Doctor of Philosophy / Department of Entomology / R. Jeff Whitworth / The Hessian fly, Mayetiola destructor (Say), has been a historically significant pest of wheat in Kansas. However, it has been 60+ years since research has been conducted examining the flies’ activity throughout the year. Results of pheromone trapping in 4 counties in Kansas shows that Hessian fly (HF) males are actively flying in the fall, at least 1 month after the historical fly-free dates. Therefore, the Hessian Fly-Free Date is no longer valid and should be referred to as the Best Pest Management Date. Using pheromones for fall and spring trapping also indicated that HF is more active throughout the spring than previously thought, with almost continuous fly emergence and numerous emergence peaks in both spring and fall. The use of resistant wheat cultivars has been adapted to protect seedling plants from HF larval feeding in the fall. However, it is unknown if these cultivars are still providing protection after winter vernalization. Greenhouse trials indicated that ‘Armour’, a cultivar considered intermediately resistant, remains resistant under infestation levels of 1 fly/tiller but significant seed weight losses occured under infestations of 3 flies/tiller. In the field, Armour did not provide protection post-vernalization, with plants containing similar numbers of flaxseeds (pupae) as the susceptible cultivar, ‘Fuller’, and having significant losses of culm height (cm), number of spikelets/spike, number of seeds/spike, and seed weight (grams) when infested. ‘Duster’, a cultivar considered highly resistant, appeared to provide resistance to HF larval feeding in both the greenhouse and the field, and even produced significantly heavier seeds when infested with 3 flies/tiller in the greenhouse. These results suggest that post-vernalization screening should be conducted on all HF resistant cultivars to determine if each continues to provide protection. Little information is available showing if and how HF larval feeding on more mature wheat (Feekes 7-10), post-vernalization, impact plants, aside from lodging. Greenhouse and field infestations of a susceptible cultivar, Fuller, showed that significant losses of culm height (cm), number of seeds/spikelet, and seed weight will result from as few as 1 larva /culm. Yield losses averaged 0.13g/spike (65 kg/ha) compared to non-infested plants.

Doctor of Philosophy / Department of Entomology / Ming-Shun Chen / C. Michael Smith / The Hessian fly, Mayetiola destructor (Say), is a major pest of wheat, and is controlled mainly through deploying fly-resistant wheat cultivars. This study investigated five M. destructor populations collected from Texas, Louisiana, and Oklahoma, where infestation by Hessian fly has been high in recent years. Eight resistance genes including H12, H13, H17, H18, H22, H25, H26, and Hdic, were found to be highly effective against all tested M. destructor populations in this region, conferring resistance to 80% or more of plants containing one of these resistant genes. The frequency of biotypes virulent to resistant genes ranged from 0 to 45%. A logistic regression model was established to predict biotype frequencies based on the correlation between the percentages of susceptible plants obtained in a virulence test. In addition to the virulence test, the log-odds of virulent biotype frequencies were determined by a traditional approach to predict the logistic regression model. Characterization of a bacterial artificial chromosome (BAC) clone identified a gene encoding a protein with sequence similarity to bacterial levanases. Blast searching with the levanase-like protein identified 14 levanase/inulase-like genes or gene fragments. In this study, we determined the expression levels of these genes in different developmental stages and different tissues of 3-d old larvae of M. destructor. Sequence analysis revealed that six genes encode full length proteins, three were truncated at the 5’ end, and five truncated at the 3’ end. Sequences of putative proteins showed approximately 42% similarities to bacterial levanases or inulases, and 36% similarity to fungal levanases or inulases. No sequence similarities were found with any known animal or plant proteins. Comparative analysis of sequences among 14 levanase/inulase-like genes revealed that positions for intron/exon boundaries are conserved among different genes even though the length of each intron and exon varied among different genes. The expression patterns of the levanase/inulase-like genes were different among developmental stages and larval tissues of M. destructor. Interestingly, three genes presented alternative splicing bands in different developmental stages, and two genes exhibited splicing bands in different tissues of 3 d old M. destructor. This study would be useful for future studies of the characterization and function of levanase/inulase-like genes of these enzymes in plant-insect interactions.

Doctor of Philosophy / Department of Entomology / Brian P. McCornack / Timely enactment of insect pest management and incursion mitigation protocols requires development of time-sensitive monitoring approaches. Numerous passive monitoring methods exist (e.g., insect traps), which offer an efficient solution to monitoring for pests across large geographic regions. However, given the number of different monitoring tools, from specific (e.g., pheromone lures) to general (e.g., sticky cards), there is a need to develop protocols for deploying methods to effectively and efficiently monitor for a multitude of potential pests. The non-random movement of the Hessian fly, Mayetiola destructor (Say) (Diptera: Cecidomyiidae), toward several visual, chemical, and tactile cues, makes it a suitable study organism to examine new sensor technologies and deployment strategies that can be tailored for monitoring specific pests. Therefore, the objective was to understand Hessian fly behavior toward new sensor technologies (i.e., light emitting diodes (LEDs) and laser displays) to develop monitoring and deployment strategies. A series of laboratory experiments and trials were conducted to understand how the Hessian fly reacts to the technologies and how environmental factors may affect the insect’s response. Hessian fly pupae distribution within commercial wheat fields was also analyzed to determine deployment of monitoring strategies. Laboratory experiments demonstrated Hessian fly attraction to green spectrum (502 and 525 nm) light (LEDs), that response increased with light intensity (16 W/m2), and that they responded in the presence of wheat odor and the Hessian fly female sex-pheromone, but, response was reduced under ambient light. These laboratory experiments can be used to build a more targeted approach for Hessian fly monitoring by utilizing the appropriate light wavelength and intensity with pheromone and wheat odor to attract both sexes, and mitigating exposure to ambient light. Together this information suggested that light could be used with natural cues to increase attraction. Therefore, a light source (green laser display) was applied to a wheat microcosm, which resulted in greater oviposition in wheat covered by the laser display. Examination of Hessian fly pupal distribution within commercial wheat fields showed that proportion of wheat within a 1 km buffer of the field affected distribution between fields. This helps to inform deployment of monitoring strategies as it identified fields with a lower proportion of wheat within a 1 km buffer to be at higher risk Hessian fly infestation, and therefore monitoring efforts should be focused on those fields. Together this work demonstrates Hessian fly behavior toward new sensor technologies, how those technologies interact with environmental cues, and how environmental composition affects pupal distribution. Collectively this information will enable cheaper, more accurate and more efficient monitoring of this destructive pest.