Changes in stored-wheat ecosystems infested with two combinations of insect species

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Abstract
The consequences of infestation of bulk-stored wheat by multiple species of insects were determined for 60 weeks at 30 ± 2 °C. Eight 204-L drums containing wheat at 15.5% moisture content were used as three distinct systems: (I) Control system (two drums), insect free; (II) RST system (three drums), infested with the grouping of Rhyzopertha dominica F., Sitophilus oryzae (L.), and Tribolium castaneum (Herbst); and (III) COT system (three drums), infested with the grouping of Cryptolestes ferrugineus (Stephens), Oryzaephilus surinamensis (L.), and T. castaneum. At triweekly intervals carbon dioxide, oxygen, temperature, grain moisture, seed damage, grain weight, dust weight, fat acidity values (FAV), seed germination, microflora, and the numbers of insects and the mite Tarsonemus granarius Lindquist were measured. Seeds died by week 15 and bacterial infection on them increased in all systems. The seed FAVs in the RST system peaked by week 30 and then declined steadily while these values were increasing continuously in the Control and levelling off in the COT systems. Insects multiplied exponentially for 6–15 weeks and then declined sharply or maintained oscillating populations; Sitophilus and Oryzaephilus were unable to survive in the presence of the other insects.