Search

Blood-seeking mosquitoes primarily rely on thermal and chemical cues as they navigatetowards hosts. Mosquitoes display specific preferences for target host temperature whileavoiding harmful ambient temperature. This behavior known as thermotaxis is in partregulated by the nociceptor transient receptor potential ankyrin 1 (TRPA1), which isexpressed in thermosensitive sensilla of mosquitoes. TRPA1 of female mosquitoes isknown to detect both noxious temperatures and chemicals; when activated by thesestimuli, TRPA1 triggers avoidance behaviors. Therefore, TRPA1 is considered apotential biochemical target for mosquito repellents and antifeedants. One aspect ofTRPA1 channels from mosquitoes and other insects that has not been fully studied is thepotential interactions between temperature and chemical agonists. In this study, Iexamined whether high ambient temperatures that activate Aedes aegypti TRPA1(AaTRPA1) influence the sensitivity of the channel and behavior of mosquitoes torepellent TRPA1 chemical agonists. First, I expressed AaTRPA1 heterologously inXenopus laevis oocytes and used whole-cell two-electrode voltage clamping to measureTRPA1 activity. I found that the electrophysiological response of AaTRPA1 to twochemical agonists (catnip oil, citronellal) was significantly reduced while the channel wasactivated by a thermal stimulus ( ~38°C). Moreover, in behavioral bioassays, I found that adult female Ae. aegypti were less repelled by catnip oil when exposed to a noxioustemperature (~50°C). Collectively, my results suggest that TRPA1-agonizing repellents,such as catnip oil, may be less efficacious during extreme heat events, which arebecoming more common as global climate change progresses.

Tomato (Solanum lycopersicum) is one of the most economically important vegetable crops grown around globe but is a host for numerous pests and pathogens. In the future, tomato breeders will have to focus on increasing fruit quantity and on enhancing pest resistance. Many accessions of the wild relative of tomato, S. habrochaites display high levels of resistance towards arthropods such as spider mites. The presence of the sesquiterpene hydrocarbon, 7-epi-zingiberene, found in S. habrochaites type IV trichomes has been associated with arthropod resistance. However, the presence of other compounds in its trichome secretions may also be related to arthropod resistance. One goal of this research was to evaluate the potential for using a spectrophotometer to enable accurate selection for 7-epi-zingiberene content by breeders. Another objective was to identify and evaluate the relative antixenotic activities on spider mites of major components present in the trichome secretions of a wild tomato. The third objective was to evaluate yield, 7-epi-zingiberene content and fruit nutrient quality in advanced interspecific hybrid lines to demonstrate that high yield and high zingiberene content have been successfully combined, and also to evaluate nutritional aspects of fruit quality of these hybrids such as phenolic content, lycopene, soluble solids, and ascorbic acid. Results for the first objective included identification of two novel compounds present in wild tomato trichome secretions as hydroxy-zingiberene and 9-hydroxy-10,11-epoxy-zingiberene. The spider mite repellency of each of these compounds was at least five times greater than that of 7-epi-zingiberene. The results for objective two showed that a spectrophotometer could be a very valuable tool for aiding selection of plants having high levels of 7-epi-zingiberene on their leaves and having low levels of other compounds such as monoterpenes, which are present on arthropod –susceptible tomato plants. Completion of the third objective indicated that high yield has been successfully combined with high 7-epi-zingiberene concentration and that the nutritional value of the fruit in the hybrids is at least equal to the recurrent parent and in some cases, the interspecific hybrids may be useful for improving tomato fruit nutritional content including: phenolics, lycopene, soluble solids, and ascorbic acid. In general, the phenolic content of interspecific hybrid tomatoes ranged from 325 to 427 μg/g fresh fruit, lycopene content ranged from 31 to 66 μg/g and soluble solids ranged from 4 to 7.8%, whereas those characteristics were lower in cultivated tomato hybrids. Ascorbic acid typically ranged between 483 and 498 μg/g fresh fruit in interspecific hybrids and was higher than that in cultivated tomato hybrids (337 μg/g). For future prospects, it may be possible to breed genotypes that have high yield, have improved nutritional value and are also resistant to arthropod pests.

The loss of managed honey bee colonies, resulting from their unintentional exposure to pesticides, is a topic of concern for the agricultural and apicultural industry. Current methods for reducing pesticide exposure to bees involve the application of pesticides before crop bloom or in the evening when foraging bees are less likely to be exposed to these applications. There is an urgent need for additional protection procedures to reduce the annual losses of managed bee colonies. Another method for protecting these pollinators is the use of chemical deterrents to reduce the interaction times of foraging bees with pesticide-treated crops. Historically, insect repellents (IRs) have been used to prevent the spread of deadly human diseases by arthropod vectors. However, it has been shown that bees can be repelled from pesticide-treated crops using DEET and bee pheromonal compounds. Here, I report the toxicological and deterrent effects of bee pheromonal compounds, as well as the deterrent effects of heterocyclic amines (HCAs) on bees. The results of this study indicate that the bee pheromonal compounds, at 8, 20, 60 and 100% concentrations, are toxic to bees and inhibit the feeding of bees within a confined space. Additionally, the pheromonal compounds and the HCAs are as efficacious as DEET in deterring bees from treated food sources. The HCA piperidine was observed to effectively deter bee foragers from a sugar feeder in a high-tunnel experiment as well as from melon flowers and knapweed in field experiments. Electroantennogram recordings were conducted to verify an olfactory response of the bees to the tested compounds. Pheromonal compounds were readily detected by bee antennae; whereas, the HCAs did not elicit significant responses in the bee antennae. These data suggest that bee pheromonal compounds, as well as HCAs, may serve as candidates for the further investigation as repellents to protect bees from unintentional pesticide exposures.

Managed honey bee colonies provide valuable pollination services and are rented by fruit orchards to improve fruit quality and yield. The placement of colonies in this agricultural setting increases the possibility of exposure to pyrethroids used for broad-spectrum pest control in orchards. Although highly toxic to bees, pyrethroids are believed to pose a relatively low hazard due to their low application rates in the field as well as their contact repellent properties. Previous studies have noted a decrease in foraging visits following pyrethroid application possibly preventing bees from acquiring a lethal dose in the field. This research quantified behaviors associated with sub-lethal exposure to orchard-applied pyrethroids, lambda-cyhalothrin, esfenvalerate, and permethrin, using video tracking software, Ethovision XT (Noldus Information Technologies). Bee locomotion, social interaction, and time spent near a food source were measured over a 24-hour period. This project also evaluated the repellency of pyrethroids currently used in orchard production to foraging worker bees under artificial feeding conditions and in a field setting. The objective of this study was to achieve a better understanding of behavioral effects associated with sub-lethal pyrethroid exposures in the laboratory and determine if a field-relevant exposure would result in repellency of foragers. This research will aid in the development of better-informed management decisions made by both growers and beekeepers and provide risk assessment tools and protocols to regulatory agencies seeking to quantify sub-lethal pesticide effects on pollinators. Advisers: Marion Ellis and Blair Siegfried

Insect-proofing of wool is usually carried out by application of insecticides during dyeing. Inefficiencies in absorption of insecticide onto wool lead to aqueous effluent containing low levels of insecticide with a significant environmental toxicity to aquatic organisms. Replacing insecticides with non-insecticidal alternatives that target the wool digestion process of insects could greatly reduce the aquatic toxicity of wool processing effluent. Three classes of non-insecticidal compounds were investigated, including surfactants, naphthalene derivatives, and antimicrobials. Selected compounds were applied to wool fabrics for testing against wool-digesting Tineola bisselliella moth and Anthrenocerus australis beetle larvae. Anti-feeding effects were measured and used to form hypotheses on molecular shape, size and polarity and their contribution to insect-proofing. The antifungal propiconazole was chosen as the most likely compound to be targeting the wool-digestion process, as seen in Anthrenocerus australis larvae. To elucidate the mode of action of propiconazole on Anthrenocerus australis, repellency trials were carried out using control versus treated wool in reversible petri dish, and irreversible olfactometer choice experiments. No repellency effect was detected. Direct contact experiments were carried out by application of propiconazole solutions directly to Anthrenocerus australis larvae and by feeding larvae propiconazole-treated wool. No short or long-term toxic effects were detected, and subsequent feeding on untreated wool was not reduced. Gut enzyme activities were measured for Anthrenocerus australis fed control wool and compared to larvae fed propiconazole-treated wool. Trypsin, chymotrypsin, and aminopeptidase activities were significantly (p-value

The common bed bug has reemerged as a major pest in the United States. Pest management professionals need reliable up-to-date information on how to manage bed bug infestations. My study was intended to evaluate the efficacy of several insecticides currently labeled for bed bug control. In product efficacy tests, field strain bed bugs were found to be 99-450 times less susceptible than laboratory strain bed bugs to several pyrethroid products. The non-pyrethroid products tested, chlorfenapyr and a non-toxic desiccant dust, killed laboratory strain bed bugs, but were extremely slow acting taking greater than 9 days to kill 50%. None of the insecticides tested, including the pyrethroids, were repellent to laboratory or field strain bed bugs. A field test was conducted comparing 2 pesticide treatments regimens (traditional and novel) for bed bug control in low income apartments. Both the traditional and novel combinations caused significant reductions in bed bug populations. Both treatments reduced the number of bed bugs by the end of the test period, but neither treatment combination completely eliminated the bed bug infestations, even after an average of 1.3 gallons of product was applied in each apartment. Laboratory assays were conducted to determine the effect of hydroprene exposure on bed bug development. Although hydroprene did not appear to interfere with nymphal development, fifty percent of the bed bugs died during the final molt. The bed bugs which survived to adulthood showed no reduction in fecundity when compared to control groups.

Mite outbreaks occur after use of pyrethroid insecticides. Dosage mortality data of two pyrethroid insecticides, fenvalerate and flucythrinate, was obtained for the two spotted-spider mite (Tetranychus urticae Koch). LC₅₀'s were determined using slide dip and leaf disc techniques. The leaf disc method was used to measure sublethal effects such as repellency and changes in oviposition. There was a four fold difference between LC₅₀'s for flucythrinate derived by slide dip and leaf disc methods (0.43 g a.i.l⁻¹ and 0.11 g a.i.l⁻respectively). LC₅₀'s for fenvalerate derived by slide dip and leaf disc methods were similar (0.34 g a.i.l⁻¹ and 0.45 g a.i.l⁻¹ respectively). Both flucythrinate and fenvalerate repelled T. urticae . At 1 g a.i.l⁻¹ of flucythrinate mean run off was 3.9+0.5 compared to 3.3±0.9 from leaf discs treated with the same concentration of fenvalerate. Mean run off from untreated controls was 0.45 ± 0.60 and 0.3 ± 0.5 for flucythrinate and fenvalerate treatments respectively. Flucythrinate was not directly toxic to TSM. Mean direct mortality of the untreated control and the highest concentration of flucythrinate (2 g a.i.l⁻¹ ) was the same (0.3±0.5). Oviposition was reduced by fenvalerate and flucythrinate. At 1 g a.i.l⁻¹ of flucythrinate mean egg production per surviving female was 0.1±0.3 compared to 1.1±0.7 at 1 g a.i.l⁻¹of fenvalerate. There were no differences in repellency, direct mortality or egg production of T. urticae treated with various formulations of flucythrinate.