Selenium (Se) has contaminated soils and plants in the western USA and other regions where pollination can be critical to the functioning of both agricultural and natural ecosystems, yet we know very little about how pollutants can impact insect pollinators. The overall goal of this dissertation was to investigate both the toxic effects of a plant-accumulated pollutant (Se) on a common pollinator, the honey bee (Apis mellifera L., Hymenoptera: Apidae).

I investigated the accumulation of Se in two phytoremediating species, Brassica juncea and Stanleya pinnata. The plants were irrigated in the greenhouse with selenate, and accumulated significantly quantities in the nectar (110 and 150 µg Se ml^-1 ww) and pollen (1700 and 12900 µg Se g^-1 dw, respectively). These concentrations are much higher than the Se LC₅₀'s for certain insects.

I used proboscis extension reflex bioassays to determine if the Se affected the gustatory response of honey bee foragers. Antennal stimulation with selenomethionine reduced PER at higher concentrations. Foragers dosed with selenate had higher mortality and reduced responses to sucrose, which may lead to decreases in incoming floral resources needed to support coworkers and larvae in the colony.

In a semi-field study, the weedy plant Raphanus sativus (radish) was exposed to selenate watering treatments to evaluate the effects on pollination ecology. Honey bee pollinators were observed to readily forage on R. sativus for both pollen and nectar despite high floral Se concentrations. Se treatments increased seed abortion and decreased plant biomass, but herbivory by birds and aphids was also reduced, indicating a potential tradeoff of phytotoxicity and protection from Se.

I used artificial diet bioassays to determine the toxicity of four Se compounds that occur in accumulating plants. Apis mellifera larvae were chronically fed Se, and the inorganic forms were more toxic (LC₅₀ selenate = 0.72 µg g^-1, LC₅₀ selenite = 1.03 µg g^-1) than the organic forms (LC₅₀ methylselenocysteine = 4.09 µg g^-1, LC₅₀ selenomethionine = 6.04 µg g^-1). All four forms decreased the percentage of larvae that pupated, and selenate and methylselenocysteine significantly decreased larval growth rates. Taken together, the dissertation research from the past five years represents a crucial first step towards understanding the impact environmental stressors can have on pollinator-plant interactions and specifically, the honey bee, Apis mellifera.

The potato/tomato psyllid, Bactericera cockerelli (Sulc) (Hemiptera: Triozidae) is a major pest of solanaceous crops. This pest causes yield loss by direct feeding on crop plants and by transmitting a bacterial pathogen known as Candidatus Liberibacter psyllaurous (a. k. a. Ca. L. solanacearum). The goal of my research is to improve pest management against this pest in potatoes by integrating sampling, insecticides, use of resistant varieties, and biological control.

Sampling plans are essential part of integrated pest management (IPM). From my research on potatoes, I determined the most efficient sampling unit, and that this pest has an aggregated distribution in the field. Binomial sequential sampling plans were developed for the potato psyllid. Current pest management practices in the USA rely on the intensive use of broad-spectrum insecticides to control the potato psyllid to lower disease incidences and increase yields. I evaluated five insecticides in the laboratory. All insecticides tested significantly reduced probing durations and increased the amount of time adult psyllids spent off the leaflets compared to untreated controls suggesting that these chemicals may be deterrents to feeding as well as repellents. Additionally, I further tested the effects of imidacloprid on potato psyllid feeding behavior using a direct current electrical penetration graph technique.

Host plant resistance can be an integral component of an integrated approach for the management of arthropod pests. I tested the effects of potato germplasm from 22 genotypes on adult potato psyllid behavioral responses for possible antixenosis and determined if specific breeding clones or varieties can decrease transmission of Ca. L. psyllaurous. Another assessment that should be made in an IPM program is the potential role of natural enemies in controlling pests. Through two years of field studies (2009-2010) at four different sites and laboratory feeding tests, I have identified Orius tristicolor (White) (Hemiptera: Anthocoridae), Geocoris pallens Stal (Hemiptera: Geocoridae), Hippodamia convergens Guerin-Meneville (Coleoptera: Coccinellidae), and the parasitoid Tamarixia triozae (Burks) (Hymenoptera: Eulophidae) as key natural enemies of the potato psyllid in southern California potatoes, tomatoes, and bell peppers. I discuss how this information can be used in an integrated pest management program for the potato psyllid.

Many countries are utilizing reclaimed wastewater for agriculture because drought, rising temperatures, and expanding human populations are increasing water demands. Unfortunately, wastewater often contains biologically-active, pseudopersistant pharmaceuticals, even after treatment. Runoff from farms and output from wastewater treatment plants also contributes high concentrations of pharmaceuticals to the environment. However, there is a lack of information on how these pharmaceuticals could affect insects living in these environments, the insects’ microbial communities, and possible pest management applications. The overall goal of this dissertation is to form a base groundwork to assess the effects of common pharmaceuticals on important insect pests in different feeding guilds. The findings of this research demonstrate a wide range of effects from insect to insect with some unexpected effects.

Culex quinquefasciatus larvae reared in water contaminated with certain pharmecuticals were found to have increased developmental time, susceptibility to Bacillus thuringiensis subsp. Israelensis, and altered microbial communities. Within control treated C. quinquefasciatus, the predominant families of bacterial symbionts change with each larval instar despite consistent diets and rearing conditions. This trend was not observed the antibiotic or the mixture treatments. Interestingly, the mixture treatments had greater richness and evenness compared to antibiotic alone treatments, possibly due to the other contaminants facilitating growth of different bacteria.

Female Megaselia scalaris flies showed no oviposition preference for treated or untreated diets. Larvae exposed to certain pharmaceuticals in artificial diets showed increased mortality, signs of slowed development, especially in females, and altered sex ratio. There was an overall effect of treatment on the flies’ microbial communities; notably, caffeine fed insects displayed higher microbial variability.

Trichoplusia ni showed increased developmental time and mortality when reared on artificial diets containing antibiotics, hormones, or a mixture of contaminants. Mortality was also increased when T. ni were reared on tomatoes grown hydroponically with the same concentrations of antibiotics. Microbial communities of T. ni changed substantially between developmental stages and when exposed to CECs in their diets.

Arsenic is a widespread contaminant of aquatic systems worldwide, and though the toxic effects on vertebrates are well understood, the impacts of chronic arsenic exposure on lower trophic levels of insects have received little attention. The overall goal of this dissertation was to investigate the sublethal effects of arsenic on aquatic primary consumers, and how they could transfer arsenic from aquatic to terrestrial environments.

I investigated the effects of arsenic on survival, growth, and reproduction of Chironomus riparius. There was a significant increase in the time between male and female emergence when exposed to 1000 μg/l as larvae, and a significant decrease in the number of eggs produced per egg mass. Total arsenic body burdens decreased 72% between larval and adult stages.

Larvae of Culex tarsalis and Culex quinquefasciatus exposed to arsenate or arsenite were assayed against Bacillus thuringiensis var. israelensis or Lysinibacillus sphaericus microbial pathogens to determine shifts in survival curves resulting from arsenic accumulation. Arsenic did not affect growth and survival of these mosquitoes compared to controls. Culex tarsalis was the more sensitive species, but both species were tolerant to arsenic exposure.

X-ray absorption spectroscopy was used to map the localization and biotransformation of arsenic in various life stages of C. riparius and Cx. tarsalis. Chironomus riparius larvae accumulated arsenic in the midgut, while adults had arsenic distributed throughout the exoskeleton. There was evidence for reduction of arsenate to arsenite, and production of an As-thiol. In Cx. tarsalis, arsenic was found throughout the larval and adult bodies.

Behavioral assays on Cx. tarsalis revealed no effects of prolonged arsenic exposure on frequency or duration of measured behaviors, including time spent resting, gliding, diving, and swimming. There was a limited effect of exposure on predator avoidance behaviors, but interactions made patterns difficult to discern.

The trophic transfer potential of arsenic from aquatic to terrestrial environments was evaluated by feeding contaminated Cx. tarsalis to aquatic and terrestrial predators. Results suggest that overall the trophic transfer of arsenic is more likely to occur within an aquatic system, although transfer to terrestrial predators may play an important role in arsenic cycling during periods of mass emergence of insect prey.

Ants have often been described as keystone species for the critical roles they play that contribute to ecosystem functioning. Evidence from Europe and Australia has improved our understanding of the impacts of disturbance, including pollution, on native ant communities. However, there is a lack of information available for North American ant communities. The overall goal of this dissertation was to assess the effects of selenium, a globally widespread element and environmental contaminant in certain regions of the U.S., on the survival, behavior and reproduction of the invasive Argentine ant, Linepithema humile. The findings of this research highlight the unexpected role of pollution to act as a potential barrier to range expansion for invasive ant species.

Chronic ingestion of four environmentally common forms of selenium at environmentally reported concentrations, were found to cause mortality among Argentine ant workers. The extent of mortality was found to be dependent on the form of selenium. In addition, mortality and bioaccumulation of selenium increased with the duration of exposure and concentration. Furthermore, Argentine ants were not deterred by lethal concentrations of selenium in the diet, regardless of background sucrose concentrations.

The transfer of selenium via a tri-trophic system was assessed. Aphid honeydew, a major component of the diet for Argentine ants in their introduced range, was found to serve as a route of selenium transfer to ant colonies.

Sub-lethal concentrations of selenium were found to impact reproduction for Argentine ant colonies, where colonies exposed to selenium sucrose diets experienced reduced queen fecundity, queen mortality, and reduced viability for offspring. Selenium did not alter the competitive ability of Argentine ant workers during interactions with the native species, Dorymyrmex bicolor, but sub-lethal concentrations did contribute to a longer food discovery time for the native species.

Native ant communities residing in a selenium-contaminated habitat were also documented. Ant species composition differed across sites, but selenium did not appear to have an overall impact on diversity. Ant concentrations differed by species, but were comparable to levels found among other arthropod trophic groups. Results suggest that these ants residing have evolved a high tolerance to this particular pollutant.