Gall Wasp Leptocybe Invasa Research Articles

Differential development times of galls induced by Leptocybe invasa (Hymenoptera: Eulophidae) reveal differences in susceptibility between two Eucalyptus clones.

The significance of morphological responses of hosts on susceptibility against gall-inducing insects is relatively unknown, especially in planted forests. Here, we investigate the temporal morphological responses (gall development) induced by the invasive gall wasp Leptocybe invasa and the subsequent insect development in two Eucalyptus clones. Our results identified a novel stage of gall development, not previously reported, termed here 'brownish ring'. In both hosts similar gall development stages were observed. Although L. invasa oviposited in both clones, comparison of external morphological traits of galls over time revealed a differential response in the number of galls between clones. Comparison of the developmental time of each gall and insect stage between clones suggests that plant defense mechanisms against L. invasa are activated shortly after oviposition by the wasp, yet before gall formation. Gall number is an important parameter that should be used to measure host susceptibility among Eucalyptus clones. To the best of our knowledge, this is the first study showing differential morphological responses induced by a galling insect, even before gall formation, revealing differences in susceptibility between different plant hosts. These findings provide insight into the use of early stages of gall formation by L. invasa to prevent invasion and establishment of this pest.

Susceptibilidad de Leptocybe invasa (Hymenoptera: Eulophidae) a insecticidas en invernadero

La avispa agalladora del eucalipto, Leptocybe invasa, es una plaga de origen australiano que afecta a plantaciones de Eucalyptus spp. La especie Eucalyptus camaldulensis es el más susceptible hospedero y es ampliamente utilizado en el mundo para madera aserrada, pulpa y carbón; inclusive, es parte del arbolado urbano, como ocurre en varias ciudades de México. La naturaleza exótica de L. invasa y su desarrollo en agallas, dificulta su regulación natural por entomófagos nativos en este país, lo que representa una amenaza para las regiones productoras de eucaliptos y áreas urbanas. El presente estudio evaluó la eficiencia de insecticidas en condiciones de invernadero, mediante aplicación al suelo y foliar, sobre los estados inmaduros de la avispa: huevo, larva joven, larva madura y pupa, utilizando plantas de E. camaldulensis menores de un año. La aplicación de Carbofurán o Imidacloprid en suelo ocasionó mayor mortalidad en huevo (35% a 79%) y larva joven (40% a 75%), mientras que en larva madura y pupa causó una mortalidad baja (< 5%). La aplicación de Spirotetramat sobresalió en las aplicaciones foliares, pero no es suficiente por sí sola para controlar a la plaga (mortalidad < 40%). Con base en los resultados de esta investigación y los antecedentes de la literatura especializada, se sugiere que el manejo químico sobre L. invasa en invernaderos es factible pero solamente como medida emergente. Esto mediante la utilización de Carbofurán o Imidacloprid en aplicación al suelo alternado con una aplicación foliar posterior de Spirotetramat.

Galling impacts of the gall wasp Leptocybe invasa (Hymenoptera: Eulophidae) on Eucalyptus trees vary with plant genotype

Impacts of galling on the distributions of plant metabolites can vary greatly with plant genotype. In this study, two Eucalyptus genotypes with different resistance levels were chosen, and the levels of several primary and secondary metabolites, as well as phytohormones in galls and ungalled portions of galled leaves infested by the gall wasp Leptocybe invasa, and gall-free (control) leaves were compared. It was found that galls of both two plant genotypes accumulated higher concentrations of carbon, total phenolics, gibberellins (GA), and abscisic acid (ABA) but had lower chlorophyll content than ungalled portions. However, galls of highly susceptible genotype contained higher nitrogen (N), cytokinins (CK), GA, and chlorophyll content but lower C/N ratio, total phenolics, tannins, and ABA than less susceptible genotype. For both two genotypes, ABA in galls and ungalled portions increased compared with adjacent control leaves. CK and GA levels increased in galls but decreased in ungalled portions of highly susceptible genotype, compared with control leaves. For less susceptible genotype, CK levels increased in both galls and ungalled portions compared with control leaves, but higher levels of tannins, total phenolics, and GA were only detected in galls. Therefore, our study found insufficient evidence that the impact of galling on the distributions of these metabolites and phytohormones extended beyond the attacked leaves, because they varied greatly with plant genotype.

Efficacy of Three Insecticides in the Control Gall Wasp Leptocybe invasa in Eucalyptus urograndis Seedlings

Forestry expertise and plantations managers are struggling to find cheaper and sustainable solutions to contain the losses caused by Leptocybe invasa in the last nine years on the forest stands in Mozambique. Aiming to help find a solution in the control of L. invasa early in the nursery, we conducted an experimental trial at the Niassa Forestry company nursery, located in the Niassa province, northern Mozambique in February 2015. Three insecticides: Acetamiprid, Thiamethoxam, Imidacloprid, with and without adherent and pH regulator were tested. The experiment had seven treatments including the control. The number of seedlings infested by the gall wasp were assessed 15, 30, 45 and 60 days after the seeds were sown in the nursery. Data were analysed in R package. Normality and homogeneity of variances were tested through Shapiro-Wilk and Bartlett's tests respectively. Analysis of Variance (ANOVA) and parametric means test (Tukey-HSD), were used to assess whether there was difference among the treatments. Results showed difference between treatments at 0.01% of significance after 15, 30 and 45 days and at 5% in the 60 days after sowing. With less seedlings infested by the gall wasp, Imidacloprid with and without adherent was almost superior compared to all other pesticides in all assessment. The use of adherent and pH regulators negatively affected the performance of insecticides, except in the Imidacloprid. This study findings should not however, be overall generalized, instead, more research can be conducted to verify the consistency of these results before being widely implemented.

The first identification of genomic loci in plants associated with resistance to galling insects: a case study in Eucalyptus L'H\xe9r. (Myrtaceae)

Genomic loci related with resistance to gall-inducing insects have not been identified in any plants. Here, association mapping was used to identify molecular markers for resistance to the gall wasp Leptocybe invasa in two Eucalyptus species. A total of 86 simple sequence repeats (SSR) markers were screened out from 839 SSRs and used for association mapping in E. grandis. By applying the mixed linear model, seven markers were identified to be associated significantly (P ≤ 0.05) with the gall wasp resistance in E. grandis, including two validated with a correction of permutation test (P ≤ 0.008). The proportion of the variance in resistance explained by a significant marker ranged from 3.3% to 37.8%. Four out of the seven significant associations in E. grandis were verified and also validated (P ≤ 0.073 in a permutation test) in E. tereticornis, with the variation explained ranging from 24.3% to 48.5%. Favourable alleles with positive effect were also mined from the significant markers in both species. These results provide insight into the genetic control of gall wasp resistance in plants and have great potential for marker-assisted selection for resistance to L. invasa in the important tree genus Eucalyptus.

The gall wasp Leptocybe invasa (Hymenoptera: Eulophidae) stimulates different chemical and phytohormone responses in two Eucalyptus varieties that vary in susceptibility to galling.

Gall-inducing insects produce various types of galls on plants, but little is known about the gall-induction mechanism of these galling insects. The gall wasp Leptocybe invasa Fisher & LaSalle (Hymenoptera: Eulophidae) forms galls of different sizes on several Eucalyptus species. To clarify the physiological responses of Eucalyptus to L. invasa infestation, we measured the dynamics of nitrogen (N), carbon (C), total phenolics, total tannins and four types of phytohormones (zeatin [Z] + zeatin riboside [ZR], gibberellins [GA], indole-3-acetic acid [IAA] and abscisic acid [ABA]) in galled and ungalled leaf tissues of two Eucalyptus horticultural varieties (DH201-2 [Eucalyptus grandis × Eucalyptus camaldulensis] and EA [Eucalyptus exserta]) with different susceptibility to galling throughout the larval developmental stages. Nitrogen, total phenolics, tannins and four kinds of phytohormones strongly accumulated in tissues galled by L. invasa (especially during early larval feeding stages). While N, Z + ZR and GA levels were higher, tannins and ABA levels were lower in the galled tissues on the highly susceptible variety. Nitrogen, total phenolics, GA, Z + ZR and IAA levels in the galled tissues gradually decreased during gall development, but ABA and tannins conversely increased in the galled tissues of the less susceptible variety. Our results suggest that the effects of gall-inducing insects on plants depend not only on the susceptibility of the plant infested but also on the developmental stage of galled tissues. Gall formation process is thus synergistically influenced by both gall-inducing insect and plant genotypes.

Life inside a gall: closeness does not favour horizontal transmission of Rickettsia between a gall wasp and its parasitoid.

The incidence of horizontal transmission as a route for spreading symbiont infections is still being debated, but a common view is that horizontal transfers require intimate between-species relationships. Here we study a system that meets ideal requirements for horizontal transmission: the gall wasp Leptocybe invasa and its parasitoid Quadrastichus mendeli (Hymenoptera: Eulophidae). These wasps belong to the same subfamily, spend most of their lives inside the same minute gall and are both infected by Rickettsia, a maternally inherited endosymbiotic bacteria that infects several arthropods, sometimes manipulating their reproduction, like inducing thelytokous parthenogenesis in L. invasa. Despite intimate contact, close phylogenetic relationship and the parasitoid's host specificity, we show that host and parasitoid do not share the same Rickettsia. We provide indirect evidence that Rickettsia infecting Q. mendeli may be inducing thelytokous parthenogenesis, as the symbiont is densely present in the reproductive apparatus and is vertically transmitted. Phylogenetic analyses based on 16S and gltA placed this symbiont in the leech group. The confirmed and presumed parthenogenesis-inducing Rickettsia discovered so far only infect eulophid wasps, and belong to three different groups, suggesting multiple independent evolution of the parthenogenesis inducing phenotype. We also show some degree of cospeciation between Rickettsia and their eulophid hosts.

Genetic Diversity of the Invasive Gall Wasp Leptocybe invasa (Hymenoptera: Eulophidae) and of its Rickettsia Endosymbiont, and Associated Sex-Ratio Differences.

The blue-gum chalcid Leptocybe invasa Fisher & LaSalle (Hymenoptera: Eulophidae) is a gall wasp pest of Eucalyptus species, likely native to Australia. Over the past 15 years it has invaded 39 countries on all continents where eucalypts are grown. The worldwide invasion of the blue gum chalcid was attributed to a single thelytokous morphospecies formally described in 2004. Subsequently, however, males have been recorded in several countries and the sex ratio of field populations has been found to be highly variable in different areas. In order to find an explanation for such sex ratio differences, populations of L. invasa from a broad geographical area were screened for the symbionts currently known as reproductive manipulators, and both wasps and symbionts were genetically characterized using multiple genes. Molecular analyses suggested that L. invasa is in fact a complex of two cryptic species involved in the rapid and efficient spread of the wasp, the first recovered from the Mediterranean region and South America, the latter from China. All screened specimens were infected by endosymbiotic bacteria belonging to the genus Rickettsia. Two closely related Rickettsia strains were found, each infecting one of the two putative cryptic species of L. invasa and associated with different average sex ratios. Rickettsia were found to be localized in the female reproductive tissues and transovarially transmitted, suggesting a possible role of Rickettsia as the causal agent of thelytokous parthenogenesis in L. invasa. Implications for the variation of sex ratio and for the management of L. invasa are discussed.

Gall Wasp <i>Leptocybe invasa</i> (Hymenoptera: Eulophidae) Management in Eucalypts

The invasive gall wasp Leptocybe invasa (Hymenoptera: Eulophidae) induces galls on the shoots of Eucalyptus camaldulensis Dehnh. and E. tereticornis Sm. and damage nursery seedlings young plantations and coppice shoots. The magnitude of the damage in nurseries and young plantations necessitates increased efforts to reduce the incidence and impacts of the pest. Identification of feasible and appropriate management methods will help in reducing the high cost of containing the pest in outbreak situations and avoid loss of planting material by state Forest Departments, Corporations and farmers while raising commercial Eucalyptus plantations. Deployment of gall tolerant clones and biological control agents has been attempted in the present study. Results show that eucalyptus gall wasp in nurseries can be managed by deploying identified gall tolerant, productive clones. Release of natural enemies like Quadrastichus mendeli and Megastigmus sp and regular monitoring of its population level in nurseries can further bring down the gall infestation.

Genetic variation in Eucalyptus camaldulensis and E. tereticornis for early growth and susceptibility to the gall wasp Leptocybe invasa in China

The gall wasp Leptocybe invasa is a major insect pest on plantation Eucalyptus in many countries. Since appearing in China in 2007 it has had major impacts on commercial plantations—some commonly planted Eucalyptus varieties have proven particularly susceptible, including hybrids involving Eucalyptus camaldulensis and E. tereticornis parent species. Intra-specific variation within each species for L. invasa susceptibility was examined in two seed source and family trials in southwest of Guangdong. The E. camaldulensis trial included 101 seedlots representing five natural stand and six seed orchard sources which also represented three sub-specific taxa. The E. tereticornis trial included 143 seedlots representing 11 natural stand and four seed orchard sources, including breeding seed orchards in China. Both trials were assessed for susceptibility to L. invasa along with height at age 9 months. Sub-specific taxa within E. camaldulensis differed significantly (P < 0.01) in L. invasa susceptibility but not height or survival; subsp. acuta had the lowest average susceptibility and subsp. simulata and obtusa were of intermediate susceptibility whilst material of uncertain sub-specific taxa from India had the highest average susceptibility. In E. tereticornis regions of origin and seed sources within regions differed significantly (P < 0.01) for both L. invasa susceptibility and height; the region China (all somewhat improved sources) had both the best average height growth and lowest susceptibility whilst the region Australia (all natural stand sources) proved inferior to China for both average susceptibility and height. A strong significant correlation was found between seed source average L. invasa susceptibility and annual rainfall at seed source geographic origin in E. tereticornis (r = −0.873; P < 0.01), implying that seedlots from higher rainfall environments are markedly less susceptible to L. invasa. The equivalent parameter in E. camaldulensis was also strong (r = −0.730) though not significant, perhaps due to having only five data points available. Differences between families within seed sources for both L. invasa susceptibility and height growth were also highly significant (P < 0.01) with the former trait proving moderately to strongly heritable (h i 2 = 0.54 ± 0.40 in E. camaldulensis; 0.52 ± 0.50 in E. tereticornis). Height had low to moderate heritability in both species (h i 2 = 0.11 ± 0.15 and 0.26 ± 0.08 respectively). Tree height and L. invasa susceptibility showed a moderate negative (favourable) genetic correlation in E. camaldulensis (−0.33 ± 0.64) and a moderate to strong negative (favourable) genetic correlation in E. tereticornis (−0.47 ± 0.31). Corresponding phenotypic correlations, though significant, were somewhat weaker (−0.16 and −0.29 respectively), indicating a trend for taller trees to have lower levels of L. invasa susceptibility.

Leptocybe invasa em Eucalyptus sp. no estado do Rio Grande do Sul, Brasil

O presente estudo relata o ataque da vespa-da-galha do eucalipto Leptocybe invasa Fisher &amp; LaSalle, 2004 (Hymenoptera: Eulophidae) no Estado do Rio Grande do Sul, Brasil. As formas imaturas de L. invasa induzem o crescimento de galhas que podem levar ao desfolhamento de árvores de eucalipto.

Selitrichodes neseri n. sp., a new parasitoid of the eucalyptus gall wasp Leptocybe invasa Fisher &amp;amp; La Salle (Hymenoptera: Eulophidae: Tetrastichinae)

Selitrichodes neseri Kelly &amp; La Salle n. sp. (Hymenoptera: Eulophidae: Tetrastichinae), is described as a parasitoid of the inva-sive eucalyptus gall wasp Leptocybe invasa Fisher &amp; La Salle (Hymenoptera: Eulophidae: Tetrastichinae), which is causingsubstantial damage particularly in commercial Eucalyptus plantations. Selitrichodes neseri was originally collected in Australiain 2010 when searching for biological control agents of L. invasa. It has since been reared in quarantine in South Africa where it is being evaluated for release as a biological control agent of L. invasa.

Occurrence of two localMegastigmus species parasitic on the eucalyptus gall waspLeptocybe invasa in Israel and Turkey

Two localMegastigmus species were found to be parasitoids on the invasive Eucalyptus gall waspLeptocybe invasa Fisher & La Salle in Turkey and Israel.Megastigmus sp, from Israel is a larval and pupal parasitoid ofL. Invasa. Both species are biparental. Features showing morphological differences between them are presented. The biology, distribution and potential efficiency as biological control agents are discussed.