Prediction of current and future potential distributions of the Eucalyptus pest Leptocybe invasa (Hymenoptera: Eulophidae) in China using the CLIMEX model.

BACKGROUND: The wasp Leptocybe invasa Fisher & LaSalle (Hymenoptera: Eulophidae), a Eucalyptus (Myrtaceae) pest native to Australia, has caused economic and ecologic losses in China. It is a serious pest in southern provinces. Because climate is a limiting factor in insect distribution, we used the model CLIMEX to predict the effect of climate change on potential current and future distributions of L. invasa in China. Data were collected on the current locations of this wasp, along with the damage incurred to Eucalyptus. These data were used to create a forecast model to predict potential current and future distribution maps of L. invasa in China. RESULTS: The verification results showed that 99.5% of the distribution samples formulated by the model are highly reliable and accurate. The result predicted that the potential current distribution of L. invasa will concentrate south of the Yellow River basin. The future distribution maps predicted a small-scale potential expansion north-northwest of Guangxi and more areas within China will provide increasingly suitable habitats for colonization by L. invasa. CONCLUSION: These distribution predications will be useful in determining where preventive and control measures should be implemented against this pest wasp in Eucalyptus throughout China. © 2019 Society of Chemical Industry.

The Sclerophyllous Eucalyptus camaldulensis and Herbaceous Nicotiana tabacum Have Different Mechanisms to Maintain High Rates of Photosynthesis.

It is believed that high levels of mesophyll conductance (gm) largely contribute to the high rates of photosynthesis in herbaceous C3 plants. However, some sclerophyllous C3 plants that display low levels of gm have high rates of photosynthesis, and the underlying mechanisms responsible for high photosynthetic rates in sclerophyllous C3 plants are unclear. In the present study, we examined photosynthetic characteristics in two high-photosynthesis plants (the sclerophyllous Eucalyptus camaldulensis and the herbaceous Nicotiana tabacum) using measurements of gas exchange and chlorophyll fluorescence. Under saturating light intensities, both species had similar rates of CO2 assimilation at 400 µmol mol-1 CO2 (A400). However, E. camaldulensis exhibited significantly lower gm and chloroplast CO2 concentration (Cc) than N. tabacum. A quantitative analysis revealed that, in E. camaldulensis, the gm limitation was the most constraining factor for photosynthesis. By comparison, in N. tabacum, the biochemical limitation was the strongest, followed by gm and gs limitations. In conjunction with a lower Cc, E. camaldulensis up-regulated the capacities of photorespiratory pathway and alternative electron flow. Furthermore, the rate of alternative electron flow was positively correlated with the rates of photorespiration and ATP supply from other flexible mechanisms, suggesting the important roles of photorespiratory pathway, and alternative electron flow in sustaining high rate of photosynthesis in E. camaldulensis. These results highlight the different mechanisms used to maintain high rates of photosynthesis in the sclerophyllous E. camaldulensis and the herbaceous N. tabacum.

Effect of the Gall Wasp Leptocybe invasa on Hydraulic Architecture in Eucalyptus camaldulensis Plants.

The gall wasp, Leptocybe invasa (Hymenoptera; Eulophidae), is a devastating pest of eucalypt plantations in the Middle East, the Mediterranean basin, Africa, India, South-East Asia, and China. Heavy galling causes the leaves to warp and in extreme cases it may stunt the growth of the trees of Eucalyptus camaldulensis. However, the physiological mechanisms underlying how L. invasa inhibits the growth of plants of E. camaldulensis are unclear. Because the growth rate of plants is mainly dependent on photosynthesis that is largely correlated with hydraulic architecture, we speculate that galling of L. invasa depresses hydraulic conductance of stem and leaf. In the present study, we examined the effects of L. invasa galling on hydraulic architecture and photosynthetic parameters in E. camaldulensis plants. We found that galling of L. invasa significantly decreased stem hydraulic conductance (K stem), midday leaf water potential (Ψmd), minor vein density, and stomatal density (SD). Furthermore, the stomatal conductance (g s), chlorophyll content, CO2 assimilation rate (A n) and photosynthetic electron flow were reduced in infected plants. Therefore, the galling of L. invasa not only declined the water supply from stem to leaves, but also restricted water transport within leaf. As a result, galled plants of E. camaldulensis reduced leaf number, leaf area, SD and g s to balance water supply and transpirational demand. Furthermore, galled plants had lower leaf nitrogen content, leading to decreases in chlorophyll content, CO2 assimilation rate and photosynthetic electron flow. These results indicate that the change in hydraulic architecture is responsible for the inhibition of growth rate in galled plants.