Alexzandra F. Murphy

Haplotypes of the Potato Psyllid, Bactericera cockerelli, on the Wild Host Plant, Solanum dulcamara, in the Pacific Northwestern United States

Abstract‘Candidatus Liberibacter solanacearum’ (Lso) is a bacterium that infects solanaceous crops and causes plant decline and yield losses, especially in potato and tomato. Lso is transmitted to these hosts by the potato psyllid (Bactericera cockerelli Sulc) vector. B. cockerelli host plants are not limited to crop plants, but also include many wild, solanaceous weeds. These wild hosts could potentially impact overwintering and breeding of the psyllids and serve as reservoirs for Lso. In the Pacific Northwestern United States, B. cockerelli was recently reported to overwinter on bittersweet nightshade (Solanum dulcamara L.). The present study utilized high resolution melting analysis of the B. cockerelli mitochondrial cytochrome c oxidase I gene to assess the psyllid populations occurring on S. dulcamara during the summer and winter months in Washington, Oregon, and Idaho. This technique has previously been used to analyze the cytochrome c oxidase I gene of B. cockerelli, and has identified four psyllid haplotypes. Lso infection was also determined for the psyllids collected from S. dulcamara. During both the summer and the winter months in the Pacific Northwest, the Northwestern psyllid haplotype was the predominant population found living on S. dulcamara. However, low levels of the Western psyllid population were also present in Washington and Oregon during the same period. No overwintering psyllids tested were Lso-infected, suggesting that these populations do not pose an imminent threat of Lso transmission to newly emerging potatoes and other solanaceous crops in the region, unless a source of Lso becomes available.Resumen‘Candidatus Liberibacter solanacearum’ (Lso) es una bacteria que infecta a cultivos de solanáceas y causa abatimiento y pérdida de cosechas, especialmente en papa y tomate. Lso se transmite a estos hospedantes por el vector psílido de la papa (Bactericera cockerelli Sulc). Las plantas hospederas de B. cockerelli no se limitan a especies cultivadas, sino que también incluyen muchas malezas silvestres solanáceas. Estas hospedantes silvestres pudieran impactar potencialmente la invernación y apareamiento de los psílidos y servir como reservorios para Lso. En el Noroeste del Pacífico de los Estados Unidos de América se ha reportado recientemente a B. cockerelli invernando en la planta “uva del diablo”, “dulcamara” o “matagallinas” (Solanum dulcamara L.). En el presente estudio se utilizó un análisis de fusión de alta resolución del gen mitocondrial del citocromo c oxidasa de B. cockerelli para analizar las poblaciones del psílido que se presentan en S. dulcamara durante los meses del verano e invierno en Washington, Oregon y Idaho. Se ha utilizado previamente esta técnica para analizar el gen mencionado, y ha identificado cuatro haplotipos del psílido. También se determinó la infección por Lso en psílidos colectados de S. dulcamara. Durante los meses de verano e invierno en el Pacífico del Noroeste, el haplotipo del psílido del Noroeste era la población dominante que se encontraba viviendo en S. dulcamara. No obstante, también se encontraba, aunque en bajos niveles de la población, el psílido del Oeste en Washington y Oregon durante el mismo período. Psílidos no invernantes probados estaban infectados de Lso, sugiriendo que estas poblaciones no representan una amenaza inminente de transmisión de Lso a papas de nueva emergencia y a otros cultivos de solanáceas en la región, a menos que una fuente de Lso estuviera disponible.

The impact of Bt maize as a natal host on adult head capsule width in field populations of western corn rootworm

The success of the current resistance management plan for transgenic maize, Zea mays L. (Poaceae), targeting the rootworm complex hinges upon high rates of mating between resistant and susceptible beetles. However, differences in the fitness of adult beetles could result in assortative mating, which could, in turn, change the rate of resistance evolution. Adult head capsule widths of naturally occurring populations of western corn rootworm, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), were examined in a variety of refuge configurations. Beetles were classified into treatments based on the hybrid – non‐Bt refuge or Bt maize targeting larval rootworms (hereafter Bt‐RW maize) – and location – proximity to other Bt‐RW or refuge plants – of the natal host plant. Treatments included the following: a refuge plant surrounded by other refuge plants, a refuge plant located near a Bt‐RW plant, a Bt‐RW plant surrounded by Bt‐RW plants, and a Bt‐RW plant located near a refuge plant. The mean head capsule width of males emerging from Bt‐RW plants was significantly smaller than the mean head capsule width of males emerging from refuge plants. These results indicate that males emerging from Bt‐RW maize plants may be exposed to sublethal doses of the Bt toxin as larvae. No differences were detected between females emerging from refuge plants compared with Bt‐RW plants. Overall mean head capsule width decreased as the season progressed, regardless of treatment. The diminished head capsule width of western corn rootworm males emerging from Bt‐RW maize may act to enhance resistance management, particularly in a seed mix refuge system.

Mating Success and Spermatophore Composition in Western Corn Rootworm (Coleoptera: Chrysomelidae)

ABSTRACT Western corn rootworm (Diabrotica virgifera virgifera LeConte) resistance management for transgenic (or Bt) corn hinges on understanding the mating behavior and biology of this adaptable insect pest. During mating, the male transfers sperm and additional, previously uncharacterized material, to the female in the form of a spermatophore. We investigated the composition of rootworm spermatophores. Proteins were found to be a major component, and the stable isotope 15N was used to assess the fate of spermatophore nitrogen in mated female beetles and their eggs. We also performed longevity studies on mated and virgin females under three different diet treatments and investigated the relationships between morphometric characteristics and spermatophore volume of mating pairs of beetles. The stable isotope analysis determined that nitrogen provided to the female in the spermatophore was incorporated into the eggs. We found that virgin female beetles on a corn diet lived significantly longer than mated female beetles on the same diet. There were significant positive relationships between male size parameters (head capsule width, pronotum width, and elytral length) and spermatophore volume, and ampulla and spermatophylax volume.

Population Dynamics of the Beet Leafhopper (Hemiptera: Cicadellidae) in the Columbia Basin as Influenced by Abiotic Variables

ABSTRACT Beet leafhoppers (Circulifer tenellus Baker) have been identified as the vector for a plant-pathenogenic phytoplasma known as beet leafhopper-transmitted virescence agent. Beet leaf-hopper-transmitted virescence agent causes purple top disease in potatoes, which can reduce yields and tuber quality. A trapping network, composed of ≈100 sites, monitors leafhoppers in the Columbia Basin of Oregon and Washington through a collaborative effort of regional researchers and stakeholders. Yellow sticky cards were used to determine the timing and spatial distribution of beet leafhoppers in the Columbia Basin; insects were counted weekly from early April through late October in 2006, 2007, and 2008. Weather data collected from a network of weather stations in Oregon and Washington were used in a nonparametric multiplicative regression analysis to determine which abiotic environmental variables might influence beet leafhopper populations. Weather conditions (mean temperature, dew point, precipitation, and wind speed) for 2006–2008 were also characterized using CIs established based on weather data from 1998 to 2004 for each weather variable. Several abiotic environmental factors significantly correlated with beet leafhopper populations, including temperatures the preceding fall and winter, elevation, and precipitation. Beet leafhopper populations appear to be highly variable across the region, with low numbers at a majority of the sites and only a limited number of high populations in localized areas.

Modeling a western corn rootworm, Diabrotica virgifera virgifera (Coleoptera: Chrysomelidae), maturation delay and resistance evolution in Bt corn

BACKGROUND Emergence delay and female-skewed sex ratios among adults of Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae) from Bt corn have been reported in field studies. The authors used a simulation model to study the effect of a maturation delay and a female-skewed sex ratio for D. v. virgifera emerging from Bt corn on the evolution of Bt resistance. RESULTS The effect of skewed toxin mortality in one sex on evolution of Bt resistance was insignificant. An emergence delay among resistant beetles from Bt corn slowed resistance evolution. A shift in the time of emergence for homozygous susceptible beetles from Bt corn did not have a significant effect on the evolution of Bt resistance in D. v. virgifera. CONCLUSION This simulation study suggested that skewed toxin mortality in one sex and an emergence delay for beetles in Bt corn are not major concerns for managing resistance by D. v. virgifera to single-toxin or pyramided Bt corn.