326 heilbron: brewing industry research foundation [Sept.-Oct, 1961 alreadyy welt characterized protein of suitable Conclusion J!? WKJ^^^^ It is an inescapable truth that the progress brewing process. therefore, to foretell when an investigation in fc) At a later date, as knowledge accumu- one division is likely to require the facilities lates, comparative work will be undertaken of its neighbours. For this reason, no attempt to determine the quantitative composition of has been made above to trace the immediate different varieties of barley with respect to inter-connections between individual divitheir protein constituents. sions# It must suffice to record that the (d) In addition to the projects outlined Foundation is designed to function as a above, the division will, of course, where it is unified whole rather than as a number of selfprofitable, work in collaboration with other sufficient divisions. In consequence, while divisions of the Foundation. the ostensible purposes of the many labora- (e) Finally, though not least in import- tones with their wide range of equipment ance, the less specialized equipment of the may at first seem bewildering, the Foundation division enables a programme of research to is in fact setting out along a few broad paths be started on the formation of foam in beer, of investigation, each being, it is believed, of and a study of the role of carbon dioxide in direct and outstanding ultimate importance this respect is being made. to the industry. MEETING OF THE MIDLAND COUNTIES SECTION, HELD AT THE WHITE HORSE HOTEL, CONGREVE STREET, BIRMINGHAM, ON THURSDAY, The following paper was read and discussed: 8th MARCH, 1951 Mr. B. V. S. Seed in the Chair PEST INFESTATION CONTROL IN BREWERIES AND MALTINGS By J. A. Freeman, B.Sc, Ph.D., A.RX.Sc. (Chief Entomologist, Ministry of Agriculture and Fisheries, Infestation Control Division) Received 22wd March, 1051 Primary and secondary pests which have been found in barley stores and in maltings are listed, and the life histories of the more important pests (grain weevil, saw-toothed grain beetle, khapra beetle, and rust-red flour beetle) and the types of damage caused are described; an account is given of the modes of spread of infestation and of conditions which favour insect development. Preventive measures include regular inspection of grain and containers, hygiene and attention to details of bin structure and storage practice* Control methods may be mechanical (screening), physical (heating), or chemical, the last involving the use of insecticides (e.g., DDT, y-bhc, pyrethrum) or fumigants (e.g., hydrocyanic acid, methyl bromide, carbon tetrachloride); precautions to be observed in the use of these materials are detailed. The conditions under which the malting saw-toothed grain beetles, flour beetles and of barley is carried out are particularly khapra beetles. Unlike conditions in flour favourable for the development of certain milling, however, insects cause little or no insect pests of stored products; the need to interference with the actual malting process, hold stocks of barley and malt for long In breweries some trouble is experienced periods encourages attacks by grain weevils, from time to time with ferment flies and
Sept-Oct, 1951] freeman: pest infestation control 327 cockroaches; by-products of brewing such as dried yeast are liable to severe infestation by spider beetles, but dried grains are seldom damaged. Insects in Maltings In the course of inspection of 117 maltings between 1943 and the end of February, 1951, by members of the staff of the Infestation Control Division of the Ministry of Agricul ture and Fisheries, over 80 species of insects and mites have been found. The general picture is still much the same as that found in 1938-39 by the survey carried out for the Department of Scientific and Industrial Research,1 despite the fact that imported grain, the main source of infestation, is no longer used. The insects found fall into two main groups. In the first (Table I) are those which are actually or potentially dangerous to barley and malt and to by-products of malting. The most important are the grain weevil (Calandra granaria Unn.), the khapra beetle (Trogoderma granariutn Everts), the saw-toothed grain beetle (Oryzaephilus surinamensis Linn.) and the rust-red flour beetle (Tribolium castaneutn Herbst.). The Aus tralian spider beetle (Ptinus tectus Boield.), although common, only breeds up to epidemic proportions when conditions are favourable. One of the worst cases known to the Division was an outbreak which occurred in 1942 in dried yeast which had been lying in store in the Manchester area for some two years. The second group (Table II) contains those insects which generally breed in dust and debris, and which are scavengers, mould feeders, predators and parasites. Few in this group ever increase sufficiently in numbers to require control, but their presence is often a sign of poor hygiene or undue toleration of the major pests. Indicators of bad hygiene are the false clothes moth {Hofmannophila pseudospretella Staint.) and the mealworm (Tenebrio molitor Linn.), both of which need long periods to complete their life cycles. Biology of the important Pests Grain weevil (Calandra granaria Linn.) This insect is not only well established in this country in granaries and farm buildings but is also regularly introduced from abroad. It readily overwinters both in the larval and adult stages, which are resistant to low temperatures. After mating, the female lays, on the average, some 100 eggs during a life of 7-8 months. Each egg is laid in a small hole excavated in the surface of the grain and this hole is sealed with a gelatinous secretion. The grub which hatches from the egg burrows in the endosperm, moults at intervals and eventually transforms within the grain into a pupa, from which the adult emerges. Thus the holes seen in weevilly grain indicate that at least one generation has already bred in the grain. Breeding and complete develop ment take place between 14 C. (55 F.) and 30 C. (86 F.), the optimum temperature being about 16-20 C. (65 F.) where the life cycle takes about 38-40 days. It cannot breed at relative humidities less than 40%, which is equivalent to a grain moisture content of 10%. This helps to explain why dry malt, stored under conditions of relatively high temperature, is not usually attacked by the grain weevil, since both conditions are unfavourable. In considering methods for the control of this species it must be kept in mind that only the adults can be reached by contact insecti cides; the eggs, larvae and pupae, within the grains, can be killed only by fumigation or by the application of heat. Calandra granaria adults are particularly susceptible to y-benzene hexachloride (y-bhc), less so to DDT, and fairly so to pyrethrins (the active principles of pyre thrum). All stages are susceptible to methyl bromide, and to ethylene dichloride-carbon tetrachloride mix tures; there is slight resistance to hydrogen cyanide. The detection of the presence of Calandra in grain which has not been infested for a sufficient length of time to show holes, is a problem of some difficulty. One method is that of incubating samples under controlled conditions, but this needs some 4-6 weeks to make sure that eggs laid at about the time of sampling have passed through all subse quent stages. Other more rapid methods are available. The first; developed in the U.S.A., depends on staining the "egg plugs" with a red dye* and so indicating whether or not eggs have been laid in the grain. This method does not differentiate between grain which * The stain consists of acid fuchsin, 0*5 gnn., glacial acetic acid, 60 ml., acid-distilled water, 950 ml.
328 freeman: pest infestation control [Sept.-Oct., 1951 has an active infestation and that which has been fumigated or otherwise treated.2 A second method, developed at the Pest Infestation Laboratory of the Department of Scientific and Industrial Research at Slough,8 depends on the great difference between the carbon dioxide production of insects and of dry grain respectively; that of grain of moisture content less than 14% is negligible, but that of insects is of measurable quantity. A sample of grain (about 1-2 lb.) is sieved to remove adult insects and is then incubated at 25 C«(77 F.) in a closed vessel for 24 hr. The concentration of carbon dioxide is then measured. A figure of 0*3% or less may be taken to indicate that the grain is clear; of 0-3-0-5% that it is slightly infested; and of 0-5-1-0% that the infestation is sufficiently great to warrant some treatment. It only needs 6-10 fourth-stage larvae of Calandra per 1 lb. of grain to produce 1% carbon dioxide; this number is very difficult to detect by other means. This method has been in use for some years, by the Infestation Control Division of the Ministry of Agricul ture, as one of the guides to the need for treatment of grain and it is also of great value as a means of rapid assessment of the results of treatment. Saw-toothed grain beetle (Oryzaephilus surinamensis Linn.). The saw-toothed grain beetle is also well established in this country in granaries and warehouses and on farms. It attacks not only whole grain, but also milled products, animal feeding stuffs, oilseeds and dried fruit Unlike the grain weevil the larva does not tunnel within the grain but moves actively from one grain to another, feeding either at places already weakened by abrasion or by attacks of other insects, or directly in the germ area. The adult female lives for from six to ten months, during which time it lays an average of 170 eggs loosely in the food. The species is resistant to extremes of temperature and humidity, the upper limit of temperature for complete development being a little below 40 C. (104 F.). The life cycle takes about 72 days at 21 C. (70 F.) and 24 days at 27 C. (81 F.). It readily overwinters in the adult stage in unheated buildings. Its resistance to lower humidities than those tolerated by Calandra offers an explanation of infestations by this species in whole grain where Calandra was also present, but did not increase in numbers. In one case the sawtoothed grain beetle was found breeding in grain of a moisture content of 9-40%. Much difficulty has been experienced in the control of this species in grain stores. This is mainly due to its ability to hide in crevices, but also to the fact that it is somewhat resistant to certain insecticides. Small-scale experiments by the Division have shown that the most immediate effects on the adults are obtained by the use of pyrethrum (1-3% pyrethrins) and derris dusts; 5% DDT dust is more effective than 0-5% y-bhc. It also breeds readily in grain dusted with 2*5 p.p.m. y-bhc, a dose which is lethal to Calandra. It is killed by the direct action of DDT smoke, but the residual effect is not sufficient to give further control. Fumigations of sound buildings with 30 oz. of HCN for 36 hr. have shown some survivors. Control is probably best effected by the use of pyrethrum sprays and, much less well, by DDT. The direct damage to barley done by the saw-toothed grain beetle is not very great, but it can reproduce rapidly and cause heating. Two examples will illustrate this point. In the late summer of 1949, English wheat placed into silos immediately after drying showed heating up to 100 F. and the presence of large numbers of beetles after only six weeks storage; in several successive years, barley stored after drying in a sound building (with one wall adjacent to a kiln), showed heating and large populations of this beetle after some 2-3 months storage. The infestation had been encouraged by the heat from the kiln. In both cases the buildings had been carefully treated before the grain was stored, so reducing the initial population to a low level. It is convenient at this point to make some observations on the heating of grain. It has been shown by a number of workers, but particularly by Oxley and Howe4 of the Pest Infestation Laboratory, that the heating of grain may be due either to excessive moisture or to the presence of insects. Grain of a moisture content of less than 14% may be kept indefinitely without fear of heating due to natural respiration, sprouting or attacks of moulds; it will, however, heat under certain circumstances due to the attacks of insects. Insects produce heat as the result of metabol ism, particularly muscular activity. Under normal exposed conditions this heat leaks away as fast as it is produced, since insects
Sept.-Oct., 1951] freeman: pest infestation control 329 are small animals with a high surface/volume ratio, and the insect remains at the tempera ture of its surroundings. Grain is a poor conductor of heat and the heat produced by small aggregations of insects inside a bulk or even a bag of grain leaks away more slowly than it is produced. Such aggregations can be produced, for example, by the egg-laying of a single female weevil. As the temperature rises, so the insects tend to be more active and the heating proceeds to accelerate. Eventually, however, the temperature at the centre of the hot spot rises above that which is preferred by the free-living insects, which migrate outwards. Larvae within the grains, however, cannot move and they continue to produce more heat until the temperature rises so high that they die. No further heat is then produced, and the temperature remains at about 38-^2 C. (100-108 F.) in the case of heating induced by Calandra granaria. Concurrent with the heating due to the insects there is a movement of water vapour from the hotter to the cooler parts of the bulk. This water tends to condense below the surface and against cool walls, stanchions, etc., causing caking, and providing conditions suitable for attacks by moulds or even for sprouting. It need not be thought that large numbers of insects are necessary to induce heating; as small a number as two final stage larvae of Calandra per 1b. of grain is sufficient. Khapra beetle (Trogoderma granarium Everts). In this country, khapra beetle is almost exclusively confined to makings, although it is a common pest of stored grain in hot, dry parts of the world. It is a relative newcomer, having apparently been introduced on Indian barley during the 1914r-18 war*. At the present time it is regularly found on imports of barley from North Africa, Syria and Irak, on groundnuts and pulses from India, and, since 1947, on groundnuts from Nigeria. The most noticeable features of an infestation by khapra beetles are the larvae and their cast skins; adults are seldom seen. With infestations of the grain weevil ancl the saw-toothed grain beetle it is the adult stage which is most prominent. This difference is due to the relative lengths of the adult and larval stages. Whereas the adult weevil or saw-toothed grain beetle lives much longer than the usual period of the life cycle, the adult khapra beetle is very short-lived, seldom surviving more than 10-12 days. During this time it does not feed or drink, its sole function being that of reproduction. Eggs are laid singly to an average number of 50, a large proportion being laid during the first few days. Eggs hatch in 5-9 days and each larva moults 4-10 times. The optimum temperature is 32-35 C. (90-95 F.), at which the life cycle is 40 days; the upper limit for development is 40 C. (104 F.). The larvae are resistant to low humidities, feeding on materials with p. moisture content as low as 4%; they are also resistant to low tempera tures, ceasing to develop at about 8 C. (46 F.) but resisting temperatures of even - 10 C. (14 F.) for short periods. The significant habit of the larvae, which makes their control so difficult, is that of massing together into cracks and crevices, where contact insecticides cannot reach them nor fumigants penetrate. Another habit is the ability of the larvae to go for long periods without food, moulting at intervals and then continuing their development when conditions again become favourable. Trogoderma larvae are relatively unaffected by DDT, and y-bhc has only a slight effect on them; pyrethrum sprays and dusts are by far the most effective, both in knock-down and kill. The adults, however, are very susceptible to DDT and y-bhc so that measures designed to kill the adults before they can lay their eggs should eventually eradicate a Trogoderma population. The larvae have the same order of resistance to HCN as Calandra; methyl bromide is particularly effective owing to its powers of penetration. Rust-red flour beetle (Tribolium castaneum Herbst.). Although the rust-red flour beetle is the most common insect found on food stuffs at the time of import into this country, it is not established here as it cannot survive the winter in unheated stores. In some maltings this species and the closely-allied confused flour beetle (Tribolium confusum Duv.) have become established in and near the malt bins, where conditions are suitable for continuous breeding. On emergence from the pupa, which lies loose in the food, the adult female beetle is light brown in colour, but rapidly darkens. During a life of some nine months, the female lays an average of 300 eggs loosely in the food. The larvae move actively in the food, attacking grains of barley or malt which have been damaged by abrasion or by other insects.
330 freeman: pest infestation control [Sept.-Oct., 1951 The life cycle takes about 90 days at 22 C. (71 F.), 37 days at 27 C. (81 F.) and 22 days at 30 C. (90 F.). It is fairly resistant to high temperatures and to low humidities, having been found breeding in one maltings in malt of a moisture content of 5-7%. Tribolium is not difficult to kill, being susceptible to all common insecticides, so that treatments applied against the three pests already mentioned should deal effectively with this one. Australian spider beetle (Ptinus tectus Boield.). This is another relative newcomer to the warehouse fauna of this country as it was first recorded here6 in 1892. The original home of this species is supposed to have been in Tasmania. It is well established all over the U.K., being resistant to cold; it breeds best under conditions of moderate tempera ture and fairly high humidity. According to Howe,7 development takes place between 10-28 C. (50-82 F.), the optimum conditions being 22-25 C. (73-77 F.) and 80-90% relative humidity. At 23 C. (73 F.) and 70% R,H. the life cycle takes about 66 days.8 Ptinus tectus cannot develop at relative humidities below 30%; under optimum conditions a single female will lay up to 600 eggs. Breeding does not take place readily on whole grains, but in maltings is particularly associated with by-products such as malt culmings. Reference has already been made to the readiness with which it breeds on dried yeast. The Australian spider beetle is generally susceptible to DDT, y-bhc and pyrethrum sprays and dusts. The habits of the larva in tunnelling in the food, or in remaining deep in floor cracks and other crevices in the building, make it necessary to persist in measures of control. Methods of spread of Insects to and front Maltings Insects spread from place to place in a number of ways, but the most important, so far as infestation of stored products is con cerned, is by carriage in infested grain and grain products, in or on empty sacks, or from machinery and transport containers. Insects can live for long periods without food, and it is not necessary for the material on which they travel from place to place to be capable of sustaining life. In any case, empty sacks often contain dust and spilt grain on which they can feed if necessary. Grain and sacks do not need to remain standing very long in an infested place, e.g. a farm granary or barn, before they become infested. Invasion of new material often takes place more rapidly at night than by day, since many stored-products insects are most active at night. The introduction of insects in barley into maltings can be largely avoided if barley can be harvested by combine or threshed directly into clean fumigated sacks and then conveyed as directly as possible to the maltster's store without lying in corn merchants* or other grain storages. The maltster, for his part, should make every effort to see that grain and empty sacks which leave his premises are as clear of insects as possible. Home-grown grain is much less infested than imported, and the present almost exclusive use of homeproduced grain protects the maltster from the introduction of many foreign pests, including the rice weevil (Calandra oryzae Linn.), the khapra beetle, the lesser grain borer (Rhyzopertha dominica Fab.) and the Angoumois grain moth (Sitotroga cerealella Oliv.), all of which have shown ability to persist in malt ings for many years after their first introduc tion (Table I). With the increase in the use of combine harvesters and the storage of grain by fanners, there is an increasing risk that home-grown grain may be rather more infested by insects than it has been in the past, when storage in the rick offered safety from storage insects, though not from rats and mice. Prevention and Control It has been demonstrated again and again that prevention of infestation, is, in the long run, much less trouble and less expensive than control, particularly with khapra beetle. Prevention Inspection of incoming grain and bags. Every effort must be made to prevent the entry of storage pests, particularly those of major importance, into maltings and grain stores. Every consignment of barley (and of malt transferred from one maltings to another) should be examined before it is taken into store; tests, as described earlier, should be made to determine whether it is infested, and, if so, it should be refused entry or treated before it comes into contact with other stocks. In this regard the provision of properly equipped silo storage has consider able advantages. A routine system of
Sept.-Oct., 1951] freeman: pest infestation control 331 inspection and treatment (either by heat or fumigation) of empty sacks should also be adopted. Hygiene. High standards of hygiene should be laid down and enforced; makings generally compare very favourably in this respect with other sections of the grain trade. Many maltsters already use industrial vacuum cleaners; their great advantage is that they pick up dust and insects into a bag, the contents of which can be destroyed by burning. Experience has shown that points needing special care are odd bags of sweepings and spilt grain, malt culms and malt dust, spillage in elevator wells and from conveyor bands, and grain and dust trapped in places difficult to clean. It is in such material that many of the insects breed and maintain themselves when the major stocks may be fairly clear. Thus, in one makings where a severe infes tation by grain weevil was found in 1943, large numbers of the lesser grain borer (Rhyzopertka dominica) were also discovered breeding in barley spillage behind an elevator. This was due to the fact that the casing was incomplete at the top, so that the buckets in turning over continually tipped a little grain TABLE I Grain Pests found in Maltings frequent; ++ occasional; + uncommon) Scientific name Common name Occurrence Commodities attacked Calandra granaria Linn Ptinus tectus Boield. Oryzaephilus surinamensis Linn. Tribolium castaneum Herbst*. Trogoderma granarium Everts*. Tribolium confusum Duv.* Laemophloeus spp. Calandra oryzae Linn.*.. Palorus ratzeburgi Wissm. Sitotroga cerealella Oliv.* Tyroglyphus farinae Linn. Rhyzoperiha dominica Fab.* Grain weevil Australian spider beetle Saw-toothed grain beetle Rust-red flour beetle Khapra beetle Confused flour beetle Flat grain beetles Rice weevil A grain beetle Angoumois grain moth Flour mite Lesser grain borer + + + + + + + + + + + + + + + + + + + + barley, malt malt culms, dried yeast barley, malt malt malt malt barley barley, malt barley barley barley barley, malt * Tropical or sub-tropical species normally unable to overwinter in unheated stores. TABLE Insects op Secondary Importance found in Maltings (+ + + frequent; + + occasional) II Scientific name Common name Occurrence Where found Cryptophagus spp. Endrosis sarcitrella Linn. (= lactella Schiff.) Hofmannophila pseudospretella Staint... Ptinus fur Linn Niptus hololeucus Fald Tenebrio molitor Linn Trigonogenius globulus Sol Psocoptera spp. Attagenus pellio linn. Anobium punctaium Deg. Lepisma saccharina Linn. Mycetaea hirta Marsh Ptinus pusillus Sturm. Enicmus minutus Linn Fungus beetles White-shouldered house moth False clothes moth A spider beetle Golden spider beetle Mealworm A spider beetle Book lice Carpet beetle Furniture beetle Silver fish Hairy cellar beetle A spider beetle Plaster beetle + 4- + + general: malting floors general: malting floors general general general: malting floors general; especially in spillage general general general; especially in floor cracks boring in structural timber general malting floors general general: malting floors
332 freeman: pest infestation control [Sept.-Oct, 1951 out between the elevator and the walls. This insect is only found in imported barley and cannot survive the winter in unheated premises. Another example concerned a maltings where, in 1946, the chief centre of infestation in certain rooms was a bag of barley sweepings. Amongst other insects this contained the Angoumois grain moth (Sitotroga cerealella Oliv.), another species only found in foreign barley and which cannot breed in this country in unheated storage. Structural matters. It is admitted that many maltings are old buildings, though generally maintained at a high standard. One of the commonest faults is the construc tion of malt and barley bins in such a way as to provide places in which grain is trapped and insects can hide. Whilst the siting of malt bins round the kilns ensures that the malt is kept dry (and hence safe from attack by Calandra), it also provides excellent conditions for the breeding of khapra beetle. The structure of malt and barley bins often encourages the persistence of a reservoir of insects which, hidden deep in cracks in brick work or in the joints of tongued and grooved boards, are difficult to reach with contact insecticides or even with fumigants. The lining of such bins with metal often defeats its object since faults in the sheeting allow insects and grain to be trapped in inaccessible places. The only radical solution is to store the malt in bins with a smooth and impervious surface (e.g., concrete or metal with riveted or welded seams). Such bins would have the added advantage of being readily sealed for fumigation if infested grain were introduced into them. It is often necessary, however, to deal with existing bins, and these should be modified in such a way as to reduce insect harbourages to a minimum. Bins in one series of maltings consist of three layers of plywood, one layer of felt and one of 1^-in. wood. The inner plywood layer is painted annually with white enamel, and when empty appears to have a smooth surface without cracks. When the bins are loaded, however, the seams stretch and khapra beetle larvae living in the inner layers come out and attack the malt. It is very doubtful if infestation in such bins could ever be eradicated without dismantling the bins. Other structural details to prevent infesta tion are the filling of cracks as far as possible with plastic materials. The Building Research Station of the D.S.I.R. has been carrying out experiments in conjunction with the Ministry and is always willing to give advice on this matter.8 Walls should be painted rather than white washed, since whitewash tends to flake and provide hiding places. Furthermore, it gives a very poor surface on which to apply residual insecticides, which remain effective much longer on glossy paint. Machinery should be designed and installed in such a way as to eliminate dead spaces and make cleaning easy. Good advice on this aspect is given in two illustrated pamphlets of the British Food Manufacturing Industries Research Association.10'11 Storage practice. Grain stored in bags should be stacked away from walls, leaving alleyways between adjacent stacks. This permits inspection for signs of infestation and also facilitates treatment should infestation develop. Centres of infestation can be isolated from other stacks and the stacks themselves can be treated by fumigation under gas-proof sheets, so long as the floor is reasonably gas-tight. Although bulk grain in barges has.been fumigated successfully using methyl bromide, the treatment of bulk grain on floors, or in bins which cannot be sealed, is very difficult since even distribution of the fumigant cannot be obtained. Some success in the treatment of local "hot-spots" has been achieved by the use of carbon tetrachloride-ethylene dichloride mixtures. In general, however, the storage of grain in bulk on floors should be avoided, and storage in bags or in concrete silos is to be preferred from the point of view of prevention of infestation and ease of treatment. Control Mechanical and physical methods. So far as the malting industry is concerned, the only mechanical method of any consequence is the screening or sieving of infested grain. This method is of very limited utility. It has the disadvantage of merely removing from the grain the free living insects, leaving untouched any stages which are within the grains (e.g. larvae and pupae of the grain weevil) or attached to them (e.g. eggs). Many freeliving insects tend to hide inside hollow grains or in the germ, and these also remain with the grain. Heat is more useful. In general all stages
Sept.-Oct., 1951] freeman: pest infestation control of insects and mites are killed by exposure to a temperature of 140 F. for a period of 3 min.; this temperature must actually be experienced by the insects, so that normally a much longer period of heating is required to bring the mass of material in which the insects are living up to the lethal temperature. The treatment of barley by heat is probably inadvisable as damage to germination may occur, but bags can readily be disinfected in this way. The use of live steam or damp hot air is the best method, otherwise heat is lost in drying the bags; damp heat, too, kills insects quicker than dry heat. The temperatures reached during the kilning of malt are generally lethal to insects, but the structure of kilns is such that insects can readily find places where the temperature is considerably cooler than in the malt; they can survive and find their way back into the malt after the kilning is completed. ChemicalmetiwAs Materials which can be applied to stored food for the prevention and control of infestation are very restricted in nature and permissible concentration. Any method used must be primarily as toxic as possible to the particular insects or mites concerned, while causing no deleterious changes to the material being treated and leaving no harmful residues. Thus, in the case of barley and malt, it is important that the germinative power of the barley should not be affected; that neither barley nor malt should be tainted; that nothing should be added which will affect the activity of yeast; and that no harmful materials should pass through into the final product, beer, or into the various extracts of malt particularly those used for the manufacture of infant foods. Chemical methods may be conveniently classified into non-fumigant and fumigant, the main distinction being in the method of application. Apart from materials used as barriers (e.g., sticky banding), the nonfumigants are principally contact insecticides which, when applied to insects, pass through the cuticle and poison them. Examples of contact insecticides are DDT, y-bhc and pyrethrins. Fumigants, such as hydrogen cyanide or methyl bromide, are gases which can either pass through the cuticle of the in sect or enter through the insect's breathing system. Contact poisons and fumigants kill insects either by direct interference with the nervous system (e.g., pyrethrins), or with 333 essential chemical processes (e.g., hydrogen cyanide upsets the respiratory enzyme sys tem). Insects can be killed by contact insecticides by being sprayed or dusted directly, but it is more effective and economical to cover sur faces with a layer of insecticide so that insects which walk over them pick up a lethal dose and are killed. It is possible to do this because most contact insecticides not only have an immediate effect on insects, known as "knock-down," but also are long lasting, having a "residual" effect. In general, pyrethrum has a quicker knock-down, but less residual effect than y-bhc or DDT, the latter having the greatest residual effect. However well applied,. contact insecticides can only affect such insects as they touch; insects hidden in cracks and crevices, or inside grains (e.g., eggs and immature stages of weevils) can only be reached by fumigants. A combination of methods is generally required to deal effectively with any par ticular outbreak of infestation. Under the heading of non-fumigants is included the use of barriers and contact insecticides applied in a number of ways. Walking insects can be prevented from moving to or from infested stacks or bulks of grain by the use of barriers, comprising insecticidal dusts or sticky bands, the latter being most useful for application to walls and stanchions. On floors, dusts should be used owing to the interference which sticky bands cause to normal working. DDT, y-bhc and pyrethrum can be applied in the form of dusts and sprays, and the two former also in the form of smokes. Dusts are convenient in use, requiring less elaborate equipment than oil sprays; they do not provide such continuous insecticidal surfaces as sprays and cannot readily be used on walls and ceilings. They are more effective than sprays in places which are dusty and which cannot be cleaned before being sprayed. Dusts are normally used at strengths of 6% DDT, 0-5% y-bhc or 1-3% pyrethrins, and are applied by hand, or by the use of bellows, agricultural dusters or special apparatus such as the Otho-Briggs mister, which has the advantage of applying very light, well-dis tributed dosages. Insecticidal dusts may be mixed with grain for the purpose of protecting it from attack by insects. Pyrethrum powder (1-3% pyrethrins) has been used by the Ministry experimentally on a commercial
334 freeman: pest infestation control scale for the treatment of imported barley. Admixture at the rate of 5$ lb. per ton was successful against the grain weevil (Calandra granaria).ia The use of DDT and y-bhc mixed with grain is subject to the need to ensure that farm animals and human beings shall not consume such amounts in their food or drink as might accumulate to lethal quanti ties. The Medical Research Council has suggested that the quantities not to be exceeded in the final products to be consumed are 7 p.p.m. of DDT and 2-5 p.p.m. of y-bhc. Experiments carried out on a small scale in the Ministry's laboratories have shown that this dosage of y-bhc is sufficient to protect grain from attacks by the grain weevil, though not by the saw-toothed grain beetle; the sug gested level of DDT is not effective. It has already been pointed out13 that quantities of y-bhc of this order of concentration are unlikely to affect the activity of yeasts. Sprays in buildings such as maltings can be applied either by high-pressure paintspraying equipment using highly refined paraffin oils as carriers for the insecticide, or by low-pressure sprayers such as knapsack sprayers or whitewashing sprayers using water as the carrier. Special spraying units can be used in silo bins. DDT, y-bhc and pyrethrins can all be applied in oil, the normal strengths being 5%, 0-35% and 1-3% respectively, for the control of beetles; application is such as will give a surface film which is just visible. Pyrethrin spray can be applied to the surface of grain without fear of taint. Its efficacy can be maintained and the cost reduced by admixture with piperonyl butoxide; a spray consisting of 3% piperonyl butoxide and 0-3% pyrethrins has about the same effect on the grain weevil as a 1-3% pyrethrins spray, but is only about twothirds the price. As an alternative to oil, DDT and y-bhc can be applied as water-emulsions, the emulsion concentrates being diluted by mixing with appropriate quantities of water. They can then be applied with a knapsack or with limewashing equipment. Water-based sprays are not suitable for direct application to foodstuffs, but can be used on walls, floors, etc. The persistence and efficacy of insecticidal sprays depends very much on the nature of the surface; glossy paint is very good and whitewashed or bare brick very poor for oil [Sept.-Oct., 1951 sprays, since the oil is absorbed into the brickwork and little or none remains to form a toxic film. For such surfaces water-dis persed powders are to be preferred, since the water is absorbed into the brickwork leaving the insecticide on the surface. DDT and y-bhc can be used in this form. Such sprays are useful for application to the walls of malting floors and the surfaces of malt and barley bins. Smokes provide a means whereby y-bhc and DDT can be volatilized into the air in the form of a fine mist which eventually settles out on the surfaces of the rooms treated. Most of the insecticide settles on horizontal surfaces and relatively little on vertical surfaces such as walls. It is not a process of fumigation, and the smoke is unable to penetrate into materials or cracks and crevices. Preliminary thorough cleaning is essential for good results. Smokes are very useful for the treatment of spaces which cannot easily be treated by sprays and where fumigation is either impracticable or unneces sary. Their convenience in use makes routine treatments of barley and malt bins and of silo bins an easy matter. As alternatives to smokes, insecticidal fogs produced by a fogging machine may be used, but the quantity of insecticide deposited on surfaces by such methods is usually too small to provide residual effects. The effect of a fnmigant depends on a combination of the average concentration of the gas in the air and the period for which the insects are exposed to that concentration. Thus a high concentration for a short time is as effective as a low concentration for a long time; the choice often depends upon economic factors. The appropriate c x t product (expressed as oz. of fumigant per 1,000 cu. ft. x hr.) can be determined in the laboratory for the particular insect concerned. After taking into account the likely losses of fumigant from leakage and absorption in the material being fumigated and in the fabric of the building, the appropriate concentration of fumigant for the period can be determined. The success of a fumigation depends to a considerable extent on the ability of the gas to penetrate as far as possible into cracks and crevices in a building and into the centre of commodities being treated. For this reason it is very important that buildings to be fumigated should be cleaned as thoroughly as possible before treatment, so that the gas
Sept.-Oct., 1951] freeman: pest infestation control 335 may have the best possible conditions for penetration. The treatment of commodities is best carried out in special chambers, but well-built warehouse rooms can be satisfactorily sealed. The fumigation of bagged goods can also be carried out under gas-proof sheets, large stocks of grain in airfield hangars having i been treated in this way. The most effective method of treating grain, however, is in silos fitted with circulatory fumigation plant by which fumigants such as methyl bromide can be passed through the grain. Treatment by such a plant is both effective and quick and the initial cost of installation during the building of a silo is small.14 Grain in silos can also be treated by the admixture of calcium cyanide powder (" Cyanogas G ") so long as the moisture content is not less than 11%, since this method depends on the production of HCN gas by the action of the moisture of the grain on the powder. The principal fumigant used for the treat ment of buildings (space fumigation as con trasted with commodity fumigation) is hydrogen cyanide, applied either as a liquid pumped from cylinders through a system of pipes erected temporarily for the purpose, or from tins containing gypsum or other absorbent material on to which the hydrogen cyanide has been applied at the factory. Each tin contains a known quantity of HCN, and this is given off when the tin is opened and the contents are scattered on the floor. Hydrogen cyanide is normally used at con centrations of from 16-30 oz. per 1000 cu. ft. for 24-48 hr. Failures in treatment are usually due to the ability of insects to find hiding places to which the gas cannot pene trate and small numbers of Trogoderma, Calandra granaria and Oryzaephilus surinamensis may often be found after a treat ment. Hydrogen cyanide does not penetrate very readily, and airs out slowly., Methyl bromide, which is also applied from cylinders through piping systems, penetrates very readily and also airs off quickly. It may be used for space fumigation, but only when such space can be very thoroughly sealed. It is more commonly used for the treatment of commodities and has been found very suc cessful for the control of Trogoderma in groundnuts in West Africa, where it has been used both in buildings and for the treatment of large pyramid stacks under tarpaulin sheets. The normal dose for commodities is of the order of 16-20 oz. per 1000 cu. ft. plus an additional quantity which varies with the kind and amount of commodity treated. The period is normally 24 hr. Both methyl bromide and hydrogen cyanide are poisonous to man, and HCN may only be used by skilled fumigators working under the provisions of the Hydrogen Cyanide Act, 1937. Methyl bromide is also best left to be used by skilled operators. The treatment of "hot-spots" in bulks of grain, of infested grain in silo bins, of small quantities of grain in bags, and of infested sacks can be carried out by the use of carbon tetrachloride alone, or in admixture with 3 parts of ethylene dichloride. The fumigant is applied as a liquid poured on to the surface of the material to be fumigated. The normal dose of the mixture is 4 pints per ton for 48 hr.; for grain in small silos the period should be 7 days. Sacks can be treated at the rate of J-l pint per 25 sacks for 48 hr. This fumigant is dangerous if breathed for some time, so that all applications other than those done out of doors should be carried out wearing a gas-mask. Prevention and Control Procedure The routine of - prevention includes the careful inspection and rejection or treatment where necessary of all incoming barley and malt. Sacks should be heat-treated or fumi gated as a routine measure. The storage of grain should be carried out in a manner which facilitates inspection and treatment should this prove necessary. All buildings should be kept as clean as possible, no dust or sweepings being allowed to accumulate; if sweepings cannot be destroyed or disposed of immedi ately they should be stored away from the main stocks of grain. Preventive insecticidal measures include the spraying of walls, ceilings, etc., with appropriate sprays; it should, for example, be possible to hold the grain weevil, flour beetle and Australian spider beetle in check by the regular use of y^bhc as spray or dust; if the saw-toothed grain beetle is at all common, DDT or pyrethrum should also be used. Floors and bins used for the storage of grain should be thoroughly cleaned and the surfaces sprayed or dusted before further use with y-bhc or sprayed with pyrethrum; the latter is particularly necessary where khapra beetles are present. Barley and malt which are to be held in
336 freeman: pest infestation control [Sept.-Oct., 1951 store for long periods might well have y-bhc (with suitable precautions regarding quan tities in the final product) or pyrethrum powder mixed with them as a protection against grain weevil and khapra beetle; whether pyrethrum powder would remain toxic under the warm conditions of storage of malt is a matter to be determined by experiment. Fumigation should be regarded as a last resort after all other measures have failed, or as a means of reducing an excessive insect population to a level at which the other measures will hold it in check. The use of methyl bromide for the treatment of malt bins infested by khapra beetle offers good prospects of success. The midsummer period when malting ceases in ordinary maltings is the time when all efforts should be directed towards reducing the insect population to a minimum, par ticularly by the use of those methods, e.g. fumigation, which are not practicable when malting is going on and when large stocks are in store. The quantity of barley held in store during this, time should be reduced to a minimum. The best course to pursue in each case depends on so many factors that expert advice should be sought, not only for the control of an infestation which has got out of hand, but even before trouble occurs, as an insurance that proper methods of prevention are being applied. The services of the Infesta tion Control Division of the Ministry are available through a staff of Inspectors stationed in various parts of England and Wales. In Scotland a similar service is run by the Department of Agriculture for Scot land. The address of the nearest inspector can be obtained by application to the Head quarters of the Division at Tolworth, Surrey. It should not be forgotten that the Division is also responsible for the enforcement of the Prevention of Damage by Pests Act, 1949,18." which provides, inter alia, for the notification of infestation (as defined in the Act) to the Minister. Conclusion Under present conditions, the risk of i ntroduction of tropical or sub-tropical pests, including the khapra beetle, is at a minimum, since foreign barleys are not used; hence there is every opportunity for the eradication of these pests from maltings without fear of re-introduction. On the other hand the increase in harvest ing of home-grown grain by combine is forcing the maltster to. acquire the major part of his stocks for the year at the time of harvest; this extends the period of storage and so increases the risk of damage from insect attack. Some grain, purchased later in the season, may have been held by the farmer in sacks or in bulk in his own buildings, again subject to insect infestation; grain held in the rick, although free from the danger of insect infestation suffers from the attacks of rats and mice. The adoption of continuous malting pro cesses with air-conditioned maltings may reduce the risk of insect damage in one way by reducing the need to maintain large stocks of malt, but stocks of barley for malting need to be held over during the warmer months of the year; there is thus less opportunity for dealing with the endemic insect population during the annual summer cleaning in ordin ary maltings. In such continuous maltings even closer attention to hygiene is necessary. It is considered, however, that the adoption of the various methods outlined in this paper should go far to controlling insect populations in maltings at a level which should cause little or no damage. Attention should be given by maltsters to the reduction of the risks by the storage of barley in silos fitted with circulatory fumigation plant and, if possible, the storage of malt under conditions much cooler than that provided by bins around the kilns, whilst at the same time keeping the malt dry. In this way danger of attack by khapra beetle and grain weevil would be considerably reduced or eliminated. This paper is published with the permission of the Director of Infestation Control, Ministry of Agriculture and Fisheries. References 1. Munro, J. W. Report on a Survey of the Infesta tion of Grain by Insects. D.S.I.R., London: H.M.S.O. 1040, p. 47. 2. Frankenfeld, J. C. U.S. Dept. Agric. Bur. Bnt. PI. Quar. E.T. 266, July, 1048. 3. Howe, R. W. and. Oxley, T. A., Bull. ent. Res.. 1044,35,11. 4. Oxley, T. A. and Howe, R. W., Ann. appl. Biol.. 1044,31,76. 5. Mason, F. A., Bur. Bio-Tech., Leeds. Bull. 2, 1021. 27.
Sept.-Oct., 1951] nicol: son. and plant 337 6. Chitty, D., Ent. won. Mag., 1904. 40, 109. emus and Furnishings with regard to the 7. Howe, R. W., Ent. num. Mag., 1049,85, 137. Contra of Moth Pests. 8. Howe, R. W., Ent. num. Mag., 1949, 85, 189. 12. Murray. Bull & Co., Ltd., Pyrethrum Post, 1949, 9. Director of Building Research. Building 1 (iv)'2< Research, 1949. D.S.I.R.. London: H.M.S.O. 13. Price, M. D., this Journ., 1948, 214. 1950. 14. 14. Turtle. E. E., Food Manuf., 1960, 25, 225. 10. British Food Manuf. Ind. Res. Ass., Leatherhead. 15. Prevention of Damage by Pests Act, 1949. 12 Machinery Design and the Control of Moth and 13 Geo. 6, ch. 56. Pests in Factories. 16. Prevention of Damage by Pests (Infestation of 11. British Food Manuf. Ind. Res. Ass., Leather- Food) Regulations, 1950. Statutory Instruhead. Factory Fittings, Mountings, Appli- ment 1960, No. 416. MEETING OF THE SCOTTISH SECTION, HELD AT THE NORTH BRITISH HOTEL EDINBURGH, ON TUESDAY, 16th JANUARY, 1951. Mr. A. Clark Doull in the Chair. A paper incorporating the following material was read and discussed: SOIL AND PLANT By Prof. Hugh Nicol, Ph.D., F.R.I.C. (West of Scotland Agricultural College, Glasgow.) Received 17th January, 1051- The mode of arrangement of the particles composing a soil, and thus the pro perties of the spaces between the particles, are fundamental in soil science. Exchange of air and water and activities of micro-organisms take place in the soil spaces; all micro-organisms of industrial importance have probably originated from the micro-flora of the soil. An analogy may be drawn between the ion-exchange potentialities of soil and those of malt. The fundamental importance of water in biochemical reactions is considered on the basis of oxidation-reduction, and a corresponding new view of fermentation is cited. Attention is drawn to the inadequacy of the chemical analyses at present avail able of crop plants such as barley. It is suggested that it is important for the brewing industry to understand the relationships between soil and the barley plant. This will not be achieved until a thorough study has been made of the chemical com position of crops at all stages of growth and under different seasonal conditions. Soil the biological matrix spread to a depth Soil has several different modes of arrangeof a few inches or feet over the surface of ment of its particles and thus of the spaces the rocks contains all the nitrogen available between the particles. It is upon these for higher life on land except for a few spaces that nearly everything depends in geochemically insignificant deposits of agriculture and horticulture. The modern nitrates. No special consideration need be way of viewing soil is to look on it as a given to the water, for life in the sea differs cellular rather than a granular material, in no fundamental characteristic from life Geological concentration on the study of the on land, except that there is no serious nature of the solids of soil is still important evidence of fixation of atmospheric nitrogen for the natural history of soil and for other in the sea. The sea differs in form from the ecological studies, but it obscures the prosoil in being structureless, and, because it ductive aspects, and ignores the arrangement has no spaces, the sea depends on solution of the particles, and the importance of the and agitation for its necessary exchanges spaces and what goes on in them. The of gases with the outside atmosphere. soil is a home for many kinds of organisms