TECHNOLOGY OF CEREALS TABLE 5.2 Thermophilic fungi die at 60C and the process Approximate Minimum Equilibruim Relative Humidity for is kept going by spore forming bacteria and thermophilic yeasts up to 70C. RHOO) limi In recent years attention has been given to the Aspergillus halophiticus toxic products of fungi such as Aspergillus flavus and Fusarium moniliforme which produce aflatoxin A. glaucus group and zearalenone(see Ch. 14) AAAAAAAAPP Insects and arachnids Insects that infest stored grains belong to the beetle or moth orders: they include those capable of attacking whole grain (primary pests)and those 80-90* that feed on grain already attacked by other pests (secondary pests). All arachnid pests belong to the order Acarina(mites)and include primary P. islandicum 83t and secondary pests. Most of the common insects Christensen,CMand Kaufmann, HH (1974)Micro- and mites are cosmopolitan species found through flora. In: Storage of Cereal Grain and their Products. Christensen, out the world where grain is harvested and stored (Storey, 1987). Insects and mites can be easily t Ayerst, G. ( 1969). The effects of moisture and temperati distinguished as arachnids have eight legs and Stored Prod.Res.5:127-141 insects, in their most conspicuous form, have six. Table adapted from Bothast, R. J (1978) Reference to the most conspicuous form is sary as some insects (including those that infest grain) develop through a series of metamorphic in equilibrium with them. Unless temperature forms. There are four stages: the egg, the larva adients are extreme the exchanges occur in the pupa and the adult or imago. Although some the vapour phase; nevertheless, variations in female insects lay eggs without mating having moisture content up to 10% within a store are occurred, this is less usual than true sexual possible. reproduction, and this and dispersion are the two If mould growth continues in the presence of principal functions of the adult. Large numbers oxygen, fungal respiration increases, producing of eggs are produced and these are very small more heat and water. If the moisture content is Those of primary pests may be deposited by the allowed to rise to 30% a succession of progressively female imago inside grains, in holes bored for the heat-tolerant micro-organisms arises. Above 40c purpose prior to the egg laying. Under suitable mesophilic organisms give way to thermophiles. conditions eggs hatch and from each a larva Alphabetical List of Primary Insect and Arachnid Pests ystematic name Common name Grain (or flour)mite Acaridae Cryptolestes ferrugineus Stephens red grain beetle coperwha dominica Lesse in borer Bostrichidae ilus granarius L. Sitotroga cerealella olivier Angoumois grain moth Gelechiidae106 TECHNOLOGY OF CEREALS TABLE 5.2 Approximate Minimum Equilibruim Relative Humidity for Growth of Common Storage Fungz Thermophilic fungi die at 60°C and the process thermophilic yeasts up to 70°C. Mould RH(%) limit In recent years attention has been given to the Aspergillus halophiticus 68* toxic products of fungi such as Aspergillus flavus A. restictus group 70* and Fusarium miliforme which produce aflatoxin A. glaucus group 73* and zearalenone (see Ch. 14). A. chevalieri 71t A. repens 71t Insects and arachnids A. candidus group 80* A. candidus 75t Insects that infest stored grains belong to the A. ochraseus group 80* A. jlavus group 85* A. jlavus 78t beetle or moth orders: they include those capable A. nidulans 78t of attacking whole grain (primary pests) and those 80-90* 82t that feed on grain already attacked by other pests A. fumigatus Penicillium spp. P. cyclopium 82t (secondary pests). All arachnid pests belong to P. martensii 79t the order Acarina (mites) and include primary 83t and secondary pests. Most of the common insects P. islandicum and mites are cosmopolitan species found through￾OUthe world where grain is harvested and stored (Storey, 1987). Insects and mites can be easily distinguished as arachnids have eight legs and insects, in their most conspicuous form, have six. Reference to the most conspicuous form is neces￾sary as some insects (including those that infest grain) develop through a series of metamorphic forms. There are four stages: the egg, the larva, the pupa and the adult or imago. Although some female insects lay eggs without mating having occurred, this is less usual than true sexual reproduction, and this and dispersion are the two principal functions of the adult. Large numbers of eggs are produced and these are very small. Those of primary pests may be deposited by the female imago inside grains, in holes bored for the purpose prior to the egg laying. Under suitable conditions eggs hatch and from each a larva is kept going by spore forming bacteria and * Christensen, C.M. and Kaufmann, H.H. (1974) Micro￾flora. In: Storage of Cereal Grain and thezr Products. Christensen, C. M., (Ed.) Amer. Assoc. of Cereal Chemists Inc. St. Paul, MN. U.S.A. t Ayerst, G. (1969). The effects of moisture and temperature on growth and spore germination in some fungi. J. Stored Prod. Res. 5: 127-141. Table adapted from Bothast, R. J. (1978). in equilibrium with them. Unless temperature gradients are extreme the exchanges occur in the vapour phase; nevertheless, variations in moisture content up to 10% within a store are possible. If mould growth continues in the presence of oxygen, fungal respiration increases, producing more heat and water. If the moisture content is allowed to rise to 30% a succession of progressively heat-tolerant micro-organisms arises. Above 40°C mesophilic organisms give way to thermophiles. TABLE 5.3 Alphabetical List of Primary Insect and Arachnid Pests Systematic name Common name Family Acarus siro. L Grain (or flour) mite Acarid a e Cryptolestes ferrugineus Stephens Rust red grain beetle Cucujidae Rhyzopertha dominica F. Lesser grain borer Bostrichidae Sitophilus granarius L. Grain weevil Curculionidae Stiophilus oryzea L. Rice weevil Sitophilus zeamais Motschulsky Maize weevil Sitotroga cerealella Olivier Angoumois grain moth Gelechiidae