitophilus oryzae

Rice weevils are pests of stored grain and seeds, where the adults can feign death by drawing up their legs close to the body, falling, and remaining silent when disturbed. Emergence holes of the rice weevil are smaller than those of the granary weevil, and tend to be smooth and round and there is no external evidence that the larvae have been eating and growing inside the seed until after about one month when the adult weevil chews through the seed coat and emerges.

The adult rice weevil is about 2.5 to 3.5 mm in length and has a slender, hard-shelled bodies that appear pitted or scarred with tiny holes and are brown-black in color while possessing a long slender snout as well as they have four faint red-brown spots on the back of the abdomen. Females drill a tiny hole in the grain kernel, deposit an egg in the cavity, then plug the hole with a gelatinous secretion and the egg hatches into a young larva which bores toward the center of the kernel, feeds, grows, and pupates there. Female rice weevils lay between 300 to 400 eggs, with the life cycle requiring about 32 days for completion. Two larvae can develop in one wheat kernel and the egg, larva, and pupa stages of these weevils occur in the grain kernels and are rarely seen. New adults bore emergence holes from the inside, then leave to mate and begin a new generation. The adults live 3 to 6 months, infesting grain in the field.

Bean Weevil – Acanthoscelides obtectus

The adult is 2.0 – 3.0mm long, which is mottled brown in colour and weevil has a ‘tear drop’ like body shape that covered in short hairs. The insect has saw-tooth like antennae and elytra which do not cover the entire abdomen. Life cycle usually lasts 2-4 months and weevils attack all legumes, including kidney beans, green beans, peas and lentils where heavily infested peas are often reduced to shells. Development and breeding goes on as long as there is any food left in the bean and if warmer temperatures are possible within the habitat. The larvae feed within the beans as they mature. The larval stage can take from a few weeks to many months to complete, depending upon temperature and moisture of the bean. Pupation is within the bean and circular holes are cut for the adult to emerge. Larvae feed mostly inside beans.

Coffee Bean Weevil - Araecerus fasciculatus

Adults are 1.5-4mm in length and dark brown coloured with light brown spots and long antennae. They mainly infest corn, cocoa, coffee beans, dried fruits, nutmegs, ginger etc., which flies to fields and lays its eggs on damaged cobs. The footless, slim larvae are curved and hairy and grow to a length of 5-6mm and bore into coffee beans in which they pupate.

Almond Moth – Cadra cautella

The almond moth is found globally in processing facilities, warehouses and households and its nicknames are “Cocoa Moth” and “Tropical Warehouse Moth”, which feeds on grain, cereal products, oilseeds and dried plant products, like nuts, fruit and tobacco. The adult is 7.5 – 10 mm long and wing span is 19 mm. The forewings are grey to dusty brown and dark straight band across the forewing, which is paler on the inner edge. The female lays about 150 - 200 eggs loosely and randomly on a food sources and larva can grow up to 12.7 mm in length and it is white to pink in colour and has a distinctive brown head. The larva burrows into food and creates silk tunnels in which it will be concealed while feeding and large larva can burrow through packing. When the larva is mature, it will actively leave the food source and search for a site to pupate and which is a silk cocoon. The almond moth infests stored products and the adults can fly. The infestation and contamination can be observed with silk webbing, frass, cast skins, pupal cases and adult remains.

Indian Meal Moth – Plodia interpunctella

The adult Indian meal moth causes no damage whereas Indian meal moth’s larvae are a very common commercial and pantry pest. Their larvae produce the web material commonly found in food, such as dried fruits, whole wheat and cornmeal, and shelled or ear corn which attracted to grain or grain products such as corn, many different dried foods including fruit, nuts, seeds, also, biscuits and powdered milk; chocolate, candy; dried red peppers; dry dog food.

Adult has wingspread of about 14 – 20mm which are pale gray wings, but the front wing is reddish brown and coppery on the outer two-thirds. The female lays approximately 200 eggs, on food material during a 1-18 day period of time. The mature larva is usually dirty white, but may vary to greenish, pinkish, or brownish, depending on the food it eats and head region is yellowish to reddish brown. The temperature and availability of food determine the length of the larval stages and the last instar larva leaves the food to find a suitable place for pupation. The complete life cycle occurs within 25-135 days, with 4-6 generations per year.

Mediterranean Flour Moth – Ephestia kuhniella

The Mediterranean flour moth larva is a very common commercial and pantry pest. It is a pest of mills and warehouses as it can clog machinery with its webs. The adult has wingspread of about 20 to 22mm and when at rest it is 10 - 14 mm long. The hind wings are dirty white in colour and the forewings are blue-grey with transverse dark wavy bars and a row of dark spots at the tip. The moth is mostly found infesting flour and meal which also been found infesting grain, bran, cereal products, nuts, chocolate, seeds, beans, biscuits, dried fruits and other stored foods.

The female lays between 100 - 700 eggs (usually 200) in and among the food source and usually fastens the eggs to the infested material. The eggs usually hatch in 3 - 5 days and the hatching larvae produce a lot of webbing and the young larvae confine themselves to silken tubes which are constantly spun. The larvae are white in color with a brown head and neck shield they can take on a pinkish or greenish hue and can reach a length of 15 - 20 mm. The larva reaches complete growth around 40 days. The larva pupates in or on top of the infested material (usually flour) or in cracks and crevices nearby which form a brown, spindle shaped cocoon approximately 9 mm. The life cycle can be completed in as few as 4 to 6 weeks but usually takes about 3 months.

Tobacco Moth – Ephestia elutella

The tobacco moth is an introduced pest species of moths which is often found in warehouses and other areas where food or tobacco is stored, which feeds on cocoa beans and tobacco, but also infests nuts, dried fruit and cereals, but adult moths do not feed. The larval feeding cause the most damage due to contamination with excrement and cocoons, where they infest not only tobacco, but cocoa, nuts, dried fruits, coffee, corn maize, wheat and spice.

The moth has a wing expanse of 14 to 17mm and when the wings at rest they folded to a roof over the body which is 8 to 11mm long. The adult moth has brownish grey forewings crossed with two light bands and the hind-wings are paler and plain grey.The female deposits about 100 eggs, singly or in small clusters which generates caterpillars that are whitish, yellowish or reddish depending on nutrition with brown head and neck shields. The caterpillars grow to a length of 10-15 mm and they cover the infested goods with webbing and their pupation occurs in a cocoon. The development period depends on the temperature and nutrition which further depend on the season, thus lifecycle is completed by 2 to 6 months.

Grain Borer – Prostephanus truncatus

Adult beetle is a pest of stored maize, but also infests other types of grain and the larva bores tubular passages into the grain, typically making one main tunnel with smaller ones branching off. The insect were originated in tropical Central America and transcended in cassava roots and tapioca products, as well as in starchy fruits and tubers. The adult is 1.5 - 4.76mm in length and brown in body colour. The antennae have 3 large segments at the end forming visible antenna clubs, which are reddish in colour. Their humped thorax covers the head, its front rim has teeth–like indentations. Elytra (wing covers) are heavily punctated and drop off sharply at the back, giving the impression of a square end when seen from above.

The female lays an average of 10 eggs on a grain of maize and the hatched larvae bore into the grain and the larva undergoes up to 4 development phases and pupates inside the corn grain. The lifecycles can be quite short, in optimum weather conditions their lifecycle can completed i.e. 25 days at 34 °C, 75% relative humidity and they can produce several generations per year.

Lesser Mealworm – Alphitobius diaperinus

The beetles are attracted to poultry operations, which have ideal conditions for their development. Nonetheless, they damage to insulations, covered places in search of seeking a safe place to pupate because the darkling beetles prey on the lesser mealworms. The adult insects are 6mm long and the newly moulted adults are reddish-brown turning black. Females can lay up to at least 110 eggs a month and eggs hatch in 4-7 days, whereas larval development takes up to 7 weeks. The larvae are 8mm long, slender, segmented and worm-like with three pairs of tiny legs on the thorax and one abdominal pro-leg at the rear. Mature larvae seek a sheltered place to pupate for between 7 and 11 days and an adult beetle may live up to two years.

Flour Mite/Grain Mite – Acarus siro 

Adult mites are about 0.5 mm in length and they have 4 pairs of legs and white or pale brown coloured body with slow moving abilities.  Under adverse conditions, it can survive through dormant stage which may pass through a long and very resistant stage called a hypopus. The larvae are 6 legged and 0.5 mm long with white coloured body which need to go through two, 8 legged nymphal stages before become an adult. The lifecycle can be completed in 9 to 11 days at 23°C and 90% relative humidity.

Cheese Mites – Tyrophagus putrescentiae

Cheese mites have soft, hairy cream white bodies with 8 hairless legs and adults grow up to an approximate size of 0.5mm in length. They are preferring for old cheese as well as young cheese, these mites also feed on nuts, dried eggs, fruit, flour and tobacco. The cheese mite favours warm, moist conditions. Females can lay up to 900 eggs in a lifetime at a rate of 20 to 30 a day and eggs mature in 10 days at room temperatures. Adult cheese mites can live around 60 to 70 days, where cheese mites are capable of contaminating foods to cause skin or gut irritation.

Ants

There are various type of ants who infest foodstuff or raw materials. The most common ants are in black or yellow/pale brown colour in nature with approximately around 2mm in length. They love warm weather conditions and usually occur in heated buildings, kitchens, hotels, residential properties, hospitals, etc. where they can often found in seemingly impenetrable food containers. All kinds of food may be attacked, although they prefer sweet, oily or high protein foods. The physical transfer of pathogens are a high possibility since they walk though drains, excreta, and soiled dressings where food is contaminated through their legs and bodies as well as excreta. Nests are difficult to detect and destroy.   

Birds

Birds which considered as food pests are usually pigeons, sparrows, seagulls, crows and other occasional birds. However, sparrows, starlings and pigeons are the most common while gulls are becoming a problem although they rarely enter the buildings. They usually lives in large warehouses, food factories, super markets and other locations or even in the residential buildings. The pathogens associated with birds include salmonella and campylobacter. The prevention is critical since the foods or raw material and equipment can be contaminated through droppings, feathers, bodies and nesting materials, which may transmit food poisoning organisms. They also damage the food packaging to fetch foods or raw materials. They also induce insect or mite infestations due their droppings, feathers, dead bodies and nesting materials which may also block the gutters, and drains resulting flooding and costly maintenance. The bird infestations may also induce defacement of buildings and roosting on fire escapes or similar structures which may create safety hazards for human occupants.        

 

Cats and Dogs

They are also considered as pests, because they are hosts for pathogens such as salmonella and campylobacter in their intestine, mouths or coat and paws, where contamination can occur through feces or urine.