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Doctor of Philosophy / Department of Physics / Thomas W. Phillips / The emergence of heritable high-level resistance to the fumigant gas phosphine in stored-product insects is of grave concern to many grain growing countries around the world. The research reported in this dissertation was designed to determine the presence of phosphine resistance in 34 field collected populations of Rhyzopertha dominica (F.) from the United States and Canada, the potential to control resistant R. dominica populations utilizing high dose and longer exposure time strategies, and to develop a rapid assay for phosphine resistance detection. Using a discriminatory dose assay called the FAO number 16 method, adult R. dominica were sampled and subjected to a phosphine dose of 20 ppm for a fumigation exposure period of 20 h to distinguish a susceptible R. dominica adult by death from a resistant beetle that survives the treatment. Results from the study showed that 32 out of the 34 geographic populations surveyed had beetles resistant to phosphine, and the frequency of resistance varied from 97% in a population from Parlier, California to 0% in beetles from both Carnduff, Saskatchewan and Starbuck, Manitoba. A 20-hour dose response assay was used to characterize the level of resistance by calculating the resistance ratio factors using beetles from a laboratory susceptible strain and those from five of the populations sampled. This resistance ratio (RR) was based on the ratio of LC50 (estimate for the concentration to kill 50% of a test group) in the sampled population to the LC50 for the susceptible strain. The highest RR for the five resistant populations was nearly 596-fold in beetles from Belle Glade, Florida, which represented the “strong” resistance phenotype, whereas the lowest RR in that group was 9-fold in Wamego, Kansas, representing the “weak” resistance phenotype. Manipulation of concentration and exposure periods can be utilized to manage strongly resistant R. dominica populations. The effect of several phosphine concentrations and fumigation exposure periods were assessed on progeny of mixed life stage colonies of the strongly resistant R. dominica. A 48 hours dose response assay was carried out on these two strongly resistant populations to re-characterize their levels of resistance. Results from this assay showed that a phosphine dose of 730-870 ppm could control all resistant adult R. dominica. Additionally, phosphine concentrations ranging from 400-800 ppm phosphine for 96 hours completely killed mixed life stage colonies of strongly resistant lesser grain borers from the two populations studied. Lastly, fumigations done beyond 4 days at phosphine concentrations between 450-700 ppm controlled all phosphine resistant populations of lesser grain identified from our previous work. Phosphine applied at high concentrations is known to elicit a knockdown effect that can vary between susceptible and resistance grain insects. Using 18 of the 34 R. dominica populations this study sought to determine among three knockdown time (KT) techniques which method had potential to be utilized in an effective rapid assay for phosphine resistance in R. dominica. Adult R. dominica were exposed to a high concentration of phosphine (3000 ppm) to assess the time to knockdown 50%, 100% of a group of ten insects and that of single insects from the 18 geographically distinct populations vis a vis the resistance frequencies using the FAO method. KT100 quick test was better than the KT50 and Ktsingle, because bioassays were able to clearly distinguish among susceptible, weak and strong resistant individuals. Time for KT100 from susceptible populations did not exceed 30 minutes, while resistant populations had KT100 times above 30 min, with strong-resistant populations times longer than 100 min.

Doctor of Philosophy / Department of Grain Science and Industry / Subramanyam Bhadriraju / The lesser grain borer, Rhyzopertha dominica (F.), females lay eggs loosely outside of wheat kernels. Larvae hatching from eggs enter wheat kernels to complete immature development. Four laboratory experiments were conducted to understand the wheat kernel infestation by first instars of R. dominica at 28°C and 65% r.h. The first experiment compared different kernel to first instar ratios on sound hard red winter (HRW) wheat class, probability of successful infestation, and subsequent adult development as affected by site of feeding on the kernels. Infested kernels were dissected 21 d after infestation to determine stage of development and larval weight. Development of larvae to adulthood was monitored for 50 d from time of infestation. Different kernel to first instar ratios did not affect probability of infestation, entry site preferences, larval development and weight, and days to adult emergence. In the second experiment one first instar was placed with a kernel on each of seven different wheat classes. Wheat kernels were artificially-damaged with a microdrill at the germ, endosperm, and brush end, and the sound kernels served as the controls. At 21 d, 82-90% of artificially-damaged HRW wheat kernels were infested by larvae versus 12% for sound kernels. Five times fewer hard white (HW) wheat sound kernels were infested by larvae compared with infestation in soft white (SW) wheat kernels. Sound kernels of durum, soft red winter (SRW), hard red spring (HRS), and hard white spring (HWS) wheat classes were more resistant to larval infestation than artificially-damaged kernels. Majority of first instars preferred germ as the entry site on HRW, HWW, SRW, and HWS wheat classes. Germ entry promoted faster larval development, leading to heavier larvae, and higher kernel weight losses. Adult emergence was earlier by 3-7 d compared with other sites across all 6 wheat classes, except for SWW class, where adult emergence was nil at 50 d. In the third experiment, speed of larval development on artificially-drilled HRW wheat kernels on different kernel sites. Three-hundred kernels each were drilled near the germ, endosperm, and brush end, and one first instar was placed per kernel in a glass vial. Kernels from glass vials were dissected every 3 d for 30 d and larval head capsule was measured. Larval development was fastest on the germ, followed by endosperm, and brush end. In the fourth experiment short-term feeding by R. dominica adults on infestation by first instars on sound wheat kernels was determined. Two laboratory tests were conducted with single and grouped (10) kernels using either two adults or two first instars per kernel. Signs of feeding were monitored for 21 d in single kernels and 7 d in grouped kernels. There was a significant association between adult feeding and larval infestation responses in single and group kernel tests. In conclusion, understanding factors that contribute to first instar establishment in wheat kernels will have impacts in breeding varieties that could be resistant and designing grain-handling equipment to minimize grain damage to mitigate R. dominica infestation of wheat.

Doctor of Philosophy / Department of Entomology / James F. Campbell / Thomas W. Phillips / Movement is a fundamental feature of animals that impacts processes across multiple scales in space and time. Due to the heterogeneous and fragmented nature of habitats that make up landscapes, movement is not expected to be random in all instances, and an increase in fitness is an expected consequence for those that can optimize movement to find valuable and scarce recourses. I studied the movement of Rhyzopertha dominica (Coleoptera: Bostrichidae), one of the most important pests of stored grain worldwide, within and between resource patches. At a fine spatial scale, I identified factors that contribute to overall and upward movement in the grain mass. Three-week-old insects tented to stay closer to the surface than one or two-week-old insects. Females tended to be more active and to explore more than males. I also found that males tended to stay closer to the surface than females and that might be related to the ability to attract females from outside the patch since there was no significant difference regarding female’s attraction within the grain patch. Interaction with feeding sites or other individuals of the same sex creates positive feedback and a more clumped spatial pattern of feeding and foraging behavior. On the other hand, interaction with individuals of different sex creates negative feedback and a more random or overdispersed pattern. At a broad spatial scale, I studied the long-term consequence of R. dominica movement on the development of population structure within the U.S. To evaluate population structure, I used reduced representation of the genome followed by direct sequencing of beetles collected from different locations across the U.S where wheat or rice is produced and stored. Ecoregions were more important in explaining structure of R. dominica populations than crop type. I also found significant isolation by distance; however, model selection primarily elected grain production and movement variables to explain population differentiation and diversity. Understanding animal movement is essential to establishing relationships between distribution and surrounding landscape, and this knowledge can improve conservation and management strategies.