Interactions of elevated carbon dioxide and temperature with aphid feeding on transgenic oilseed rape: Are Bacillus thuringiensis (Bt) plants more susceptible to nontarget herbivores in future climate?

Climate change factors such as elevated carbon dioxide (CO₂) and temperature typically affect carbon (C) and nitrogen (N) dynamics of crop plants and the performance of insect herbivores. Insect‐resistant transgenic plants invest some nutrients to the production of specific toxic proteins [i.e. endotoxins from Bacillus thuringiensis (Bt)], which could alter the C–N balance of these plants, especially under changed abiotic conditions. Aphids are nonsusceptible to Lepidoptera‐targeted Bt Cry1Ac toxin and they typically show response to abiotic conditions, and here we sought to discover whether they might perform differently on compositionally changed Bt oilseed rape. Bt oilseed rape had increased N content in the leaves coupled with reduced total C compared with its nontransgenic counterpart, but in general the C : N responses of both plant types to elevated CO₂ and temperature were similar. Elevated CO₂ decreased N content and increased C : N ratio of both plant types. Elevated temperature increased C and N contents, total chlorophyll and carotenoid concentrations under ambient CO₂, but decreased these under elevated CO₂. In addition, soluble sugars were increased and starch decreased by elevated temperature under ambient but not under elevated CO₂, whereas photosynthesis was decreased in plants grown under elevated temperature in both CO₂ levels. Myzus persicae, a generalist aphid species, responded directly to elevated temperature with reduced developmental time and decreased adult and progeny weights, whereas the development of the Brassica specialist Brevicoryne brassicae was less affected. Feeding by M. persicae resulted in an increase in the N content of oilseed rape leaves under ambient CO₂, indicating the potential of herbivore feeding itself to cause allocation changes. The aphids performed equally well on both plant types despite the differences between C–N ratios of Bt and non‐Bt oilseed rape, revealing the absence of plant composition‐related effects on these pests under elevated CO₂, elevated temperature or combined elevated CO₂ and temperature conditions.     

The influence of cypermethrin and oxydemeton-methyl treatment on Lygus damage in young Scots pine seedlings

Laboratory experiments were carried out to evaluate the efficiency of two insecticides, cypermethrin and oxydemeton-methyl, in controlling the nymphs and adults of Lygus bugs and the resulting damage caused by these bugs to small pine seedlings. Both insecticides significantly increased the mortality of bugs on the seedlings compared with bug mortality on untreated controls. Mortality of bugs was higher in the oxydemeton-methyl treatment than in the cypermethrin treatment. The occurrence of seedlings with multiple leaders and the number of leader shoots per seedling were significantly decreased in insecticide-treated seedlings. Mean number of leader shoots was significantly higher in seedlings treated with oxydemeton-methyl than in seedlings treated with cypermethrin after a 24-h exposure to nymphal instars of Lygus. The mortality of the pine seedlings was very low but significantly decreased in insecticidal treatments. Factors affecting the effects of different insecticides on bug mortality and their efficiency in controlling the multiple-leadering phenomenon are discussed.     

Emission of herbivore-induced volatile terpenoids from two hybrid aspen (Populus tremula×tremuloides) clones under ambient and elevated ozone concentrations in the field

Tropospheric ozone levels are continuously rising due to human activities in the 21st century. Although the phytotoxic impact of ozone on plants has been well documented, the effect of ozone on plant emissions has received little attention. We have conducted a field-based investigation utilizing two clones of hybrid aspen ( Populus tremula L. × P . tremuloides Michx.) in a free-air ozone concentration enrichment (FACE) facility. The effects of chronic exposure to moderately increased concentrations of ozone on insect-induced terpene emissions by these trees were investigated. We used two herbivore species, Phyllobius piri , and Epirrita autumnata , both of which can reach outbreak levels on deciduous trees in Northern Europe. Our results indicated only very small changes in emissions due to increased ozone levels, but showed induction of some terpenes, particularly the monoterpene trans- β -ocimene and the homoterpene ( E )-4,8-dimethyl-1,3,7-nonatriene, in response to insect feeding. Here, we consider the positive aspects of conducting this type of study in the field and consider the possible influences of other field-based environmental factors.     

Carbon dioxide balance of a fen ecosystem in northern Finland under elevated UV-B radiation

The effect of elevated UV‐B radiation on CO₂ exchange of a natural flark fen was studied in open‐field conditions during 2003–2005. The experimental site was located in Sodankylä in northern Finland (67°22′N, 26°38′E, 179 m a.s.l.). Altogether 30 study plots, each 120 cm × 120 cm in size, were randomly distributed between three treatments (n=10): ambient control, UV‐A control and UV‐B treatment. The UV‐B‐treated plots were exposed to elevated UV‐B radiation level for three growing seasons. The instantaneous net ecosystem CO₂ exchange (NEE) and dark respiration (R_TOT) were measured during the growing season using a closed chamber method. The wintertime CO₂ emissions were estimated using a gradient technique by analyzing the CO₂ concentration in the snow pack. In addition to the instantaneous CO₂ exchange, the seasonal CO₂ balances during the growing seasons were modeled using environmental data measured at the site. In general, the instantaneous NEE at light saturation was slightly higher in the UV‐B treatment compared with the ambient control, but the gross photosynthesis was unaffected by the exposure. The R_TOT was significantly lower under elevated UV‐B in the third study year. The modeled seasonal (June–September) CO₂ balance varied between the years depending on the ground water level and temperature conditions. During the driest year, the seasonal CO₂ balance was negative (net release of CO₂) in the ambient control and the UV‐B treatment was CO₂ neutral. During the third year, the seasonal CO₂ uptake was 43±36 g CO₂‐C m⁻² in the ambient control and 79±45 g CO₂‐C m⁻² in the UV‐B treatment. The results suggest that the long‐term exposure to high UV‐B radiation levels may slightly increase the CO₂ accumulation to fens resulting from a decrease in microbial activity in peat. However, it is unlikely that the predicted development of the level of UV‐B radiation would significantly affect the CO₂ balance of fen ecosystems in future.