The tobacco hornworm Manduca sexta has been an important model system in insect biology for more than half a century. Here we report the evolutionary divergence in thermal sensitivity and diapause initiation between field and laboratory populations that were separated for more than 35 yr (>240 laboratory generations) and that are descendants from the same field populations in central North Carolina. At intermediate rearing temperatures (20 degrees-25 degrees C), mean body size was significantly larger and development time significantly faster in the laboratory than in the field populations. At higher temperatures (30 degrees -35 degrees C), these mean differences between populations were reduced or eliminated, and larval survival at 35 degrees C was significantly lower in the laboratory population than in the field population. F(1) crosses had survival and development time to wandering similar to the field population times at both 25 degrees and 35 degrees C; body mass at wandering for F(1) crosses was intermediate compared with that of the field and laboratory populations. Comparisons with earlier field and laboratory studies suggest evolutionary reductions in thermal tolerance and performance at high temperatures in the laboratory population. The critical photoperiod initiating diapause in field populations in North Carolina did not change detectably between the 1960s and 2005. In contrast, the laboratory population has evolved a reduced tendency to diapause under short-day conditions, relative to the field population.
Sudden oak death, caused by Phytophthora ramorum, has resulted in high levels of coast live oak (CLO) mortality. However, some CLO survive in areas with high disease pressure and may thus be resistant. We tested the hypothesis that such field-resistant trees contain constitutively higher levels of phenolics than susceptible trees. Phloem was sampled from the trunks of two groups of trees (one previously inoculated, one naturally infected with P. ramorum) categorized over the course of several years as putatively resistant (PR, no symptoms), in remission (IR, showed symptoms but then recovered) and symptomatic (S). Individual and total soluble phenolics from these trees were quantified. There were no significant differences in individual or total soluble phenolics between groups of naturally infected trees. However, inoculated PR and IR trees were characterized by higher constitutive levels of ellagic acid, a tyrosol derivative, and an unidentified phenolic than S trees. Ellagic acid and tyrosol-like compounds in CLO phloem are promising resistance biomarker candidates.
A decline syndrome and widespread mortality of mature white oak tree (Quercus alba) associated with wet and low-lying areas has been recently observed in southern Ohio forests. Previous studies have isolated Phytophthora cinnamomi from white oak rhizospheres. In 2008 and 2009, P. cinnamomi population densities in two healthy and two declining white oak stands at Scioto Trail State Forest were quantified and potential roles of three environmental drivers of Phytophthora spp.–induced decline were assessed: soil texture, soil moisture, and topography. Significantly higher P. cinnamomi propagule densities were found in declining stands in both years but propagule densities were not associated with soil moisture content. Trends in population densities were not correlated with soil moisture or topographic position within field sites. There was a positive, exponential relationship between overall P. cinnamomi population levels and soil moisture on a seasonal scale in 2008 but not 2009. Sites with greater soil clay content were associated with greater decline. Effects of P. cinnamomi inoculum and periodic flooding on root health of 1-year-old potted white oak trees grown in native soil mixes in the greenhouse were examined. Root systems of potted oak were significantly damaged by soil inoculation with P. cinnamomi, especially under flooding conditions. Results of these studies support the hypothesis that P. cinnamomi is a contributing agent to white oak decline in southern Ohio.
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