Master of Science / Department of Grain Science and Industry / Subramanyam Bhadriraju / The development, relative retention, and oviposition of the red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae), on six different types of starches, wheat flour, and wheat flour plus yeast were investigated in the laboratory. The particle size of starch and flours were different; the mean size of 90% of particles for starches ranged from 15 μm for high amylose corn starch to 58 μm for potato, whereas that of the flour was ≤ 133 μm. Larval length, head capsule width, and weight gain of T. castaneum larvae were measured every 3 d on starches, flour, and flour plus 5% (by wt) yeast diet for 30 d at 28oC, 65% r.h., and 14:10 (L:D) photoperiod. Larvae reared on flour and flour plus yeast developed normally and showed better survival compared to those reared on starches. Larvae on the starches failed to develop beyond second, and rarely, third instars. Adults of T. castaneum did not show any preference to flour over starches in dual-choice tests in circular arenas. On average, T. castaneum laid less than 3 eggs/female over a 15-d period on starches compared to 97 and 109 eggs/female on flour and flour plus yeast diet, respectively. These studies suggest that starches are poor substrates for larval survival and development. Starches were as attractive as flour to adults; however, starches do not appear to be a suitable medium for egg-laying. Both aggregation pheromone and volatiles did not trigger oviposition behavior. Experiments by moving adults between wheat starch and wheat flour and vice versa showed that feeding on wheat flour was necessary for egg-laying, indicating the absence of essential nutrients in wheat starch. On wheat flour, feeding for 0.5 d was necessary to lay eggs. Females that were starved failed to lay eggs, reinforcing that the nutrional status of females and not males was essential for egg-laying. A minimum of 4% of wheat gluten (wheat protein) elicited egg-laying on starches, although 4-5 times fewer eggs were laid in starch gluten compared with wheat flour alone. Supplementing wheat starch with 1% cholesterol, in addition, to gluten, did not result in an increase in egg-laying by T. castaneum females. These findings suggest that starches may have potential in managing development and reproduction of T. castaneum—a pest that is common and severe in food-processing facilities. Furthermore, starches can be used as a suitable substrate for studying the nutritional ecology of T. castaneum.

Doctor of Philosophy / Department of Grain Science and Industry / Bhadriraju Subramanyam / Alternatives to chemical grain protectants are needed that have low mammalian toxicity and high specificity to insects with no adverse environmental impacts. This project investigated the viability of using a synthetic amorphous zeolite as a potential alternative to chemical insecticides and phosphine in Australian grain. We evaluated the impacts of moisture content and application rates on dust and grain physical properties; compared registered dusts with this promising novel dust in terms of impact on grain flowability; investigated changes in bulk properties of inert-dust treated grain; and we constructed dynamic dewpoint isotherms of hard red winter wheat and amorphous silica dusts for a better understanding of moisture interactional behavior of the synthetic amorphous dust based on wheat initial moisture content. Full sorption isotherms of zeolite and wheat obtained at 25, 35, and 45⁰C clearly exhibited the hysteresis phenomenon. The intensity of hysteresis remained unchanged with increasing temperatures for Hard Red Winter wheat (HRW), whereas, the intensity of hysteresis decreased with increased temperatures during water adsorption for the porous synthetic amorphous zeolite powder. Considering the IUPAC classification of isotherms, HRW had typical type II sigmoid shape isotherm, whereas, zeolite powder had a sorption isotherm close to resembling a type IV sigmoid shape isotherm. The hysteresis loops were of type H3 for HRW, and of type H4 for zeolite powder. Irrespective of sorption direction, DLP model was the best model to estimate zeolite and HRW sorption isotherms, followed by GAB and BET models, although BET model provided almost perfect fitting to sorption data in the water activity range 0-0.5. Particle size of the amorphous dust increased with increasing moisture content. Conversely, shape parameters (circularity, aspect ratio, convexity, and solidity) generally decreased with increasing dust moisture contents. When wheat was mixed with the amorphous dust at different rates and moisture levels, the bulk density of wheat decreased, while the tapped density and the angle of repose increased, resulting in higher Hausner ratios and Carr Index values. Treating wheat with the amorphous dust caused the treated wheat to transition from an acceptable flowability to a poor flowability, based on angle of repose, Hausner ratio, and Carr index data, which do not account for the interaction of wheat with the storage vessel. Our data suggest that a range of moisture content (2-6%) and an application rate (0.5 g/kg) mitigate the adverse effects on wheat flowability. However, based on flow rate index and specific energy requirements, flowability of wheat was generally enhanced by admixing wheat with the amorphous dusts. Wheat treated with Odor-Z-Way was comparable with wheat treated with Celite or Diafil as they all exhibited low cohesion, moderate permeability, and moderate sensitivity to aeration. Wheat treated with each of the three dusts became almost unstable due to segregation, moisture uptake, lower adhesion, and coating of the blade and test vessel. A decrease in bulk density was however observed, although the decrease was smaller when wheat was admixed with Odor-Z-Way. The susceptibility to Celite, Diafil, and Odor-Z-Way varied among stored-product insect species and also among the type of substrate (wheat or concrete). Adults of the lesser grain borer, Rhyzopertha dominica, were generally least susceptible to all three amorphous silica dusts; however, a complete suppression of progeny production was possible using Celite. Adult emergence was generally not prevented by Celite, Diafil, and Odor-Z-Way which suggested a lower insecticidal efficacy of the three dusts against early developmental stages. On concrete, Odor-Z-way was particularly effective at controlling all stored-product insect species after 24 h of exposure. In view of the bulk and dynamic flow properties and the insecticidal activity, Odor-Z-Way has potential to become a grain protectant provided that segregation and the decrease in bulk density are mitigated and that the insecticidal activity is not adversely affected by the seemingly low adhesion on wheat kernels.