Browsing by Author "Coby Schal, Committee Co-Chair"

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Host Location by Adults and Larvae of Specialist Herbivore Heliothis Subflexa G. (Lepidoptera: Noctuidae)
(2007-03-26) Benda, Nicole Denise; Coby Schal, Committee Co-Chair; John Godwin, Committee Member; George Kennedy, Committee Member; Fred Gould, Committee Co-Chair
Heliothis subflexa is a specialist herbivore, whose larvae feed on fruits of Physalis species (Solanaceae). Although Physalis surface extracts have been shown to elicit attraction and oviposition by adult ovipositing females, little else was known as to how adults locate their host plants for oviposition. Also, larvae are sometimes dislodged from the plant when the plant abscises the fruit they are feeding on. The ability of larvae to re-locate their host plant from the ground had not been evaluated. The purpose of this research was to evaluate the host location and oviposition behavior of H. subflexa adult females and larvae using common garden studies, behavioral assays in the lab and in the field, and direct field observations. H. subflexa showed a clear preference for some Physalis species over others in the common garden. Plant age and date also affected incidence of eggs and fruit damage on the Physalis plants. In laboratory two-choice simultaneous and sequential behavioral assays, H. subflexa showed a preference for P. philadelphica over tobacco. However, preference for Physalis was not to the complete exclusion of tobacco and a portion of eggs were placed on tobacco (˜20% on average). Field observations found that this was not a lab artifact. Females laid an average of 20% of eggs on non-hosts in the field, though most were placed very close to the plant. An evaluation of the host location ability of neonates found a high fitness cost to ovipositing on non-hosts. The ability of larger larvae (third and fifth instar) to re-locate the host plant after being dislodged from the plant via fruit abscission was affected by larval size, plant architecture, and host-specific behavior as compared to a close relative, H. virescens.
Nestmate recognition and population genetic structure in the Argentine ant, Linepithema humile.
(2003-11-16) Buczkowski, Grzegorz Andrzej; Jules Silverman, Committee Chair; Coby Schal, Committee Co-Chair; Charles S. Apperson, Committee Member; Edward L. Vargo, Committee Member
The Argentine ant, Linepithema humile, is a widespread invasive species characterized by reduced intraspecific aggression within its introduced range. To gain an understanding of mechanisms underlying nestmate recognition in the Argentine ant, I studied its population genetic structure and the role of genetic vs. environmental cues on aggression. I combine behavioral, genetic, and analytical data to explore the role of exogenous cues and recent changes in the population genetic structure on nestmate recognition in this ant. In Chapter II, I examined population genetic structure and intercolony aggression in two portions of the Argentine ant introduced range: California and the southeastern U.S. I describe factors that may have contributed to the present-day differences in genetic diversity between these two regions and I also suggest ecological factors that may have contributed to regional differences in current distribution patterns of the Argentine ant. In Chapter III, I examined the context-dependency of nestmate discrimination in the Argentine ant and the effect of action thresholds on exogenous cue recognition. I also tested hypotheses that explain a change in action thresholds as well as factors that affect action thresholds. I examined changes in intraspecific aggression in various discrimination contexts. I tested the importance of isolated nest referents on aggression thresholds. In Chapter IV, I examined the impact of different diet-derived hydrocarbons on intraspecific aggression in the Argentine ant and the potential of shared, diet-derived hydrocarbons to produce colony uniformity where intercolony genetic and/or environmental differences exist. In Chapter V, I examined the role of environmental cues on nestmate recognition in two populations of the Argentine ant. I tested the hypothesis that there is geographical variation in the response of Argentine ants to nestmate recognition cues derived from prey. In Appendix I, I use the Argentine ant to compare four aggression bioassays for consistency between replicates, similarity between assays, and ability to predict whole colony interactions. I tested four different aggression assays with two or three scoring methods per assay. I also determined whether isolated aggressive encounters could predict whole colony interactions.
Population Genetic Structure, Dispersal & Gene Flow in the German Cockroach, Blattella Germanica: A Structural Pest in the Urban Environment
(2008-10-27) Crissman, Jonathan Ross; Coby Schal, Committee Co-Chair; Edward Vargo, Committee Co-Chair; David Tarpy, Committee Member
The goal of the current study was to explore German cockroach population differentiation and dispersal in urban residences at several spatial scales. Little differentiation was expected within buildings due to frequent active dispersal of the German cockroach. However, differentiation was expected between spatially separated buildings because the German cockroach cannot survive beyond human structures and dispersal must be human-mediated. Differentiation was expected to increase with increasing spatial distance as human-mediated dispersal becomes successively less frequent. Cockroaches were collected in a geographical hierarchy, with samples at the scale of single apartments, apartment buildings, and apartment complexes within Raleigh, North Carolina in addition to 16 other cities in the United States and six Eurasian cities. All individuals were genotyped at ten microsatellite loci. Microsatellite diversity was generally high across our samples, with average alleles per locus as high as 9.11, and observed heterozygosity in excess of 0.6 in most populations. However, global differentiation was lower than expected, with a global FST of 0.046 across Raleigh, 0.099 across the U.S. with Raleigh excluded, and 0.158 across global samples with Raleigh excluded. No departure from panmixia was found between German cockroach samples within apartments by pairwise G-tests (P > 0.05). G-tests did detect highly significant departures from panmixia between all but one pair of apartments within Raleigh (all P < 0.001). These tests indicate that each separate apartment represents an individual population. Global FST values suggested that dispersal and gene flow occurred more often within buildings than between them and more within apartment complexes than between them. Similarly, significant Mantel tests of isolation by distance within Raleigh (P < 0.001), across the U.S. (P = 0.029), and across global samples (P < 0.005) indicated a significant positive correlation between genetic distance and geographic distance. These tests suggested that German cockroach dispersal and gene flow occurred less frequently at successively larger spatial scales. However, phylogenetic trees constructed from genetic distances for each spatial scale were unable to cluster apartments according to geographic proximity, except for apartments within a single building. The individual-based clustering program Structure was also unable to detect any informative underlying structure beyond a single building when no a priori population information was used. A similar lack of geographic pattern was shown in B. germanica mitochondrial 16S diversity. Only 10 unique 16S haplotypes were found for 66 individuals across 40 global populations, and haplotypes varied greatly in their frequency and geographic ranges. Beyond the scale of a single building, gene flow by passive dispersal seems to have formed no spatial clustering of genetic similarity, even at the global scale. This may be due to non-equilibrium conditions and non-linear evolution caused by dramatic declines in population size due to insecticides or large fluctuations in temperature, humidity, and food availability. These population bottlenecks are known to rapidly change allele frequencies and affect various evolutionary estimates, including genetic distance. The challenge for future studies will be to find markers conserved enough to be robust to these non-equilibrium conditions but variable enough for fine scale analysis.
Production, Developmental Expression, Physiological Regulation, and Mitigation of German Cockroach Allergens
(2004-11-29) Gore, Jonathan Chad; Coby Schal, Committee Co-Chair; D. Wes Watson, Committee Co-Chair; Charles S. Apperson, Committee Member; Monte B. McCaw, Committee Member
The German cockroach, Blattella germanica (L.) (Dictyoptera: Blattellidae), produces several allergens, including B. germanica allergen 1 (Bla g 1). Although the clinical significance and abatement of German cockroach allergens continues to be extensively studied, little is known about their basic biology. Using molecular and physiological approaches, my research elucidated where Bla g 1 is produced, its tissue distribution, developmental expression patterns, and its physiological regulation in the German cockroach. Bla g 1 is found predominantly in, and produced exclusively by, the midgut. Although it is produced by all stages and both sexes, adult females produce and excrete in their feces significantly more Bla g 1 than adult males and nymphs. Quantitative analyses of Bla g 1 mRNA expression in the female gut, and Bla g 1 content of the female and her feces showed a cyclic pattern in relation to the gonadotrophic cycle; Bla g 1 increased during the first 5 d after adult eclosion, when food intake increases, decreased before oviposition, as food consumption declines, and remained low while the female carried an egg case. After hatch, when the female resumed feeding, feces and Bla g 1 production increased. Forced starvation depressed both Bla g 1 mRNA expression and protein levels in adult females; Bla g 1 production increased and the gonadotrophic cycle resumed when food was returned. Bla g 1 mRNA expression also increased significantly in response to feeding compared to starved females. These data show that Bla g 1 is produced in relation to food intake and may be involved in digestion. The best approach to allergen mitigation is to remove the source of the allergen, or cockroach control. Pest control in the confined swine production industry relies primarily on broad-spectrum residual organic sprays. However, recent regulatory restrictions that limit the use of organophosphate insecticides and a rising frequency of resistance to pyrethroid insecticides have led to a renewed search for alternative pest control methods. Furthermore, recent evidence suggests that integrated cockroach management in infested structures can reduce environmental cockroach allergen levels below clinically relevant thresholds. I sought to develop a liquid formulation of boric acid bait for the management of German cockroaches in infested swine farms. The efficacy of various liquid borate solutions was assessed in no-choice and two-choice assays. While three borates provided effective kill under no-choice conditions, boric acid resulted in faster kill than sodium tetraborate or disodium octaborate tetrahydrate when cockroaches were given a choice between the borate-laced water and clean water. To evaluate whether various sugars could enhance the insecticidal activity of boric acid, solutions of 0.5% boric acid and 1 M sugar were tested. Finally, dose-mortality studies were conducted with the most promising sugars (maltose, sucrose, glucose, and fructose) at concentrations ranging from 0.01 to 2.0 M and boric acid concentrations of 0.5, 1.0, and 2.0%. From these studies, I concluded that a combination of boric acid and sucrose provided excellent control of the German cockroach. In field evaluations, prototype J-shaped bait dispensers filled with liquid boric acid bait solution were applied in a cockroach-infested nursery of a swine farm. Results of this 2-year field study showed that the cockroach population was significantly reduced by >90% within 1–2 months. These data also showed that when baits were deployed continuously for ~10 months the cockroach populations declined by 90–99%. In addition to providing an alternative management strategy, this approach also provides an option for the potential mitigation of cockroach allergens in infested swine farms and homes.