Changes in Defense of an Alien Plant Ambrosia artemisiifolia before and after the Invasion of a Native Specialist Enemy Ophraella communa

The evolution of increased competitive ability hypothesis (EICA) predicts that when alien plants are free from their natural enemies they evolve lower allocation to defense in order to achieve a higher growth rate. If this hypothesis is true, the converse implication would be that the defense against herbivory could be restored if a natural enemy also becomes present in the introduced range. We tested this scenario in the case of Ambrosia artemisiifolia (common ragweed) – a species that invaded Japan from North America. We collected seeds from five North American populations, three populations in enemy free areas of Japan and four populations in Japan where the specialist herbivore Ophraella communa naturalized recently. Using plants grown in a common garden in Japan, we compared performance of O. communa with a bioassay experiment. Consistent with the EICA hypothesis, invasive Japanese populations of A. artemisiifolia exhibited a weakened defense against the specialist herbivores and higher growth rate than native populations. Conversely, in locations where the herbivore O. communa appeared during the past decade, populations of A. artemisiifolia exhibited stronger defensive capabilities. These results strengthen the case for EICA and suggest that defense levels of alien populations can be recuperated rapidly after the native specialist becomes present in the introduced range. Our study implies that the plant defense is evolutionary labile depending on plant-herbivore interactions.     

Successful establishment of the invasive fire ant Solenopsis invicta in Taiwan: insights into interactions of alternate social forms

Aim Understanding the factors underlying the successful establishment of invasive ant species is critical for developing quarantine strategies to prevent additional invasions as well as for determining how such species overcome the selective pressures in invaded areas. Although several studies have revealed differences in the social organization and population genetics of invasive ants in their native and introduced ranges, few studies have considered the potential interactions between alternate social forms within newly‐invaded areas simply because many invasive ants are characterized as polygyne or unicolonial. Location Taoyuan and Chiayi County, Taiwan. Methods Both social forms (polygyne and monogyne) of the red imported fire ant, Solenopsis invicta, occur in two separately invaded areas in Taiwan (Taoyuan and Chiayi). We employed intensive sampling methods and diagnostic polymerase chain reaction assays to determine the distribution of these two social forms in both infested areas in Taiwan. Results The distribution of social forms differs dramatically between the two infested areas, consistent with different invasion histories regarding the original make‐up of individuals comprising the initial founder group. The Taoyuan population likely was colonized initially by ants of both social forms, with the subsequent spread characterized by continuous outward movement of the two forms, particularly the monogyne form. In contrast, the initial founders of the Chiayi population likely were of the polygyne social form only, suggesting the monogyne social form in this population appeared only recently and likely arose directly from polygyne queens converting to the alternate social form. Main conclusions Our results provide detailed insights into the invasion history of S. invicta in Taiwan and suggest that the distinct reproductive biology of the two social forms may have shaped the current distribution of S. invicta in these infested areas and that the dynamics of two forms may affect the long‐term persistence and potential for spread of this pest ant species.     

Inadvertent biological control: an Australian thrips killing an invasive New Zealand tree in California

Transport hubs of international trade and tourism are sites of unprecedented long-distance dispersal of species and novel ecological interactions. In cases of invasive plants released from their specialist natural enemies, novel interactions with both resident enemies and new arrivals can accumulate and potentially reduce weed competitiveness. I present here one dramatic example of this, where an invasive woody weed in southern California is being rapidly controlled by an accidentally introduced genus-specialist herbivorous insect. The New Zealand native shrub/small tree, Myoporum laetum, is a long-time popular ornamental plant in California and has become an invasive woody weed. In 2005, a Myoporum-specific thrips, Klambothrips myopori, was discovered (and described) in California feeding on M. laetum leaves. Several searches have failed to find K. myopori in New Zealand and a population has recently been discovered in Tasmania, Australia, feeding on Myoporum insulare. In 5 years, K. myopori has killed off about half of southern Californian M. laetum with almost all surviving individuals being gradually defoliated. Inadequate border biosecurity has resulted in inadvertent biological control, in a rapid timeframe, caused by a novel enemy. Unfortunately, K. myopori has subsequently been accidentally transported from California to Hawaii where it is now killing off Hawaiian native Myoporum sandwicense. Transport hubs can both connect weeds with natural enemies and disperse those enemies more widely.     

Multiple virus infections occur in individual polygyne and monogyne Solenopsis invicta ants

Concurrent infections of Solenopsis invicta colonies with S. invicta virus 1 (SINV-1), SINV-2, and SINV-3 has been reported. However, whether individual ants were capable of supporting multiple virus infections simultaneously was not known, nor whether the social form of the colony (polygyne or monogyne) had an influence on the occurrence of multiple infection rates in individual ants. S. invicta field populations were sampled sequentially to establish whether multiple virus infections co-occurred in individual worker ants. In addition, the intra-colony virus infection rates were compared in monogyne and polygyne field colonies to determine whether social form played a role in the viral infection prevalence. All combinations of virus infection (SINV-1, SINV-2, or SINV-3 alone, SINV-1 & SINV-2, SINV-1 & SINV-3, SINV-2 & SINV-3, and SINV-1, SINV-2 & SINV-3) were detected in individual worker ants as well as queens in the field. Thus, individual S. invicta ants can be infected simultaneously with all combinations of the S. invicta viruses. Colony social form did have an influence on the intra-colony prevalence of multiple S. invicta virus infections. Polygyne colonies exhibited significantly greater intra- and inter-colony single and multiple virus infections compared with monogyne colonies.     

Exploitation of a high genomic mutation rate in Solenopsis invicta virus 1 to infer demographic information about its host, Solenopsis invicta

The RNA-dependent RNA polymerase (RdRp) region of Solenopsis invicta virus 1 (SINV-1) was sequenced from 47 infected colonies of S. invicta, S. richteri, S. geminata, and S. invicta/richteri hybrids collected from across the USA, northern Argentina, and northern Taiwan in an attempt to infer demographic information about the recent S. invicta introduction into Taiwan by phylogenetic analysis. Nucleotide sequences were calculated to exhibit an overall identity of >90% between geographically-separated samples. A total of 171 nucleotide variable sites (representing 22.4% of the region amplified) were mapped across the SINV-1 RdRp alignment and no insertions or deletions were detected. Phylogenetic analysis at the nucleotide level revealed clustering of Argentinean sequences, distinct from the USA sequences. Moreover, the SINV-1 RdRp sequences derived from recently introduced populations of S. invicta from northern Taiwan resided within the multiple USA groupings implicating the USA as the source for the recent introduction of S. invicta into Taiwan. Examination of the amino acid alignment for the RdRp revealed sequence identity >98% with only nine amino acid changes observed. Seven of these changes occurred in less than 4.3% of samples, while 2 (at positions 1266 and 1285) were featured prominently. Changes at positions 1266 and 1285 accounted for 36.2% and 34.0% of the samples, respectively. Two distinct groups were observed based on the amino acid residue at position 1266, Threonine or Serine. In cases where this amino acid was a Threonine, 90% of these sequences possessed a corresponding Valine at position 1285; only 10% of the Threonine¹²⁶⁶-containing sequences possessed an Isoleucine at the 1285 position. Among the Serine¹²⁶⁶ group, 76% possessed an Isoleucine at position 1285, while only 24% possessed a Valine. Thus, it appears that the Threonine¹²⁶⁶/Valine¹²⁸⁵ and Serine¹²⁶⁶/Isoleucine¹²⁸⁵ combinations are predominant phenotypes.     

Response to enemies in the invasive plant Lythrum salicaria is genetically determined

Background and Aims

The enemy release hypothesis assumes that invasive plants lose their co-evolved natural enemies during introduction into the new range. This study tested, as proposed by the evolution of increased competitive ability (EICA) hypothesis, whether escape from enemies results in a decrease in defence ability in plants from the invaded range. Two straightforward aspects of the EICA are examined: (1) if invasives have lost their enemies and their defence, they should be more negatively affected by their full natural pre-invasion herbivore spectrum than their native conspecifics; and (2) the genetic basis of evolutionary change in response to enemy release in the invasive range has not been taken sufficiently into account.

Methods

Lythrum salicaria (purple loosestrife) from several populations in its native (Europe) and invasive range (North America) was exposed to all above-ground herbivores in replicated natural populations in the native range. The experiment was performed both with plants raised from field-collected seeds as well as with offspring of these where maternal effects were removed.

Key Results

Absolute and relative leaf damage was higher for introduced than for native plants. Despite having smaller height growth rate, invasive plants attained a much larger final size than natives irrespective of damage, indicating large tolerance rather than effective defence. Origin effects on response to herbivory and growth were stronger in second-generation plants, suggesting that invasive potential through enemy release has a genetic basis.

Conclusions

The findings support two predictions of the EICA hypothesis – a genetically determined difference between native and invasive plants in plant vigour and response to enemies – and point to the importance of experiments that control for maternal effects and include the entire spectrum of native range enemies.     

Invasive Eupatorium adenophorum suffers lower enemy impact on carbon assimilation than native congeners

Enemy release hypothesis predicts that alien plants that escape from their natural enemies suffer lower enemy regulation in their introduced ranges than in native ranges. An extension of this theory suggests that if enemy release plays a crucial role in invasive success, then in the introduced range, invasive plants should also suffer lower local enemy impact than native residents (local enemy release hypothesis, LERH). In order to test LERH, we compared invasive Eupatorium adenophorum with two native congeners (E. heterophyllum and E. japonicum) in terms of damage by leaf enemies at two natural field sites and two manipulated sites. We also determined enemy impact on carbon assimilation at two manipulated sites. In each site, E. adenophorum was only damaged by herbivores, while in native congeners, leaf scabs or (and) leaf rolls was found in addition to herbivory damage. In both manipulated sites, the total enemy impact on carbon assimilation was lower for E. adenophorum than for native congeners; this observation was consistent with LERH. The results of this study indicate that a short co-existence time with generalist enemies (behavior constraint) might be the main contributor to the lower enemy impact on E. adenophorum.     

Infection characteristics of Solenopsis invicta virus 2 in the red imported fire ant, Solenopsis invicta

Solenopsis invicta virus 2 (SINV-2) is the second virus identified from the fire ant, S. invicta Buren. SINV-2 is unique among positive-strand RNA viruses from insects by possessing four cistrons in a monopartite genome. Fire ant colonies testing positive for SINV-2 by RT-PCR did not exhibit any discernable symptoms. RT-PCR-based surveys for SINV-2 among 688 fire ant mounds in Alachua County, Florida, sampled during the period January, 2006 through December, 2007 showed that the prevalence of SINV-2 among nests ranged from 1.6% to 16.4%. Unlike S. invicta virus 1, no seasonal-associated prevalence was observed with regard to SINV-2 infection among fire ant colonies. No social form specificity was evident; SINV-2 was found in both monogyne and polygyne S. invicta ants. Real-time quantitative PCR experiments showed that SINV-2 genome equivalents per individual ant ranged from 1.9 × 10⁷ in. pupae to 4.3 × 10¹¹ in. inseminated queens. The SINV-2 infection was detected in all ant stages examined (eggs, larvae, pupae, workers, and queens). Tissue tropism studies indicated that the alimentary canal (specifically the midgut) is most likely the susceptible tissue. SINV-2 was successfully transmitted to uninfected S. invicta ants by feeding a partially purified homogenate of SINV-2-infected ants. The SINV-2 transmission rate ranged from 30% to 80%, and both positive (genomic) and negative (replicative) SINV-2 RNA strands accumulated in recipient ants over the course of the experiment. These results indicated that SINV-2 replicates within S. invicta.     

Geographic mosaics of plant–soil microbe interactions in a global plant invasion

Aim Our aim in this study was to document the global biogeographic variation in the effects of soil microbes on the growth of Centaurea solstitialis (yellow starthistle; Asteraceae), a species that has been introduced throughout the world, but has become highly invasive only in some introduced regions. Location  To assess biogeographic variation in plant–soil microbe interactions, we collected seeds and soils from native Eurasian C. solstitialis populations and introduced populations in California, Argentina and Chile. Methods To test whether escape from soil‐borne natural enemies may contribute to the success of C. solstitialis, we compared the performance of plants using seeds and soils collected from each of the biogeographic regions in greenhouse inoculation/sterilization experiments. Results  We found that soil microbes had pervasive negative effects on plants from all regions, but these negative effects were significantly weaker in soils from non‐native ranges in Chile and California than in those from the non‐native range in Argentina and the native range in Eurasia. Main conclusions The biogeographic differences in negative effects of microbes in this study conformed to the enemy‐release hypothesis (ERH) overall, but the strong negative effect of soil biota in Argentina, where C. solstitialis is invasive, and weaker effects in Chile where it is not, indicated that different factors influencing invasion are likely to occur in large scale biogeographic mosaics of interaction strengths.     

Examination of host genome for the presence of integrated fragments of Solenopsis invicta virus 1

A series of oligonucleotide primer pairs covering the entire genome of Solenopsis invicta virus 1 (SINV-1) were used to probe the genome of its host, S. invicta, for integrated fragments of the viral genome. All of the oligonucleotide primer sets yielded amplicons of anticipated size from cDNA created from an RNA template from SINV-1. However, no corresponding amplification was observed when genomic DNA (from 32 colonies of S. invicta) was used as template for the PCR amplifications. Host DNA integrity was verified by amplification of an ant-specific gene, SiGSTS1. The representation of fire ant colonies included both social forms, monogyne and polygyne, and those infected and uninfected with SINV-1. Furthermore, no amplification was observed from genomic DNA from ant samples collected from Argentina or the US. Thus, it appears that SINV-1 genome integration, or a portion therein, has not likely occurred within the S. invicta host genome.     

Range-expanding populations of a globally introduced weed experience negative plant-soil feedbacks

Background

Biological invasions are fundamentally biogeographic processes that occur over large spatial scales. Interactions with soil microbes can have strong impacts on plant invasions, but how these interactions vary among areas where introduced species are highly invasive vs. naturalized is still unknown. In this study, we examined biogeographic variation in plant-soil microbe interactions of a globally invasive weed, Centaurea solstitialis (yellow starthistle). We addressed the following questions (1) Is Centaurea released from natural enemy pressure from soil microbes in introduced regions? and (2) Is variation in plant-soil feedbacks associated with variation in Centaurea''s invasive success?

Methodology/Principal Findings

We conducted greenhouse experiments using soils and seeds collected from native Eurasian populations and introduced populations spanning North and South America where Centaurea is highly invasive and noninvasive. Soil microbes had pervasive negative effects in all regions, although the magnitude of their effect varied among regions. These patterns were not unequivocally congruent with the enemy release hypothesis. Surprisingly, we also found that Centaurea generated strong negative feedbacks in regions where it is the most invasive, while it generated neutral plant-soil feedbacks where it is noninvasive.

Conclusions/Significance

Recent studies have found reduced below-ground enemy attack and more positive plant-soil feedbacks in range-expanding plant populations, but we found increased negative effects of soil microbes in range-expanding Centaurea populations. While such negative feedbacks may limit the long-term persistence of invasive plants, such feedbacks may also contribute to the success of invasions, either by having disproportionately negative impacts on competing species, or by yielding relatively better growth in uncolonized areas that would encourage lateral spread. Enemy release from soil-borne pathogens is not sufficient to explain the success of this weed in such different regions. The biogeographic variation in soil-microbe effects indicates that different mechanisms may operate on this species in different regions, thus establishing geographic mosaics of species interactions that contribute to variation in invasion success.     

Release from natural enemies mitigates inbreeding depression in native and invasive Silene latifolia populations

Inbreeding and enemy infestation are common in plants and can synergistically reduce their performance. This inbreeding ×environment (I × E) interaction may be of particular importance for the success of plant invasions if introduced populations experience a release from attack by natural enemies relative to their native conspecifics. Here, we investigate whether inbreeding affects plant infestation damage, whether inbreeding depression in growth and reproduction is mitigated by enemy release, and whether this effect is more pronounced in invasive than native plant populations. We used the invader Silene latifolia and its natural enemies as a study system. We performed two generations of experimental out‐ and inbreeding within eight native (European) and eight invasive (North American) populations under controlled conditions using field‐collected seeds. Subsequently, we exposed the offspring to an enemy exclusion and inclusion treatment in a common garden in the species’ native range to assess the interactive effects of population origin (range), breeding treatment, and enemy treatment on infestation damage, growth, and reproduction. Inbreeding increased flower and leaf infestation damage in plants from both ranges, but had opposing effects on fruit damage in native versus invasive plants. Inbreeding significantly reduced plant fitness; whereby, inbreeding depression in fruit number was higher in enemy inclusions than exclusions. This effect was equally pronounced in populations from both distribution ranges. Moreover, the magnitude of inbreeding depression in fruit number was lower in invasive than native populations. These results support that inbreeding has the potential to reduce plant defenses in S. latifolia, which magnifies inbreeding depression in the presence of enemies. However, future studies are necessary to further explore whether enemy release in the invaded habitat has actually decreased inbreeding depression and thus facilitated the persistence of inbred founder populations and invasion success.     

Survey of bumble bee (Bombus) pathogens and parasites in Illinois and selected areas of northern California and southern Oregon

Pathogens have been implicated as potential factors in the recent decline of some North American bumble bee (Bombus) species, but little information has been reported about the natural enemy complex of bumble bees in the United States. We targeted bumble bee populations in a state-wide survey in Illinois and several sites in California and Oregon where declines have been reported to determine presence and prevalence of natural enemies. Based on our observations, most parasites and pathogens appear to be widespread generalists among bumble bee species, but susceptibility to some natural enemies appeared to vary.     

Inferring the introduction history of the invasive apomictic grass Cortaderia jubata using microsatellite markers

Aim Reconstructing the introduction history of exotic species is critical to understanding ecological and evolutionary processes that underlie invasive spread and to designing strategies that prevent or manage invasions. The aims of this study were to infer the introduction history of the invasive apomictic bunchgrass Cortaderia jubata and to determine if molecular data support the postulated horticultural origin of invasive populations. Location Invaded areas in the USA (California, Maui) and New Zealand; native areas in Bolivia, Ecuador and Peru. Methods We used nuclear microsatellite markers to genotype 281 plants from invaded areas in California, Maui and New Zealand, and 77 herbarium specimens from native South America, and compared the genotypic and clonal variation of C. jubata from the invaded and native ranges. Clonal diversity was determined from genotypic diversity using two analytical methods. Results Invasive C. jubata from invaded regions in California, Maui and New Zealand consisted of the same single clone that probably originated from a single introduced genotype. In contrast, 14 clones were detected in herbarium specimens from the native areas of Bolivia, Ecuador and Peru. The invasive clone matched the most common clone identified in herbarium specimens from southern Ecuador where horticultural stock is presumed to have originated. Main conclusions The lack of clonal and genotypic diversity in invasive plants, but moderately high diversity detected in native plants, indicates a significant reduction in genetic variation associated with the introduction of C. jubata outside of its native range. Based on historical accounts of the horticultural introduction of C. jubata and the results of this study, a severe founder effect probably occurred during deliberate introduction of C. jubata into cultivation. Our results are consistent with the postulated horticultural origin of invasive C. jubata and point to southern Ecuador as the geographical source of invasive populations.     

The Role of Natural Enemy Foraging Guilds in Controlling Cereal Aphids in Michigan Wheat

Insect natural enemies (predators and parasitoids) provide important ecosystem services by suppressing populations of insect pests in many agricultural crops. However, the role of natural enemies against cereal aphids in Michigan winter wheat (Triticum aestivum L.) is largely unknown. The objectives of this research were to characterize the natural enemy community in wheat fields and evaluate the role of different natural enemy foraging guilds (foliar-foraging versus ground-dwelling predators) in regulating cereal aphid population growth. We investigated these objectives during the spring and summer of 2012 and 2013 in four winter wheat fields on the Michigan State University campus farm in East Lansing, Michigan. We monitored and measured the impact of natural enemies by experimentally excluding or allowing their access to wheat plants infested with Rhopalosiphum padi (L.) and Sitobion avenae (F.) (Hemiptera: Aphidae). Our results indicate that the natural enemy community in the wheat fields consisted mostly of foliar-foraging and ground-dwelling predators with relatively few parasitoids. In combination, these natural enemy groups were very effective at reducing cereal aphid populations. We also investigated the role of each natural enemy foraging guild (foliar-foraging versus ground-dwelling predators) independently. Overall, our results suggest that, in combination, natural enemies can almost completely halt early-season aphid population increase. Independently, ground-dwelling predators were more effective at suppressing cereal aphid populations than foliar-foraging predators under the conditions we studied. Our results differ from studies in Europe and the US Great Plains where foliar foraging predators and parasitoids are frequently more important cereal aphid natural enemies.     

No Evidence of Enemy Release in Pathogen and Microbial Communities of Common Wasps (Vespula vulgaris) in Their Native and Introduced Range

When invasive species move to new environments they typically experience population bottlenecks that limit the probability that pathogens and parasites are also moved. The invasive species may thus be released from biotic interactions that can be a major source of density-dependent mortality, referred to as enemy release. We examined for evidence of enemy release in populations of the common wasp (Vespula vulgaris), which attains high densities and represents a major threat to biodiversity in its invaded range. Mass spectrometry proteomic methods were used to compare the microbial communities in wasp populations in the native (Belgium and England) and invaded range (Argentina and New Zealand). We found no evidence of enemy release, as the number of microbial taxa was similar in both the introduced and native range. However, some evidence of distinctiveness in the microbial communities was observed between countries. The pathogens observed were similar to a variety of taxa observed in honey bees. These taxa included Nosema, Paenibacillus, and Yersina spp. Genomic methods confirmed a diversity of Nosema spp., Actinobacteria, and the Deformed wing and Kashmir bee viruses. We also analysed published records of bacteria, viruses, nematodes and fungi from both V. vulgaris and the related invader V. germanica. Thirty-three different microorganism taxa have been associated with wasps including Kashmir bee virus and entomophagous fungi such as Aspergillus flavus. There was no evidence that the presence or absence of these microorganisms was dependent on region of wasp samples (i.e. their native or invaded range). Given the similarity of the wasp pathogen fauna to that from honey bees, the lack of enemy release in wasp populations is probably related to spill-over or spill-back from bees and other social insects. Social insects appear to form a reservoir of generalist parasites and pathogens, which makes the management of wasp and bee disease difficult.     

Relationships among leaf damage, natural enemy release, and abundance in exotic and native prairie plants

The Enemy Release hypothesis holds that exotic plants may have an advantage over native plants because their specialized natural enemies are absent. We tested this hypothesis by measuring leaf damage and plant abundance for naturally-occurring plants in prairies, and by removing natural enemies in an enemy exclusion experiment. We classified plants as invasive exotic, noninvasive exotic, or native, to determine if their degree of invasiveness influenced their relationships with natural enemies. Our field surveys showed that invasive exotic plants generally had significantly lower levels of foliar damage than native species while there was no consistent pattern for noninvasive exotics compared to natives. The relationship between damage and abundance was different for exotic and native plants: foliar damage decreased with increasing abundance for exotic plants while the trend was positive for native plants. While these results from the field surveys supported the Enemy Release Hypothesis, the enemy exclusion experiment did not. There was no relationship between a species?? status as exotic or native and its degree of release from herbivory. Pastinaca sativa, the invasive exotic in this experiment, experienced gains in leaf area and vegetative biomass when treated with pesticides, indicating substantial herbivore pressure in the introduced range. These results show that foliar damage may not accurately predict the amount of herbivore pressure that plants actually experience, and that the Enemy Release hypothesis is not sufficient to explain the invasiveness of P. sativa in prairies.     

Prey naïveté rather than enemy release dominates the relation of an invasive spider toward a native predator

Ecosystems may suffer from the impact of invasive species. Thus, understanding the mechanisms contributing to successful invasions is fundamental for limiting the effects of invasive species. Most intuitive, the enemy release hypothesis predicts that invasive species might be more successful in the exotic range than resident sympatric species owing to the absence of coevolution with native enemies. Here, we test the enemy release hypothesis for the invasion of Europe by the North American spider Mermessus trilobatus. We compare the susceptibility of invasive Mermessus trilobatus and a native species with similar life history to a shared predator with which both species commonly co‐occur in Europe. Contrary to our expectations, invasive Mermessus trilobatus were consumed three times more frequently by native predators than their native counterparts. Our study shows that invasive Mermessus trilobatus is more sensitive to a dominant native predator than local sympatric species. This suggests that the relation between the invasive spider and its native predator is dominated by prey naïveté rather than enemy release. Further studies investigating evolutionary and ecological processes behind the invasion success of Mermessus trilobatus, including testing natural parasites and rapid reproduction, are needed to explain its invasion success in Europe.     

Lack of enemy release for an invasive leafroller in California: temporal patterns and influence of host plant origin

The enemy release hypothesis posits that the success of invasive species can be attributed to their escape from natural enemies. Invading hosts are expected to encounter an enemy assemblage consisting of fewer species, with lower representation of specialists, and to experience less mortality as a result. In this study, we examined parasitism of the Light Brown Apple Moth (LBAM), Epiphyas postvittana (Walker), in California, an exotic leafroller that is native to southeastern Australia. From 2008 to 2011 we monitored parasitoid species richness, representation of the more specialized koinobiont parasitoids, and parasitism rates of LBAM collected three times per year from four plant species of Australian origin and six plant species of non-Australian origin, at two locations in coastal California. We found the resident parasitoid assemblage of LBAM in California to have comparable levels of species richness, to have a similar representation of koinobionts versus idiobionts, and to inflict similar parasitism rates as in its native range. The two dominant parasitoids were Meteorus ictericus (Braconidae) and Enytus eureka (Ichneumonidae). Parasitoid species richness varied with season and plant origin and decreased slowly, but significantly, over the 4 year period. Parasitism rates were lowest in spring and highest on plants of Australian origin, but did not change with year. Hyperparasitism rates were higher on E. eureka (36.5 %) compared with M. ictericus and other parasitoids combined (3.3 %) and were highest on plants of Australian origin. We subsequently discuss the lack of both apparent enemy reduction and realized enemy release for LBAM in California and the unique finding that a shared plant origin enhanced the parasitism of this exotic leafroller by resident parasitoids.