___________________________________ Chapter 1 Introduction Raw and processed commodities must be protected from rodents, birds, insects, mites, and microorganisms throughout the marketing system. The mobility and the ability of many stored-product insects to find and reproduce on many different foods throughout the marketing system make them particularly difficult to manage. This chapter provides an overview of the relative importance of different stored-product insect species and the types of economic losses that can be attributed to these insects. The types of regulations and business practices that can impact pest management programs for stored-product insects and the resources available for identifying storedproduct insects also are covered in this chapter.
Storage habitat Crops are harvested at the end of a growing season, and the harvested grain must be stored with minimal loss of quality until needed for human and animal consumption during the year. Grain reserves also are stored to prevent famine in years when the harvested crop is insufficient. The moisture and temperature at which the grain is stored determine its susceptibility to stored-product insects. Traditional grain storage structures are still used in some parts of the world (see recommended reading by Reed).1 Storage structures made of materials available locally are designed to protect grain from weather, insects, mites, fungi, rodents, and birds. Grain may be stored in the field in piles or on vertical poles for varying periods after the harvest. Underground storage in pits is among the most ancient methods still in use today. Grain may be stored in the attic over the kitchen or the living space. It is stored in boxes, baskets, jars, gourds, clay pots, jute bags, and metal drums. Unthreshed grain may be covered with a thatched roof or left uncovered when stored on horizontal poles or platforms. Larger traditional granaries are made of stone, brick, or mud. The first step toward the development of a marketing system involved production of cash crops by subsistence farmers. As cash-crop production grew and fewer people were needed to grow food crops, a more elaborate marketing system developed. Grain was stored on farms, first in wooden granaries and cribs and later in metal bins. More grain could be produced after mechanical harvesting equipment was invented, and larger storage and marketing facilities were necessary to handle the large quantities of harvested grain. This resulted in increased quantities of grain being stored at grain elevators2 rather than on the farm. The first elevators were constructed of wood. Later elevators were made of concrete (see recommended reading by Bailey). Recently, large metal bins or flat storage sheds have been added at elevators because of their lower cost and larger capacities. 1 Recommended readings cited in the text can be found at the end of the chapter as well as in the list of
references at the end of the book. 2 Explanations of the words in bold letters in the text and more information on the subject can be found in
Chapter 22. 3
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Insects are moved through the marketing system along with the grain and grain products. Habitats of stored-product insects include the entire marketing system, from the fields in which a crop is grown to the storage and processing facilities, transportation vehicles, warehouses, and retail stores in which many raw and processed commodities spend some time. For subsistence farmers, only the field and storage environments may be important. Insects have adapted to this diversity of habitats by moving to find essential resources, eating many types of food, and producing lots of offspring. Large numbers of offspring can ensure a new generation even when insect mortality is high. Many stored-product insect species are thought to have been spread by international trade and now have a worldwide distribution (see recommended readings by Buckland and by Howe). The geographical origin of most stored-product insect pests is not known, because they were distributed worldwide by 1800, before the precise identification of insect species was possible. Heated facilities and bulk storage have allowed insects to survive in geographical regions and during seasons in which outside temperatures would otherwise kill them.
Species associated with stored products Many insect species have adapted to survive and multiply on raw, dry, durable cereal grains, their processed products, and many other stored commodities (Table 1.1). The majority of these species are beetles (order Coleoptera), but several species of moths (order Lepidoptera) also are serious pests. Booklice (order Psocoptera) are often found under warm, humid conditions and can cause economic losses when they reach high numbers. On the other hand, several species of mites (order Acarina), wasps (order Hymenoptera), and bugs (order Hemiptera) often attack insect pest species in stored commodities. Knowing which species of pests and beneficial insects are present is important in developing and implementing the best insect pest management program. Figure 1.1, which includes one species from each of the nine families of Coleoptera and one species of Lepidoptera, may allow the species capable of causing significant or extensive damage to stored commodities to be identified to the family level, narrowing the list of possible species. Sixteen of the insect pest species listed in Table 1.1 are capable of rapidly causing extensive damage, and another 16 species are capable of causing significant damage. An additional 51 species of insect pests in Table 1.1 can cause some damage to commodities or are minor pests that rarely cause damage. Although the insect species ranked as minor pests in Table 1.1 may not reproduce on stored commodities, they may be contaminants that reduce the market value of a commodity. Several hundred species of minor insect pests have been reported to infest stored commodities and facilities that store, handle, and process commodities for human and animal food. Stored-product insect species that belong to the families Bostrichidae, Bruchidae, Curculionidae, and Gelechiidae feed and complete their immature development inside a seed. Larvae of Cryptolestes ferrugineus and Ephestia elutella feed within the germ of wheat kernels. Larvae of Cadra cautella and Plodia interpunctella feed on peanuts inside their shells and between the two halves of the peanut kernels. All of the Hymenoptera are parasitoids, and Acaropsis docta, Blattisocius keegani, B. tarsalis, Cheyletus malaccensis, C. eruditus, Teretrius nigrescens, Xylocoris flavipes, X. sordidus, Lyctocoris campestris, and some psocids are predators. Many of these stored-
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Figure 1.1. Insects capable of causing significant or extensive damage to stored products. Insect lengths: L. serricorne, 2–3.5 mm; R. dominica, 2–3 mm; A. obtectus, 2–3.7 mm; S. oryzae, 3–4.6 mm; T. granarium, 1.8–3.8 mm; Cryptolestes ferrugineus, 1.6–2.2 mm; Carpophilus hemipterus, 2–4.1 mm; O. surinamensis, 1.7–3.2 mm; T. castaneum, 2.3–4.4 mm; P. interpunctella, 8 mm. (A and G, reprinted from Beetles associated with stored products in Canada: An identification guide [Bousquet 1990], Figs. 176 and 216, Agriculture and Agri-Food Canada, 1990, reproduced with the permission, of the Minister of Public Works and Government Services Canada, 2005; J from Linsley and Michelbacher 1943; B–F, H, and I used with permission of the Central Science Laboratory of the U.K. Ministry of Agriculture, Fisheries and Food)
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product insect species have a worldwide distribution. Exceptions include Prostephanus truncatus, Zabrotes subfasciatus, and Cadra calidella, which are pests mainly in countries with tropical climates. Sitophilus granarius, Cynaeus angustus, and some dermestid species are pests mainly in countries with temperate climates. Pheromones have been identified for many of the beetles and moths, and their importance for insect pest reproduction, host finding by natural enemies, and insect pest management programs is discussed in Chapter 3. Table 1.1 lists the types of commodities infested by each stored-product insect species. Table 1.2 gives a more complete description of the foods infested by three of these species. However, the lists in Table 1.2 use categories that include many different foods, such as grain; dried fruit; drugs; nuts; spices; herbs; herbarium specimens; packaged processed foods from all types of cereals, oil seeds, and pulses; pulses and pulse products; and seeds of trees and other plants. Also, not all of the foods in these lists are equally suitable for insect development, and insect developmental times are longer on the less-suitable foods. When insect developmental times exceed 100 days, survival is often very low. Studies identifying the stored-product insect species found at various locations in the marketing system are one way to document the role of commerce in spreading these insects throughout the world (Table 1.3). Alphitobius diaperinus or Alphitobius spp., Lasioderma serricorne, Oryzaephilus surinamensis, Rhyzopertha dominica, and Tribolium castaneum were found in all 12 of these studies. Cadra cautella was found in all of these studies that looked for Lepidoptera, and Plodia interpunctella was found in all except the study on packaged-food warehouses. In total, 76 species of storedproduct insects were found in more than one of these studies, and 86 other species were identified in only one study. In these studies, imports into England were from West Africa; those into California and Arizona were from Mexico and South America but mostly Asia; and those into Japan were mostly from Asia but came from all over the world. Empty shipping containers were studied in Australia; food and food-handling areas were studied for ships docking in New Orleans, Louisiana, and in Miami, Florida; bakeries, food stores, restaurants, warehouses, processing plants, a school, and a vending operation were studied in Connecticut; and warehouses were studied in California, Hawaii, Latin America, Africa, and Asia. The study in Hawaii used light traps, food-bait traps, and facility inspections. Insects were found in 93% of the cargos from West Africa and, more recently, in 12.6% of the commodities imported into California. Insects were found in 61% of the Los Angeles, California, port warehouses and all of the 20 packaged-food warehouses in nine countries. One of the recommended readings for this chapter (by Freeman) is a study of insect infestations in raw commodities imported into Great Britain. This study was not included in Table 1.3 because it does not include a complete list of the stored-product insect species found. The percentage of cargos infested decreased from 52% in 1957 to 34% in 1966 and 23% in 1973. The ranked order by country of the percentage of cargos infested remained fairly constant between 1967 and 1973. The number of cargos received in shipping containers increased from 0.7% in 1968 to 33% in 1973. Cadra cautella and Tribolium castaneum were the predominant species. Interceptions of Trogoderma granarium ranged from 46 to 131 per year (six to 18 per 1,000 inspections); T. granarium was intercepted mostly in rice and peanuts from Burma, India, Nigeria, and Sudan.