Fitness cost estimates associated with resistance suggest that heterozygous and homozygous resistant insects are equally fit with susceptible insects. This may affect initial allele frequencies in field populations and persistence in resistant populations (e.g. Puerto Rico).

Behavior experiments suggest that there is not a strong difference between resistant and susceptible phenotypes in S. frugiperda and O. nubilalis. However, behavioral differences were observed between species. O. nubilalis exhibited increased movement between leaf discs, with susceptible neonates avoiding Cry1F tissue. In contrast, S. frugiperda selected plant tissue regardless of the presence of Cry1F, suggesting that refuge in a bag might be a suitable strategy for this pest. Understanding resistance in field-derived resistant populations will provide information for better risk assessments, improve predictions of resistance and maximize the benefits of current and future generations of transgenic crops.

Advisor: Blair D. Siegfried

Grasshoppers belonging to subfamilies Melanoplinae, Gomphocerinae and Oedipodinae differ in biology and ecology, and were tested in a greenhouse experiment for feeding preference on switchgrass cultivars (Shawnee, Kanlow) and big bluestem. The data indicated a strong preference of Melanoplus differentialis for switchgrass (P ≤0.001). Melanoplus femurrubrum and Arphia xanthoptera also preferred the Shawnee cultivar. Further, the relative water content of the plants influenced consumption by M. differentialis which ate more healthy leaves than wilted leaves. The differences among grasshopper species suggested that Melanoplinae grasshoppers could become destructive pests of switchgrass fields.

In addition to consumption, grasshoppers also cause feeding damage through vegetation clipping. Two grasshopper species were tested to quantify the amount of clippings at high, moderate and low moisture levels for little bluestem, Schizachyrium scoparium and buffalograss, Bouteloua dactyloides. All tested grasshopper species generated clippings. Relative water content of the grass affected the amount of clipping and differed by grasshopper and plant species. The results indicated that water content of the plant and species of grasshopper are important factors in damage. This study will aid in defining economic injury levels for rangeland grasshopper species.

Two unidentified forms Melanoplus bowditchi "frigidus" and Melanoplus bowditchi "tridentatus" along with described subspecies of M. bowditchi were compared for morphological and genetic variations. No consistent differences among the aedeagal parameres or basal rings of the four forms were found. Amplified Fragment Length Polymorphism markers (AFLP) were used to test the genetic variation among the forms. Although the forms show behavioral and minor morphological differences, the genetic data showed all forms interbreed. The results of this study indicate that host plants can influence phenotype and suggest the need for further genetic analysis of subspecies recognized based on morphology.

Advisors: W. Wyatt Hoback, John E. Foster

Advisers: Thomas E. Hunt and Tiffany M. Heng-Moss

Experiments testing the effectiveness of bait away methods revealed that bait stations did not draw significant numbers of ABBs out of mock “construction” zones and did not successfully keep ABBs at bait stations. Even with the use of vertebrate excluder cages, there was mortality caused by northern leopard frogs (Lithobates pipiens Schreber), and without the cages, video captured opossum (Didelphis virginiana (Kerr)) consuming ABBs at a bait station. Bait away stations should no longer be used to clear areas of ABBs for habitat alteration.

In Nebraska, a large portion of the known ABB distribution overlaps with distributions of economically damaging grasshoppers that are managed using Dimilin and Malathion pesticides. Dimilin was found to have some negative effects on N. orbicollis Say brood success when carcasses were exposed to the pesticide and then later used for larval development. Malathion caused direct mortality of N. marginatus Fabricius, a diurnal species, when sprayed directly, but would be unlikely to directly harm nocturnal ABBs. Indirectly, Malathion on a carcass might stress parental beetles and cause changes in brood size. Dimilin use should be restricted to periods with little ABB aboveground activity until further research can pinpoint the associated risks.

Advisors: W. Wyatt Hoback and Shripat T. Kamble

Results of these studies show that thiamethoxam is highly active against adult bean leaf beetles. Commercial rates and bioassay concentrations of thiamethoxam provide effective control causing lethal and sublethal effects. The quantification of insecticide levels in soybean leaves from new nodes over time indicate that thiamethoxam provides control at early vegetative growth stages, but insecticide concentrations fall off as the plant grows and insecticide available for uptake becomes limited. These results provide a foundation for resistance monitoring and detection.

Advisors: Thomas E. Hunt and Blair D. Siegfried

Traditional stable fly management employing sanitation and insecticides is costly and often fails to provide acceptable levels of control. A novel method for managing stable flies involves the use of attractants and repellents. This approach could be used to enhance the current level of stable fly control and ultimately be incorporated into a sustainable stable fly management program.

Gravid females’ stable flies use chemical cues from host animals and the environment to locate suitable hosts, mates, and oviposition sites. Understanding stable fly olfaction and the electrophysiological responses to host seeking and ovipositional stimuli is essential for exploring stable flies’ behaviors stimulated by odor cues. This study characterized the number, location and types of stable fly sensilla on antennae. Accompanying electroantennogram studies assessed antennal responses to host-associated volatile compounds. The attractiveness / repellency of selected naturally occurring compounds to stable fly feeding and oviposition were investigated under laboratory and field conditions. Four majors’ types of sensilla were documented: basiconic, clavate, coeloconic, and trichoid with three subtypes. Results of electroantennogram studies revealed significant antennal responses to host-associated compound; for example, 1-octen3-ol, phenol, p-cresol, indole, and dimethytrisulfide. Catnip (Nepeta cataria L.) oil and its constituent nepetalactones compounds provided significant repellency of stable flies. Combinations of host derived volatile compounds (phenol and m- or p-cresol) were more attractive to stable flies than a single compound alone.

Advisors: Frederick P. Baxendale and Junwei J. Zhu

Currently, three colonies of WCM have been characterized by differential responses to mite resistant genes (biotypes) in wheat and differential transmission of WMoV. A study was designed to determine TriMV transmission for these various wheat curl mite colonies. For each source plant, individual mites were transferred to 10 separate test plants and virus transmission determined via ELISA. Results indicate that TriMV is only transmitted by one of the three wheat curl mite colonies using single mite transfers.

An additional study was conducted to determine the impact of TriMV on the biology of the WCM. TriMV infected and uninfected plants were infested with 10 mites from each colony with population counts being taken every seven days. Results indicated that TriMV had a negative impact on the reproductive potential of the WCM. The results demonstrate the importance of the mite source on virus epidemiology.

Management tactics to reduce the impact of the wheat-mite-virus complex have focused primarily on the control of volunteer wheat; however, these tactics are not always effective at reducing yield losses. A field study was conducted from 2007-2011 to determine the impact of the combination of resistant variety and planting date on wheat yields under high virus pressure. Results indicated that both management tactics had a significant impact on yield; however, the combination of tactics provided the greatest yield potential under high virus pressure.

Advisor: Gary L. Hein

Adjacent land use, shelterbelt composition, and time of day were all factors which did not influence the number of questing ticks collected. Differences in relation to aspect and distance from the shelterbelt were significant. The east side had continually higher numbers of questing ticks than the north, south and west. The duration of tick activity was reduced on the north side. Solar radiation, soil moisture and soil temperature could influence tick emergence from diapause resulting in the first cohort of the year.

Based on my findings, the entomological risk for land management can be augmented, tick control strategies can become more effective and less wasteful, and knowledge of the presence of the various species of ticks can impact policies on public health and education.

Advisor: Manuel Roberto Cortinas

Advisers: Tiffany Heng-Moss and Thomas E. Hunt

To address this, the current project was composed of two experiments. Experiment one was conducted to investigate the effect of surface type on carcass decomposition and evaluate soil ecology methods. Experiment two was conducted to investigate the presence of an insect population (Lucilia sericata Meigen) on gravesoil microbial communities. Both experiments were conducted in a laboratory setting using freshly killed mouse carcasses. Mouse carcasses were placed on either a plastic petri dish without soil or on a sand/soil mix (90/10 or 50/50) and calibrated to 55% water holding capacity. Carcass decomposition was measured as mass loss and total body score. Gravesoil microbial communities were analyzed as lipid-phosphorous and fatty acid methyl esters. Carcass decomposition was measured over 35 days at 20˚C (experiment 1) and 22˚C (experiment 2).

Major findings were that surface type affects the rate of carcass decomposition; carcasses decompose faster on soil. Also, the presence of a carcass on soil resulted in a significant increase in soil microbial biomass. Interestingly, the presence of insects did not affect soil microbial biomass, but it did affect the soil microbial community. Changes in microbial community structure were observed after seven days of decomposition. These gravesoils were associated with significantly different concentrations of bacteria, eukaryotes, and arbuscular mycorrhizal fungi. These findings are insightful, because they show that soil based methods in forensic science must account for the presence of insects to be accurate in estimating postmortem interval.

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Comparison of the attractiveness of native and exotic herbivore, carnivore, and omnivore dung yielded 9,089 dung beetles from 15 species. Significant differences were observed in mean dung beetle capture and individual species preference among the dung of omnivores, herbivores, and carnivores. Omnivore dung and carrion were most attractive; however, preference for a specific dung type was not correlated with dung quality or mammalian diet.

Dung beetles are exposed to hypoxic conditions throughout much of their life cycle. Data on hypoxia tolerance of five species of adult dung beetle (Aphodius haemorrhoidalis, Canthon pilularius, Melanocanthon nigricornis, Onthophagus hecate, and Phanaeus vindex) yielded no differences in mean survival time (LT50) among behavioral groups, which ranged from 7-37 hours.

Digitonthophagus gazella (F.) has been intentionally released in numerous areas around the world. Using amplified fragment length polymorphism (AFLP) analysis, genetic variation was examined between two populations of D. gazella from South Africa and Vieques, Puerto Rico. Analysis of molecular variance (AMOVA) revealed 69% of genetic diversity to be within populations, while 31% of genetic diversity was between the populations indicating little gene flow. Genetic diversity was high in both South Africa and Vieques with no evidence of inbreeding depression on Vieques. These data are helpful in understanding the population dynamics of dung beetles through knowledge of the effects of agricultural practices, niche separation, and genetics.

Studying the population genetics of stable flies could provide information on their population dynamics, origins of outbreaks, and geographical patterns of insecticide resistance. Many studies have been conducted on a local scale, most reporting a high level of gene flow between locations. To date, few studies have been conducted on a global scale. Here I report a study of samples acquired from

4 biogeographical regions: Nearctic, Neotropical, Palearctic and Australian. No samples were acquired from the Oriental region.

The results indicate a high level of gene flow on a global scale. F_ST and G_ST values are low, and Nm values very high. The tests of neutrality suggest population expansion, and tests for genetic differentiation simply reported “no differentiation”. AMOVA results show the majority of genetic diversity is within groups, and very little among groups. These results suggest that stable flies have a panmictic population, with no isolation by distance or across geographical barriers.

Advisors: Steven R. Skoda and John E. Foster

Adviser: Lance J. Meinke

Analysis of molecular variance (AMOVA) using AFLP revealed that the majority (71.2%) of the total variation is within FAW populations; only 28% of the variation was among populations. This indicates significant gene flow for FAW throughout the Western Hemisphere. Also, cluster analysis showed the lack of regional genetic structuring. Moreover, there was no significant correlation between genetic dissimilarity and geographic distance, except for the Argentina samples, suggesting the presence of gene flow.

The FAW population in Puerto Rico remains susceptible to the insecticides used for its control. The insecticides Radiant, Orthene, and Larvin caused ˃ 60% FAW mortality 16 h after application. Generally larval mortality increased with time after insecticide application; 96 h after application the majority of the insecticides gave ˃ 80% control. Moreover, the dose rate study on selected insecticides showed that the current dosage used by DAS is sufficient to control the FAW.

I also studied the beneficial insects associated with native Nebraska flora. Seventeen species of native, perennial flora were established in 3 separate plots located in eastern Nebraska. I transplanted four plants of each species in randomized 0.61 m x 0.61 m squares of a 3.05 m x 9.14 m plot. Arthropods were sampled using a modified leaf blower/vacuum. Insects and other arthropods were identified to family and organized into groups of predators, parasites, pollinators, herbivores, and miscellaneous. Associations between plant species and families of beneficial arthropods (predators, parasites, and pollinators) were made. Pycnanthemum flexuosum Walter attracted significantly more beneficial arthropod families than 7 other species of plants tested. Dalea purpurea Vent and Liatris punctata Hook also attracted significantly fewer beneficial arthropod families than 4 other species of plants tested. In total, 31 predator, 11 parasitic, 4 pollinator, 31 herbivore, and 10 miscellaneous families of arthropods were recorded.