Developing and using expressed sequence tags to study the predatory mite Phytoseiulus persimilis Athias-Henriot (Paraistiformes, Mesostigmata, Phytoseiidae)

Doctor of PhilosophyDepartment of EntomologyDavid C. MargoliesYoonseong ParkThe predatory mite Phytoseiulus persimilis (Acari, Phytoseiidae) is one of the most frequently released natural enemies for biological control of spider mites in greenhouse and outdoors crops. In this research, I utilized Expresses Sequence Tags (ESTs), the most cost effective approach for transcriptome exploration, to study three different aspects of this arachnid species for which there is little genomic information. I combined two EST datasets from different whole body cDNA libraries and analyzed by bioinformatics means. Approximately 54% of 10,256 uniESTs were annotated based on the homology to sequences in the National Center for Biotechnological Information (NCBI) database. A list of these uniESTs, sorted from most to least likelihood based on the expected value from the blast search in public databases, was used to create tools for each of the three studies. First, I described sixty-one genes encoding products known to be important in pesticide metabolism and in endocrinology, including cytochrome P450s, glutathione-S-transferases, acetylcholinesterase homologs, neuropetides and neurohormones. Findings on arachnid specific esterases and neuropetides, and possible benefits to pest management programs, were discussed. Next, I inferred divergence time for Acari and the point of divergence of two lineages within anactinotrichid mites, Ixodes scapularis and Phytoseiulus persimilis. I used expresses sequence tags from the predatory mite P. persimilis to pull out 74 orthologous amino acid sequences of invertebrates species: nine insect species, Daphnia pulex, Ixodes scapularis, and Caenorhabditis elegans. I estimated a similar origin for Chelicerata (578.1 ± 38.2 - 482.2 ± 7.2 Mya) as in other recent studies. However, divergence dating using amino acid sequences suggested a Devonian origin of anactinotrichid mites (487.6 ± 32.2 - 410.1 ± 6.1 Mya) based on four reference dates (two fossil records and two molecular clocks) and four amino acid substitution methods; this estimate is much earlier that those in the current literature. This discrepancy of divergence times may be due to the use of a global clock. Finally, I developed molecular markers from the EST dataset to examine inheritance in the haplodiploid system in P. persimilis. Biparental contribution of chromosomes is required among the predatory mites but the paternal chromosome set seems to be eliminated or loss (Paternal genome loss, PGL) in male offspring. However, genetic studies in other two phytoseiid species were suggested diploid males with PGL only in the germ cells. In the present study, haploid adult males of P. persimilis have been observed using five independent EST-derived markers. Single mites derived from inter-population crosses were genotyped after whole genome amplification. The parahaploid genetic system in P. persimilis is supported by this study, in which both sexes arise from fertilized eggs but the paternal chromosome set is subsequently lost in males

Natural History and Larval Behavior of the parasitoid Zatypota petronae (Hymenoptera: Ichneumonidae)

The koinobiont ectoparasitoid Zatypota petronae Gauld (Ichneumonidae) parasitizes medium-sized immatures of the cobweb spider Theridion evexum Keyserling (Theridiidae). Zatypota petronae apparently attacks the spider inside its retreat. An egg is glued on the antero-lateral dorsal section of the spider’s abdomen. First-instar larvae remain partially inside the egg chorion which is attached to the spider’s abdomen. In later instars, a layer of a brownish material (saddle), to which the 7th and 8th abdominal segments of the larva adhere ventrally, anchors the larva to the spider. In the last instar the saddle includes the egg chorion and the shed exoskeletons of previous instars. A row of retractile, dorsal protuberances, crowned with hooklets, is present on abdominal segments 1 to 8 of the final-instar larva. The larva uses the hooklets to grab silk lines of the retreat of the spider’s web. Hanging on the spider’s web the larva kills the spider and sucks out its body tissues. Then the larva pushes vigorously laterally with its head against the spider’s corpse, and alternately presses the corpse against the saddle. These movements, in combination with peristaltic movements, free the larva from the saddle that falls to the ground with the dead spider. The larva then constructs its pupal cocoon. Prior to cocoon construction, the larva induces the spider to reinforce the retreat by adding more threads. Parasitism rate and host behavior are also described.UCR::Vicerrectoría de Docencia::Ciencias Básicas::Facultad de Ciencias::Escuela de Biologí

Natural history, courtship, feeding behaviour and parasites of Theridion evexum (Araneae: Theridiidae)

Theridion evexum constructs webs in the understory of wet middle-elevation forests in Costa Rica. The spiders construct retreats by curling a leaf and produce a mesh in front of the opening. Long, more or less vertical viscid lines extend from the mesh, and are attached to other leaves. The spiders feed on a large variety of prey (e.g. flies, beetles, earwigs, centipedes), indicating that both flying and walking arthropods are trapped in their webs. The wrapping threads have large viscid globules that rapidly disperse on the prey’s surface, forming a thin film. Adult males guard subadult females in their retreats, possibly waiting for them to moult and copulate. As part of courtship, the male places his pedipalps several times on the female’s mouthparts, then one pedipalp on her mouthparts and the other on her epigynum before insertion. Eggs were parasitised by Baeus (Scelionidae) and juveniles and subadults by Zatypota petronae (Ichneumonidae). Eggs were eaten by Argyrodes sp. (Theridiidae), and Solenopsis ants stole prey accumulated in the retreats and attacked spiderlings and older juveniles.UCR::Vicerrectoría de Docencia::Ciencias Básicas::Facultad de Ciencias::Escuela de Biologí

Carrion Feeding By Spiderlings Of The Cob-Web Spider Theridion evexum(Araneae, Theridiidae)

The use of carrion to feed spiderlings has never previously been observed in spiders. Here we show that the theridiid Theridion evexum Keyserling 1884 stored dead insectan prey for up to one week prior to the emergence of spiderlings from the egg sac, and continued to feed spiderlings dead prey for six weeks until spiderlings molted to the fourth instar. Spiderlings survived and molted on an experimental diet of exclusively rotten insects.UCR::Vicerrectoría de Docencia::Ciencias Básicas::Facultad de Ciencias::Escuela de Biologí

Seasonal patterns of parasitism of the tropical spiders Theridion evexum (Araneae, Theridiidae) and Allocyclosa bifurca (Araneae, Araneidae) by the wasps Zatypota petronae and Polysphincta gutfreundi (Hymenoptera, Ichneumonidae)

Las tasas de parasitismo de Theridion evexum por la avispa parasitoide Zatypota petronae y de Allocyclosa bifurca por Polysphincta gutfreundi fueron estudiadas durante dos años. El parasitismo en T. evexum fue muy bajo (promedio 1.39+1.8%) y restringido a aproximadamente siete meses del año. El parasitismo en A. bifurca fue más alto (promedio 7.8+7.6%) y no mostró un claro patrón estacional. La reproducción de la araña hospedera T. evexum fue muy estacional, con solamente una generación por año, mientras que los adultos de A. bifurca estuvieron presentes todo el año. Autocorrelaciones de las tasas de parasitismo entre censos consecutivos en diferentes sitios sugiere que P. gutfreundi tiende a retornar a los mismos sitios para parasitar las arañas hospederas durante algunas semanas.The rates of parasitism of Theridion evexum by the parasitoid wasp Zatypota petronae, and Allocyclosa bifurca by Polysphincta gutfreundi, were followed for two years. Parasitism of T. evexum was very low (mean 1.39+1.8%), and restricted to nearly seven months of the year. Parasitism of A. bifurca was higher (mean 7.8+7.6%), and did not show a seasonal pattern. Reproduction of the host spider T. evexum was highly seasonal, with only one, highly coordinated generation per year, while adults of A. bifurca were present year round. Short-term autocorrelation on parasitism rates over time at different sites suggest that P. gutfreundi tend to return to the same sites to hunt hosts over periods of a few weeks.Universidad de Costa RicaUCR::Vicerrectoría de Docencia::Ciencias Básicas::Facultad de Ciencias::Escuela de Biologí

The mystery of how spiders extract food without masticating prey

Standard accounts of how spiders obtain food without masticating their prey are probably largely wrong. Species in the families Uloboridae, Thomisidae, Araneidae and Theridiidae do not inject digestive fluid into the prey’s interior, nor do they suck fluids directly from its interior. Rather they regurgitate fluid onto the surface of the prey, and then suck it back up from there. Philoponella vicina and other uloborids are extreme in this respect: they wet the entire outer surface of the prey package simultaneously with digestive fluid, and their mouthparts often never touch the prey. Capillarity (along with digestion of prey membranes in Philoponella) is apparently responsible both for the dispersion of digestive fluid into the prey, and the exit of liquids from inside the prey.Instituto Smithsoniano de Investigaciones Tropicales (STRI)Universidad de Costa RicaSmithsonian Tropical Research Institute, Panama, USAUCR::Vicerrectoría de Docencia::Ciencias Básicas::Facultad de Ciencias::Escuela de Biologí

Pityriasis lichenoid-like mycosis fungoides in a 9-year-old boy: A case report

No abstract availabl

The effects of water and microstructure on the performance of polymer electrolyte fuel cells

n this paper, we present a comprehensive non-isothermal, one-dimensional model of the cathode side of a Polymer Electrolyte Fuel Cell. We explicitly include the catalyst layer, gas diffusion layer and the membrane. The catalyst layer and gas diffusion layer are characterized by several measurable microstructural parameters. We model all three phases of water, with a view to capturing the effect that each has on the performance of the cell. A comparison with experiment is presented, demonstrating excellent agreement, particularly with regard to the effects of water activity in the channels and how it impacts flooding and membrane hydration. We present several results pertaining to the effects of water on the current density (or cell voltage), demonstrating the role of micro-structure, liquid water removal from the channel, water activity, membrane and gas diffusion layer thickness and channel temperature. These results provide an indication of the changes that are required to achieve optimal performance through improved water management and MEA-component design. Moreover, with its level of detail, the model we develop forms an excellent basis for a multi-dimensional model of the entire membrane electrode assembly