Otiorhynchus sulcatus (Fabricius) is a serious pest of various horticultural crops in the United States. Despite its economic importance, this pest remains very challenging to manage. Integrated Pest Management Program for O. sulcatus has not yet been implemented due to lack of accurate information on its ecology. Investigation of temperature-dependent development and reproduction of O. sulcatus was conducted to enable the prediction of stage emergence more accurately. Immature-development study at constant temperatures 11-30 oC showed that there was the difference in optimal temperature regime among immature stages, which suggests that temperature can play a role to adapt each stage to the different temperature condition of the season. By applying mathematical models, optimum temperature for the fastest development was estimated to be 27.5, 25.1, and 24.1 oC for eggs, larvae, and pupae, respectively. Temperature also significantly influenced the adult reproductive life history traits, including preovipositional period, ovipositional period, longevity, per capita egg production, and egg viability. At 27 oC or above, reproductive success of O. sulcatus was substantially impaired due to shortened longevity, delayed reproduction, and lowered egg viability. Endosymbiont bacteria Wolbachia infect many arthropod species and they may alter the reproduction of their hosts. I first documented that Wolbachia is highly prevalent in O. sulcatus populations in the United States. Given that two antibiotics (tetracycline and gentamicin) differing only in their efficacy against Wolbachia, results strongly support the hypothesis that Wolbachia may be required for normal egg development of O. sulcatus. Despite intensive insecticide application, O. sulcatus populations often remain at unacceptable levels. I ask whether sublethal dosages of newer insecticides, imidacloprid and thiamethoxam, influence offspring production of O. sulcatus adults and its progeny under laboratory conditions. Weevils that survived short-term exposure to sublethal dosages of imidacloprid and thiamethoxam produce viable offspring when they have access to insecticide-free leaves after the exposure. Toxicity test showed the potential of imidacloprid and thiamethoxam for the control of first-instars but not for the control of eggs. / Ph. D.

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The temperature-dependent development of pupae and adults of strawberry root weevil (SRW) Otiorhynchus ovatus (L.) was studied in strawberry (Fragaria x ananassa Duch. var. 'Totem'). The development of pupae and adults was investigated at constant temperatures from 3-33��C at 3��C intervals. Major emphasis was on the development of a weighted linear temperature-based pupal prediction model. The predictive ability of this weighted model was compared to a traditional non-weighted linear degree-day model by relating predictions to the observed occurrence of SRW lifestages determined by field sampling. The upper thermal lethal limit for SRW pupae was between 30 and 33��C. Pupae did not eclose below 6��C. Mean pupal duration was 127 d at 6��C and 7 d at 30��C. Rate of development (1/days) was greatest at 30��C. The weighted linear pupal prediction model produced a developmental threshold of 4.3��C and a degree-day requirement of 227.3. The non-weighted linear pupal prediction model produced a developmental threshold of 6.2��C and a degree-day requirement of 163.9. Adults fed at all temperatures from 3-33��C and oviposited at temperatures between 18 and 30��C . The longest preoviposition period (32.8 d) and the least total number of eggs (2.2) were observed at 18��C. The shortest preoviposition period (15.1 d) and the greatest total number of eggs (282.5) were observed at 27��C. A temperature range of 21 to 27��C appeared to be optimum for oviposition; i.e. relative to other temperatures, preoviposition time was short, mortality was low, and total number of eggs laid was high. / Graduation date: 2000

<p>Asexual reproduction and polyploidy are relatively rare in animals with chromosomal sex determination and always represent a derived condition. To accomplish asexual reproduction several changes in gene expression are required in the mechanism of oogenesis. Polyploidy increases the cell volume and also gives rise to alterations in general physiology. Nevertheless, there are asexual animals that not only survive but seem to be doing better than their sexual progenitors. This is expressed in the distribution pattern called geographical parthenogenesis. Using molecular phylogeny, I here examine the evolution of Otiorynchid weevils, mainly <i>Otiorhynchus scaber</i> and <i>sulcatus</i> in an attempt to trace the evolutionary history and find out what causes the variation in success of different parthenogens. I also evaluate the contribution of asexuality, hybridity and polyploidy as explanations behind geographical parthenogenesis in insects. I conclude that what is called <i>O. scaber</i> is, in fact, a set of geographical polyploids as polyploidy and not asexuality explains the difference in clonal success. I also argue that <i>O. sulcatus</i> is a recently formed clonal species of non-hybrid origin that may well be a good example of a true general purpose genotype. I find little support for asexuality or a hybrid origin as explanations behind geographical parthenogenesis in insects. Finally, I argue that polyploidy in all eukaryotes should be seen as an opportunity for the species evolution, not as a limitation that ensures the demise of the taxa.</p>

Asexual reproduction and polyploidy are relatively rare in animals with chromosomal sex determination and always represent a derived condition. To accomplish asexual reproduction several changes in gene expression are required in the mechanism of oogenesis. Polyploidy increases the cell volume and also gives rise to alterations in general physiology. Nevertheless, there are asexual animals that not only survive but seem to be doing better than their sexual progenitors. This is expressed in the distribution pattern called geographical parthenogenesis. Using molecular phylogeny, I here examine the evolution of Otiorynchid weevils, mainly Otiorhynchus scaber and sulcatus in an attempt to trace the evolutionary history and find out what causes the variation in success of different parthenogens. I also evaluate the contribution of asexuality, hybridity and polyploidy as explanations behind geographical parthenogenesis in insects. I conclude that what is called O. scaber is, in fact, a set of geographical polyploids as polyploidy and not asexuality explains the difference in clonal success. I also argue that O. sulcatus is a recently formed clonal species of non-hybrid origin that may well be a good example of a true general purpose genotype. I find little support for asexuality or a hybrid origin as explanations behind geographical parthenogenesis in insects. Finally, I argue that polyploidy in all eukaryotes should be seen as an opportunity for the species evolution, not as a limitation that ensures the demise of the taxa.