Australian Megastigmus (Hymenoptera: Megastigmidae) associates of eucalypt galls as potential biocontrol agents of Leptocybe spp. (Hymenoptera: Eulophidae)

Ngoc Hoan Le

doi:10.25907/00472

This thesis facilitates the use of Megastigmus in biological control of Leptocybe spp. through an increased understanding of Megastigmus species composition and distribution in eucalypt galling systems in Australia, their association with other insects in eucalypt gall communities, and taxonomy/biology of key species in Leptocybe spp. biocontrol. Molecular DNA markers, including COI mitochondrial DNA (mtDNA) and 28S ribosomal DNA (rDNA), were applied to understand the species composition of Megastigmus in eucalypt galls in Australia and to build a partially resolved phylogeny of these species. Automatic Barcoding Gap Discovery (ABGD) confirmed the occurrence of thirteen discrete Megastigmus species and a species complex associated with eucalypt galls. Specimens collected from the invasive range of Leptocybe spp. were additionally identified. A reconstructed phylogeny based on rDNA molecular marker sequences placed Leptocybe-associated Megastigmus into four different clades. A set of morphological characters is provided to assist identification of eucalypt gall associates, and the use of molecular markers for museum specimens was proposed in resolving taxonomic uncertainty. Distribution maps of megastigmids (Megastigmus and Bootanomyia) collected from eucalypt galls in Australia based on geographic data, gall morphology and Leptocybe spp. associations are presented. Occurrence of megastigmids with gall associates from different commonly found families (Cecidomyiidae, Mymaridae, Eulophidae and other Chalcidoidea families) were analysed. In Leptocybe spp. galls, megastigmids frequently coemerged with the eulophids Quadrastichus mendeli, Selitrichodes neseri, S. kryceri, and unidentified representatives of the families Cecidomyiidae and Mymaridae. In non- Leptocybe spp. galls, the most common associates of Megastigmidae were from the families Eulophidae, Eurytomidae and Cecidomyiidae. Associates of Leptocybe sp. lineage B were identified as M. lawsoni, M. zvimendeli, M. manonae sp. nov. and Megastigmus sp. 1. Among these species, incidence-based data confirmed significant association of M. lawsoni and M. zvimendeli with Leptocybe sp. lineage B. Difficulties in taxonomic identification of Leptocybe-associated Megastigmus were resolved through a case study using a combination of morphometric analysis and molecular ABGD-based species delimitation. While morphometric data demonstrated high variation of several body characters currently used in morphological keys, multivariate analysis of body ratio confirmed a clear separation of two closely related species, M. zvimendeli and M. manonae. This observation was supported by the phylogeny reconstructed from concatenated sequence data (mtDNA and rDNA) of the studied specimens, and confirmed the discovery of a new species, M. manonae, described herein. Based on morphological variation and DNA data, several described species (M. judikingae, M. icipeensis, M. sichuanensis) were recognised as junior synonyms of M. zvimendeli. Establishment of M. zvimendeli in Israel was confirmed and occurrence of the species in India, Kenya and China were reported for the first time under this name. A specimen previously identified as M. viggianii in India was reattributed to M. zvimendeli and the link between M. viggianii with Leptocybe was rejected. Regarding biological aspects of common Leptocybe spp. parasitoids in Australia, abundance data from selected collection sites in South East Queensland and northern New South Wales recorded M. lawsoni complex (16.4% total emergence) and M. zvimendeli (11.6%) as the most abundant Megastigmus in Leptocybe spp. galls, although proportions varied temporally and spatially. Emergence from field collected galls revealed a male-biased sex ratio of M. lawsoni haplotype 4 and a balanced sex ratio of Megastigmus sp. 1 and M. zvimendeli. All four species successfully reproduced upon exposure to laboratory maintained Leptocybe spp. galls on Eucalyptus grandis seedlings. Within-gall development time, from oviposition to the emergence of the next generation, ranged from 18 to 26 days at 25 oC, 50 - 70% RH. Female M. zvimendeli survived 6.5 days on average when exposed to Leptocybe spp. galls on Eucalyptus grandis + honey solution, with maximum reproduction capacity at 3 - 4 days after emergence. Overall, this study contributes to the use of Australian Megastigmus in worldwide biological control of Leptocybe spp. through an increased understanding of species delineation, identities and relationships. It provides enhanced tools and recommendations for taxonomic review of eucalypt-associates in the genus, and reveals the previously unrecognised success of M. zvimendeli as a biocontrol agent of Leptocybe spp. worldwide. The results vastly improve our knowledge concerning the biodiversity of eucalypt gall associates, particularly Megastigmus species, in Australia.

Australian Megastigmus (Hymenoptera: Megastigmidae) associates of eucalypt galls as potential biocontrol agents of Leptocybe spp. (Hymenoptera: Eulophidae)

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