Brett Phillip Hurley

A comparison of control results for the alien invasive woodwasp, Sirex noctilio, in the southern hemisphere

1 Sirex noctilio has resulted in one of the most damaging biological invasions of pine forestry in the southern hemisphere.

Retracing the routes of introduction of invasive species: the case of the Sirex noctilio woodwasp

Understanding the evolutionary histories of invasive species is critical to adopt appropriate management strategies, but this process can be exceedingly complex to unravel. As illustrated in this study of the worldwide invasion of the woodwasp Sirex noctilio, population genetic analyses using coalescent‐based scenario testing together with Bayesian clustering and historical records provide opportunities to address this problem. The pest spread from its native Eurasian range to the Southern Hemisphere in the 1900s and recently to Northern America, where it poses economic and potentially ecological threats to planted and native Pinus spp. To investigate the origins and pathways of invasion, samples from five continents were analysed using microsatellite and sequence data. The results of clustering analysis and scenario testing suggest that the invasion history is much more complex than previously believed, with most of the populations being admixtures resulting from independent introductions from Europe and subsequent spread among the invaded areas. Clustering analyses revealed two major source gene pools, one of which the scenario testing suggests is an as yet unsampled source. Results also shed light on the microevolutionary processes occurring during introductions, and showed that only few specimens gave rise to some of the populations. Analyses of microsatellites using clustering and scenario testing considered against historical data drastically altered our understanding of the invasion history of S. noctilio and will have important implications for the strategies employed to fight its spread. This study illustrates the value of combining clustering and ABC methods in a comprehensive framework to dissect the complex patterns of spread of global invaders.

Sirex Woodwasp: A Model for Evolving Management Paradigms of Invasive Forest Pests

The Sirex woodwasp, Sirex noctilio, and its fungal mutualist, Amylostereum areolatum, together constitute one of the most damaging invasive pests of pine. Despite a century of research and well-established management programs, control remains unpredictable and spread continues to new areas. Variable success in managing this pest has been influenced by complex invasion patterns, the multilayered nature of biological interactions, the varying local ecologies, and microevolutionary population processes in both the biocontrol organisms and in the wasps. Recent research findings are challenging the historical perspectives on methods to manage the Sirex woodwasp, calling for management programs to incorporate the variable local dynamics affecting this pest complex. In this regard, the Sirex woodwasp provides a superb model to illustrate the need for a different approach to develop efficient and sustainable management tools to deal with the growing and global nature of pest invasions in forests and plantations.

Biological control of forest plantation pests in an interconnected world requires greater international focus

The worldwide homogenization of genetic resources used in plantation forestry (primarily Pinus, Eucalypus, Populus and Acacia spp.) together with accelerating rates of human-aided dispersal of exotic pests, is resulting in plantation pests becoming broadly distributed extremely quickly, sometimes reaching a global distribution within a decade. This unprecedented rate of establishment and spread means that the risk associated with new and emerging pests is shared globally. Biological control represents a major component of the strategy to mitigate such risk, but the current efforts and scope for developing such controls are woefully inadequate for dealing with the increasing rates of pest spread. Given the global nature of the problem, biological control would benefit enormously from an international, collaborative focus. Though inherent difficulties and potential pitfalls exist, opportunities for cost-sharing, growth and maintenance of resources and capacity, and more comprehensive research programmes are critical to the long-term success of biological control. Governments and industries will need to increase their strategic investment in structures specifically designed to promote such focus if they are to successfully protect their forest resources.

Novel and co-evolved associations between insects and microorganisms as drivers of forest pestilence

Some of the most devastating diseases of trees involve associations between forest insects and microorganisms. Although a small number of native insect-microorganism symbioses can cause tree mortality, the majority of associations with tree health implications involve one or more exotic organisms. Here, we divide damaging symbioses between forest insects and microorganisms into four categories based on the native/exotic status of the species involved: (1) insect and microorganism are native; (2) insect is native, microorganism is exotic; (3) insect is exotic, microorganism is native; and (4) insect and microorganism are both exotic. For each category, we describe several well-researched examples of forest insect symbioses and discuss some of the consequences of the types of interactions within each category. We then discuss priorities for research on forest insect symbioses that could help to further elucidate patterns in the complexity of such interactions in the context of invasion biology. We argue that a nuanced understanding of insect-pathogen relationships is lacking, even for the few well-studied examples. Because novel associations between insects, microorganisms, and trees are increasing with globalization, such symbioses and their potential to negatively impact forest ecosystems demand focused research in the future.

Increasing numbers and intercontinental spread of invasive insects on eucalypts

Abstract Native to Australasia, Eucalyptus (sensu lato) is one of the most planted genera of trees in the world. However, the sustainability of Eucalyptus species as plantation trees in non-native areas is increasingly threatened by the introduction and spread of Eucalyptus-feeding insects from Australia. We examine patterns and potential trends with respect to the global spread of Eucalyptus-feeding insects. Likely pathways of introduction and drivers of the rapid distribution of these insects, as well as management options are considered. The rate of introductions is shown to have increased nearly fivefold since the 1980s. As a result, the number of non-native pests of eucalypts outside of Australia has doubled in less than three decades. Furthermore, the rate of secondary spread among continents has also increased. Surprisingly, we found no association between area planted and the number of pests or new introductions. Only a small number of countries have been the points of first detection outside the native range; these countries have acted as bridgeheads to other regions. Quarantine regulations aimed at reducing the spread of invasive organisms appear to be ineffective at a global scale, and pathways allowing these invasions to occur are poorly understood or unknown. An expanded suite of management options are needed to provide resilience against the rapid accrual and homogenization of eucalypt pests, thereby ensuring the sustainability of eucalypt forestry worldwide.

Diversity in Eucalyptus susceptibility to the gall-forming wasp Leptocybe invasa.

1 Extensive variation to damage by the invasive gall‐forming wasp Leptocybe invasa Fisher & LaSalle (Hymenoptera: Eulophidae) is known to exist amongst Eucalyptus genotypes. 2 In the present study, 30 of the 50 tested genotypes were susceptible to gall formation and development of the wasp. Gall development on the petiole and leaves of plants was compared to calculate the percentage of infestation per plant and per genotype. 3 A positive correlation between galls on petioles and leaves indicated an absence of specificity at this level, and also that either leaves or petioles could be used to obtain an accurate estimate of the level of infestation. 4 Genotypes of E. nitens×E. grandis and E. grandis×E. camaldulensis were most susceptible, with a maximum damage index value for leaves and petioles of 0.52 and 0.39, respectively. Eucalyptus dunii, E. nitens, E. smithii, E. urophylla and E. saligna×E. urophylla showed little or no infestation. 5 The results obtained in the present study suggest that the selection and planting of resistant/less susceptible genotypes will be an important aid in managing damage from L. invasa invasion.

Lack of fidelity revealed in an insect–fungal mutualism after invasion

Symbiont fidelity is an important mechanism in the evolution and stability of mutualisms. Strict fidelity has been assumed for the obligate mutualism between Sirex woodwasps and their mutualistic Amylostereum fungi. This assumption has been challenged in North America where the European woodwasp, Sirex noctilio, and its fungal mutualist, Amylostereum areolatum, have recently been introduced. We investigate the specificity of the mutualism between Sirex and Amylostereum species in Canada, where S. noctilio co-infests Pinus with native Sirex nigricornis and its mutualist, Amylostereum chailletii. Using phylogenetic and culture methods, we show that extensive, reciprocal exchange of fungal species and strains is occurring, with 75.3 per cent of S. nigricornis carrying A. areolatum and 3.5 per cent of S. noctilio carrying A. chailletii. These findings show that the apparent specificity of the mutualism between Sirex spp. and their associated Amylostereum spp. is not the result of specific biological mechanisms that maintain symbiont fidelity. Rather, partner switching may be common when shifting geographical distributions driven by ecological or anthropogenic forces bring host and mutualist pairs into sympatry. Such novel associations have potentially profound consequences for fitness and virulence. Symbiont sharing, if it occurs commonly, may represent an important but overlooked mechanism of community change linked to biological invasions.

Biology and rearing of Cleruchoides noackae (Hymenoptera : Mymaridae), an egg parasitoid for the biological control of Thaumastocoris peregrinus (Hemiptera : Thaumastocoridae)

ABSTRACT Cleruchoides noackae Lin and Huber (Hymenoptera: Mymaridae) is a solitary egg parasitoid of Thaumastocoris peregrinus Carpintero and Dellapé (Hemiptera: Thaumastocoridae). The parasitoid was first described in 2009 and its biology and rearing are poorly understood. A key obstacle to the use of C. noackae as a biological control agent has been the ability to consistently rear it under quarantine conditions. This study reports on a series of experiments conducted in quarantine to rear C. noackae and to examine the effects of diet on longevity, per capita reproduction, and progeny sex ratio, as well as to determine development time, and preference and suitability of host eggs of different ages. When supplemented with honey solution, the longevity of C. noackae females increased significantly by 2.4 d and that of males by 1.7 d, relative to the unfed adults. Mean per capita reproduction for the honey-fed wasps was 7.7 offspring per female, with progeny sex ratio slightly skewed toward males. Mean percentage parasitism was 32.2%. C. noackae was capable of parasitizing and completing development from oviposition to adult eclosion within 15.7 d in host eggs between 0 and 5 d old. The ability of C. noackae to parasitize a wide range of host egg ages increases the period of vulnerability of T. peregrinus to attack, increasing its potential efficacy as a biological control agent. The methods and results reported here represent a crucial step in the ongoing efforts to develop this potential biological control system.

Factors Affecting the Efficacy of Deladenus siricidicola in Biological Control Systems

The nematode, Deladenus (=Beddingia) siricidicola, represents the cornerstone of Sirex noctilio biological control programs across the Southern Hemisphere. There is, however, significant variation in its efficacy in different regions. In this review, we consider emerging issues related to the biology and handling of the nematode that might influence its efficacy in biological control systems. Most practical aspects concerning the handling of D. siricidicola have been streamlined over the past half-century and these appear to be very efficient. However, large gaps remain in our knowledge about some key aspects of the biology of D. siricidicola. For example, very little is known regarding the evolution of virulence in the nematode populations, and the consequent evolution of resistance in S. noctilio populations. Furthermore, the levels of diversity in D. siricidicola and its ability to adapt to fungal, wasp and environmental variation are poorly understood. In this regard, new collections and storage of native populations of the Deladenus spp. are critical for the future research and management of this key biological control agent of S. noctilio.