1,721,033 research outputs found
Patterns of Host Use in Mosquitoes: Implications for Virus Transmission
Get PDFMosquitoes do not feed indiscriminately among hosts, but demonstrate various patterns of host use. Each mosquito species may specialize in feeding within a group of related hosts or may utilize a wide variety of hosts. Mosquito host use may vary with season, habitat or weather and may be affected by factors, such as age, defensive behavior, and daily activity period. Patterns of host use by mosquitoes drive the transmission of mosquito-borne viruses. For zoonotic diseases, a vector must first acquire a pathogen from a reservoir host prior to infecting a human. Birds, for example, are reservoirs for many mosquito-borne viruses such as West Nile virus and eastern equine encephalomyelitis virus. Epidemics of West Nile virus and eastern equine encephalomyelitis virus in humans and horses usually occur in the summer and early fall, when mosquito populations shift from feeding on avian hosts. The work presented here reports on studies examining host use by mosquitoes and the impact of patterns of host use on the transmission of mosquito-borne viruses.
To determine host preference of ectotherm-feeding mosquitoes, host use and host abundance data were analyzed to determine whether mosquitoes select some host species over others. Culex peccator was a generalist in its feeding patterns within ectotherms, and Culex territans appeared to select Bullfrogs and Spring Peepers. To determine the importance of nestling birds as hosts for mosquitoes, I examined patterns of host use in adult and nestling birds, by introducing mosquitoes into nest boxes of eastern bluebirds, and then determining which birds were fed upon by comparing microsatellite loci in mosquito blood meals. Mosquitoes did not target nestling birds, but fed on nestlings in proportion to their abundance. I tested the hypothesis that temporal patterns of host selection by mosquitoes reflect reproductive phenology of hosts by comparing seasonal patterns of host use with host reproductive phenology. Regardless of host group, mosquitoes fed on host species that were in the process of mate attraction or recruitment. I investigated the relationship between epidemiology of eastern equine encephalitis virus (EEEV) and host shift by vectors in southeastern states. Mammal-feeding intensity by mosquitoes was highly correlated with EEEV cases in horses, indicating that host shifts in vector mosquitoes is critically important in the initiation of epizootics of EEEV in nature
Beetle Biodiversity Response to Vegetation Restoration of Mid-Valley Riparian Woodland in the Lower Rio Grande Valley of Southern Texas
Get PDFIn ecological restoration, habitat managers intervene in a degraded ecosystem to aid its recovery. To assess a restored habitat, one or more characteristics such as biodiversity, ecosystem functioning, and community structure are measured in relation to a reference habitat. While many restoration projects focus on vertebrates, arthropod taxa may be a more informative group, and beetles (Insecta: Coleoptera) in particular are a significant part of most ecosystem functions.
In the four southernmost counties of Texas, the Rio Grande forms a fertile flood plain and delta; however, 98% of the riparian habitat on the Texas side has been cleared for farmland and urban expansion. Recent ecological restoration in some regions of the Lower Rio Grande Valley has consisted of revegetating reclaimed farmland and protecting it from further degradation. Here, an evaluation of the success of the restoration of mid-valley riparian woodland sites based on a survey of beetle communities is conducted at five sites between September 2008 and June 2010. The five sites included three reference sites of primary habitat from coastal brushlands potholes, a sabal palm forest, and a mid-valley riparian woodland, and two restored sites of mid-valley riparian woodland which varied in the age of their restored habitat vegetation. Beat samples and ultraviolet blacklight bucket trap samples were taken once every two weeks, while pitfall traps and Lindgren funnel traps ran continuously and were serviced once every two weeks. The sampling methods employed were designed to capture a wide variety of beetles with different biological characteristics
Recruitment to and Defense of Aphids by Fire Ants and Native Ants and an Estimate of Their Trophic Positions Using Stable Isotopes
No full textThe red imported fire ant, Solenopsis invicta, is an invasive ant known to form facultative mutualisms with aphids. Fire ants significantly reduce the abundance of aphid predators and herbivores on plants infested with aphid colonies. However, to develop a broader understanding of the ecological consequences of facultative mutualisms involving invasive ants, differences in the recruitment to aphid colonies by fire ants and native ants must be known. Furthermore, it is necessary to quantify and compare differences in aphid defense between fire ants and native ants to determine if fire ants are more effective mutualists than native ants. I used two field sites, one at Tuskegee National Forest and the other at Auburn University’s Mary Olive Thomas Tract to compare recruitment to aphids by fire ants and native ants. I used a choice field experiment using plants with and without cotton aphids to identify other ant species that respond to the presence of cotton aphid colonies and to estimate the number of workers per species that recruit to aphids. At Tuskegee National Forest, the native pyramid ant, Dorymyrmex bureni, was the only native ant species to recruit to cotton aphids. Fire ants were far more abundant at aphid colonies than native ants. Fire ants averaged almost 8 workers per aphid colony while pyramid ants averaged only 2 workers per aphid colony. At the Mary Olive Thomas Tract, the native ant, Camponotus pennsylvanicus, was the only native ant to recruit to aphids, but averaged less than one ant per aphid colony. Fire ants averaged more than 3 workers per aphid colony. At both sites fire ants were far likelier to recruit to aphids than either of these native ants. I also suppressed fire ants in half of my plots at each site to determine if fire ants were competitively excluding native ants from aphids. After fire ant suppression, the recruitment of D. bureni to aphid colonies increased 5-fold and Camponotus pennsylvanicus recruitment to aphids also significantly increased, although to a lesser extent. These data suggest that the presence of fire ants inhibits native ants from recruiting to aphid colonies, but the mechanism of this inhibition remains unknown. In my aphid colony defense experiment, aphid colonies tended by fire ants increased by more than 80 aphids per aphid when aphid predators were present, suggesting that fire ants were effective defenders of the aphids. Conversely, D. bureni tended aphid colonies declined by more than 100 aphids per colony when aphid predators were present, suggesting that this native ant was not an effective defender of aphids. My results suggest that fire ants are better than some native ants in aphid colony defense and may be better mutualistic partners for aphids.
I also performed a stable isotope analysis to estimate the trophic level of fire ants in Alabama. Stable isotope analysis measures the ratio of heavy to light, biologically important isotopes and is a quick method to ascertain the trophic level of an organism in a food web. Three native ant species occupy a trophic level above fire ants, suggesting a more carnivorous diet than fire ants. Three other native ant species occupied a nearly identical trophic level to fire ants, suggesting they exploit similar resources. Most importantly, fire ants occupied an intermediate trophic level between arthropod leaf-chewing herbivores and predacious, non-ant arthropods. This suggests that carbohydrates acquired from facultative mutualisms with honeydew-producing insects are an important component of the diet of fire ants and probably contribute substantially to colony growth and maintenance
Mutualisms, Commensalisms, and Predation: The Direct and Indirect Effects of Fire Ants on Arthropods and Plants
Get PDFThe red imported fire ant, Solenopsis invicta, is a voracious generalist predator that has dramatically affected the native arthropod community since its introduction approximately 75 years ago. Most research suggests S. invicta negatively affects most native arthropods by consumption or displacement. However several studies have found that S. invicta forms mutualisms (positive species interactions) with honeydew-producing insects such as aphids. In field and greenhouse experiments we found evidence that S. invicta also forms a positive interaction with spittlebug nymphs. The presence of S. invicta has a significant negative effect on spittlebug predators such as spiders which in turn increases spittlebug nymph abundance. Therefore spittlebug nymphs indirectly benefit from the presence of S. invicta and thus fire ants and spittlebug nymphs form a comensalistic relationship. We hypothesize that the impact of red imported fire ants on arthropod communities varies due to the formation of these positive species interactions.
Additionally we quantify the direct benefits that the cotton aphid, Aphis gossipii, and the red imported fire ant, Solenopsis invicta, receive from their mutualistic relationship in a series of greenhouse experiments. We compared the growth of aphid populations, alate production, and the composition of honeydew of ant attended and unattended colonies in the absence of natural enemies. In addition, we examined worker and brood survival among ant colonies with and without access to aphid colonies. We found strong evidence that both aphids and ants receive direct benefits from the mutualism. Aphid population growth was significantly higher in the presence of fire ants. The presence of fire ants also decreased the proportion of aphids that developed wings (alates) and increased honeydew production by aphids. Survival of fire ant workers and larvae (brood) was significantly higher when fire ant colonies had access to aphids than when they did not. This suggests that honeydew is a high quality food source for fire ants and honeydew consumption directly affects colony survival and growth
The potential effects of red imported fire ants (Solenopsis invicta) on arthropod abundance and Cucumber mosaic virus
No full textMutualisms involving ants and honeydew-producing insects such as aphids, scales, and whiteflies may dramatically affect the population dynamics of these herbivorous insects. Furthermore, changes in the population size of honeydew-producing insects may have important consequences for other interacting organisms. We tested the hypothesis that ant-aphid mutualisms result in significant increases in aphid population size and aphid dispersal which, in turn, increases the spread of aphid-vectored plant viruses. We studied the invasive red imported fire ant (Solenopsis invicta), several common aphids that form facultative mutualisms with these ants, and a ubiquitous, aphid-vectored plant virus (Cucumber mosaic virus (CMV)). We found that aphids were significantly more abundant in small plots of tomato plants (Lycopersicon esculentum) with large fire ant populations than in small plots of tomato with suppressed fire ant populations. In a greenhouse experiment, we found that aphids dispersed to neighboring plants 59% more often in the presence of fire ants than in the absence of fire ants, suggesting that fire ants increase aphid movement. Most importantly, in a large-scale field study (˜ 2.4 hectare fields), we found that the abundance of alate aphids and the incidence of CMV (the proportion of plants infected with virus) were significantly higher in fields with high densities of fire ants than in fields with suppressed fire ant populations. This study suggests that ant-aphid mutualisms may have dramatic, previously undocumented effects on the dynamics of aphid-vectored plant viruses. This study also suggests that the continued range expansion of red imported fire ants could result in larger levels of virus infection in both agricultural crops and wild plants.
Understanding epidemiology of plant viruses requires knowledge of their ecology and hosts. Identifying reservoir hosts and inoculum sources of plant viruses is often imperative for understanding virus outbreaks in agricultural plants. We present here a 2-year analysis of the population dynamics of Cucumber mosaic virus (CMV) in herbaceous plants around fresh-market tomato fields in northern Alabama, a region where a persistent CMV epidemic has been ongoing for over ten years. Over the two year study, at least 50 herbaceous plant species belonging to 27 families were identified and tested for the presence of CMV. 18 plant species belonging to 12 plant families tested positive for CMV. In 2005, CMV incidence was positively correlated with planting date of the field for both tomato and herbaceous plants. There was no correlation between the overall CMV incidence in weed plots and CMV incidence in neighboring tomato fields, but there were strong, positive correlations between CMV incidence in tomato fields and the relative abundance of greenbriar (Smilax spp.), the relative abundance of ivy-leaf morningglory (Ipomoea hederacea), the abundance of aphids on ivy-leaf morningglory, and the number of aphids on blackberry (Rubus spp.). These results suggest that most herbaceous plants near Alabama tomato fields are relatively unimportant in the spread of CMV to neighboring tomato fields and that control efforts should be focused on only a handful of species
The effects of herbivory on plant mating systems
Get PDFInbreeding is common in many plant species. Inbreeding reduces heterozygosity and increases the expression of recessive deleterious alleles that cause inbreeding depression. The level or intensity of inbreeding depression plays an important role in the evolution of plant mating systems. Furthermore, high levels of inbreeding depression increase the probability of extinction for small, isolated populations. The vast majority of studies that have quantified inbreeding depression have been conducted under controlled conditions. Inbreeding depression, however, is not static and can vary with environmental conditions. Thus, by altering the magnitude of inbreeding depression, environmental and ecological interactions could alter the rate and direction of mating system evolution or dramatically increase the threat of extinction of small plant populations. An important ecological interaction that affects plant fitness is herbivory. Because inbreeding alters genetic variation, it is likely that inbred offspring will have pronounced physiological and morphological changes, making them more susceptible to herbivory.
Compromised defense in inbred plants may serve as the mechanism whereby herbivory increases inbreeding depression. In the first chapter of my thesis, I tested the hypotheses that herbivory by the sunflower spittlebug, Clastoptera xanthocephala (Cercopidae) affects the expression of inbreeding depression in the yellow monkeyflower, Mimulus guttatus. In addition, I tested the hypothesis that changes in morphological traits in inbred plants are responsible for changes in the interaction between spittlebugs and inbred plants. My results suggest that herbivory increases inbreeding depression by reducing plant tolerance of herbivory, but this effect varied among plant genotypes and populations. Inbreeding did not affect resistance to sunflower spittlebugs.
Thus, herbivory can increase inbreeding depression and potentially alter the evolutionary dynamics of plant populations and the persistence of plant populations. The results of this and other studies, however, suggest that the effect of herbivory on inbreeding depression varies among plant genotypes and populations. The goal of my second chapter was to explain variation in the effects of selfing on plant-herbivore interactions. I hypothesized that variation in the effect of selfing on plant defense may be explained by the mating history of plant populations. Plant populations with a history of outcrossing often exhibit high levels of inbreeding depression. Plant populations with a long history of selfing typically exhibit low levels of inbreeding depression.
To test this hypothesis, I correlated the level of inbreeding depression due to herbivory with flower size. I used flower size as an estimate of mating history because plants with smaller flowers are significantly more likely to inbreed, and typically come from lineages with a long history of inbreeding. Deleterious alleles are much more likely to have been purged within these lineages resulting in reduced inbreeding depression. I found that as flower size increased, so did the effects of herbivory on inbreeding depression. Corolla width was significantly correlated with inbreeding depression due to herbivory.
This study adds to a growing body of work that suggests that environmental and ecological interactions can alter the expression of inbreeding depression and alter the rate and direction of mating system evolution and the persistence of plant populations. This is particularly important for conservation biology. As changes in habitats increase, populations of native plants are often isolated and reduced in size. The effects of ecological interactions on inbreeding depression may be amplified in these situations and in order to conserve these populations the effects of ecological interactions may need to be included in management plans
Olfactory Cues Mediate Multitrophic Interactions Among Cucumber Plants, Cucumber Beetle Larvae and Entomopathogenic Nematodes
Get PDFOlfactory cues mediate a wide variety of ecological interactions among organisms at different trophic levels. There is abundant evidence that these cues play critical roles for organisms foraging for resources and defending against potential attackers. Some of the best-studied examples include plants producing volatile organic compounds to defend themselves against herbivores and natural enemies using prey-associated odors while hunting. While much of this research has focused on aboveground systems, there is growing recognition that olfactory cues also facilitate multitrophic interactions among soil-dwelling organisms. The overall purpose of this thesis was to examine how olfactory cues from plants and natural enemies guide the foraging decisions of herbivores and their natural enemies, focusing on a belowground tritrophic system.
First, I review the literature to examine how plant-associated microorganisms alter plant phenotypes to influence herbivore foraging behavior. Next, I investigate the roles of herbivore-induced plant volatiles (HIPVs) from roots of cucumber plants (Cucumis sativus) as foraging cues for a specialist herbivore, striped cucumber beetle (Acalymma vittatum) and its natural enemies, entomopathogenic nematodes (EPNs, Heterorhabditis bacteriophora). I predicted HIPVs from A. vittatum���damaged roots would attract EPNs, while repelling conspecific larvae that avoid competition, and increased risk of predation by EPNs. Finally, I evaluated how olfactory cues emitted by 3 species of EPNs with differing foraging strategies affect the behavior of their insect herbivore prey (A. vittatum) and competing EPNs. I hypothesized olfactory cues from the more sedentary ���ambush��� EPN species (Steinernema carpocapsae) would be the most repulsive to prey and potential competitors, compared to cues from the active-hunting (H. bacteriophora) or intermediate-foraging (Steinernema riobrave) species.
In the second study, I found that 24 hours of wounding by A. vittatum herbivory, or mechanical damage, induced greater production of volatiles from C. sativus roots compared to undamaged controls, repelling foraging larvae and recruiting EPNs. However, after sustained herbivory for 7 days, larvae reduced HIPVs to levels indistinguishable from undamaged roots, while mechanically damaged roots continued to produce higher levels of volatiles. Attenuation of HIPVs impaired C. sativus indirect defenses by reducing recruitment of EPNs and deterrence of A. vittatum larvae.
In the final study, I found that foraging A. vittatum larvae avoided olfactory cues from the active-hunting EPN species, Heterorhabditis bacteriophora, but did not respond to cues from the ambush hunter, S. carpocapsae, or intermediate hunter, S. riobrave. In contrast, foraging H. bacteriophora EPNs were attracted to odors produced by the two Steinernema EPN species and did not respond to olfactory cues from conspecifics.
Taken together, these results suggest that A. vittatum larvae can navigate risk within the soil environment, first, by avoiding volatile cues associated with increased predation risk or competition ( i.e., volatiles from herbivore-damaged plants or odors from EPN-infected) and, second, through direct attenuation of plant indirect defenses. Our findings also indicate that active-hunting ���cruiser��� EPNs are attracted to multiple host-associated cues, including volatiles from herbivore-wounded C. sativus roots and odors from heterospefic EPN-infected insect cadavers, suggesting that these cues can provide information for foraging natural enemies about resource availability
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Effects of Landscape Structure on Herbivorous Pests and Native Pollinators in the Cotton Agroecosystem: Implications for Pest management
Get PDFThis body of work investigates the role the landscape plays on the spatial relationships of cotton pests and native be pollinators at the local level, with the goal of improving pest management strategies at a larger scale while conserving native pollinators that have potential benefits for cotton production. This will be done through four objectives represented as chapters. In chapter two, I investigated the interplay that edges and ecotone type (agricultural interfaces) have on the populations of cotton fleahopper and verde plant bug and associated cotton injury. Findings indicated that field edge and ecotone type play a significant role in the pest pressure seen within cotton. Land managers should consider the spatial arrangements of fields when developing pest scouting and management strategies. In chapter three, I test the feasibility and applicability of using unmanned aerial systems (UAS���s) in detecting cotton fleahopper damage. The data suggest that differences in cotton fleahopper stress on cotton may be reflected in NDVI values, but the form seen may be complicated by the feeding site (immature fruiting bodies) of cotton fleahopper. In chapter four, I investigated potential benefits the native bee M. tepaneca has on cotton production via pollination services. Cotton flowers that were caged and hand-crossed along with flowers exposed to caged M. tepaneca had higher pre-gin weights and post gin weights, compared to those flowers of caged plants excluded from pollinators. This bee-mediated service resulted in a 12.8% seed cotton increase in 2018 and a 32% increase in 2019. In Chapter Five, I investigated the effects of landscape structure on the biodiversity and abundance of native pollinators within the cotton agroecosystem. Bee bowls used over two years, a total of 32 species of native bee pollinators in 13 genera across 3 families were collected. Communities of native bees at crop-crop interfaces tended to be more consistent in the abundance and number of species at each sampling site across samples. On the other hand, sites at semi- natural habitat interfaces contained more species, but abundances varied across samples. This suggests that even in highly large-scale cotton agroecosystems, a community of native bees persists, and some species may even thrive
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