No description available.

No description available.

No description available.

No description available.

Doctor of Philosophy / Department of Entomology / C. Michael Smith / The Russian wheat aphid, Diuraphis noxia (Kurdjumov) (Hemiptera: Aphididae) (RWA), is an important pest in the U.S. Western Plains, causing hundreds of millions of dollars of losses to wheat and barley production through reduced yields and insecticide application costs. The objectives of this research were to evaluate the performance of two RWA-resistant barley varieties planted approximately one month earlier than normal in experimental fields at Fort Collins, Colorado; Tribune, Kansas; and Sidney, Nebraska during 2007, 2008, and 2009. The experimental design was a split-plot design with two main plot treatments (early and normal planting dates), and four split plot treatments (barley varieties) that were randomized within each main treatment plot. The varieties included two RWA-barley resistant varieties, Sidney and Stoneham, and the susceptible variety, Otis, under thiamethoxam-protected and unprotected regimes. Sampling of RWA, other cereal aphids, and natural enemy populations was conducted on four dates from mid May through early July. RWA populations collected from early-planted plots (first week of March) were significantly lower than normal-planted plots in 2007-2009 at the Fort Collins, Colorado and Tribune, Kansas sites. In samples collected from early planting date plots, RWA-resistant varieties yielded RWA populations similar to those found on the insecticide-treated susceptible variety at both Fort Collins and Tribune. At the Sidney, Nebraska site, very low RWA populations were present and there were no differences between either planting date or varietal treatments. The combined effect of early planting and RWA-resistant varieties reduced RWA populations at the Fort Collins, Colorado site in all three years. Results were similar at the Tribune, Kansas site in 2007, but differences due to planting date or variety were not observed in 2008 or 2009. The lowest RWA populations occurred at the Sidney, Nebraska site, were independent of planting date and varietal treatments. The RWA-resistant barley varieties had no negative impact on populations of other cereal aphids compared to those found on the susceptible variety, Otis at any of the three research sites. The only treatment effective in reducing other cereal aphids was the insecticide, thiamethoxam. There was also no clear response of populations of other cereal aphids to different planting date. Neither the RWA-resistant barley varieties nor the systemic, short residual action insecticide treatment had adverse affects on the abundance of natural enemies.

Master of Science / Department of Entomology / David C. Margolies / James R. Nechols / A two-year greenhouse experiment was conducted to compare the relative effectiveness of biological control versus chemical control for western flower thrips, Frankliniella occidentalis, as a means of reducing the spread of Tomato spotted wilt virus (TSWV) on tomatoes. To compare efficacy of different thrips management tactics for reducing TSWV incidence, tomatoes were subjected to one of three treatments: 1) biological control based on weekly releases of the predatory mite, Amblyseius cucumeris, at a commercially-recommended rate, 2) a single chemical treatment with Conserve®, a spinosad formulation, or 3) no treatment. TSWV was introduced into the greenhouse either by starting with 20% of the crop already infected and releasing non-viruliferous thrips, or by making a single release of viruliferous thrips. Analyses were done among thrips management tactics for each virus introduction method to examine the cumulative number of weeks plants were infected, the weekly proportion of infected plants, and total marketable yield. The effects of different virus introduction methods were also compared. A comparison of virus introduction methods showed that, among all plants, the average number of weeks they were infected by TSWV was significantly lower when virus was introduced through infected plants than by infected thrips. In addition, when virus was introduced by infected thrips, a significantly greater proportion of plants were infected in any given week than when virus was introduced on infected plants. Finally, crop yields were significantly lower when virus was introduced via infected thrips than on infected plants. Among thrips management methods, plants were infected for significantly less time, and the proportion infected was lower in any given week, when biological or chemical control was applied compared to no thrips management. Tomato yields were not affected by thrips management tactic. There was no significant difference between biological and chemical control in the length of time that plants showed symptoms. However, the proportion of infected plants was marginally greater with biological control in weeks 4 and 5 than with chemical control; differences were not significant thereafter. My findings suggest that inundative releases of biological control may provide as adequate a level of protection from TSWV as chemical control in commercial greenhouse tomato crops.

Master of Science / Department of Entomology / Yoonseong Park / Neuropeptides are diffusible signal molecules mediating vital physiological processes. We have been interested in a group of neuropeptides and their receptors involved in osmoregulatory neuroendocrine system which has been suggested as a possible target for development of new biopesticides. Since the genome sequence of the T. castaneum has recently been completed, we were able to identify the respective genes encoding three peptide hormones from T. castaneum that were characterized for their diuretic activities in other insects: one calcitonin-like (CT-like DH31) and two corticotropin releasing factor-like (CRF-like DH37 and DH47, the numbers indicates the number of amino acid residues). This peptide is expressed at all developmental stages and in the central nervous system (CNS), Malpighian tubules (MT) and gut. The synthetic peptide TricaDH31 also has been show to be biologically active, inducing significant excretions in adults beetles. When Tcdh31 was silenced using RNAi, adults had deformed wings and abnormal body shape. Mortality in adults was high, the number of eggs laid was reduced as well as the hatchability of the eggs. The two biologically active CRF-like peptides in T. castaneum, are encoded by one gene which undergoes alternative splicing. When Tcdh47 was knocked down, high mortality occurred as well as low oviposition and egg hatchability. Similar effects were observed with silencing of both CRF-like genes. However, RNAi of Tcdh37 transcripts had similar, but less severe effects. Adults also had deformed wings when both CRF-like genes were silenced, but not when just one of them was knocked down. These results indicate that CRF-like genes could have additional biological functions to their roles in dieresis. We tested the in vivo activity of these peptides. TenmoDH47 induced high excretions in adults, whereas TenmoDH37 induces smaller excretions. We identified the respective genes encoding two putative receptors for TricaDH31 as Glean_13321 and Glean_02694 (Trica-ctr1 and Trica-ctr2, respectively) and two receptors for CRF-like peptide as Glean_12799 and Glean_07104 (Trica-crfr1 and Trica-crfr2, respectively). The CT-like receptors are expressed at all developmental stages, in the CNS and MT. RNAi of the receptors revealed that only Trica-ctr2 silencing caused significant mortality and reduction in the number of eggs laid. The CRF-like receptors are expressed at all developmental stages. Adults also had deformed wings and laid fewer eggs after RNAi of Trica-crfr1. RNAi of Trica-crf2 also caused significant mortality. These peptides and receptors seem to fine tune the beetle physiology and may have functions not yet known.

Doctor of Philosophy / Department of Biology / Rollie J. Clem / Apoptosis is an extremely conserved process among metazoans. This dissertation will describe apoptotic regulation in two orders of insects, Lepidoptera and Diptera. In the lepidopteran host Trichoplusia ni, we describe phenotypes of infection with the baculovirus AcMNPV lacking the caspase inhibitor gene P35. In the lepidopteran host Spodoptera frugiperda, infection with this mutant virus results in apoptosis, which dramatically hinders spread of the virus in the host. In T. ni, however, infection with this mutant virus is similar to wild-type with normal spread, but the end result of liquefaction does not occur. Experiments indicated that infection of T. ni cells with the P35 mutant virus (P35Δ) resulted in caspase activation, and the P35Δ virus lacked the ability to inhibit these active caspases. With the P35Δ virus a slower entry phenotype was observed, but when the P35Δ virus was grown in the presence of a caspase inhibitor the entry phenotype was rescued. This indicated that caspases have detrimental effects on budded virions, and illustrated that P35 is needed to make robust virions. With regards to Diptera, apoptosis-regulatory genes were annotated in the yellow fever mosquito, Aedes aegypti. The genes annotated included multiple caspases and caspase regulators. Phylogenetic relationships were determined among the caspases from Anopheles gambiae, Ae. aegypti and Drosophila melanogaster, expression patterns were determined for all the annotated genes in Ae. aegypti, and one of the genes, an IAP antagonist named IMP, was functionally characterized. Further characterization of the phylogenetic relationships of caspases from fifteen dipteran species was performed by obtaining gene models for caspases of recently sequenced genomes for twelve Drosophila species and three mosquito species. Furthermore, several Drosophila and mosquito species were found to contain caspase genes with substitutions in critical active site residues. These genes were proposed to encode caspase-like decoy molecules. While these have been found in humans and nematodes, this is the first report for these molecules in insects. One of the caspase-like decoy molecules was found to increase the activity of its paralog caspase.

Clearcut harvesting can create conditions unfavourable to forest regeneration. In response, variable retention harvest methods are being investigated in montane forests on Vancouver Island, Canada. The effect of this overstory removal is unknown for canopy microarthropods, especially oribatid mites. As mites contribute significantly to nutrient cycling and decomposition processes in the canopy, changes in community structure and abundance may have dramatic effects on forest productivity. I studied the effects of two variable retention treatments, patch-cut and shelterwood systems, on arthropod communities associated with Abies amabilis (amabilis fir) branches and lichens. Changes in community structure were evident among the treatments and an old-growth control site. I also investigated the use of lichen abundance as a surrogate for oribatid mite abundance because it is time consuming and laborious to collect, count and identify microarthropods. Lichen abundance was a good predictor of mites in the old-growth and shelterwood, but not in the patch-cuts. Lichen abundance estimates should not replace biotic inventories, but can he used as an indicator when rapid biodiversity assessments are required.

Clearcut harvesting can create conditions unfavourable to forest regeneration. In response, variable retention harvest methods are being investigated in montane forests on Vancouver Island, Canada. The effect of this overstory removal is unknown for canopy microarthropods, especially oribatid mites. As mites contribute significantly to nutrient cycling and decomposition processes in the canopy, changes in community structure and abundance may have dramatic effects on forest productivity. I studied the effects of two variable retention treatments, patch-cut and shelterwood systems, on arthropod communities associated with Abies amabilis (amabilis fir) branches and lichens. Changes in community structure were evident among the treatments and an old-growth control site. I also investigated the use of lichen abundance as a surrogate for oribatid mite abundance because it is time consuming and laborious to collect, count and identify microarthropods. Lichen abundance was a good predictor of mites in the old-growth and shelterwood, but not in the patch-cuts. Lichen abundance estimates should not replace biotic inventories, but can he used as an indicator when rapid biodiversity assessments are required.