INFLUENCE OF FOUR CEREAL FLOURS ON THE GROWTH OF TRIBOLIUM CASTANEUM HERBST (COLEOPTERA: TENEBRIONIDAE)

Abstract

The red flour beetle, Tribolium castaneum Herbst is a major pest of damaged grains and cereal flours. The influence of four food media namely flours of wheat (Triticum aestivum L.), millet (Pennisetum glaucum L.), sorghum (Sorghum bicolor) and maize (Zea mays L.) on the growth and development of T. castaneum was investigated at ambient tropical laboratory conditions of 30±2˚C and relative humidity of 75±5%. Studies involved estimation of anti-nutrients, mineral profile and proximate compositions of the four flour types and their effects on the developmental activity of the flour beetle. Results showed that the moisture content of the cereal flours ranged from 9.24% in maize to 7.64% in wheat, while protein content ranged from 17.23% in wheat flour to 10.91% in millet and the ash content in the flours ranged from 2.59% in millet to 1.05% in maize. The anti-nutrient analysis of the four cereal flours revealed that sorghum flour was highest in oxalate (0.54%), tannin (0.88%) and saponin (3.46%), while maize flour had the lowest values of oxalate (0.36%) and saponin (2.02%). Tannin content was lowest in millet (0.49%). The results further showed that the four cereal flours had sufficient nutrients to support the growth of T. castaneum. Larval emergence commenced from 14-days post-infestation in all flour types. Millet flour had the highest mean number of larvae (435.50) at 56-day post-infestation thus depicting millet flour as the most preferred substrate for oviposition and egg incubation.; while the lowest (286.25±0.65) number of larvae was obtained in maize flour and it was significantly (p≤0.05) lower than the number of emerging larvae in other flour types. Pupation started at day 28 post-infestation. The highest number of pupae was recorded in millet (52.50) and lowest in maize flour (29.25). Development from egg to adult took 35 days. The highest mean number of emergent adult Tribolium was recorded in millet (166.50) and lowest in maize (56.00). Host preference (choice and no-choice) studies revealed millet flour as the most preferred food medium and maize flour as the least preferred food medium, this is probably due to the grey flour colour of millet and its rich nutrient composition. The negative correlation of saponin (-0.04) in millet compared with saponin (0.04) in maize is probably responsible for the significant reproductive success obtained in millet flour. Based on the flour colour, anti-nutrient composition and population of the immature forms of the flour beetle, maize flour was the most resistant, while millet flour was the most susceptible to T. castaneum. Key words: Rust- red flour beetle, Tribolium castaneum, millet, maize, wheat, sorghum, antinutrients, proximate composition, flour colour