| Factors affecting the storability of pearl millet (Pennisetum americanum (L.) Leeke) lines were assessed in studies of resistance to stored product insects, pericarp structure by scanning electron microscopy (SEM) and moisture content/relative humidity equilibria. Experiments were conducted with two major internal feeders, Sitotroga cerealella (Oliv.) and Sitophilus oryzae (L.), and an external feeder, Tribolium castaneum (Herbst).;Susceptibility of twelve millet lines was assessed by infesting threshed and in-head samples with S. cerealella, S. oryzae and T. castaneum for two months. Major differences in susceptibility were dependent upon the form of storage and attacking insect. S. oryzae was the most destructive in both forms of storage and produced 1.5 times more offspring in threshed grain than in-head millet. Emergence and/or feeding sites on the damaged kernels were either in the endosperm (89.4%) or at the tip cap (10.6%). Reproduction of S. cerealella was 10.4% greater in-head than in threshed samples, with exit holes limited to the exposed crown. In threshed grain 52.5% of emergence holes were in the tip cap and 47.5% in the crown. T. castaneum did not multiply successfully in either form of millet storage.;Selected millet lines were compared for the effect of attached glumes and kernel aggregates on insect infestation. Attached glumes caused female weevils to oviposit over the endosperm instead of the preferred germ area and progeny numbers decreased slightly.;S. cerealella larvae survival was enhanced by presence of glumes on kernels and an apparently resistant line became susceptible. Artificial aggregates of glume-attached and glume-free kernels, simulating the effect of moth larvae webbing, increased weevil progeny and moth larvae survival. In a resistant line weevil progeny increased 12-fold when kernels were aggregated, there was no additive effect of attached glumes. S. cerealella increased 6-fold in aggregated glume-attached kernels.;Development of S. cerealella in single kernels of millet, sorghum, wheat and corn were compared over two generations. The largest moths were produced in corn and the smallest in millet regardless of sex or generation, with no consistent differences noted in moths obtained from wheat and sorghum. Eggs from females reared in millet were fewer, smaller and had lower hatch-ability than eggs from females reared in other grains. Loss caused over two generations was ranked corn > wheat (GREATERTHEQ) sorghum (GREATERTHEQ) millet and was correlated (P < 0.01) to body weight of emerged moths for all grains, except millet. Body and wing lengths were related to initial kernel weight of millet and wheat but not to that of sorghum or corn.;SEM micrographs showed pericarp structural differences among lines which influenced resistance to internal feeders. Surface texture had a distinguishable effect on S. oryzae; more eggs were deposited on smooth-seeded lines than on rough ones. Smooth-seed lines with loose layer arrangement were more susceptible to weevil infestation than smooth lines with compact pericarp layers. Smooth kernel surfaces seemed to be preferred by S. cerealella larvae as well.;The moisture content/relative humidity equilibria of four lines were compared. Adsorption isotherms were not represented by a single curve; however, no differences (P < 0.05) were found in desorption curves. At 70% R.H., maximum adsorption equilibrium moisture contents (EMC) for all samples were 13.5, 13.4 and 13.0% at 15(DEGREES), 25(DEGREES) and 40(DEGREES)C, respectively; and maximum desorption EMC's were 15.8, 14.5 and 14.0%. In a selected line the adsorption EMC of small seeds was 0.09% higher than that of large seeds at 70% R.H. and 25(DEGREES)C. Small seeds contained less crude fat and more protein, ash and crude fiber than large. |
