Plant resistance, plant traits, and host plant choice of the leaf-folding sawfly on the arroyo willow

Abstract. 1. The hypotheses that genetic variation in host plant resistance of the arroyo willow affected leaf folder ( Phyllocolpa sp.) (Hymenoptera: Tenthredinidae) density and that genetic variation in shoot length and leaf length was correlated with resistance were tested.
2. Willows grown in pots and exposed to ovipojsition by the leaf folding sawfly in cages had significantly different densities among clones, indicating variation in resistance caused by genetic differences among conspecific host plants.
3. There was a general correspondence between leaf folder density on potted cuttings and on the plants in the field that were the sources of cuttings.
4. In behavioural choice experiments, susceptible clones (with highest leaf fold densities) had the highest oviposition activity of female leaf folders compared to clones that were resistant to the leaf folder.
5. Clones differed significantly in shoot length and leaf length among clones grown in pots, among clones in the field, and between shoots with galls and shoots without galls on clones in the field.
6. Leaf folder density was significantly positively correlated with mean shoot length on field clones in 1985 and 1986, but was not correlated with leaf length, although leaf length and shoot length were correlated.
7. Leaf length variation among willow clones accounted for a significant portion of the variation in resistance of potted willows, but shoot length was unimportant.     

Infochemicals influencing the host foraging behaviour of Dahlbominus fuscipennis, a pupal parasitoid of the European spruce sawfly (Gilpinia hercyniae)

The chalcidoid wasp Dahlbominus fuscipennis Zett. (Hymenoptera: Eulophidae) parasitises pupae of the European spruce sawfly Gilpinia hercyniae Htg. (Hymenoptera: Diprionidae). In this parasitoid-host system the role of infochemicals for successful parasitisation was studied. Olfactometer experiments and dual choice bioassays in petri dishes showed that D. fuscipennis was not attracted by volatiles from a plant-host complex consisting of spruce, sawfly larvae and pupae. On the other hand, odours from needles of Picea abies (L.), that were collected from the ground, attracted D. fuscipennis to the habitat of the sawfly. Volatiles from host pupae were not attractive, whereas a contact kairomone from sawfly pupae elicited frequent antennal drumming, a behaviour that indicates host recognition. This contact kairomone was extracted with methanol from the outer cocoon layer of the pupa. The kairomone is not produced by the silk glands of the last instar larva spinning the cocoon, since a methanolic extract of silk gland secretion did not elicit any response in D. fuscipennis. Further bioassays revealed that non-volatile components of the integument of the prepupa within the cocoon also elicited antennal drumming. We suggest that chemicals of the prepupal integument diffuse from inside the cocoon to the outside where they inform the parasitoid on the suitability of the host.     

Host plant recognition in monophagous weevils: Specialization ofCeutorhynchus inaffectatus to glucosinolates from its host plantHesperis matronalis

Several aphid honeydews were incorporated into sucrose solutions and presented to hop aphids, Phorodon humuli (Schrank), as artificial diets in free-choice bioassays. Small additions of honeydew collected from two species of aphid feeding on hop, Humulus lupulus L., arrested the searching behavior of the hop aphid and appeared to stimulate prolonged periods of ingestion. This effect was more dependent on the host plant honeydew source than the species of aphid that produced the honeydew. Aphid honeydews collected from plants other than hop (non-hosts to P. humuli) contained hop aphid phagostimulants that were less effective. Our results indicate that analysis of aphid honeydew could help describe chemical cues involved in the recognition of appropriate host plants by aphid species.     

Host specificity ofCostesia yakutatensis [Hym.: Braconidae] on lepidoptera in peppermint and alfalfa

Seven species of Lepidoptera, common to alfalfa and peppermint in western Oregon, were tested as potential hosts forCotesia yakutatensis (Ashmead). Laboratory and field studies demonstrated that onlyAutographa californica (Speyer) andTrichoplusia ni (Hubner) were suitable. Percent parasitism, duration of oviposition, and number of parasitoids per host were highest whenC. yakutatensis was associated withA. californica.     

Host specificity,phenotype matching and the evolution of reproductive isolation in a coevolved plant–pollinator mutualism

Coevolutionary interactions between plants and their associated pollinators and seed dispersers are thought to have promoted the diversification of flowering plants ( Raven 1977 ; Regal 1977 ; Stebbins 1981 ). The actual mechanisms by which pollinators could drive species diversification in plants are not fully understood. However, it is thought that pollinator host specialization can influence the evolution of reproductive isolation among plant populations because the pollinator’s choice of host is what determines patterns of gene flow in its host plant, and host choice may also have important consequences on pollinator and host fitness ( Grant 1949 ; Bawa 1992 ). In this issue of Molecular Ecology, Smith et al. (2009) present a very interesting study that addresses how host specialization affects pollinator fitness and patterns of gene flow in a plant host. Several aspects of this study match elements of a seminal mathematical model of plant–pollinator codivergence ( Kiester et al. 1984 ) suggesting that reciprocal selection for matched plant and pollinator reproductive traits may lead to speciation in the host and its pollinator when there is strong host specialization and a pattern of geographic subdivision. Smith et al.’s study represents an important step to fill the gap in our understanding of how reciprocal selection may lead to speciation in coevolved plant–pollinator mutualisms.     

Host specificity of a generalist parasite: genetic evidence of sympatric host races in the seabird tick Ixodes uriae

Due to the close association between parasites and their hosts, many ‘generalist’ parasites have a high potential to become specialized on different host species. We investigated this hypothesis for a common ectoparasite of seabirds, the tick Ixodes uriae that is often found in mixed host sites. We examined patterns of neutral genetic variation between ticks collected from Black‐legged kittiwakes (Rissa tridactyla) and Atlantic puffins (Fratercula arctica) in sympatry. To control for a potential distance effect, values were compared to differences among ticks from the same host in nearby monospecific sites. As predicted, there was higher genetic differentiation between ticks from different sympatric host species than between ticks from nearby allopatric populations of the same host species. Patterns suggesting isolation by distance were found among tick populations of each host group, but no such patterns existed between tick populations of different hosts. Overall, results suggest that host‐related selection pressures have led to the specialization of I. uriae and that host race formation may be an important diversifying mechanism in parasites.     

Diversity of ectomycorrhizal fungi in Britain: a test of the species–area relationship, and the role of host specificity

The host range of ectomycorrhizal (ECM) fungi in Britain was examined by compilation of a data matrix from published literature sources, based primarily on accounts of sporocarp associations with particular host genera. Information was gathered for 577 species of ECM fungi belonging to 51 genera, and 25 genera of host trees, representing the majority of ECM fungal species and host genera recorded in Britain.
Pronounced variation was recorded in the number of ECM fungal species associated with different host genera, with over 200 species recorded with Betula , Fagus , Pinus and Quercus . There was a positive linear relationship ( r ²=0·47, P =0·007) between the number of species of ECM fungi associated with different host genera and the total area occupied by each tree genus in Britain (both values log-transformed). There was also variation in the number of species of ECM fungi which were apparently specific to particular host genera, values ranging from zero (in 15 genera) to >40 in the case of Betula and Fagus . In total, 233 fungal species appeared to be specific to a single host genus (i.e. 40% of those surveyed). Comparison of the ECM mycota associated with different host genera by PCA accounted for 17% of the total variation, with genera belonging to the Fagaceae ( Quercus , Fagus and Castanea ) tending to cluster together, indicating a degree of overlap in their ECM associates. Exotic conifer species, which displayed a lower ECM diversity than would be expected from their distributional areas, were characterized by a high degree of overlap with the ECM associates of Pinus and Betula .
These results indicate that the abundance of different genera of host trees and variation in host specificity could provide a basis for understanding patterns of diversity in ECM fungi within Britain.     

Field assessment of host plant specificity and potential effectiveness of a prospective biological control agent, Aceria salsolae, of Russian thistle, Salsola tragus

The eriophyid mite, Aceria salsolae de Lillo and Sobhian, is being evaluated as a prospective classical biological control agent of invasive alien tumbleweeds, including Salsola tragus, S. collina, S. paulsenii and S. australis, in North America. Previous laboratory experiments to determine the host specificity of the mite indicated that it could sometimes persist and multiply on some nontarget plants, including Bassia hyssopifolia and B. scoparia. These are both European plants whose geographic range overlaps that of the mite, but the mite has never been observed on them in the field. A field experiment was conducted in Italy to determine if the mite would infest and damage these plants under natural outdoor conditions. The results indicate that this mite does not attain significant populations on these nontarget plants nor does it significantly damage them. Salsola tragus was heavily infested by A. salsolae, and plant size was negatively correlated to the level of infestation. Although S. kali plants were also infested, their size did not appear to be affected by the mites. The other nontarget plants were not as suitable for the mite in the field as in previous laboratory experiments. We conclude that there would be no significant risk to nontarget plants as a result of using A. salsolae as a biological agent to control Salsola species in North America.     

Biology, host specificity tests, and risk assessment of the sawfly Heteroperreyia hubrichi, a potential biological control agent of Schinus terebinthifolius in Hawaii

Heteroperreyia hubrichiMalaise (Hymenoptera: Pergidae), a foliagefeeding sawfly of Schinusterebinthifolius Raddi (Sapindales:Anacardiaceae), was studied to assess itssuitability as a classical biological controlagent of this invasive weed in Hawaii. No-choice host-specificity tests were conductedin Hawaiian quarantine on 20 plant species in10 families. Besides the target weed, adultfemales oviposited on four test species. Females accepted the Hawaiian native Rhussandwicensis A. Gray (Sapindales:Anacardiaceae) as an oviposition host equallyas well as the target species. The other threespecies received significantly fewer eggs. Neonate larvae transferred onto test plantssuccessfully developed to pupae on S.terebinthifolius (70% survival) and R.sandwicensis (1% survival). All other 18test plant species failed to support larvaldevelopment. A risk analysis was conducted toquantify the acceptability of non-targetspecies as host plants for H. hubrichi onthe basis of the insect's performance atvarious stages in its life cycle. Risk ofdamage to all plant species tested wasinsignificant except for R. sandwicensis. Risk to this native plant relative to S.terebinthifolius was estimated at 1%. Currently this level of risk is too high torequest introduction of this insect into theHawaiian environment. Detailed impact studiesin the native range of S. terebinthifoliusare needed to identify thepotential benefit that this insect offers. Also, field studies in South America withpotted R. sandwicensis would give a morereliable analysis of the risk this nativeHawaiian plant would face from naturalpopulations of H. hubrichi.     

Consistency in the host specificity and host sensitivity of the Bacteroides HF183 marker for sewage pollution tracking

Aims: The host specificity (H‐SPF) and host sensitivity (H‐SNV) values of the sewage‐associated HF183 Bacteroides marker in the current study were compared with the previously published studies in South East Queensland (SEQ), Australia, by testing a large number of wastewater and faecal DNA samples (n = 293) from 11 target and nontarget host groups. This was carried out to obtain information on the consistency in the H‐SPF and H‐SNV values of the HF183 marker for sewage pollution tracking in SEQ. Methods and Results: Polymerase chain reaction (PCR) analysis was used to determine the presence/absence of the HF183 marker in wastewater and faecal DNA samples. Among the human composite wastewater (n = 59) from sewage treatment plants and individual human (n = 20) faecal DNA samples tested, 75 (95%) were PCR positive for the HF183 marker. The overall H‐SNV of this marker in target host group was 0·95 (maximum of 1·00). Among the 214 nontarget animal faecal DNA samples tested, 201 (94%) samples were negative for the HF183 marker. Six chicken, five dog and two bird faecal DNA samples, however, were positive for the marker. The overall H‐SPF of the HF183 marker to differentiate between target and nontarget faecal DNA samples was 0·94 (maximum of 1·00). Conclusions: The H‐SNV (0·95) and H‐SPF (0·94) values obtained in this study was slightly lower than previous studies (H‐SNV value of 1·00 in 2007 and 1·00 in 2009; H‐SPF value of 1·00 in 2007 and 0·99 in 2009). Nonetheless, the overall high H‐SNV (0·98) and H‐SPF (0·97) values of the HF183 marker over the past 4 years (i.e. 2007–2011) suggest that the HF183 marker can be reliably used for the detection of sewage pollution in environmental waters in SEQ. Significance and Impact of the Study: In the current study, the HF183 marker was detected in small number nontarget animal faecal samples. Care should be taken to interpret results obtained from catchments or waterways that might be potentially contaminated with dog faecal matter or poultry litter.     

Environmental variation in physical and chemical cues used by the parasitic wasp,Aphytis melinus, for host recognition

O-caffeoyltyrosine is a host recognition kairomone forAphytis melinus DeBach (Aphelinidae) found in the covers of its host, California red scale,Aonidiella aurantii (Maskell) (Diaspidae). This study tests the hypothesis that the concentration ofO-caffeoyltyrosine and scale cover size are reliable indicators of scale body size, an important component of host quality forA. melinus, over a range of scale rearing conditions. Both scale cover area andO-caffeoyltyrosine concentrations were only qualitatively related to scale body size during the third instar, the scale life stage most suitable forA. melinus. Scale cover area andO-caffeoyltyrosine concentrations were reduced, relative to scale body size, when scale were reared on bark and leaves compared to fruits. Scale cover area andO-caffeoyltyrosine concentration were also relatively reduced when scales were reared in mid-summer compared to spring and fall, and when reared on orange cultivars compared to lemon cultivars in the field. Finally, scale cover area andO-caffeoyltyrosine concentration were reduced when scale were reared at 52% compared to 100% humidity in the laboratory. Scales appear to be chemically conspicuous toA. melinus for a short period of the time in which they are physiologically susceptible. Scales that minimize their cover size and maximize the incorporation rate ofO-caffeoyltyrosine into covers may minimize their conspicuousness toA. melinus. Minimizing scale cover size, but not necessarily incorporation rates, may make scales more vulnerable to predators, however.     

The biology and host specificity of the onion weed rust, Puccinia barbeyi, a potentially useful agent for biological control in Australia

Onion weed, Asphodelus fistulosus L., (Liliaceae) a weed of Mediterranean and Middle Eastern origin is widespread in southern Australia where it invades pastures making them unsuitable for grazing. A program of research is underway to discover natural enemies of this plant and to study their possible role in the biological control of onion weed. A rust fungus Puccinia barbeyi (Roum.) Magnus has been found to severely attack A. fistulosus . Observations on the biology of the rust confirmed that it is monoecious and microcyclic and multiplied essentially by aecial and telial stages, although occasionally urediniospores also appeared among teliospores. Several members of the Liliaceae exposed to the aeciospores of the rust remained unattacked indicating that it is most probably specific to Asphodelus spp. and thus its potential for the biological control of A. fistulosus in Australia should be studied further.     

Rapid evolution of host specificity in a parasitic nematode

Summary In eastern North America, the nematodeHowardula aoronymphium parasitizes four species of mushroom-breedingDrosophila:D. falleni andD. recens of the quinaria species group, andD. putrida andD. testacea of the testacea group. One strain ofH. aoronymphium, designated Mendon-87, was initially capable of infecting all four of these host species. After less than 3 years in laboratory culture usingD. falleni as the sole host, this strain had completely lost the ability to infectD. putrida. Two other nematode strains parasitizedD. falleni andD. putrida at equal rates. These results demonstrate the existence of genetic variation for host specificity within this nematode species. More importantly, they show that host specificity can evolve rapidly when only one host is available for parasitization. Ecological conditions are such that natural populations ofH. aoronymphium may comprise numerous host races, lineages incapable of parasitizing the full range of host species. However, I argue that such host races are probably ephemeral and thus unlikely to persist long enough to undergo speciation.     

Host specificity,pathogenicity and the presence of virulence genes in Iranian strains of Pseudomonas syringae pv. syringae from different hosts

Pseudomonas syringae pv. syringae (Pss) strains were isolated from almond, apricot, peach, pear, sweet cheery and wheat in Kohgiluye and Boyer-Ahmad, Kordestan, Fras and Chaharmahal and Bakhtiari provinces of Iran. The strains were examined for host specificity, the presence of virulence genes and pathogenicity on different hosts. After inoculation of isolates, in compatible reactions bacterial populations increased within six days of inoculation and final cell numbers increased several-fold over initial inoculum levels, but in incompatible reactions, bacterial populations declined within four days of inoculation. Almond, sweet cherry and wheat isolates induced progressive necrotic symptoms on almond leaves and stems. Apricot, peach and sweet cherry isolates induced necrotic lesions when inoculated on apricot leaves. On pear leaves and stems, only the pear isolate incited pathogenic reaction and isolates from other hosts did not. The syrB gene was detected in all of the tested isolates. Almond and pear isolates did not have the syrD gene. The sypA gene was detected in the almond, peach, pear and sweet cherry isolates while the sypB gene was detected in the apricot, peach, sweet cherry and wheat isolates. Almond, apricot, pear and wheat isolates gave negative results for the detection of nit gene. The gene Ach, was detected only in the peach isolate and gene hrmA, was detected only in the wheat isolate. This study indicates that host specificity exists among different Pss strains, and genes responsible for syringomycin and syringopeptin production contribute to the virulence of Pss strains.     

Involvement of host recognition by oncomiracidia and post-larval survivability in the host specificity of Heterobothrium okamotoi (Monogenea: Diclidophoridae)

Heterobothrium okamotoi, a monogenean gill parasite, shows high host specificity for tiger puffer, Takifugu rubripes. In the present study, in vivo and in vitro experimental infections were conducted using various fish species, including T. rubripes, to understand the mechanisms of specificity. In in vivo experiments, T. rubripes, grass puffer, Takifugu niphobles, olive flounder, Paralichthys olivaceus, and red sea bream, Pagrus major, were exposed to oncomiracidia of H. okamotoi labelled with a fluorescent dye, 5- (and -6) carboxyfluorescein diacetate succinimidyl ester, and the numbers of parasites on the gills and skin were recorded at intervals. Oncomiracidia were attached to gills and skin of all the experimental fish species immediately after exposure, and the infection intensity on T. rubripes was higher than that on T. niphobles and much higher than those on the other two species. After 2 days, the attached parasites remained on the gills of T. rubripes, but disappeared from the other hosts. During in vitro experiments, gill filaments excised from seven different fish species (four fish species used in the in vivo experiments and panther puffer, Takifugu pardalis, southern flounder, Paralichthys lethostigma and spotted halibut, Verasper variegates) were exposed to oncomiracidia and the attachment to each fish species and subsequent larval behaviour was observed. The percentage of post-larvae that attached to T. rubripes was slightly higher than those which attached to congeneric fish species and much higher than those of non-tetraodontid fish species. In vivo and in vitro experiments demonstrated that oncomiracidia of H. okamotoi have an affinity for their natural host, T. rubripes, and congeneric fish species. The disappearance of attached post-larvae from 'alien' hosts within 2 days during in vivo experiments suggested that host recognition by oncomiracidia and subsequent post-larval survivability are involved in the host specificity of H. okamotoi.     

Macroptilium atropurpureum (siratro) host specificity genes are linked to a nodD-like gene in the broad host range Rhizobium strain NGR234

Summary A 6.7 kb HindIII fragment from the Sym-plasmid of strain NGR234 was found to code a nodD-like gene flanked by two loci which were required for siratro host range. Transfer of the 6.7 kb fragment from NGR234 to R. trifolii strain ANU843 conferred extended host range ability to this strain on siratro plants but not to other plants normally nodulated by strain NGR234. Tn5 mutagenesis of the 6.7 kb fragment showed that insertions located into loci flanking the nodD-like gene abolished the extended host range phenotype. A hybridization probe spanning one of the host specificity loci was shown to hybridize to three specific bands in the NGR234 genome. Complementation and DNA hybridization data showed that the nodD-like gene of strain NGR234 was functionally similar to that in R. trifolii. The introduction to R. trifolii of the 6.7 kb HindIII fragment containing Tn5 insertions located in the nodD-like gene did not abolish the ability to extend the host range of R. trifolii to siratro plants. However, transfer of the 6.7 kb HindIII to R. trifolii derivatives containing Tn5 insertions into either nodA, B or C or other R. trifolii nod genes failed to confer siratro nodulation to these recipients. Reconstruction experiments showed that the 6.7 kb fragment from strain NGR234 and the 14 kb nodulation region of R. trifolii could induce the nodulation of siratro plants when introduced together into Sym-plasmid-cured Rhizobium strains.     

Changes in host acceptance and host suitability as an effect of rearing Trichogramma maidis on a factitious host

Host acceptance and suitability of Ostrinia nubilalis Hbn. for Trichogramma maidis Pint. et Voeg. (Hymenoptera: Trichogrammatidae) were studied, after rearing the parasitoids on O. nubilalis or Ephestia kuehniella Oliv. (Lepidoptera: Pyralidae) for various numbers of generations. In cages, containing two maize plants with in total 30 egg masses of the natural host (O. nubilalis), wasps continuously reared on either E. kuehniella or O. nubilalis found egg masses in equal proportions. The former however, did not parasitize the eggs successfully, due to either low degree of host acceptance or insufficient host suitability or both. Subsequently, host acceptance behaviour of individual females from different strains was studied by means of direct observations after releasing them into a small arena containing eggs of O. nubilalis or E. kuehniella. Wasps continuously reared on O. nubilalis or 1–3 generations on E. kuehniella accepted egg masses of the natural host better than wasps continuously reared on E. kuehniella. Acceptance of O. nubilalis by the wasps gradually decreased with increasing numbers of generations reared on E. kuehniella. By rearing T. maidis, previously cultured on E. kuehniella, for five generations on O. nubilalis, acceptance of egg masses of this host species did not change. Host suitability of O. nubilalis appears to correspond with host acceptance of the strains. Contrary to the observations on O. nubilalis, acceptance and suitability of E. kuehniella were not influenced by the host on which T. maidis was reared. Results of this study show that host acceptance and suitability of the natural host are important quality factors for T. maidis when mass produced on a factitious host.

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Zusammenfassung Wirtsakzeptanz und Wirtseignung von Ostrinia nubilalis Hbn. für den Eiparasitoiden, Trichogramma maidis Pint. et. Voeg., wurden untersucht nach der Zucht auf dem natürlichen Wirt, O. nubilalis, oder auf dem Ersatzwirt, der Mehlmotte, Ephestia kühniella Zell.. Versuche mit Käfigen, in denen je zwei Maispflanzen mit insgesamt 30 Eigelegen von O. nubilalis und 40 Weibchen von T. maidis eingesperrt waren, zeigten, dass Weibchen, die seit über 150 Generationen auf O. nubilalis bzw. E. kühniella gezüchtet worden waren, die Eigelege gleich gut fanden. Während die auf O. nubilalis gezüchteten Parasitoide die Eigelege zu 80% parasitierten, war die Parasitierungsrate der auf E. kühniella gezüchteten Parasitoide gleich Null. Die Ursachen dieses Phänomens wurden in weiteren Versuchen durch direkte Beobachtungen über Wirtsakzeptanz und Wirtseignung untersucht. Einzelne Weibchen von Stämmen, die nur auf O. nubilalis oder während einer zunehmenden Generationenzahl auf E. kühniella gezüchtet worden waren, untersuchte man während 15 Minuten unter der Stereoskoplupe in einer kleinen Arena, die ein Eigelege des Maiszünslers oder Eier der Mehlmotte enthielt. Dabei zeigte sich, dass Wespen, die ausschliesslich auf Maiszünslereiern oder nur 1–3 Generationen auf Mehlmotteneiern gezüchtet worden waren, die Eigelege von O. nubilalis besser akzeptierten als solche, die seit vielen Generationen auf E. kühniella vermehrt worden waren. Die Wirtsakzeptanz verschlechterte sich mit zunehmender Generationenzahl auf E. kühniella. Wenn T. maidis nach 23 Generationen auf E. kühniella wieder während 5 Generationen auf O. nubilalis gezüchtet wurde, verbesserte sich die Akzeptanz der Eigelege von O. nubilalis nicht. Die Wirtseignung der Eigelege von O. nubilalis, stimmt überein mit der Wirtsakzeptanz der verschiedenen Stämme. Dies ergaben Versuche mit 15 Minuten Direktbeobachtung und bei 24 Stunden Expositionszeit. Im Gegensatz zu den Beobachtungen auf Eigelegen von O. nubilalis wurde die Akzeptanz und Eignung der Eier von E. kühniella durch die Zucht auf verschiedenen Wirten nicht beeinflusst. Das Ergebnis dieser Untersuchung zeigt, dass Akzeptanz und Eignung des natürlichen Wirtes wichtige Qualitätsfaktoren für T. maidis in der Massenzucht auf Ersatzwirten sind.

     

The Host Range ofEccritotarsus catarinensis(Heteroptera: Miridae), a Potential Agent for the Biological Control of Waterhyacinth (Eichhornia crassipes)

The host range ofEccritotarsus catarinensiswas determined using 33 plant species to assess the risk of using this insect, a native of South America, for the classical biological control of waterhyacinth (Eichhornia crassipes) in Australia and Papua New Guinea. The results, in conjunction with the results of Hillet al.(1999) who tested 67 species (mostly South African), strongly suggest thatE. catarinensisis restricted to the Pontederiaceae, a family of aquatic plants. All five species of Pontederiaceae in the Australian testing,E. crassipes, Pontederia cordata, Monochoria vaginalis, M. cyanea,andM. australasica,were suitable for insect development. Colonies persisted for at least four generations onE. crassipes, P. cordata,andM. vaginalis.Two-way choice and multiple-choice preference trials were conducted and discussed.E. catarinensisdid not exhibit a clear preference for waterhyacinth over other Pontederiaceae in these trials. Most oviposition occurred into the upper surface of the lamina during laboratory testing despite observations that the underside was preferred in the field. Although not considered suitable for release in Australia, this insect may be useful in other countries where more serious waterhyacinth problems occur and whereM. vaginalisis a serious weed, such as in Southeast Asia.     

Interplay of host specificity and biogeography in the population structure of a cosmopolitan endoparasite: microsatellite study of Ligula intestinalis (Cestoda)

Organisms with wide geographical or phenotypic diversity often constitute assemblages of genetically distinct species or lineages. Within parasites, an emergence of host-specific lineages is assumed to create such cryptic variability; however, empirical evaluation of these processes is scarce. Here, we analyse populations of a parasite with a complex life cycle, wide host spectrum and global distribution, with the aim to reveal factors underlying the evolution of host- or geography-dependent lineages. Using 15 microsatellite loci, deep genetic distances were observed between populations from distant geographical areas. On the local scale, host-mediated genetic structure was found among sympatric samples. Two lineages differing in the spectrum of infected hosts co-occurred in the Euro-Mediterranean area, and two distinct lineages were recovered from Lake Tana in Ethiopia. Although sampled across several host taxa and multiple localities, a lack of marked genetic structure was seen in the populations belonging to one of the European lineages. Only weak genetic differentiation between sympatric samples from two host species was found. Complexity of the parasite life-cycle contributed to such a stratified pattern. Differences in the immune response between fish hosts were suggested as the factor diversifying the populations locally; conversely, high mobility of the parasite due to migration with its bird (definitive) host were assessed to homogenize populations across the area of distribution. However, despite the high mobility, large bodies of salt water prevent the parasite from long-distance migrations, as was demonstrated in an example of the Mediterranean Sea which represented an effective barrier to gene flow.