Host-related variability in arbuscular mycorrhizal fungal structures in roots of <Emphasis Type="Italic">Hedera rhombea</Emphasis>, <Emphasis Type="Italic">Rubus parvifolius</Emphasis>, and <Emphasis Type="Italic">Rosa multiflora</Emphasis> under controlled conditions

The arbuscular mycorrhizal (AM) morphology of three host plant species inoculated with single and mixed fungal culture and the distribution of AM fungal species in roots of the hosts treated with a mixed culture of AM fungi were determined. The aim was to investigate the effect of host plants and AM fungi on AM morphology of coexisting plant species. Noncolonized rooted cuttings of Hedera rhombea (Miq) Bean, Rubus parvifolius L., and Rosa multiflora Thunb. were inoculated with five fungal species as single and mixed culture inocula. The fungal species used were Gigaspora rosea and Scutellospora erythropa, previously isolated from H. rhombea; Acaulospora longula and Glomus etunicatum from R. parvifolius; and Glomus claroideum from both plant species. A few hyphal and arbusculate coils were seen in the mixed culture-inoculated roots of R. parvifolius; all fungal treatments produced this Paris-type AM in H. rhombea and Arum-type AM in R. parvifolius, and R. multiflora indicates that AM morphology is strongly controlled by the identity of the host plants used in this study. AM fungal rDNA was extracted separately from roots of each replicate plant species inoculated with the mixed fungal culture, amplified, cloned, sequenced, and analyzed to determine the AM fungal species and their respective proportions in roots of each plant species. Glomus etunicatum and G. claroideum of the family Glomaceae generally occurred more frequently in R. parvifolius and R. multiflora, which form Arum-types, whereas S. erythropa, of the family Gigasporaceae, was the most frequently detected species in H. rhombea, which produced Paris-type AM. Although the genotype of the plant species used appears to determine the AM morphologies formed, there was preferential association between the hosts and AM fungal inoculants.     

Supplementary host specificity testing of the sawfly <Emphasis Type="Italic">Heteroperryia hubrichi</Emphasis>, a candidate for classical biological control of Brazilian peppertree, <Emphasis Type="Italic">Schinus terebinthifolius</Emphasis>, in the USA

Supplementary host specificity tests were conducted with the defoliating sawfly Heteroperreyia hubrichi (Hymenoptera: Pergidae), a candidate for classical biological control of Brazilian peppertree, Schinus terebinthifolius (Sapindales: Anacardiaceae), in the United States. These tests were conducted as part of the environmental assessment required by the National Environmental Policy Act (NEPA). The suitability of the federally listed endangered native plant Rhus michauxii (Anacardiaceae) and the economically important Litchi chinensis (Sapindaceae) as potential host plants for H. hubrichi was evaluated in a series of no-choice larval development tests conducted in a Florida quarantine laboratory. Neonate larvae transferred to individual test plants failed to develop to the pupal stage on R. michauxii or L. sinensis, whereas Brazilian peppertree supported development of the sawfly to pupation. The results of the additional host specificity tests indicated these critical non-target plants are not at risk from attack by H. hubrichi if it were released in Florida, USA.     

Assessing the risks of releasing a sap-sucking lace bug, <Emphasis Type="Italic">Gargaphia decoris</Emphasis>, against the invasive tree <Emphasis Type="Italic">Solanum mauritianum</Emphasis> in New Zealand

The South American tree Solanum mauritianum Scopoli (Solanaceae), a major environmental weed in South Africa and New Zealand, has been targeted for biological control, with releases of agents restricted to South Africa. The leaf-sucking lace bug, Gargaphia decoris Drake (Tingidae), so far the only agent released, has become established in South Africa with recent reports of severe damage at a few field sites. To evaluate the insect’s suitability for release in New Zealand, host-specificity testing was carried out in South Africa in laboratory and open-field trials, with selected cultivated and native species of Solanum from New Zealand. No-choice tests confirmed the results of earlier trials that none of the three native New Zealand Solanum species are acceptable as hosts. Although the cultivated Solanum muricatum Aiton and S. quitoense Lam. also proved unacceptable as hosts, some cultivars of S. melongena L. (eggplant) supported feeding, development and oviposition in the no-choice tests. Although eggplant was routinely accepted under laboratory no-choice conditions in this and previous studies, observations in the native and introduced range of G. decoris, open-field trials and risk assessment based on multiple measures of insect performance indicate that the insect has a host range restricted to S. mauritianum. These results strongly support the proposed release of G. decoris in New Zealand because risks to non-target native and cultivated Solanum species appear to be negligible. An application for permission to release G. decoris in New Zealand will be submitted to the regulatory authority. Handling editor: John Scott.     

Host specificity of <Emphasis Type="Italic">Tectococcus ovatus</Emphasis> (Hemiptera: Eriococcidae), a potential biological control agent of the invasive strawberry guava, <Emphasis Type="Italic">Psidium cattleianum</Emphasis> (Myrtales: Myrtaceae), in Florida

Strawberry guava, Psidium cattleianum Sabine, is a woody tree or shrub native to coastal southeastern Brazil. Strawberry guava was introduced into Florida in the late 1800s as an ornamental species. The plant escaped cultivation and is invading natural areas throughout the southern half of the state. In addition to negative effects on Florida’s native ecosystems, strawberry guava also is a preferred host of the Caribbean fruit fly, Anastrepha suspensa Loew (Diptera: Tephritidae). In total, 57 plant species representing 21 families were included in the host range tests. First instar nymphs of Tectococcus ovatus Hempel fed on two closely related guava species, Brazilian guava (Psidium friedrichsthalianum O. Berg), and Costa Rican guava (Psidium guineense Sw.). However, none of the nymphs completed their development on these two non-target species. The results of the host specificity tests suggest that T. ovatus is a suitable candidate for classical biological control of strawberry guava in Florida.     

Specialist <Emphasis Type="Italic">Osmia</Emphasis> bees forage indiscriminately among hybridizing <Emphasis Type="Italic">Balsamorhiza</Emphasis> floral hosts

Pollinators, even floral generalists (=polyleges), typically specialize during individual foraging bouts, infrequently switching between floral hosts. Such transient floral constancy restricts pollen flow, and thereby gene flow, to conspecific flowers in mixed plant communities. Where incipient flowering species meet, however, weak cross-fertility and often similar floral traits can yield mixed reproductive outcomes among pollinator-dependent species. In these cases, floral constancy by polyleges sometimes serves as an ethological mating barrier. More often, their foraging infidelities instead facilitate host introgression and hybridization. Many other bee species are oligolectic (taxonomic specialists for pollen). Oligoleges could be more discriminating connoisseurs than polyleges when foraging among their limited set of related floral hosts. If true, greater foraging constancy might ensue, contributing to positive assortative mating and disruptive selection, thereby facilitating speciation among their interfertile floral hosts. To test this Connoisseur Hypothesis, nesting females of two species of oligolectic Osmia bees were presented with randomized mixed arrays of flowers of two sympatric species of their pollen host, Balsamorhiza, a genus known for hybridization. In a closely spaced grid, the females of both species preferred the larger flowered B. macrophylla, evidence for discrimination. However, both species’ females showed no floral constancy whatsoever during their individual foraging bouts, switching randomly between species proportional to their floral preference. In a wider spaced array in which the bouquets reflected natural plant spacing, foraging oligolectic bees often transferred pollen surrogates (fluorescent powders) both between conspecific flowers (geitonogamy and xenogamy) and between the two Balsamorhiza species. The Connoisseur Hypothesis was therefore rejected. Foraging infidelity by these oligolectic Osmia bees will contribute to introgression and hybridization where interfertile species of Balsamorhiza meet and flower together. A literature review reveals that other plant genera whose species hybridize also attract numerous oligolectic bees, providing independent opportunities to test the generality of this conclusion.     

Cytoplasmic incompatibility involving <Emphasis Type="Italic">Cardinium</Emphasis> and <Emphasis Type="Italic">Wolbachia</Emphasis> in the white-backed planthopper <Emphasis Type="Italic">Sogatella furcifera</Emphasis> (Hemiptera: Delphacidae)

Cytoplasmic incompatibility (CI) is a reproductive phenotype induced by bacterial endosymbionts in arthropods. Measured as a reduction in egg hatchability resulting from the crossing of uninfected females with bacteria-infected males, CI increases the frequency of bacteria-infected hosts by restricting the fertilization opportunities of uninfected hosts in populations. Wolbachia, a type of alpha-proteobacteria, is well known as a CI inducer in a wide range of arthropod species, while Cardinium, a member of the phylum Bacteroidetes, is known to cause CI in one wasp and three spider mite species. In this study, dual infection with Cardinium and Wolbachia induced strong CI in a single host, Sogatella furcifera (Horváth), a planthopper species that is naturally infected with both bacteria. Specifically, infection with Cardinium alone was found to cause a 76 % reduction in egg development, and dual infection with Cardinium and Wolbachia a 96 % reduction, indicating that Cardinium induces CI and the dual infection raises the CI level. This study was the first to document reproductive alteration by Cardinium in a diploid host species.     

Colony founding and social parasitism in <Emphasis Type="Italic">Lasius</Emphasis> (<Emphasis Type="Italic">Acanthomyops)</Emphasis>

We investigated colony foundation behavior of three species of the Lasius claviger group, L. latipes, L. interjectus and L. claviger, using field observations and laboratory experiments. Laboratory studies included observing gyne behavior prior to interaction with host colonies (e.g. grouping, overwintering, feeding) and experiments in which gynes were introduced to putative host colonies. Observations of gyne parasitic behavior immediately after mating flights in the field and the discovery of mixed colonies both confirm the parasitic behavior of these species and point toward a wide host species range including two cases of hyperparasitism. L. interjectus and L. latipes enter the host colony immediately after the nuptial flight, while L. claviger may hibernate and enter in the spring. Laboratory experiments showed that L. interjectus gynes prefer to group and suffer lower mortality when in a group, which is consistent with field observations of L. interjectus gynes entering host colonies in large numbers. Details on behavior of L. latipes alpha and beta form gynes are also given.     

Winter and spring ecology of <Emphasis Type="Italic">Anaphes nitens</Emphasis>, a solitary egg-parasitoid of the <Emphasis Type="Italic">Eucalyptus</Emphasis> snout-beetle <Emphasis Type="Italic">Gonipterus scutellatus</Emphasis>

We investigated the effects of temperature, photoperiod, food and host availability, and body size on the overwintering abilities of the egg parasitoid Anaphes nitens Girault (Hymenoptera, Mymaridae) under natural conditions. Seven groups of eighty females received one of four treatments (n = 20): (i) honey and hosts, (ii) water and hosts, (iii) honey, or (iv) water. Seven groups of forty males received only honey or water (n = 20). To test if short day-length is the main cue for larval dormancy, the experiment was replicated inside a climate chamber at 20°C and under a winter photoperiod. A. nitens overwinters because of quiescence or oligopause inside the hosts and increased adult longevity. Mean pre-emergence mortality was up to 26% indoors and 15.2% outdoors, males being more affected. Development time had a significant and positive effect on body size. Honey-fed females without hosts had the highest longevity (53 days). Mother’s diet and size affected development time, body size, longevity, and fecundity of the progeny. The results confirm the good adaptation of the parasitoid to the environmental conditions of NW Spain and its ability to synchronize its life cycle with the phenology of the host. Handling editor: Drik Babendreier.     

The influence of two endoparasitic wasps, <Emphasis Type="Italic">Hyposoter didymator</Emphasis> and <Emphasis Type="Italic">Chelonus inanitus</Emphasis>, on the growth and food consumption of their host larva <Emphasis Type="Italic">Spodoptera littoralis</Emphasis>

The influence of parasitism by Hyposoter didymator (Thunberg; Hymenoptera: Ichneumonidae) and Chelonus inanitus (Linnaeus) (Hymenoptera: Braconidae) on the growth and food consumption of their host Spodoptera littoralis (Boisduval) (Lepidoptera: Noctuidae) was studied in the laboratory. Parasitised larvae consumed significantly less artificial diet than unparasitised ones. Egg parasitisation by C. inanitus affected host larval consumption from the second day after emergence and it was significantly different from that of unparasitised ones. H. didymator, however, started to reduce larval consumption 4 days after parasitisation on the third instar host larvae. The overall reduction achieved by the larval endoparasitoid H. didymator is higher than that caused by the egg-larval endoparasitoid C. inanitus. The final body weight of a parasitised host larva by H. didymator and C. inanitus was only 6.7 and 13.0% of the maximum weight of an unparasitised sixth instar larva respectively. Moreover, parasitised larvae never reached the last instar. Results indicated that parasitised larvae might cause considerable less damage to the host plant than unparasitised ones.     

Potential for endophyte symbiosis to increase resistance of the native grass <Emphasis Type="Italic">Poa alsodes</Emphasis> to invasion by the non-native grass <Emphasis Type="Italic">Microstegium vimineum</Emphasis>

Microbial symbionts can improve the competitive ability and stress tolerance of plant hosts and thus may enhance native plant resistance against invaders. We investigated whether symbiosis between a native grass, Poa alsodes, and a fungal endophyte (Neotyphodium sp.) improved the grass’s ability to compete against Microstegium vimineum (Japanese stiltgrass), a common invader in the eastern USA. We challenged naturally endophyte-symbiotic and experimentally endophyte-free P. alsodes plants with the invader. In the first experiment, we manipulated symbiosis and water availability to test for context-dependency in symbiont benefits. In the second experiment, we manipulated symbiosis and M. vimineum diversity (the number of invader populations), since greater intraspecific diversity is expected to improve invasion success and might alter the efficacy of symbiosis in invasion resistance. In both experiments, presence of the endophyte reduced the per plant biomass of M. vimineum and increased P. alsodes biomass. We found no evidence that benefits of the symbiont depended on water availability, and population-level diversity had a minor influence on M. vimineum: inflorescence number showed a parabolic relationship with increasing numbers of M. vimineum populations. Overall, symbiosis in the native grass had stronger effects on invader growth than either water availability or invader genetic diversity. Our results suggest that endophyte symbioses in native plants can increase host performance against an invader, although this conclusion needs confirmation in more complex field settings where other important factors, such as herbivores and fluctuating abiotic conditions, come into play.     

Differences between sympatric populations of <Emphasis Type="Italic">Eotetranychus carpini</Emphasis> collected from <Emphasis Type="Italic">Vitis vinifera</Emphasis> and <Emphasis Type="Italic">Carpinus betulus</Emphasis>: insights from host-switch experiments and molecular data

Eotetranychus carpini (Oudemans) is an important pest of grapevine (Vitis vinifera L.) in southern Europe. This mite is also found on a number of different plants, including Carpinus betulus L., which commonly occurs in stands and hedgerows bordering vineyards, where it may serve as a potential mite reservoir. The economic importance of this pest has motivated a number of studies aimed at investigating whether the mites found on V. vinifera and C. betulus are conspecific. The results obtained to date have been inconclusive. In this study, we used biological and molecular approaches to investigate this issue. First, we conducted host-switch experiments to test the ability of E. carpini to develop on an alternative host plant, using mite populations originally collected on either C. betulus or V. vinifera plants from the same area. Second, we investigated DNA-based differentiation using nucleotide sequences of the ITS1-5.8S-ITS2 region of the ribosomal DNA of individual E. carpini from the populations examined in our host-plant experiments. We also analyzed sequences of individuals collected in other regions (Italy and Slovenia) to estimate species variation. The results from our host-switch experiments suggest the differentiation of mites collected on the two hosts. Mites collected from C. betulus did not survive and reproduce on V. vinifera and vice versa. Our molecular work revealed significant genetic differentiation between the mites collected from the two hosts, but no evidence of genetic variation among specimens collected from the same host species. Our results indicate the existence of host races of E. carpini.     

Fitness and life history parameters of <Emphasis Type="Italic">Leptomastix epona</Emphasis> and <Emphasis Type="Italic">Pseudaphycus flavidulus</Emphasis>, two parasitoids of the obscure mealybug <Emphasis Type="Italic">Pseudococcus viburni</Emphasis>

Fitness and life table parameters of two endoparasitoids of the obscure mealybug Pseudococcus viburni (Signoret), the solitary Leptomastix epona (Walker) and the gregarious Pseudaphycus flavidulus (Brèthes), were examined in relation to temperature and host size with a view to determine the efficacy of the parasitoids as biocontrol agents of the pest. Three temperature levels (21°C, 26°C and 31°C) and two host sizes classes (small, which mostly comprised third instar nymphs and large, which consisted of female adults) were studied. The lower developmental threshold and thermal constant of the host and the parasitoids were found similar so the coincidence of pest and parasitoids is likely. The rate of development of the parasitoids increased with a linear trend as the temperature increased from 21°C to 31°C. Temperature had a significant effect on mummification in both parasitoid species and on successful parasitism by P. flavidulus. Host size had a significant effect on the mummification caused by L. epona and on the proportion of the male offspring which emerged as well as on the successful parasitism by P. flavidulus. Life table parameters of the parasitoids were estimated in small and large hosts at 26°C in the laboratory. Both parasitoids achieved a greater intrinsic rate of natural increase and gross reproductive rate in addition to a shorter generation and doubling time in large mealybugs compared with small ones. Consequently, large hosts are expected to have a higher impact on the rise of the parasitoids population and the potential of the parasitoids to control the mealybug population improves with the increase of host size. Handling Editor: Torsen Meiners.     

Biology,host range and varietal preference of the leaf-feeding geometrid, <Emphasis Type="Italic">Leptostales ignifera</Emphasis>, a potential biocontrol agent for <Emphasis Type="Italic">Lantana camara</Emphasis> in South Africa,under laboratory conditions

Lantana camara L. (Verbenaceae) is a weed of major importance in South Africa. It invades indigenous forests and veld, valuable commercial and agricultural forests, plantations and orchards, as well as river-catchment areas. Several natural enemies, including insect and pathogen species, have been released in South Africa, some of which established successfully. These do not exert sufficient control and additional natural enemies are required. Leptostales ignifera Warren (Lepidoptera: Geometridae), one of several new species being investigated as potential biocontrol agents, was collected in the subtropical parts of Florida, USA and Mexico. Host specificity trials indicated L. camara to be the preferred host plant of this quick-developing, voracious leaf-feeder, with some of the African indigenous Lippia species qualifying as very marginal hosts. The possible preference that L. ignifera might have for different South African naturalized L. camara varieties was studied during quarantine laboratory preference trials. Variety 029WP was the most suitable host for L. ignifera, although the other four tested varieties were able to support viable populations of the insect. Not taking other abiotic and biotic factors such as climate and predation into consideration, once released, L. ignifera should be able to establish on all five of the tested varieties in the field and contribute to the biological control of the complex of L. camara as a whole. Based on the above studies, permission has been granted for the release of L. ignifera in South Africa.     

<Emphasis Type="Italic">Galleria</Emphasis><Emphasis Type="Italic">mellonella</Emphasis> are Resistant to <Emphasis Type="Italic">Pneumocystis</Emphasis><Emphasis Type="Italic">murina</Emphasis> Infection

Studying Pneumocystis has proven to be a challenge from the perspective of propagating a significant amount of the pathogen in a facile manner. The study of several fungal pathogens has been aided by the use of invertebrate model hosts. Our efforts to infect the invertebrate larvae Galleria mellonella with Pneumocystis proved futile since P. murina neither caused disease nor was able to proliferate within G. mellonella. It did, however, show that the pathogen could be rapidly cleared from the host.     

Host specificity of <Emphasis Type="Italic">Anagrus epos</Emphasis>: a potential biological control agent of <Emphasis Type="Italic">Homalodisca vitripennis</Emphasis>

Anagrus epos Girault (Hymenoptera: Mymaridae) is a candidate for a classical biological control program targeting the glassy-winged sharpshooter (GWSS), Homalodisca vitripennis (Germar) (Hemiptera: Cicadellidae), in California. Because mass production of GWSS is expensive and labor-intensive, a factitious host that is more economical to produce is desirable to mass produce A. epos for colonization and augmentation efforts. Here, we report the results of host specificity tests and potential rearing techniques for A. epos under laboratory conditions. Females discriminated and oviposited into eggs of seven cicadellid species: H. vitripennis, Circulifer tenellus (Baker), Erythroneura variabilis Beamer, Amblysellus grex (Oman), Graphocephala atropunctata (Signoret), Macrosteles severini Hamilton, and H. liturata Ball, and two cerambycid species: Phoracantha recurva Newman and P. semipunctata (F.). Anagrus epos successfully completed development in the eggs of H. vitripennis, C. tenellus, E. variabilis, A. grex, G. atropunctata, M. severini, and H. liturata. The use of a factitious host and potential nontarget effects of this generalist parasitoid are discussed.     

Development of parasitic <Emphasis Type="Italic">Maculinea teleius</Emphasis> (Lepidoptera,Lycaenidae) larvae in laboratory nests of four <Emphasis Type="Italic">Myrmica</Emphasis> ant host species

Maculinea butterflies are social parasites of Myrmica ants. Methods to study the strength of host ant specificity in the Maculinea–Myrmica association include research on chemical and acoustic mimicry as well as experiments on ant adoption and rearing behaviour of Maculinea larvae. Here we present results of laboratory experiments on adoption, survival, development and integration of M. teleius larvae within the nests of different Myrmica host species, with the objective of quantifying the degree of specialization of this Maculinea species. In the laboratory, a total of 94 nests of four Myrmica species: M. scabrinodis, M. rubra, M. ruginodis and M. rugulosa were used. Nests of M. rubra and M. rugulosa adopted M. teleius larvae more readily and quickly than M. ruginodis colonies. No significant differences were found in the survival rates of M. teleius larvae reared by different ant species. Early larval growth of M. teleius larvae differed slightly among nests of four Myrmica host species. Larvae reared by colonies of M. rugulosa which were the heaviest at the beginning of larval development had the lowest mean larval body mass after 18 weeks compared to those reared by other Myrmica species. None of the M. teleius larvae was carried by M. scabrinodis or M. rubra workers after ant nests were destroyed, which suggests a lack of integration with host colonies. Results indicate that Myrmica species coming from the same site differ in their ability to adopt and rear M. teleius larvae but there was no obvious adaptation of this butterfly species to one of the host ant species. This may explain why, under natural conditions, all four ants can be used as hosts of this butterfly species. Slight advantages of particular Myrmica species as hosts at certain points in butterfly larval development can be explained by the ant species biology and colony structure rather than by specialization of M. teleius.     

Molecular detection of <Emphasis Type="Italic">Rickettsia</Emphasis>, <Emphasis Type="Italic">Coxiella</Emphasis> and <Emphasis Type="Italic">Rickettsiella</Emphasis> DNA in three native Australian tick species

Three Australian native animal species yielded 60 samples composed of three indigenous ticks. Hosts included twelve koalas, two echidnas and one wombat from Victoria, and ticks were of the species Ixodes tasmani (n = 42), Bothriocroton concolor (n = 8) and B. auruginans (n = 10), respectively. PCR screening and sequencing detected a species of Coxiella, sharing closest sequence identity to C. burnetii (>98%), in all B. auruginans, as well as a species of Rickettsia, matching closest to R. massiliae, in 70% of the same samples. A genotype sharing closest similarity to Rickettsia bellii (>99%) was identified in three female B. concolor collected from one of the echidnas. Three samples of I. tasmani, taken from three koalas, yielded different genotypes of Rickettsiella. These results represent the first detection of the three genera in each tick species and identify a high level of previously undetected bacterial diversity in Australian ticks.     

The trimorphic flea-beetle, <Emphasis Type="Italic">Alagoasa extrema</Emphasis>, not suitable for biocontrol of <Emphasis Type="Italic">Lantana camara</Emphasis> in Africa

The biology and host range of the flea-beetle, Alagoasa extrema (Harold) (Coleoptera: Chrysomelidae: Galerucinae: Alticini), was studied under quarantine laboratory conditions to evaluate the insect’s suitability for release as a biological control agent for the noxious weed, Lantana camara L. (Verbenaceae), in South Africa. Identification of this species proved noteworthy. The adults of A. extrema display three freely interbreeding and very distinct colour morphs, which can be confused with no less than 11 species of Alagoasa found in Mexico and the southwestern U.S. Initially, specimens were identified as two species of the genus Alagoasa Bechyné, i.e. A. quadrilineata (Harold) and A. extrema. Thirteen additional Alagoasa species and Kushelina petaurista (F). that can be confused with A. extremabased on external morphology of adults or larvae are discussed. Favourable biological characteristics included long-lived adults, several overlapping generations per year, and high adult and larval feeding rates. Observations from the insect’s native Mexican range and studies in South Africa suggest that A. extrema would probably be more suited to subtropical, rather than temperate areas in Africa. Host-specificity studies showed A. extrema to be an oligophagous species, capable of feeding and developing on several non-target species, especially two indigenous, African Lippia species (Verbenaceae). The host suitability of these indigenous species was only marginally lower than that of L. camara, and the potential risk to them was deemed to be too high to warrant release. It was therefore recommended that A. extrema be rejected as biocontrol agent for lantana in Africa.     

Field persistence of the entomopathogenic nematode <Emphasis Type="Italic">Heterorhabditis bacteriophora</Emphasis> in different crops

To investigate nematode establishment and persistence, dauer juveniles (DJs) of Heterorhabditis bacteriophora were applied at 50 cm^-2 in different crops in June and July with conventional spraying equipment and 420 l water ha^-1. Application hardly had any effects on survival and infectivity. The number of DJs reaching the soil was assessed and the establishment and persistence recorded by baiting soil samples with larvae of the wax moth Galleria mellonella. The better the plant canopy was developed the fewer DJs reached the soil during application. Whereas in pasture 77% and in potatoes 78% of the applied nematodes reached the soil, in wheat and peas little less than 50%, in oil-seed rape only 5% and in lupine 6% were recorded. Between 50 and 60% of the soil samples contained H. bacteriophora a month after application with the exception of wheat (>90%) and potatoes (<5%) indicating that the number of nematodes reaching the soil during application had no influence on their establishment in the soil. Probably DJs can survive in the plant canopy and reach the soil later after application. The percentage of nematode-positive soil samples dropped considerably after tillage. In potatoes no nematodes were recovered after two months, which probably was also due to the intensive movement of the soil. Although nematodes are susceptible to freezing, temperatures below 0°C during the winter did not extinguish the H. bacteriophora population. In field crops EPN usually persisted not much longer than one year. The longest persistence of H. bacteriophora was detected 23 months after release in beans followed in rotation by wheat with red clover as cover crop. In this field larvae of the pea weevil Sitona lineatus (Coleoptera: Curculionidae) were detected in soil samples and found infected with the released nematode population. In the laboratory the field soils were tested for persistence of H. bacteriophora at 8°C and a half-life of 24.8 days was recorded in the absence of host insects and plants. Thus long-term persistence in the field was a result of recycling in host insects, which could not be detected in other crops than beans and clover. As H. bacteriophora seems to be restricted in its host potential, this species disappears after release once the host population is not available anymore.     

<Emphasis Type="Italic">Piriformospora indica</Emphasis> and <Emphasis Type="Italic">Sebacina vermifera</Emphasis> increase growth performance at the expense of herbivore resistance in <Emphasis Type="Italic">Nicotiana attenuata</Emphasis>

A Sebacinales species was recovered from a clone library made from a pooled rhizosphere sample of Nicotiana attenuata plants from 14 native populations. Axenic cultures of the related species, Piriformospora indica and Sebacina vermifera, were used to examine their effects on plant performance. Inoculation of N. attenuata seeds with either fungus species stimulated seed germination and increased growth and stalk elongation. S. vermifera inoculated plants flowered earlier, produced more flowers and matured more seed capsules than did non-inoculated plants. Jasmonate treatment during rosette-stage growth, which slows growth and elicits herbivore resistance traits, erased differences in vegetative, but not reproductive performance resulting from S. vermifera inoculation. Total nitrogen and phosphorous contents did not differ between inoculated and control plants, suggesting that the performance benefits of fungal inoculation did not result from improvements in nutritional status. Since the expression of trypsin proteinase inhibitors (TPI), defensive proteins which confer resistance to attack from Manduca sexta larvae, incur significant growth and fitness costs for the plant, we examined the effect of S. vermifera inoculation on herbivore resistance and TPI activity. After 10 days of feeding on S. vermifera-inoculated plants, larval mass was 46% higher and TPI activity was 48% lower than that on non-inoculated plants. These results suggest that Sebacina spp. may interfere with defense signaling and allow plants to increase growth rates at the expense of herbivore resistance mediated by TPIs.