Stored products are man-made immature ecosystems with a simple structure and an abundant but nonregenerating food supply (Sinha 1977) often with several trophic levels, including granivores, fungivores, omnivores, and natural enemies. The dominant species in a series of successional communities often exist at very low levels in a grain bulk long before conditions favor their dominance (Arbogast and Mullen 1988). Internal feeders result in fragments when grain is milled into flour, germ feeders can reduce seed germination, and external feeders may only feed on damaged kernels, cereal dust, dockage and fungi associated with kernels but may also be important as contaminants or by creating hot spots that can reduce quality and result in economic losses.
Cotton in 1964 wrote that “the old custom of waiting for large mill insect populations to develop and then knocking them out with one massive assault was abandoned in favor of a program which would hold insect population to a low level at all times.” This is true for on-farm and elevator storage of grain as well and throughout marketing channels. Insect density and their damage are kept at very low levels, Australia (Nayak et al. 2020), Canada (Neethirajan et al. 2007) and Europe (Hamel et al. 2020) even try to maintain a zero tolerance, so succession is likely to be less important in properly managed grain. Good storage practices and the usual duration of storage generally prevent succession from proceeding very far (Arbogast and Mullen 1988). In studies on succession by Coombs and Woodroffe (1963, 1968) and Arbogast and Mullen 1988), insect densities quickly exceeded regulatory standards so grain deteriorated, becoming unmarketable.
Pest management can alter species composition. Kiritani (1958) found that the damage to rice by Sitophilus oryzae prior to fumigation supported scavengers after fumigation, so this rice needed to be fumigated earlier. As insecticdes degraded, Cryptoletes ferrugineus, and Tribolium castaeum reappeared in low numbers and populations of Aeroglyphus robustus began to recover after 2 years (White et al. 1986).Sitophilus zeamais was the dominant species when in interspecific competition prevailing in natural conditions (without insecticide exposure), but the species prevalence shifted from S. zeamais to Rhyzopertha dominica under intermediate dose insecticide of 5.0 ppm fenitrothion, a dose that is nearly 2 times lower than the range recommended for maize protection (Cordeiro et al. 2013). This higher tolerance of R. dominica to fenitrothion may be due to its physiology and/or behavior, e.g., adults of this species are less active than S. zeamais, remaining longer within the grain and potentially minimizing insecticide exposure. Phosphine killed most insects and mites except Aeroglyphus robustus and within 3 months Acarus siro and Lepidoglyphus destructor reappeared partially because the predator Cheyletus eruditus was eliminated (Sinha et al. 1967).
Arbogast, R. and Mullen, M. 1988. Insect succession in a stored-corn ecosystem in Southeast Georgia. Ann. Entomol. Soc. Amer. 81: 899–912.
Coombs, C. and Woodroffe, G. 1963. An experimental demonstration of ecological succession in an insect population breeding in stored wheat. J. Anim. Ecol.32: 271–279.
Coombs, C. and Woodroffe, G. 1968. Changes in the arthropod fauna of an experimental bulk of stored wheat. J. Appl. Ecol.5: 563–574.
Cordeiro, E. M. G., A. S. Correa and R. N. C. Guedes. 2014. Insecticide-Mediated Shift in Ecological Dominance between Two Competing Species of Grain Beetles. PloS One 9, E100990
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Hamel, Darka, Vlatka Rozman and Anita Liska. 2020. Storage of cereals in warehouses with or without pesticides. Insects 11(12): 846.
Kiritani, K. 1958. On the distribution and seasonal prevalence of stored grain insects in a farm premises. Botyu. Kagaku23, 164–172.
Nayak, Manoj K., Gregory J. Daglish, Thomas W. Phillips and Paul R. Ebert 2020. Resistance to the fumigant phosphine and its management in insect pests of stored products: A global perspective. Annual Review Entomology 65: 333-350.
Neethirajan, S., C. Karunakaran, D. S. Jayas and N. D. G. White. 2007. Detection techniques for stored-product insects in grain. Food Control 18(2): 157–162.
Sinha R. N. 1977. Use of multivariate methods in the study of stored grain ecosystems. Environ. Entomol. 6: 185-192.
Sinha, R. N., B. Berck and H. A. H. Wallace 1967. Effect of phosphine on mites, insects, and microorganisms. J. Econ. Entomol. 60: 125-132.
White N. D. G., Sinha R. N. and Mills J. T. 1986. Long-term effects of an insecticide on a stored-wheat ecosystem. Can. J. Zool. 64: 2558-2569.
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