Browsing by Subject "Entomology"

Seasonal polyphenism in insects is the phenomenon whereby multiple phenotypes can arise from a single genotype depending on environmental conditions during development. Many butterflies have multiple generations per year, and environmentally induced variation in wing color pattern phenotype allows them to develop adaptations to the specific season in which the adults live. Elements of butterfly color patterns are developmentally semi-autonomous allowing for detailed developmental and evolutionary changes in the overall color pattern. This developmental flexibility of the color pattern can result in extremely diverse seasonal phenotypes in a single species. In this study, we asked the following questions: a) How do wing phenotype elements such as shape and pattern vary between seasonal forms? b) Can this variation be explained phylogenetically? c) If so, what are the various pattern development strategies used to achieve crypsis in the dry season form? To answer these questions, we used high resolution images to analyze pattern element variation of 34 seasonally polyphenic butterfly species belonging to the tribe Junoniini (Lepidoptera: Nymphalidae). We show that forewing shape and eyespot size both vary seasonally, and that the methods by which phenotype elements change in the dry seasonal forms is different in different clades and may therefore have independent and diverse evolutionary origins.

Background: Despite widespread access and use of insecticide-treated bed nets (ITN) in Bungoma County in Kenya, there has been little reduction in malaria infection rates. It has been hypothesized that this gap between theoretical and actual ITN efficacy is caused by improper use of ITNs, poor physical condition of ITNs, or insecticide resistance in local mosquitos. This study aims to examine potential factors that affect the efficacy of the ITNs in Western Kenya.

Methods: In order to assess the aforementioned aim, a longitudinal observational study was conducted. The study enrolled 9 households and performed weekly data and mosquito collections. Data and sample collection was conducted over an 8-week duration, from June 2016 to July 2016.

Results: The study found high ITN usage in the study households (99.3% coverage), a negative association between the number of mosquitoes collected and time, a high proportion of blood fed mosquitoes (0.409), and statistically significant associations with the proportion of blood fed mosquitos and twelve different predictor variables. Conclusion: This study shows that it is feasible to examine factors reducing ITN efficacy in the area and lays down a potential template to be scaled up to examine these factors more specifically.

While the Madre de Dios department of Peru has the nation's highest leishmaniasis incidence, limited research on the disease and its sand fly vector exists in the region. Considering the diverse and adaptive nature of sand flies, understanding vector ecology is essential to directing leishmaniasis control efforts. This study addresses this need by investigating the following aims: 1) describe sand fly abundance and biodiversity in communities along the Madre de Dios River; 2) identify environmental and socio-demographic factors associated with sand fly abundance and biodiversity in these communities; and 3) examine ecological risk factors associated with leishmaniasis in the communities. In order to accomplish these aims, the research team collected sand flies, obtained leishmaniasis case data, conducted community and household surveys, measured soil samples and studied land cover data in communities along the Madre de Dios River. We compared sand fly abundance, sand fly biodiversity and leishmaniasis incidence with soil chemistry, socio-demographic and land cover measures. We ran negative binomial regressions and Poisson regressions to investigate bivariate relationships between dependent and independent variables. We developed a multivariate model that predicts greater potential vector and non-vector abundance in areas with greater forest coverage, lower infrastructure indices and lower soil pH. This study provides an important overview of endemic sand fly fauna in Madre de Dios and presents an initial description of factors associated with sand fly populations in the region.

This dissertation analyzes the develop and evolution of insect phenotypes, ranging from the level of individuals to colonies. The first four chapters focus on wing patterning in the bella moth Utetheisa ornatrix. I begin by quantifying the pattern variation in the species, then attempt to identify some of the mechanisms that give rise to the observed phenotypic differences. After describing how the primitive patterns of U. ornatrix can be construed as evidence that nymphalid groundplan symmetry systems arose from the fusion of irregular spots, I present the results of a series of artificial selection experiments that highlight the species’ capacity for phenotypic evolvability. I then detail how changes in Wnt expression can lead to the evolution of bold phenotypes, and show that pterin pigments provide the primary source of coloration in U. ornatrix patterns. The final chapter focuses on the evolution of social phenotypes in insect societies. I suggest that the evolution of a physically differentiated reproductive and worker castes marks an irreversible major evolutionary transition to superorganismality. Social groups of this type are fundamentally different than monomorphic cooperative breeders, and can meaningfully be compared to metazoan organisms with differentiated germ and soma.

Insecticide-treated bed nets (ITNs) are widely used in Kenya to prevent the mosquitoes, which can transmit malaria, from biting people at night. However, there is a concern that mosquitoes become resistant to the ITN environment by changing their feeding behavior. The research goal was to observe the current feeding behavior of female Anopheles in Webuye, Western Kenya. Prokopack aspirators, CDC light traps, and sticky barrier screens were used for mosquito collection during May – July 2018. 662 collected female Anopheles, most of which were Anopheles gambiae sensu lato, were included. Descriptive and statistical analyses were applied, and the results show that the feeding proportion was 79.3% in mornings and 13.7% at nights, which was not significantly affected by the frequency of bed net use. 35.9% and 4.3% of the female Anopheles were human and Plasmodium (P.) Falciparum gDNA positive, respectively. Most of the P.falciparum positives were also fed and human gDNA positive, meaning that most of the infected or infectious mosquitoes had human blood meals and may have already attended malaria transmission. The study failed to observe outdoor feeding behavior by sticky barrier screens, and behavioral adaptation may not be responsible for most of the persistence of transmission. The study implicates a full investigation of ITN condition, more research on chemical resistance, and further surveillance of mosquito biting time.

The sense of taste enables animal survival and reproduction by allowing them to detect and discriminate different chemosensory stimuli so as to select for food options that are suitable for ingestion for both themselves and their progeny. A dominant model in the eld suggests that animals' taste coding generally follows a relatively simple and clean scheme - the "labeled-line" model - such that individual taste neurons are predetermined to detect one specific category of tastants (e.g., sweetness) and drive predetermined category-specific behaviors (e.g., acceptance). However, results from several recent studies started to challenge this model, and thus the question of how taste information is processed to drive behaviors remains unsolved. Here, I used the Drosophila melanogaster sweet taste system as a model to address this question. By utilizing multiple approaches of genetic manipulation and neural activity recording, I discovered three unexpected features of the taste system at the molecular, cellular, and circuit levels. First, sweet neurons can sense two categories of taste - sweetness and sourness. Second, the sensitivity of sweet neurons is actively dampened by specific molecules. Third, sweet neurons are composed of at least two functionally distinct subgroups that allow for behavioral responses to sweet taste to be adjusted according to context. Together, this study identifies previously unknown mechanisms by which the Drosophila taste system decodes the identities and the intensities of stimuli and promotes proper behaviors towards them.

Over the past several decades, developing countries such as Myanmar have increased industrialization and use of natural resources resulting in dramatic geographical, ecological and climatological changes. The effects of these human-driven landcover changes on the population densities, distribution, and ecology of mosquitoes, the most important disease-carrying insect in humans, are anticipated but largely undocumented in many resource-limited countries. In this study the effects of landcover variability on the abundance s of Anopheles, the vector responsible for transmitting malaria parasites from one human to the next, were assessed. Mosquitoes were systematically collected at randomized locations across specified landcovers throughout participating villages in Ann Township, Rakhine State, Myanmar, where malaria is highly endemic. This study was part of a longitudinal multiyear study, and data collected in the first six months were included in this study. Of trapped mosquitoes, Anopheles mosquitoes were identified morphologically, and speciated using molecular and genomic methods. The number of Anopheles per trap was determined across specified landcovers. Over six months, the number of Anopheles per trap was highest in the built structures (mean 13 Anopheles/trap; 95% confidence interval (CI) (12.15-13.96)/trap) than any other landcovers where the mean (95% CI) Anopheles/trap ranged from 0 to 1.61 (1.24-2.05). Anopheles species, determined via sequencing of the ITS2 gene, showed the three most prevalent species were An. maculatus, An. pallidus, and An. varuna. The species considered to be most dominant vectors in the region were absent from our study. The study findings raise questions about potentially changing species dominance over time, due to environmental changes, or the accuracy of a traditional wisdom. Research is ongoing in the region, and compiling data in the next few years will help fill this important knowledge gap.

Insecticide treated bed nets and indoor residual spraying are the most widely used vector control methods in Africa. The World Health Organization now recommends four classes of insecticides for use against adult mosquitoes in public health programs. Of these four classes of insecticides, pyrethroids have become the insecticides of choice in treating mosquito bed nets and in the use of indoor spraying to prevent malaria transmission. Pyrethroids are not only used in malaria control but also in agriculture to protect against pest insects. This concurrent use of pyrethroids in vector control and protection of crops from pests in agriculture may exert selection pressure on mosquito larval population and induce resistance to this class of insecticides. The main objective of our study was to explore the role of agricultural chemicals and the response of mosquitoes to pyrethroids in an area of high malaria transmission.

We used a cross-sectional study design. This was a two-step study involving both mosquitoes and human subjects. In this study, we collected larvae growing in breeding sites affected by different agricultural practices. We used purposive sampling to identify active mosquito breeding sites and then interviewed households adjacent to those breeding sites to learn about their agricultural practices that might influence the response of mosquitoes to pyrethroids. We also performed secondary analysis of larval data from a previous case-control study by Obala et al.