Description of Warehouse

Moth
(Ephestia elutella)

Habitat
Temperate species, widespread in UK. Indoors only in warehouses, food factories and shops on wide range of stored food. Sometimes on surface of stored grain. Damage by larvae only.

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Biology
Egg – larva – pupa – adult. Usually one generation per year.

Eggs   – whitish up to 200 per female on larval food over 2 week period. Larvae – caterpillar, whitish with brown head. Forms silk sheets on surface of food. Develop in 2–4 months with 5–6 moults. In autumn larvae migrate upwards on structure of food store. Most enter diapause (resting stage) to overwinter. A few pupate immediately.

Pupae – on structure in silk cocoon in autumn or, more usually, the following sprIng .

Adults – 8–1 C)mm long, greyish wings. Rest on structure when not flying. May fly between adjacent buildings. Appear in early summer and also sometimes in autumn.

Importance
Significant stored food pest causing contamination by silk and frass (droppings), and some direct damage. Related species also important (see text).

Control
Monitor with pheromone traps. Residual sprays on structure at appropriate time to kill resting adults or migrating larvae. Pyrethrin or pyrethroid space spray / mist to knock down adults. Larvae in foodstuffs by fumigation.

Distribution and Habitat

Common throughout temperate regions, the warehouse moth is apparently absent from the tropics. It is widespread in the UK. It is an indoor insect that thrives in protected environments such as warehouses, food factories and shops. Most stored food materials (animal and human) will be attacked, although white flour is not attractive to the larvae.

Biology

The emergence of adult moths starts in the spring and continues through to autumn, with the male moths flying in response to the pheromones released by the waiting females. Mating usually takes place on stacks of foodstuff, with the mated females laying up to 200 eggs over a two week period. Although the small larvae will easily penetrate most bagged and some bulk food stocks (and even well-sealed packages), the larger larvae tend to move towards the 

surface of the food material, and it is here that their habit of trailing thin strands of silk becomes obvious. Heavily infested foodstuffs will be covered with sheets of larval silk hanging in festoons from the edges of the stacks. After five or six moults the larvae are fully grown in the autumn, and they gradually migrate away from their food source and up the walls of the store.

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They usually stop at the first ceiling intersection, spinning a silk cocoon well attached to the structure. Only a small proportion of every population pupates immediately, the rest spending the winter months in a resting state called diapause. For these larvae late winter or spring pupation occurs giving rise to the extended adult emergence period mentioned above.

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The warehouse moth can withstand very low relative humidities (down to 30%), but is susceptible to low temperatures. It will only survive in unheated buildings in the winter if temperatures inside the larval food material do not fall below 10 °C.

Importance
 

This is the commonest and most serious moth pest of food storage in the UK. Although physical damage caused by the moth larvae can be considerable, contamination is usually far more important. The silk produced by the larvae is difficult to remove from foods, and may make packaging materials unacceptable. The frass (faecal pellets) combined with the silk and the inevitable sticking together of food particles produces an obvious level of contamination, even though this may be inside the finished packed goods. Cross-infestation by flying moths is possible and can sometimes be caused by infested packaging materials and pallets being brought into food manufacturing areas.

This species causes serious infestations in long-term grain stocks in Germany, although not significantly in the UK. However, a wide range of raw and processed materials is attacked including cocoa beans and manufactured chocolate products.

Control

Control of this species is best achieved by attempting to kill emerging adult moths in the summer months using a residual insecticide applied to likely moth resting places (especially on ceilings and upper walls). If a space spray is to be used it must be targeted to coincide with adult emergence. Moth pheromone traps (which contain a synthetic female sex lure) can help pinpoint emergence dates. However, space sprays on their own (even linked to a monitoring system) are unlikely to be able to kill all emerging adults before some mating and egg laying takes place.

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Since the larval stages are rather inaccessible to insecticide treatments (apart from fumigation) subsequent attempts at control should concentrate on the upward migrating larvae seeking a pupation site. Residual treatments of the structure using approved products should be timed to coincide with the migration period of the larvae.

 

Bulk foodstuffs can only be successfully treated by fumigation in which case a specialist company should be consulted.

 

Control of the other stored product moths is similar in principle to that described for the warehouse moth. In some species there may be more than one generation per year, particularly at higher temperatures.

Other Moths Associated With Stored Food
 

Tropical Warehouse Moth (Ephestia cautelIa) – also known as the dried currant moth, and almond moth. Possibly the most commonly occurring storage moth species worldwide and frequently imported into the UK. Very similar to the endemic warehouse moth but larvae often do not diapause and may not survive severe winters in untreated stores and factories. Life cycle, breeding requirements and damage potential are all similar to E. elutella . Larval identification is typically difficult but may be important for determining origin, and for the prevention/control of infestations.

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Mill Moth, or Mediterranean Flour Moth (Ephestia kuehniella) . This species has been endemic in Britain for over 80 years. It favours a cereal or cereal product-based diet and is the dominant moth pest in UK flour mills and flour stores and is also a pest in bakeries and shops. Larval silk production is a major cause of blockages of flour chutes and machinery, and can cause product contamination. The distinctly grey forewings and whitish hind wings of the adults may help in identification but larval characteristics are more reliable.

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Indian Meal Moth (Plodia interpunctelIa) . The adult moths are easily identifiable (if in good condition) by the distinctive forewing colouration: the third nearest the head/body is a creamy colour and the outer two-thirds are a copper brown (or reddish brown). The larvae may be prominently coloured yellowish or pale greenish, according to the predominant food eaten and they do not have the distinct black speckles of the previous three species. The Indian meal moth is commonly found on imported foods (peanuts, cocoa beans, dried fruit and some cereals) but is less common in the food industry. The larvae diapause and can survive cold winters in buildings and cause serious contamination of raw and processed human foods.

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Rice Moth (Corcyra cephalonica) . Adult moths are similar in size to Ephestia spp. but have uniformly coloured pale buff forewings without spots, although wing veins are slightly darker. Larvae are typical, whitish with a brown head. A cosmopolitan pest which is most important in the tropics where it often replaces the mill moth (E kuehniella) as a pest of flour mills. Larvae feed on a wide range of stored products including oilseeds (nuts), cocoa beans, rice, dried fruit, cereals, flour, millet and copra. However it is probably best known as a pest of rice and other cereals, hence the common name. Minimum development temperature is 18 °C. Often

imported from hotter climates, an infestation may continue to develop in the UK but the moth will eventually die out in unheated premises.