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

You-Gui Tong,Xin Yang,Wei Huang,Xiao-Xi Ding,Kai-Cun Zhang

doi:10.3389/fpls.2016.00130

Abstract

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 (Kstem), midday leaf water potential (Ψmd), minor vein density, and stomatal density (SD). Furthermore, the stomatal conductance (gs), chlorophyll content, CO2 assimilation rate (An) 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 gs 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.

Highlights

In China, Eucalyptus sp. has been introduced for plantation in many tropical and subtropical areas for economic and social development because they can tolerate and grow well on degraded, unfertile soils, where it is very difficult to establish other tree species
Because minor vein density (MVD) is significantly and positively correlated with leaf hydraulic conductance (Kleaf ), the decrease in MVD in galled plants can cause a decline in Kleaf
Gall density decreased with maturity of the host plant and was three times higher on juvenile plants compared with mature plants (Pires and Price, 2000)

Summary

Introduction

In China, Eucalyptus sp. has been introduced for plantation in many tropical and subtropical areas for economic and social development because they can tolerate and grow well on degraded, unfertile soils, where it is very difficult to establish other tree species. Has been introduced for plantation in many tropical and subtropical areas for economic and social development because they can tolerate and grow well on degraded, unfertile soils, where it is very difficult to establish other tree species. The wood of Eucalyptus species can be used for production of paper, which providing income for local people and government. The genus Eucalyptus in its native range sustains a rich fauna of gall-inducing insects (Blanche and Westoby, 1995; Blanche, 2000). Eucalyptus is a unique genus in hosting several Eulophidae wasps (Hymenoptera: Chalcidoidea) such as Leptocybe invasa Fisher & LaSalle. Is one of the most susceptible species to this gall wasp L. invasa (Thu et al, 2009). The massive presence of galls induced by L. invasa cause severe damage

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