Nematode Deladenus Siricidicola Research Articles

Unexpected diversity in historical biological control programs: Population genetics of the nematode Deladenus siricidicola in Australia and New Zealand

The nematode Deladenus siricidicola is used for the biocontrol of the invasive woodwasp, Sirex noctilio, that infests Pinus globally. In New Zealand, D. siricidicola was accidentally introduced along with S. noctilio, after which its potential for biological control was realized in the 1960s. Additional strains of the nematode were collected from across its Eurasian distribution for the development of a biological control program in Australia in the 1970s. A strain from Hungary (Sopron) was originally selected for large-scale releases and later replaced by a strain that was collected from previously released populations in Tasmania (Kamona). The Kamona strain is still used today in biological control programs in Australia, South Africa and South America. Despite the long history of biocontrol, the nematode’s genetic diversity has not been studied in Australia and New Zealand. We assessed the population genetic diversity and structure of D. siricidicola in these countries using mitochondrial COI sequence data and 12 microsatellite markers. We also compared our data to that of a recent global diversity study. The results show a higher than expected diversity of the nematode in these Australasian countries, especially Australia. Three lineages previously defined from North America (A), Southern Hemisphere (B) and Spain (C) were identified in Australia (A, B, C) and New Zealand (A, B). A previously undescribed lineage (D), was identified in both Australia and New Zealand. Despite the evidence of admixture with other lineages, including the widely distributed biocontrol lineage (B; Kamona), lineage D remained distinguishable and dominant in these populations, even where Kamona has been released intensively for decades. Surprisingly, the results also revealed a shared history between populations in New Zealand and North America. These findings highlight the importance of understanding and monitoring genetic diversity in biological control programs and hold opportunities to improve both the selection and deployment of this nematode for the management of diverse populations of S. noctilio.

Demography of an invading forest insect reunited with hosts and parasitoids from its native range

The Sirex woodwasp Sirex noctilio Fabricius (Hymenoptera: Siricidae), a widespread invasive pest of pines in the Southern Hemisphere, was first detected in North America in 2004. This study assessed the impacts of life history traits, host resistance and species interactions on the demography of S. noctilio in New York, Pennsylvania and Vermont, then compared key metrics to those found in the native range in Galicia, Spain. Many trees naturally attacked by S. noctilio in North America produced no adult woodwasps, with 5 of 38 infested trees (13%) sampled across six sites yielding 64% of emerging insects. Reproductive success was highest in the introduced host scots pine, Pinus sylvestris, but native red pine, Pinus resinosa, produced larger insects. Sirex noctilio required one or sometimes two years to develop and sex ratios were male biased, 1:2.98 ♀:♂. Body size and fecundity were highly variable, but generally lower than observed in non-native populations in the Southern Hemisphere. Hymenopteran parasitoids killed approximately 20% of S. noctilio larvae and 63% of emerging adults were colonized by the parasitic nematode Deladenus siricidicola, although no nematodes entered eggs. Demographic models suggested that S. noctilio in the northeastern USA have a higher potential for population growth than populations in the native range: estimated finite factor of increase, λ, was 4.17–4.52 (depending on tree species colonized), compared to λ = 1.57 in Spain.

Genetic variability among native and introduced strains of the parasitic nematode Deladenus siricidicola

Sirex noctilio is an invasive Eurasian woodwasp that can kill pine (Pinus spp.) trees and has been introduced to areas of the Southern Hemisphere where plantations of introduced pines are grown. The main method of control of this invasive pest has been introduction and augmentation of a parasitic nematode, Deladenus siricidicola. The strain of D. siricidicola used for biological control of S. noctilio in the Southern Hemisphere originated in Sopron, Hungary. The genotype of D. siricidicola used for biological control sterilizes females of the strain of S. noctilio present in Australia. However, different strains of S. noctilio have been introduced to different geographic areas that have been invaded and different combinations of D. siricidicola and S. noctilio genotypes vary in whether these nematodes sterilize female S. noctilio. Moreover, even in the event of sterilization, partial sterilization can occur, where not all woodwasp eggs are compromised. Sirex noctilio has now invaded North America accidentally, putatively accompanying D. siricidicola, but these host/parasite pairings do not result in female sterilization. More information is needed about the genetic diversity of D. siricidicola both where it is native and introduced. In addition, the host range of these nematodes is necessary to understand to evaluate their potential use in areas where pine communities are native. We collected and evaluated Deladenus parasitizing S. noctilio, S. juvencus, and associated insects in Hungary, Denmark, Spain, and Italy, as well as in the United States. Phylogenetic analyses were unable to fully provide fine resolution, although some community structure was evident. Many D. siricidicola samples from Hungary had identical COI and ITS sequences to the strain of D. siricidicola accidentally introduced to North America putatively when S. noctilio invaded. The same or similar strains of D. siricidicola parasitize two different Sirex species that utilize pines as well as a Sirex parasitoid and a pine-boring beetle, demonstrating some limited variability in host specificity of this species. These results highlight the genetic diversity of Deladenus siricidicola in its native range in Europe.

The global diversity of Deladenus siricidicola in native and non-native populations

The nematode Deladenus siricidicola is the primary biological control agent of Sirex noctilio, a globally invading woodwasp pest of Pinus species. Preliminary studies on the diversity of populations of D. siricidicola revealed very low diversity in the Southern Hemisphere where they have been introduced for the purpose of biological control. The potential to augment biocontrol efficacy by increasing genetic diversity in biocontrol programs motivated this study, which investigated the patterns of genetic diversity in D. siricidicola across eight countries, including the presumed native range (Spain), areas of accidental introduction (Canada and the USA) and countries D. siricidicola has been intentionally released (Argentina, Brazil, Chile, New Zealand and South Africa). Nematodes were screened using mitochondrial COI sequence data and twelve microsatellite markers. Analyses of these data identified three distinct lineages from North America (Lineage A), the Southern Hemisphere (Lineage B) and Spain (Lineage C). Strains from Chile were an exception as they appear to represent an admixture of lineages A and B. This suggests a common origin of populations throughout the Southern Hemisphere, with a second introduction from North America into Chile. The introduction into North America is distinct from that in the Southern Hemisphere and probably originated from Europe. It is evident that substantial genetic diversity exists in D. siricidicola globally, which could be exploited to augment the reduced diversity in some populations used in biocontrol programs.

The Draft Genome of Deladenus siricidicola.

The nematode Deladenus siricidicola is used as biological control agent against the invasive woodwasp Sirex noctilio, a serious invasive pest of Pinus plantations globally. The draft genome of this ecologically and economically important entomoparasitic nematode was determined.

Biocontrol of Sirex noctilio by the parasitic nematode Deladenus siricidicola: A five season field study in southern Chile.

In 2001, the woodwasp Sirex noctilio was detected in Pinus radiata plantations in the Biobio region of southern Chile. Subsequently, an intense biological control program using the female sterilizing nematode Deladenus siricidicola was implemented in 2010. During five seasons between 2012 and 2017, we studied the parasitism of D. siricidicola nematode and its effect on woodwasp populations and infestation of P. radiata in different locations within the Biobio region. Parasitism was assessed by dissecting adult females of S. noctilio obtained from infested P. radiata logs. The total population of S. noctilio was determined by the emergence of individuals from the same logs. The level of damage caused by the S. noctilio pest was determined by establishing plots in stands of P. radiata at an intensity of 1 plot every 5 ha-1. During the study period, parasitism of S. noctilio by the nematode D. siricidicola increased from 29.6% in 2012 to 93.1% in 2016, while pest population decreased 3.4% in the same time period. Infestation increased from 0.3 to 11,6% of trees between 2012 and 2015, but subsequently decreased to 5.9% by 2017. We confirmed establishment of the nematode in the region under study and its natural dispersion to non-inoculated areas. Finally, we determined that the effect of inoculation age (antiquity) on parasitism levels reached 90% after three years of inoculation.

Growth of the Sirex-parasitic nematode Deladenus siricidicola on the white rot fungus Amylostereum

The Kamona strain of the nematode Deladenus siricidicola has been extensively used as a biological control agent against invasive Sirex noctilio woodwasps in the Southern Hemisphere, where it sterilizes female hosts. In North America, a non-sterilizing (NS) strain of D. siricidicola, thought to have been introduced with S. noctilio, is commonly found parasitizing this invasive woodwasp. Species of Deladenus that parasitize Sirex have a parasitic form, as well as a mycophagous form. The mycophagous form feeds on Sirex fungal symbionts in the genus Amylostereum. The goal of this study was to compare reproduction of NS and Kamona D. siricidicola when feeding on four isolates of Amylostereum areolatum (three introduced and one native in North America) and one native strain of Amylostereum chailletii isolated from Sirex nigricornis. Mycophagous forms of the two D. siricidicola strains displayed relatively similar production of offspring when feeding on most of the A. areolatum found associated with S. noctilio in this continent, except for strain BD on which NS produced more offspring than the biological control strain Kamona. Growth of both nematodes was greater on the introduced versus the native A. areolatum isolates.

Eat or be eaten: fungus and nematode switch off as predator and prey

Use of the parasitic nematode Deladenus siricidicola to control invasive pine-killing Sirex noctilio woodwasps in the Southern Hemisphere is one of the most successful examples of classical biological control. Both nematode and woodwasp rely on the white rot fungus, Amylostereum areolatum , for continued survival, and the nematode is commercially mass produced in its mycophagous phase on this fungus. We tested the hypothesis that a role reversal can occur wherein fungal hyphae invade and kill nematode eggs. Deladenus siricidicola eggs were exposed to A. areolatum to quantify the number of eggs lost to fungal invasion. Additionally, A. areolatum and A. chailletii were observed via cryogenic scanning electron microscopy and fluorescence microscopy to document their ability to parasitize eggs and adults of D. siricidicola , D. proximus , and an undescribed Deladenus species. This study reports evidence of a basidiomycete destroying nematode eggs, as well as a novel trapping mechanism used to capture and parasitize three species of adult female Deladenus nematodes. • Pathogenic fungus of Pinus trees kills mycophagous nematodes. • Novel trapping mechanism used to parasitize Deladenus nematodes. • First description of Basidiomycete parasitizing nematode eggs. • Amylostereum areolatum grows over and kills Deladenus nematode eggs.

Parasitism of Sirex noctilio by non-sterilizing Deladenus siricidicola in northeastern North America

The parasitic nematode Deladenus siricidicola Bedding (Tylenchida: Neotylenchidae) has been extensively used for biological control of the wood wasp Sirex noctilio F. (Hymenoptera: Siricidae), an invasive pest of pine trees (Pinus spp.) in the Southern Hemisphere. The virulent strain of D. siricidicola used for biological control sterilizes S. noctilio females, although non-sterilizing strains of this nematode also occur. A non-sterilizing (NS) strain is established in the most recent invasion of S. noctilio, in northeastern North America. This study analyzed the effects of the NS strain of D. siricidicola on invasive S. noctilio collected from New York State and Pennsylvania. Nematode parasitism had a direct negative relationship on the number of eggs produced by the pro-ovigenic adult female S. noctilio. Nematode presence also negatively influenced the number of eggs indirectly, due to smaller size in nematode-parasitized females. Nematode-parasitized females produced an average of 29 fewer eggs than healthy females. On average, male and female nematode-parasitized S. noctilio emerged earlier from trees than healthy S. noctilio, and the size of female S. noctilio was not related to emergence date. S. noctilio with NS nematodes were found in 44.0% of trees and 26.9% of all individuals diagnosed, reaching 27.9±26.0% parasitism (mean±S.D.) when averaged across sites. There was greater parasitism of female S. noctilio than males. We also examined parasitism by hymenopteran parasitoids in association with parasitism by NS D. siricidicola. Parasitism by nematodes averaged 31.9±35.4% per tree, while parasitism by hymenopteran parasitoids averaged 41.8±19.6%. In terms of management, NS D. siricidicola may be less effective in providing biological control compared with sterilizing D. siricidicola or parasitic hymenopterans; the latter two natural enemies prevent all or most reproduction of S. noctilio, while the NS strain is primarily associated with a reduction in S. noctilio size and fecundity.

Phylogenetic analysis of Deladenus nematodes parasitizing northeastern North American Sirex species

The parasitic nematode Deladenus siricidicola is a biological control agent of the invasive woodwasp, Sirex noctilio. Since the discovery of S. noctilio in pine forests of northeastern North America in 2005, a biological control program involving the Kamona strain of D. siricidicola has been under consideration. However, North American pine forests have indigenous Sirex spp. and likely harbor a unique assemblage of associated nematodes. We assessed phylogenetic relationships among native Deladenus spp. in the northeastern United States and the Kamona strain of D. siricidicola. We sequenced three genes (mtCO1, LSU, and ITS) from nematodes extracted from parasitized Sirex spp. collected inside and outside of the range of S. noctilio. Our analyses suggest cospeciation between four North American Sirex spp. and their associated nematode parasites. Within two S. noctilio individuals we found nematodes that we hypothesize are normally associated with Sirex nigricornis. One individual of the native S. nigricornis contained Deladenus normally associated with S. noctilio. We discuss nematode-host fidelity in this system and the potential for non-target impacts of a biological control program using D. siricidicola against S. noctilio.

Distinguishing isolates of Deladenus siricidicola, a biological control agent of Sirex noctilio, from North America and the Southern Hemisphere using PCR–RFLP

The woodwasp Sirex noctilio Fabricius, along with its obligate symbiotic fungus Amylostereum areolatum (Chaillet ex Fr.) Boidin, is amongst the most damaging invasive species to many commercial pine plantations. The most effective biocontrol agent for management of this woodwasp has been the nematode Deladenus siricidicola Bedding. Before this agent can be used in North America, answering key questions about its interaction with native siricids and other strains of the nematode is essential, as would be the need to track its spread after release. The aim of this study was to develop tools to differentiate between the North American D. siricidicola isolates and the Southern Hemisphere Kamona strain of this species. We sequenced a region from ribosomal DNA and the cytochrome oxidase subunit 1 and developed a PCR–RFLP method based on a single nucleotide polymorphism flanking a microsatellite sequence. These markers will be useful for science-based operational biocontrol of S. noctilio.

Natural Enemies Associated With <I>Sirex noctilio</I> (Hymenoptera: Siricidae) and <I>S. nigricornis</I> in Ontario, Canada

Sirex noctilio F. is an exotic woodwasp now found in eastern North America where it shares natural enemies with native woodwasps of Pinus spp. To study the extent to which native hymenopteran parasitoids and parasitic nematodes could affect woodwasp populations, 60 Pinus trees with symptoms of S. noctilio attack were felled in 2007 and 2008 in Ontario, Canada. Each tree bole was cut into 1-m sections that were placed in individual rearing tubes; emergence was monitored from May to November of the year of felling. Female S. noctilio were dissected to assess parasitism by the nematode Deladenus siricidicola Bedding. Two species of Siricidae emerged from these trees; S. noctilio, which accounted for most of the specimens collected, and S. nigricornis F. Of the three species of parasitoid that emerged, Ibalia leucospoides (Hochenwarth) was the most abundant, accounting for an overall hypothetical Siricidae parasitism rate of almost 20%. This parasitoid emerged over a similar time period as S. noctilio-between early July and early September. Except in trees >15 m in height, parasitism by I. leucospoides generally appeared uniform throughout the bole. Parasitism rates did not vary between the 2 yr, but did between sites in 1 yr. Parasitic nematodes were found in the haemocoel of about one third of S. noctilio females dissected but were never found sterilizing the eggs; none were found in S. noctilio emerging from P. resinosa. These findings suggest that I. leucospoides is currently the primary invertebrate natural enemy of S. noctilio in Ontario.

The influence of Amylostereum areolatum diversity and competitive interactions on the fitness of the Sirex parasitic nematode Deladenus siricidicola

The Sirex noctilio (woodwasp)–Amylostereum areolatum (fungus) complex has caused substantial losses to pine industries in its introduced range. The nematode Deladenus siricidicola that parasitizes S. noctilio and feeds on A. areolatum is widely used as a biological control agent for S. noctilio, but not with consistent success. This variable success could be due to factors that influence the feeding and reproductive ability of the nematode on A. areolatum. We test two main hypotheses that emerge from this prediction. First, we compared the survival of D. siricidicola on the South African field strain and the Australian laboratory strain of A. areolatum, to examine a possible incompatibility between nematode and fungal strain. Second, we examined the competitive interactions of these two A. areolatum strains with two common sapstain fungi, Diplodia pinea and Ophiostoma ips, that occur in S. noctilio infested trees in South Africa. The effect of water potential on the outcome of these fungal interactions was also considered. The data showed that D. siricidicola survives at comparable levels on the two A. areolatum strains. Water potential of the media significantly influenced growth of the fungi and their ability to capture host resource in competitive interactions. D. pinea competed increasingly better against A. areolatum with decreasing water potential. The results suggest that competitive interactions between A. areolatum and sapstain fungi could negatively influence the success of D. siricidicola, especially under conditions of lowered water potential.

Extreme homozygosity in Southern Hemisphere populations of Deladenus siricidicola, a biological control agent of Sirex noctilio

The woodwasp Sirex noctilio, together with its mutualistic fungal symbiont Amylostereum areolatum, is the most damaging invasive pest of Pinus spp. in the Southern Hemisphere. The nematode Deladenus siricidicola parasitizes Sirex noctilio larvae and is the most effective biological control agent against this woodwasp. Nothing is known regarding the genetic diversity of D. siricidicola, even though such knowledge would be invaluable in improving sustainable biological control programs. The aim of this study was to develop microsatellite markers to study the genetic diversity of D. siricidicola populations. Microsatellite enrichment was performed using Fast Isolation by AFLP of Sequences Containing repeats (FIASCO) and fragments were then sequenced using 454 GS-FLX pyrosequencing. From the 1.2 megabases of sequence data, 166 microsatellite containing contigs were identified. Twenty-six primer pairs were designed using the web-based program Primer3 and screened for polymorphism in populations of the nematode from different sources in the Southern Hemisphere. Seventeen primers amplified microsatellite-containing loci of interest. No length polymorphism was present in any of the microsatellite repeats in these populations. Regions flanking the microsatellites also showed no polymorphism, except for one transition observed in an Argentinean strain for locus Ds316. Twelve of the loci showed polymorphism between the Southern Hemisphere and Canadian sources of D. siricidicola. The lack of diversity in Southern Hemisphere populations of D. siricidicola could affect the ability of this nematode to adapt to different environments and host types where it is used in biological control programs, and should thus be considered as a factor in future control strategies and research projects.

Test of Nonhost Angiosperm Volatiles and Verbenone to Protect Trap Trees for Sirex noctilio (Hymenoptera: Siricidae) From Attacks by Bark Beetles (Coleoptera: Scolytidae) in the Northeastern United States

Sirex noctilio F. (Hymenoptera: Siricidae) is an invasive woodwasp, currently established in northeastern North America. In other regions of the world, stressed trap trees are used to monitor populations of S. noctilio and to provide inoculation points for the biological control nematode Deladenus siricidicola Bedding. However, the operational use of trap trees for S. noctilio in North America may be compromised by the large community of native organisms that inhabit stressed and dying pine trees. Common bark beetles such as Ips pini (Say) and Ips grandicollis (Eichhoff) (Coleoptera: Scolytidae) could potentially compete with S. noctilio and associates for resources on trap trees, possibly reducing the efficacy of trap trees as habitats for the woodwasp. In an attempt to develop a technology to mitigate this potential issue, three common semiochemical interruptants--conophthorin, green leaf volatile mix, and verbenone--were tested for effectiveness in reducing arrivals of I. pini and I. grandicollis on trap trees treated with herbicides in northeastern United States. In addition, the effects of these compounds were determined independently with pheromone-baited multiple-funnel traps. None of the interruptants reduced numbers of I. pini or I. grandicollis either arriving on trap trees or caught in pheromone-baited traps. However, verbenone increased catches of I. grandicollis in traps baited with its pheromone, ipsenol. The mix of green leaf volatiles reduced catches of a native ambrosia beetle, Gnathotrichus materiarius (Fitch), whereas verbenone reduced trap catches of an exotic ambrosia beetle, Xylosandrus germanus (Blandford). Catches of X. germanus in traps adjacent to trap trees were enhanced with conophthorin.

Factors influencing parasitism of Sirex noctilio (Hymenoptera: Siricidae) by the nematode Deladenus siricidicola (Nematoda: Neotylenchidae) in summer rainfall areas of South Africa

Control of the invasive wasp, Sirex noctilio Fabricius using the parasitic nematode Deladenus siricidicola Bedding is a well known example of a successful classical biological control program. Despite its wide-scale success, this control method has recently had poor success in the summer rainfall areas of South Africa. Data from previous studies showed variation in nematode parasitism from inoculated trees (inoculation success) between different tree sections and among inoculation times. They also pointed to moisture content of the wood or virulence of the nematode as the most likely underlying factors influencing variations in inoculation success. The results from our study showed that the highest levels of parasitism was obtained from early inoculations and from the bottom sections of trees, where moisture content of the wood was highest, supporting the hypothesis that moisture content influences parasitism. However, even when moisture content was adequate, average inoculation success remained below 25% and was often 0%, suggesting that there are other barriers to inoculation success. Different sources from which the nematodes were produced did not influence inoculation success, indicating that nematode virulence is most likely not the cause of the low success. Another interesting finding was that parasitized wasps were larger than unparasitized wasps. Background parasitism was present despite the poor success with past inoculations, but the data also suggest that the natural build-up of this population could be constrained by the same factors that influence inoculations.

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

Abstract1 Sirex noctilio has resulted in one of the most damaging biological invasions of pine forestry in the southern hemisphere.2 An intensive, integrated control programme has been developed for this pest and is generally considered very successful. However, a critical comparison of S. noctilio infestations and control efforts throughout the southern hemisphere reveals that control has not been uniformly effective. Of particular concern is the apparently unexplained variability in establishment and success of biological control agents, including various parasitic wasps and the parasitic nematode Deladenus siricidicola.3 An overlooked aspect in the establishment of the biological control interventions for S. noctilio is the potential influence of genetic bottlenecks on the ability of the agents to adapt to different environments and different populations of S. noctilio.4 Despite established biological control agents, stress in forests caused by silvicultural practices or the environment will predispose trees to heavy infestation. Unfortunately, improved silvicultural practices are not always economically feasible and environmental changes are often unavoidable.5 Sirex noctilio continues to pose a serious threat to pine forestry in many areas. Despite extensive earlier research into a single integrated control for S. noctilio, it is important to recognize that such a strategy will probably require significant local adaptation in new areas of infestation and over time.

Sirex noctiliocontrol program in response to the 1987 Green Triangle outbreak

Summary In 1987, 1.8 million tree deaths resulted from a Sirex noctilio outbreak in Pinus radiata plantations in southeastern South Australia and southwestern Victoria. The major response was to inoculate 147 000 trees with the parasitic nematode Deladenus siricidicola. Also, projects to salvage sirex-infested trees and to release the parasitoid Megarhyssa nortoni were implemented. The inoculation program cost $1.3 million. Productivity and costs were calculated for the seven procedures used to introduce the nematode. Efficiency was increased by using machines to fell and delimb the trees and by redesigning the inoculation hammer. Knowledge gained from this outbreak should prompt a review of the control recommendations. Forest managers should implement a rigorous control program, as soon as sirex is detected in a region, to minimise the risk of a future outbreak. Key words: Sirex noctilio, Deladenus siricidicola, biological control, forest pest management, Pinus radiata.

Influence of natural enemies on theSirexwood wasp in herbicide-treated trap trees of radiata pine in north-eastern Victoria

From 1979 to 1982 in north-eastern Victoria, interactions between the European tree-killing wood wasp Sirex noctilio, the parasitic nematode Deladenus siricidicola, and the parasitoids Ibalia leuco...