Moths of economic importance infesting stored products: Selected notes on bionomics and identification
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Moths, skippers and butterflies are some of the most common and familiar insects and make up the insect order Lepidoptera. The name of the order comes from two Latin derivatives meaning "scaly wings" which refers to the tiny flat scales that cover the two pairs of membranous wings like shingles and gives them their characteristic colours and patterns. It is the second largest order of insects exceeded only by the Coleoptera or beetles, and contains approximately 150,000 described species. They range in size from tiny leaf-miners with wingspans of only 3 mm, to the huge cossids, saturniids and birdwing butterflies (Ornithoptera spp.) which have wingspans exceeding some 25 cm. The colouring and elegance have given them considerable popular appeal, while the destructive qualities of the larvae of many species establish the economic significance of the order. There are Lepidoptera in various diverse habitats such as arctic tundras to tropical forests to arid deserts and in every environment they play a major ecological part in their relationship with plants and other animals.
Despite their numbers and complexity, the members of this order are surprisingly alike with respect to their food source, nearly all of which are green-plant feeders concentrating primarily on the foliage. The great majority of larvae chew up leaves, many tunnel inside leaves feeding on the soft juicy tissue, while some bore into fruits, seeds, plant galls or wood, or are scavengers on dead and decaying plant or animal matter. Some adults do not feed at all, while others usually visit flowers for nectar and many are attracted to sap, juicy carrion, excrement or rotting fruit.
Moths and butterflies are therefore primary consumers feeding directly on plant matter and transforming this into animal matter, a process in which they are not rivalled by any other group of land animals, either numerically or quantitatively.
Unlike many other insect orders, only a small minority of moths feed on other animals as parasites or predators (i.e., members of the subfamily Gerydinae, the harvesters, while most other Lycaenid caterpillars are cannibalistic).
The evolution of the endopterygotes based on fossil history begins in the Permian period 250 million years ago, in which the remains of Neuroptera (lacewings, antlions and snakeflies) and Mecoptera (scorpionflies) are found. It is not difficult to imagine that an ability to fly might have evolved several times but it is unlikely that the same pattern of wing venation would have evolved more than once, which strongly suggests a monophyletic origin of the Pterygota. The Neuroptera remain as rather an isolated case, but evidence suggests from studies on wing venation that the Mecoptera played a more crucial role in endopterygote evolution. Loss of some veins and modification of others has led to the Trichoptera (caddie-flies) and Lepidoptera in one direction and to the Diptera and Syphonaptera (fleas) in another, while the Coleoptera and Hymenoptera were probably derived from a neuropteran ancestor. The first beetles appeared in the Permian period and there are traces of Hymenoptera from the Jurassic, but the explosion of diversity in the main orders did not begin until the end of the Cretaceous period 70 million years ago, when flowering plants began to appear (see Table 1). The adaptation for feeding on the nectar of flowers by a modification of the mouthparts, has allowed the Lepidoptera to make the most of the rich food resources made available by the flowering plants that are insect dependent for cross-pollination, a symbiotic process called entomophily (see Fig. 1).
General life history of the order
Like other endopterygotes such as beetles, flies and wasps, moths, skippers and butterflies go through a complete metamorphosis (holometabolous) involving a decided morphological change from the immature forms to the reproductively mature adult or imago forms. This "complete" or "abrupt" metamorphosis involves four distinct stages: egg, larva (or caterpillar), pupa (or chrysalis) and finally, the adult.
Two types of eggs maybe distinguished in the Lepidoptera. A flat type with the micropyle at one end, and an upright type with the long axis vertical and the micropyle positioned at the top. They are small, usually hard-shelled while the chorion is sometimes smooth or may exhibit a regular or irregular sculptured pattern with prominent ribs. In some species, the female may produce as many as one or two thousand, laid individually or in groups.
The larva or caterpillar, exhibits a clear division into head, 3-segmented thorax, and 10-segmented abdomen, whose chief function is to eat, digest and grow. The head capsule is heavily sclerotized while the prothorax carries a large dorsal sclerotized area, the prothoracic shield. They are per ipneustic, bearing one pair of lateral mesothoracic spiracles and one pair of spiracles on segments 1-8 of the abdomen. The antennae are usually short, 3-segmented, and bear several sensilla. Posterior to the antennae, the eyes are merely represented by two groups of 6 simple ocelli which maybe reduced in number or even absent. The mandibles are normally well developed and dentate, adapted for biting and chewing, but are modified in the sap feeding instars of leaf-miners. The maxillae are well differentiated with 3-segmented palpi, while the labium or second maxillae bears a median spinneret connected to very large silk glands and a pair of minute, lateral 2-segmented palpi. There is nearly always three pairs of 5-segmented thoracic legs, which terminate in a single claw. Those found in stored foods may be immediately distinguished from the larvae of all other insects occurring in similar situations by having paired pseudopods or prolegs on abdominal segments 3-6 and 10. Each of these prolegs is armed with a fine, curved apical "teeth" (crochets) which maybe of different lengths to form a definite series and are usually arranged in a circle. The head and body of the larva bear setae and punctures which follow distinct patterns (chaetotaxy) and these setal maps are widely used for the identification of larvae.
The larva is the nutritive stage of the life cycle and consequently possesses an enormous and efficient digestive tract. As the larva grows, it must shed its entire outer covering or cuticle to accommodate the increase in size. This occurs a number of times, and at each moult forms a new and larger head capsule and integument, discarding the remains of the old cuticle. Sometimes the larval life may last a couple of weeks although is usually longer, or may extend as long as three years in some species under extreme or unfavourable conditions. Many larvae are relatively plain in shape and colour, with only sparse hairs such as the moth larvae that infest stored products, but others especially those that feed out in the open, show a startling variety of colours and patterns and may bear dense hairs or spines or strong projections which perform a protective function.
When fully grown the larvae moults for the last time and transforms into a pupa. During this seemingly inactive quiescent stage, incredible histological, physiological and morphological changes are taking place internally as the adult structures develop. The pupa maybe formed inside a silk cocoon spun by the larva while a great many are formed in a cell in the ground. Most moth and skipper pupae are quite plain, smooth and brown while many butterfly pupae (or chrysalids) are irregularly shaped, often metallic and brightly coloured.
The pupae and pharate adult stages of all primitive endopterygotes are passed in a cell or cocoon of some kind, and it is only in some specialized Coleoptera, Lepidoptera, Hymenoptera and Diptera that do not possess one. In the higher Diptera (sub-order Cyclorrhapha) and some others the last larval cuticle forms the puparium which somewhat resembles a barrel (coarctate pupa). An exarate pupa is one in which the appendages are free and not cemented to the body wall conversely, an obtect pupa has the appendages more or less strongly cemented to the body, presumably by tanning of a particular protein in the moulting fluid, and the cuticle is much more strongly scterotized than in exerate pupae (see Fig. 2).
Various modifications have evolved to allow the adult to excape from its cell or cocoon. In primitive forms, the pupal cuticle is not generally shed by the adult, until is has escaped by using its pupal mandibles (decticous pupae). A pupa without articulated mandibles, and therefore one which cannot be utilized by the pharate adult, are called adecticous pupae.
Fig. 1. Modified mouthparts of a butterfly, adapted for sucking. (Source: "Pests of stored products" by J. W. Munro)
Fig. 2. The three kins of pupae: (a) exarate; (b) obtect; (c) coarctate. (Source: "Pests of stored products" by J. W. Munro)
The methods of emergence of pharate adults of this kind are very varied. When the pupa is exarate, ecdysis normally occurs within the cocoon and the adult simply bites its way out, as in most Coleoptera and Hymenoptera. When obtect as in most Lepidoptera, the mobile abdomen of the more primitive forms are often armed with backwardly directed dorsal spines which force the abdomen forward when the body is wriggled, and the pupae partially emerge from the cocoon before adult edysis takes place. Such pupae often possess cocoon cutters on the head as in both Lepidoptera and Dipteral
In the more advanced forms, ecdysis occurs within the cocoon or shelter which often has a weak area to allow easy escape for the newly emerged adult. Some regurgitate a fluid which softens the silk while others cut a hole means by means of a sharp hook on the forewing.
On emergence, the adult is very much different from the workaday larva from which it developed. Its whole life is oriented towards sensitivity and mobility, enabling it to carry out its primary functions of mating, multiplying and dispersing its species. Feeding, though important is secondary. Its two large compound eyes are excellent for detecting motion, patterns and colours of preferred flowers, and for potential mates. If simple eyes are present, they are normally paired one above each eye. The antennae are many segmented, with or without scales, the flagellum of the male usually more specialized than the females and vary greatly in structure.
Mandibles are usually absent and rarely functional, while the maxillae (galeae) are greatly elongated, usually grooved internally and fastened together by interlocking spines to form the tubular haustellum (proboscis) which is coiled beneath the head. In some cases, the proboscis is vestigial or absent, therefore adults cannot feed and subsist on food reserves stored when they were larvae. Labium is small, usually with well developed 3-segmented palpi.
The prothorax is small compared to the mesa-and metathorax which house the powerful flight muscles. Wings sometimes reduced or absent in females of some families such as Cossidae, Oecophoridae, Lymantriidae and Arctlidae. Similarly, the three pairs of well developed thoracic legs maybe reduced as in the Numphalidae and the hind legs in some Geometridae.
They are usually 5-segmented with 5-segmented tarsi which often bear various tibial spurs or bristles and in some species, sensitive taste structures on the soles of the feet capable of detecting minute concentrations of sugars which result in a reflex coiling of the proboscis. The abdomen is usually 10segmented with functional spiracles on segments 1-7. A pair of auditory tympanal organs are situated laterally near the base in the Pyraloidea and Geometroidea, while ;hey maybe present on the metathorax of most Noctuoidea.
Many species are weak fliers, and then for only comparatively short distances. Others however are capable of sustained flight for hours or days, or a fast darting flight and some are even capable of flying backwards. The North American monarch, Danaus plexippus, is deservedly famous through its regular southward migrations and has crossed the Pacific oceans and colonized Australia and New Zealand. Members of Pieridae, Numphalidae and Hesperiidae undertake regular migratory flights, while the noctuid, Agrotis infuse (Boisd) a serious pasture and field crop pest, is known to undertake a remarkable annual twoway migration.
The Lepidoptera cannot physically resist attacks with strong jaws, hard shells, or poison stings as many other insect employ, and have consequently evolved other means of protection and adaptations that are unparalleled in any other group of animals. Many make cases in which the live hidden during critical periods, others have adaptations in form and colour that enable them to escape unnoticed or deceive predators, some are clothed in poisonous hairs and spines or loose scales which enable some moths to escape from spider webs, while others have developed chemical defenses from the plants they consume, and have also developed aposematic or warning colourations to advertise these defenses. Many unprotected species have taken advantage by mimicing these colourations and therefore gain similar protection, while others may resemble distasteful or poisonous wasps and Iycid beetles.
The classification of the Lepidoptera is exceedingly complex, and is based on many technical features. Opinions vary considerably, but the order is divided into four suborders, twenty-three superfamilies, and in excess of one hundred or more families. Despite their prominence and familiarity, butterflies are grouped in one super family - the Papilionoidea - and skippers which are often confused with the butterflies, another-the Hesperoidea, which together comprise no more than 10% of the order, the rest being moths. These is no definite demarcation between butterflies, skippers and moths since many overlapping characteristics exist. Butterflies are thought to be diurnal while moths are nocturnal, but many moths are day-fliers. Butterflies are generally brightly coloured while moths are dull and drab but in many instances the reverse occurs. Butterflies have clubbed antenae while most moths are hairlike tapering or plumy, but some moths also possess clavate antennae. The majority of moths have a special wing-coupling apparatus (the frenulum) while butterflies rely largely on the friction of overlapping parts of the fore and hindwings (the humeral and jugal lobes), the amplexiform method of coupling. But a great many moths do not possess this mechanism. At rest, the wings may be folded in various ways, the ancestral method of folding roofwise over the abdomen is characteristic of most moths. In the Papilionoidea, the wings are generally held back to back above the body. In the true skippers, flight is generally very fast, without the characteristic fluttering as in the butterfly flight. The antennae has a thinner end portion beyond the club and is hooked at the tip.
Lepidoptera associated with stored products are all moths and cause damage only in larval stages. One species the Angoumois grain moth, Sitotroga cerealella (Oliv.) is capable of destroying sound, unbroken grain kernels, but most infest broken damaged kernels or milled products. This distinction provides a grouping of species into major and minor or primary and secondary accordary to their pest potential. For example, species such as Ephestia Keuhniella (Zell.), Ephestia cautella (Walk.), Plodia interpunctella (Hbn.), and Hofmannophila pseudospretella (Staint.) the primary pests of processed cereals but secondary pests of whole grain. However, while grain usually contains a proportion of broken grain, thereby allowing the establishment of secondary species as serious pests, especially if the moisture content is high. A common characteristic associated with larval development is the production of webbing. Adult moths rarely live longer than 14 days.
Some seventy five species, all of cosmopolitan distribution, are known to infest a range of stored products. The major species are small and exhibit a remarkable consistency in structure and appearance, which has led to difficulties in identification.
Identification of Larval Specimens
Moth larvae are best prepared for identification by placing them in a test tube containing either water or, preferably ten percent aqueous alcohol and heating the liquid until they are killed. This technique causes the larvae to become fixed in an elongate position which is most suitable for easy handling and identification. The fine hairs or setae on the larvae and their position, relative to each other and to the spiracles, are used as a diagnostic feature. The presence or absence of small brown sclerotized areas around the base of some of these setae is also a distinguishing areas around the base of some of these setae is also a distinguishing feature; such as in the genus Ephestia, the presence of these dark areas gives the larvae a characteristically speckled appearance.
Identification of Adult Specimens
The coloured patterns formmed by the minute scales which cover the top side of the forewings of adult moths provide a useful means of direct visual identification. When the moth is sitting at rest these forewing patterns are readily visible and the hindwings are hidden. The scales, however, are easily removed by rubbing, and adult specimens of the stored products species then appear remarkably similar; for example, moths which are held in a collecting jar will rapidly become de-scaled by their fluttering which renders direct identification dificult. Other more accurate methods of identification which rely on alternative diagnostic features must be employed when this occurs.
To identify moths by means of the pattern on the wings, it becomes necessary to be familiar with the more important parts of the wings. The margin of the wing nearest the head is the costa, that nearest the body, the dorsum and that farthest from the body the termen: the costa and the termen meet at the apex, while the angle formed by the termen and dorsum is the tornus. In some moths, the apices of the wings are acuminate produced almost to a point. Almost all of the moths infesting stored products have similar wing patterns in both sexes, the exception being Paralipsa gularis, the stored nut moth.
Two structural characters are employed in identification of adults, namely the form of the labial palpi and the position of vein 8 on the hindwing. The labial palpi are paired 3-segmented appendages visible in front of the head and arising between the eyes from heneath. These structures should not be confused with the much longer thread-like antennae situated above the eyes, or with the legs attached to the underside of the thorax. The basal segment is small and inconspicuous, but the second and third segments display considerable diversity in form and scaling. Some may project horizontally in front of the head and resemble an open or closed beak, or they may be curved upwards or downwards.
Fig. 3. Larva of Ephestia kuehniella.
Fig. 4. Diagram showing parts of a moth. (After Hintor and Corbet, 1972)
Moth wings are thin membranous expansions of the body which are strengthened by hollow veins which carry blood. The cell pattern formed by the vein structure can be utilized as a diagnostic feature. To examine the veins the wings should be removed by cutting the base with a fine scalpel and placing them in xylene. The scales can then be removed by scrubbing the immersed wings very carefully with a fine brush to expose the veins; the structure of veins can then be examined using a X 20 hand lens.
From the venation of fossil insects and living primitive insects it is possible to construct a hypothetical primitive venational pattern from which the venation of living insects can be derived. This pattern is shown in Fig. 5 and the name and convex or concave nature of each vein is indicated by positive and negative signs).
Atrophy of certain vein stems in both fore and hindwings of the Lepidoptera, have resulted in an approximately triangular area called the discal cell and the veins closing it are known as the discoidals. Normally, the forewing has 10 veins arising from the discal cell or originate from veins arising from the cell, while 6 veins originate in this manner on the hindwing, but there are many variations with some veins absent or fused with one another.
In the Tineidae, vein 8 of the hindwing is free throughout its length and is situated near the costar margin of the cell, while in the Pyralidae, it often is united with vein 7 beyond the discal cell but separates again before reaching the costa (see figure).
Adult moths which are very similar in appearance or which have had their wings or wing patterns damaged may be positively identified by examination of their genitalia. This may be done by removing the abdomen soaking it in a ten percent aqueous solution of potassium hydroxide for twenty-four hours and then carefully dissecting the genitalia from it. However, it is emphasized that an examination of this sort is almost impossible with a hand lens and genitalia obtained by this means are best examined by mounting them on a glass slide in a suitable medium for microscopic study (Winks, 1975).
BIOLOGY OF STORED PRODUCTS LEPIDOPTERA
This term includes only those moths capable of destroying sound, unbroken grain kernels when stored at or below the safe moisture level. They are not as abundant in terms of the number of species involved, as compared to the flour moths or secondary pests, which are principally pests in broken or damaged kernels or in milled products.
Sitotroga cerealella (oliv.) - The "Angoumois Grain Moth"
This moth is the only species in this family which is associated with stored products.
A small buff or yellow-brown moth with a wing span of approximately 12 mm; the wings are narrow with wide fringes and the hindwings narrow sharply to points at the apices. When the moth is at rest, the wings are folded in a sloping manner over the abdomen, the antennae point backwards and are slightly raised above the wings, while the labial palpi are raised upwards like two horns (Fig. 7)
This moth is capable of attacking grains in the field and in store. The eggs are laid on the surface of the grain and after hatching the larvae bore into the grain and complete their development within the endosperm. The larvae are always inside the grain kernel except in the first instar. Under optimum conditions the life cycle is completed in approximately four to five weeks. Each female lays an average of 40 eggs deposited either singly or in clusters, but individual moths have been known to lay as many as 400 eggs. The eggs which are white when first laid, soon change to a reddish colour and are laid on wheat heads, exposed tips of corn ears in the field. or in stored grain. After hatching, each larva crawls to a kernel of grain and often spins a small entrance cocoon to assist in boring into the hard kernel. Aften entering the grain, it feeds on the endosperm or the germ until fully developed. It then channels out a groove to the outside of the seed and makes a weakly fastened flap over the exit hole. The last larval instar then spins a silken cocoon in preparation for the transformation into a reddish brown pupa. The adult moth emerges after pushing open the flap prepared by the larva, since the adult is incapable of chewing its way out. The larval period lasts from 2 to 3 weeks, and pupates in 5 to 6 days.
Fig. 5. Hypothetical primitive pattern of wing venation. (Based on various authors). C, costa; SC, subcosta; R. radius; Rs, radial sector; M, media; MA, anterior media; MP, posterior media; Cu. cubitus; A, anal.
Fig. 6. Ephestia elutella: wings de-scaled to show venation. (Numerical system of notation after Hinton and Corbett, 1972)
Fig. 7. Neuration of S. cerealella (Oliv.), $:
Fig. 8. Sitotroga cerealella (Olivier), the "Angoumois grain moth".
Fig. 9. Sitotroga cerealella (Oliv.), the "Angoumois grain moth". Dorsal view of resting adult.
The advent of combine-harvesting has restricted the distribution of this pest; infestation often occurred in the field when harvested wheat was stacked to dry, but combining now reduces the possibility of this type of infestation occurring. Field infestation is now restricted to sorghum and maize (corn) when these grains are harvested without threshing or shelling. In bulk grain, infestations are restricted to the surface layers only.
This family contains 2 species associated with stored products, Sathrobrota rileyi (Walsingham) the "pink corn worm" or "pink scavenger caterpillar", which is a pest of cotton and corn in the southern United States causing considerable damage in both the field and storage, and S. badia Hodges, which is of little economic importance.
Sathrobrota rileyi (Wals.) "pink scavenger caterpillar" slightly smaller than the Angoumois grain moth, the forewings banded and mottled with yellow, reddish brown and black. The pale grey hindwings are very narrow and edged with long fringes.
A reliable indication of the presence of this pest is a large amount of loosely webbed frass that fills the interstices between the kernels or the cavities of partially consumed kernels. The white eggs are normally laid singly but sometimes in small groups of two or three eggs. The pinkish larva feeds on the seed, husk or cob with equal voracity and is capable of inflicting serious damage to corn if allowed to mature in the field.
TINEIDAE ·"clothes moths"
Many of the species of this family feed on animal products such as wool, fur, skins and rarely infest stored cereals or seeds. However, they are sometimes encountered in established infestation where the larvae are scavenging on dead bodies of other insects. The major species likely to be identified in these circumstances are:
Trichophaga tapetzella (Linnaeus). The white tip clothes moth.
Tineola bisselliella (Hummer). The common clothes moth.
Tinea pallescentella Stainton. The large pale clothes moth.
Tinea pellionella (Linnaeus). The case-bearing clothes moth.
Niditinea fuscipunctella (Haworth). The brown-dotted clothes moth.
Some species, however, will feed on dried material of plant origin.
i) Nemapogon granella (Linnaeus) "European Grain moth"
A small moth (wingspan 10-14 mm) approximately the same size as S. cerealella but is creamy white and heavily mottled with brown. It infest all kinds of grain, both in the field and in storage. The larva feeds on the grain and webs the kernels together but is generally considered a minor pest of grain and spillage in temperate climates, and is found through the northern states of the US, but is less abundant than S. cerealella. It is more important on rye, less important on wheat and of no economic importance on barley and oats.
ii) Setomorpha rutella Zeller. The tropical tobacco moth
This species infests seeds, tobacco, stored cereals, flour, and dried vegetable materials in tropical and subtropical regions. It is of little economic significance except in stored tobacco.
There are 9 species of the family associated with stored products, while only Corcyra cephalonica (Staint.) is of economic significance on stored grain and seeds. Galleriinae is considered to be a subfamily of Pyralidae by Hinton (1943), Corbett and Tams (1943) and Hinton and Corbett (1972), which also includes the Phycitinae as well. Wing venation of the forewing separates the two subfamilies according to Corbett and Tams (1 943).
Corcyra cephalonica (Stainton). The rice moth.
A medium-sized moth, with a wing span of approximately 25 mm, the wings of which are uniformly pale buff brown or grey with the veins slightly darkened. It has a tuft or crest of scales on the head, the wings are folded in a sloping manner over the abdomen with the antennae lying straight on the wings. Labial palpi are colse together and straight giving the appearance of a closed beak. It is a cosmopolitan species more important in tropical areas and attacks a wide range of commodities including whole grain particularly rice, milled and processed cereal products, oilseeds, and nuts, and occasionally dried fruits. Larvae produce dense webbings, and when feeding on grain form silken tubes, which bind the grain kernels together into lumps.
The moths live for 1 to 2 weeks, in which time the female lays betwwen 90 and 200 eggs, laid indiscriminately and loosely in the grain mass. The incubation period lasts 4 to 6 days, the larval period 3 to 4 weeks and the pupal stage, approximately 10 days; while the total life cycle requires 97 days at 24°C, the optimum being between 28°C-32°C.
Although it is frequently assumed to be predominantly a pest of rice, it is found that most other cereal grains and occasionally oilseeds and pulses are attacked. It is essential that the food source contains either linoleic acid or biotin, and the species flourishes on a low protein intake diet, but is limited by low levels of carbohydrates. Thus cereals are considered the best diet and at 30°C and 70% RH, larval development takes 35.5, 39, 50 and 78 days on pearl millet, broken wheat, chick peas and black gram respectively. The number of larval instars is variable, generally seven to eight, with the males having one fewer than the females, but both sexes taking about the same time to develop.
The females mate only once during a 1-2 day period after emergence, and if copulation has not taken place, the females lay unfertilized eggs and are disinclined to mate. Males mate several times (up to four times in a period of nine days) thus at a normal 1:1 sex ratio, many males may be deprived of the opportunity to copulate.
C. cephalonica is a cosmopolitan pest of mills in tropical climates where it fills the niche occupied by E. Kuehniella in more temperate climates. The contamination of the food caused by webbing activity of the larvae, larval galleries, cocoons and frass may prove more economically significant in terms of reconditioning of the grain to make it saleable than the actual weight loss incurred through larval feeding.
Paralipsa gularis (Zell.). The "stored nut moth"
The forewings are greyish buff marked in the female with a distinct black patch or spot, while in the males, the spot is smaller and has a zig-zag, reddishyellow streak across the hindportion of the forewing. The wingspan is approximately 15-20 mm and is particularly attracted to walnuts, almonds, hazelnuts and ground nuts, but attacks a wide range of other commodities.
Among the flour moths are some of the commonest and most serious of grain pests. They are designated as secondary grain pests because they seldom attack sound undamaged kernels and prefer broken grains, grains previously damaged by the primary grain feeders, and more especially milled and processed cereal products. The Indian meal moth, Plodia interpunctella (Hubner) and the meal snout moth Pyralis farinalis Linnaeus may under favourable conditions become established in whole grain causing damage by consuming the germ. This is especially true if the grain is stored at an unacceptably high moisture content.
The 9 species of this family associated with stored products are widely distributed and are general feeders in the larval stages upon cereals and cereal products. Infestations are indicative of poor storage hygiene associated with damp or "wet" storage conditions. Pyralis and Aglossa are the most important genera.
i) Pyralis farinalis (Linnaeus). The moth meal
A cosmopolitan species, more plentiful in temperate than tropical areas. The wing span is approximately 25 mm, and the forewings are characteristically patterned - overall light brown with basal and apical purple borwn areas demarked by wavy transverse white lines. It breeds mainly in grain spillage, moist flour, bran, peanuts and hay that have been held for some time in damp conditions. Pyralis manihotalis (Guenee) is a cosmopolitan species that appears to take the place of P. farinalis throughout tropical regions.
The female lives for about one week and lays 200400 eggs (average 250). The mealmoth larvae is white and when fully grown some 25 mm long. The larva shows a contrast between the black of the head capsule and thoracic shield and the white of the remainder of the body, which is often tinged with orange towards each end. The larvae spin peculiar tubes of silk that contain mixed particles of food material. These- tubes are extremely resilient, and the larvae rest feed from the openings at the ends. When fully developed, the larvae migrate from the tubes, spin silken cocoons which are also camouflaged by adhering food particles.
Although common, this moth is not a serious pest of stored grain as it prefers damp conditions and commonly breeds on out-of-condition grain or grain spillage. The presence of this pest is usually indicative of poor hygiene and damp local conditions. It has, however, been recorded as attacking sound grains which have a relatively high moisture content.
Mealmoth larvae often attract much attention due to their capacity to "web-up" and bind together seeds of various kinds, as well as their capacity to cut through hessian sacks causing considerable damage and spillage, especially when present is large numbers.
ii) Aglossa caprealis (Hubner). The murky meal caterpiIlar.
A medium-sized moth, with a wing span of approximately 25 mm. The basal quarter of the forewing is deep ferruginous brown, outwardly defined by a narrow highly zigsagged pale pinkish buff antemedial line, sloping outwards from costa to dorsum; the pale, narrow, sigsagged postmedial line touching, or almost touching the termen between veins 2 and 6. Hindwing is greyish white and unmarked. It is cosmopolitan, and found associated with damp grain spillage, clover, and lucerne hay, but is of minor importance.
This family contains several notable species. These are Ephestia cautella (Walk.), Ephestia elutella (Hbn.), Ephestia kuehniella (Zell.), and Plodia interpunctella (Hbn.). They infest a wide range of commodities from cereals and tobacco, to dried fruits and nuts. Diapause has been recorded from species of the family. It is emphasised that it is usually necessary to examine genitalia to confirm identifications of species, particularly within the genus Ephestia.
i) Plodia interpunctella (Hubner). The Indian meal moth.
A small cosmopolitan species with a wing span of approximately 20 mm, the forewings of which are characteristically red-brown with a copper lustre, the inner third being creamy white. When the adult moths are at rest, the wings are folded touching each other closely along the posterior margin and lie flat on the abdomen. The antennae lay crossed over the wings, and the labial palpi are slightly separated and project straight forward giving an appearance of an open beak (see Fig. 13). It is a serious pest of stored grains, oilseeds, and of processed and milled products, nuts, dried fruits, and chocolate. Females lay approximately 200 eggs either singly or in clusters and the larvae burrow into the food mass where they remain till completion of larval growth.
When fully grown, the larva is approximately 1214 mm long, and is sometimes dirty white, varying to greenish and pinkish hues. The larva spin a silken cocoon and transform into a light brown pupa, as well as creating webbed sheets in the grain mass. The larval period is about 3 weeks, but is known to live under adverse conditions for up to 2 years. The pupal stage lasts approximately 2 weeks. Pupation occurs in crevices in the fabric of the surrounding store, similar to Ephestia spp. Larva are moderately resistant to low temperatures and overwinter in this stage; the life cycle in summer is 4 to 6 weeks. This species does not reach the high population levels in grain often seen in other members of the family and infestations often tend to be localised.
P. interpunctella gets its common name from the United States where it was recorded as a pest of "Indian corn" or maize. It is perhaps of S. American origin, but is now cosmopolitan; and attracts more at tension as a pest of dried fruit particularly raisins, currants and sultanas.
ii) Ephestia elutella (Hubner). The tobacco moth.
The adult is a small, grey or brownish-gray moth with a span of approximately 16 mm. The moth is similar in appearance to E. cautella, with with markings on the top side of the forewings very similar, while E. elutella the outer transverse band is pale, weel defined, wavy and bordered on each side by a narrow dark line. It is a cosmopolitan species which is most prevalent in temperate regions, attacking almost all grains, ground cereal products, tobacco and dried fruit. It is common in tropical and subtropical areas where its occurrence is restricted usually to stored tobacco. Females lay approximately 200 eggs which are deposited singly or in small groups on the food material. Winter is passed in the larval stage, in loose cocoons in cracks or crevices. The life cycle maybe completed in 5 to 6 weeks, while the final instar larva is responsible for enveloping commodities and surrouding structures in dense webbing during their migration.
Control of this moth is often difficult because the mature larvae finds pupation sites in the surrounding storage structure which renders it inaccessible to normal applications of contact insecticides. When feeding on raw cereals, the larvae will preferentially attack the germ.
Ephestia cautella (Walker). "the tropical warehouse moth".
The adult moth is cosmopolitan, grey in colour with a wing span of approximately 20 mm. The upper sides of the forewings are marked with two transverse bands, the inner one being straight, dark and continuous with a pale band along its inner edge.
Fig. 10. Neuration of S. rutella Zell., (after Diakonoff). (Note: Vein 8 of hindwing completed separated from vein 7, a distinguishing feature between the Tencid and Pyralid venation)
Fig. 11. Neuration of Corcyra cephalonica (Staint.),
Fig. 12. Neuration of Pyralis farinalis (L.)
Fig. 13. Plodia interpunctella, "the Indian meal moth". Dorsal view of resting adult.
As with other insect pests, the time required for this moth to complete its life cycle from the egg to the emergence of the adult varies greatly according to environmental conditions. Under the optimum conditions of 30°C-32°C and 70%-80% relative humidity the cycle is completed in approximately thirty days and the egg, larval and pupal stages account for 10%, 70% and 20 % of this time respectively. Development does not take place above 36°C or below about 14°C and at 15.5°C the life cycle is extended to approximately 145 days.
The female moth lays about 250 eggs loosely in the infested commodity. Pupation takes place in small aggregates of grain held together with webbing.
This is the most important moth pest of stored grains in Australia, being particularly active in the warmer states. The larvae will feed on a wide range of commodities including grains, grain products, dried fruits, nuts, cacao beans and chocolate. They can attack whole sound grains but prefer the seed coat to be slightly damaged; grain which is combine-harvested is usually damaged to a sufficient degree to render it suitable for infestation by this pest.
As with some of the other species in this family, E. cause/la tends, by preference, to attack the grain germ, moving from grain to grain consuming these parts; damage to the commodity is therefore much greater than the actual weight of grain consumed due to this high spoilage factor. Contamination of the infested commodity also occurs from the large quantity of webbing which is spun over its surface; in heavy moth infestations of stored grain this webbing looks like a fine white film covering the whole surface of the bagged stack or bulk.
E. cautella is also a serious pest in tropical flour mills where it infests ground cereal products. Webbing produced by the moth larvae is often responsible for damage to milling and conveying equipment.
Ephestia calidella (Guenee), and Ephestia figuliella Gregson, are of minor significance infesting dried fruits and meal in temperate regions.
Ephestia kuehniella (Zeller)-The Mediterranean Flour Moth.
E. kvehniella which is a cosmopolitan species native to Europe, has a wing span of approximately 25 mm and is slightly larger than the two members of this genus which have just been described. The top side of the forewing is slate-gray in colour and the inner transverse band is almost z-shaped and consists of dark streaks and spots; it does not have a pale band along its inner edge.
The complete life cycle may require as little as six to seven weeks under optimum conditions. The female moth lays between 50 and 300 eggs during a period of five to seven days and there is no egg laying below 12°C or above 34°C. In temperate climates there is only one generation per year in unheated stores and four to six generations in heated flour mills. The life cycle may be completed in 8 to 9 weeks under optimum conditions.
The larvae of this moth are prolific spinners of silk and it is this characteristic which has made them a serious pest in flour mills.
The copious webbing which they produce blocks milling machinery, conveying ducts and equipment, and generally interferes with production; large clumps of webbed flour also provide harbourage for other insect pests. Under experimental conditions the moth will breed in ground cereal food with a moisture content as low as 1%-2%; it very rarely attacks stored whole grains.
This pest was once widespread in Australian flour mills but its incidence is now restricted due to the introduction of more efficient control methods particularly fumigation specifically aimed at curtailing its development.
In tropical climates E. cautella (Walk) usually replaces E. kuchniella as the major Phycitid pest of flour mills.
General Notes on the Biology of the Phycitids
The Phycitids are undoubtedly the most important members of the stored product Lepidoptera associated with milling premises and grain storages. Consequently, efforts have been directed towards a better understanding of the behaviour of these moths with a view to more efficient control either from new techniques or more effective usage of existing control measures. The most vulnerable stage is the adult, but little is gained by controlling adults unless they are prevented from producing viable eggs, since the larvae is the most damaging trophic phase.
Although most females mate once only, up to 7 matings have been reported for some individuals. During mating activity, females of Phycitid moths emit sex pheromones to attract the males, and males emit pheromones to stimulate copulation. The nature of these pheromones is complex and is species specific although individual components may be produce by a number of species.
The fecundity of females of E. cautella has been found to be related with their weight there appears to be no correlation between longevity and weight. The fertility of males of E. cautella persists for up to 8 matings with subsequent matings resulting in decreased egg fertility and fecundity of females. Females of E. cautella exposed to a lethal dose of insecticide discharge their eggs by involuntary abdominal peristalsis prior to death. Eggs have been found to be equally viable to those discharged normally, and this oviposition response to stress, has enormous implications in control using insecticides.
First instar larvae commence feeding immediately, forming small galleries of silk and frass. In large populations larvae may enter a migratory phase which aggravates the problems associated with silk production. In E. keahniella, larvae have been observed to secrete a droplet of fluid when encountering other larvae in dense populations causing increased wandering in the larvae, increased developmental period, reduced fecundity in the adult and influence the choice of egg-laying sites. These secretions are therefore density dependent and density regulating.
Mature larvae normally leave the food medium in which they develop and pupate within a cocoon of webbing in adjoining cracks or crevices. In bulk grain, the cocoon is constructed within several kernels of grain causing familiar grain aggregations.
Diapause has been observed to occur in a number of the Phycitids but is more a feature of populations in colder climates. In E. elutella and P. interpunctella, late instar larvae enter diapause in response to shortened photoperiod or to crowding. Again diapausing larvae increase the problems of obtaining sufficient control by insecticides due to their higher tolerance.
The presence of species from this family, 3 of which are associated with stored products, is indicative of poor hygiene and damp conditions. The hind wings are acutely narrowed at the tips, but less so than members of Gelechiidae, and generally have a larger wingspan (12-22 mm).
i) Hofmannophila pseudospretella (Stainton). The brown house moth.
A small to medium-sized moth (15-22 mm wingspan), the forewings of which are dark brown or bronze-brown with a number of blackish brown flecks. The larvae are omnivorous scavengers feeding on spillage, bagged flour, seeds, dried fruit, and clothes. Larvae prefer high humidities (80% R.H.) for development, and the life cycle in Summer is completed in 8-12 weeks, but varies between 152-266 days at 24°C and 90% R.H. to 192-440 days at 20°C and 90% R.H. Although the developing larvae require high humidities, the eggs and resting (diapause) larvae are tolerant to dessication. Under most conditions, H. pseudospretella caterpillars enter diapause which may be prolonged and in temperate climates is univoltine (i.e., only one generation per year). According to studies by Woodroffe, the only biological check on the increase of Hofmannophila is the predacious prostigmatid mite, Cheyletus cruditus. Coombs and Woodroffe have also reported an interesting interaction under high population densities of H. pseudospretella in bulk wheat, where numerous mutilated beetles were found trapped in the copious amount of webbing on the surface. Presumably the caterpillars had been responsible for biting off the appendages.
ii) Endrosis sarcitrella (Linnaeus). The whiteshouldered house moth.
This moth has similar habits and is often found with H. pseudospretella. It is responsible for more damage to stored spoducts particularly grain in bag stacks, and is less a scavenger than the previous species.
The head and "shoulders" (prothorax) of this moth are conspicuously white; the upper side of the forewing is shining buff or grayish-white and speckled with dark brown and blackish spots. The wing span is approximately 17 mm and the hindwings are slightly narrowed towards the tip but not nearly as noticeably as those of S. cerealella.
The adult female of this species lays between 50 to 230 eggs and lives between five to nine days. Complete development from eggs to adult requires 235 days approximately at 10°C and 62 days at 24°C and 90% R.H. High humidity levels are required for completion of the life cycle. It is multivoltine producing several generations in a year.
This moth is of sporadic economic importance, while both H. pseudospretella and E. sarcitrella are often associated with birds' nests which provide harbourage for these insects in otherwise clean warehouse.
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