Capacity of Japanese Asobara species (Hymenoptera; Braconidae) to parasitize a fruit pest Drosophila suzukii (Diptera; Drosophilidae)

Drosophila suzukii is a pest of soft fruit such as cherry, strawberry or blueberry and recently colonized North America and Europe from Asia. In this study, we assessed the utility of Japanese Asobara species as agents for the biological control of this pest species by examining their host use in nature and their capacity to parasitize this pest species. From Japan, eight Asobara species including putative three undescribed species were found; Asobara japonica was recorded from all over Japan, Asobara tabida from high altitude areas in central and northern Japan, Asobara rossica and Asobara rufescens from central to northern Japan, three undescribed species from central to western or southern Japan and Asobara pleuralis from a subtropical island of Japan. Among them, an undescribed species Asobara sp. TK1 may be useful as an agent for the biological control because it was recorded only from D. suzukii. All of the remaining seven species were generalists mainly using drosophilid species associated with fermenting fruits, and four of them had no or very low abilities to parasitize D. suzukii, indicating that these seven species are not or less appropriate as agents for biological control.     

Geographical variation in habitat choice and host suitability in the parasitoidAsobara rufescens

In the Netherlands, Asobara rufescens (Förster) (Hymenoptera: Braconidae) is a parasitoid of drosophilid larvae in decaying plant material. In several places in the Mediterranean, parasitoids looking very similar to A. rufescens were collected on fermenting substrates. A hybridization experiment showed that the parasitoids were indeed A. rufescens. In an olfactometer Portuguese A. rufescens do not have a preference for either the odour of yeast or decaying leaves, while their Dutch conspecifics prefer the odour of decaying leaves. The survival probability of Portuguese A. rufescens in Drosophila melanogaster Meigen (Diptera: Drosophilidae), a species typical for fermenting substrates, is much higher than the survival probability of Dutch A. rufescens in this host species. It is hypothesized that decaying plant material may be unsuitable for drosophilid larvae during part of the year in the Mediterranean, forcing A. rufescens there to broaden its microhabitat choice. The use of fermenting substrates brings A. rufescens in contact with its sibling A. tabida Nees, a species typical for fermenting substrates in most of Europe. Portuguese A. rufescens appear to be genetically isolated from A. tabida. In the Netherlands, where the two species occupy different microhabitats, there is only a premating barrier.     

The influence of conditioning on olfactory microhabitat and host location in Asobara tabida (Nees) and A. rufescens (Foerster) (Braconidae: Alysiinae) larval parasitoids of Drosophilidae

Olfactory responses of parasitoids can be variable. This was shown by olfactometer experiments with females of two sibling Asobara species, larval endoparasitoids of Drosophilidae. Oviposition experiences of adult female parasitoids significantly altered their behavioural responses in microhabitat and host location. Females needed prior exposure to a host before they were capable of using volatile compounds related to the presence of their host. Asobara tabida (Nees) attacks Drosophila in fermenting fruits and A. rufescens (Foerster) attacks Drosophilidae in decaying plant materials. Naïve females show a strong preference for the odour of their own microhabitat. After experience with their own host and microhabitat, females were repelled by odours of the other microhabitat. Enforced experience with this repellent microhabitat in the laboratory modified the olfactory response from repellency to attraction. It was shown that even the microhabitat odour preference pattern could be changed through experience. This kind of behavioural flexibility may be the rule rather than the exception in many other Hymenopterous parasitoids.     

Toxicity of venom of Asobara and Leptopilina species to Drosophila species

The Drosophila parasitoid Asobara japonica Belokobylskij (Hymenoptera: Braconidae) has highly toxic venom that kills host larvae if its injection is not followed by an injection of lateral oviduct components along with egg‐laying. In the present study, the venoms of seven other Drosophila parasitoids (Asobara rossica, Asobara rufescens, Asobara pleuralis, Leptopilina heterotoma, Leptopilina japonica, Leptopilina ryukyuensis, and Leptopilina victoriae) are tested against three kinds of Drosophila species (i.e. Drosophila species that are suitable as host for focal parasitoids, those that are resistant to the parasitoids, and a cosmopolitan species, Drosophila simulans). Venoms of the three Asobara species are not toxic to any of Drosophila species, whereas those of the four Leptopilina species are toxic to some Drosophila species. The toxicity of venom varies among Leptopilina species, and the susceptibility to venom also varies among host Drosophila species. Furthermore, toxicity and paralytic effects of venom are not correlated. Because the toxicity of venom is not adaptive for parasitoids, it may be an inevitable side effect of some components that play an essential role in parasitism.     

Intra- and interspecific host discrimination in two closely related egg parasitoids

Intraspecific host discrimination is frequently found in solitary parasitoids, but interspecific host discrimination, where female parasitoids recognize hosts already parasitized by females of other species, is rare. This particular behaviour appears to be adaptive only under specific circumstances. In this paper, we quantified intraspecific host discrimination in Anaphes n. sp. (Hymenoptera: Mymaridae), an endoparasitoid of the eggs of Listronotus oregonensis (LeConte) (Coleoptera: Curculionidae) and interspecific host discrimination toward eggs parasitized by Anaphes sordidatus (Girault), a sympatric species competing for the same resource in similar habitats. To examine host discrimination, choice experiments were used where the females had to choose between different categories of eggs (unparasitized, parasitized by Anaphes n. sp. or A. sordidatus). Superparasitism and multiparasitism were avoided in experiments where the female had a choice between unparasitized hosts and hosts parasitized by the same female, by a conspecific or by a female A. sordidatus. When all hosts available were parasitized, conspecific superparasitism occurred more often than self-superparasitism or multiparasitism. These results indicated that females Anaphes n. sp. were capable of self-, conspecific and interspecific discrimination. Self-discrimination followed recognition of an external marking while interspecific discrimination occurred mostly after insertion of the ovipositor. Interspecific discrimination could result from the recent speciation of these species and could be associated with a genotypic discrimination. This behavior appears to be adaptive because of the competition for common hosts between the two parasitoid species.     

Rapid Establishment of a Regular Distribution of Adult Tropical Drosophila Parasitoids in a Multi-Patch Environment by Patch Defence Behaviour

Females of the larval parasitoid of Drosophila, Asobara citri, from sub-Saharan Africa, defend patches with hosts by fighting and chasing conspecific females upon encounter. Females of the closely related, palearctic species Asobara tabida do not defend patches and often search simultaneously in the same patch. The effect of patch defence by A. citri females on their distribution in a multi-patch environment was investigated, and their distributions were compared with those of A. tabida. For both species 20 females were released from two release-points in replicate experiments. Females of A. citri quickly reached a regular distribution across 16 patches, with a small variance/mean ratio per patch. Conversely, A. tabida females initially showed a clumped distribution, and after gradual dispersion, a more Poisson-like distribution across patches resulted (variance/mean ratio was closer to 1 and higher than for A. citri). The dispersion of A. tabida was most probably an effect of exploitation: these parasitoids increasingly made shorter visits to already exploited patches. We briefly discuss hypotheses on the adaptive significance of patch defence behaviour or its absence in the light of differences in the natural history of both parasitoid species, notably the spatial distribution of their hosts.     

Microhabitat location and niche segregation in two sibling species of Drosophilid parasitoids: Asobara tabida (Nees) and A. rufescens (Foerster) (Braconidae: Alysiinae)

Summary Olfactometer tests with Asobara tabida (Nees 1834), a larval endo-parasitoid of frugivorous Drosophilidae showed that females are attracted to the odour of host food: a suspension of living yeast. This attraction decreased as the fermenting medium grew older and became less likely to contain suitable host stages. Olfactometer tests with — what was considered to be — A. tabida from two different microhabitats (fermenting fruits and decaying plants) showed a genetically determined difference in microhabitat odour preference between the two microhabitat strains. Each strain preferred the odour of its own microhabitat. This odour preference was not modified by larval conditioning. Hybridization tests indicated that we were dealing with two sibling species: A. tabida and A. rufescens (Foerster 1862), reproductively isolated by a pre-mating isolation mechanism only. Enforced matings resulted in fertile female offspring. Some small morphological differences were detected. The two species live sympatrically, although each inhabits and is most attracted to its own microhabitat.     

Costs of reproduction and geographic variation in the reproductive tactics of the mosquito Aedes triseriatus

Intraspecific host discrimination is widespread in solitary parasitoids whose adult females forage for and evaluate host suitability, whereas interspecific discrimination is less common. In some parasitoid species, mostly Diptera and Coleoptera, the larva performs the last step of host searching. It has been suggested that host discrimination will rarely occur in such host-seeking larvae because their low mobility results in a low host encounter rate. We determined the extent to which the larvae of Aleochara bilineata Gyllenhal (Coleoptera: Staphylinidae), a solitary parasitoid of aggregated Diptera pupae: (1) discriminated between unparasitized hosts and hosts parasitized by conspecifics; (2) used semiochemical cues to discriminate; (3) were influenced by life expectancy, presence of conspecifics and host availability in their host acceptance decision; and the extent to which (4) A. bilineata and A. bipustulata L., a species exploiting the same hosts and occurring sympatrically, showed interspecific host discrimination. A. bilineata larvae were able to discriminate between unparasitized hosts and hosts parasitized by conspecifics in a choice experiment. Such behavior has never previously been described for a coleopteran parasitoid or for a parasitoid species whose larvae perform host searching. Host discrimination in this species was not based on the presence of visual or tactile cues (e.g., entrance holes) but rather on chemical cues. The life expectancy of A. bilineata larvae was significantly shorter in the presence than in absence of hosts, and older larvae had lower parasitism success than young larvae in a 24-h experiment. However, the host acceptance decision of A. bilineata larvae was not influenced by larval age or the presence of conspecifics when the ratio of hosts per larva was greater than or equal to 1. When hosts were scarce, the degree of superparasitism increased significantly with the number of foraging conspecifics and the age of the larvae. Both species of Aleochara showed intra- and interspecific host discrimination in a choice experiment. In contrast to A. bipustulata, A. bilineata larvae more frequently parasitized hosts parasitized by A. bipustulata than those parasitized by conspecifics. We suggest that host discrimination will be frequent in solitary parasitoids with host-seeking larvae when hosts are aggregated. Received: 4 June 1998 / Accepted: 1 September 1998     

Kleptoparasitism as an explanation for paradoxical oviposition decisions of the parasitoid Asobara tabida

It is known that the braconid Asobara tabida, a parasitoid of Drosophila larvae, takes oviposition decisions in accordance with survival probabilities in several host species. Nevertheless, larvae of D. simulans, in which the survival probability is virtually zero, are readily accepted for oviposition by searching females. This even happens when they are offered together with D. melanogaster larvae, in which the parasitoid can develop. Here I show that A. tabida can act as a kleptoparasitoid in D. simulans larvae: it can develop in D. simulans larvae, once these larvae are parasitized by another parasitoid, the eucoilid Leptopilina boulardi. Analysis with an optimal foraging model suggests that the increase in survival probability and the occurrence of L. boulardi in the field are high enough to make this kleptoparasitic behaviour of A. tabida pay.     

Variation in diapause and sex ratio in the parasitoidAsobara tabida

Asobara tabida Nees (Hymenoptera: Braconidae) is a widespread parasitoid, attacking larvae ofDrosophila (Diptera: Drosophilidae) species in fermenting substrates. In this species, geographic variation is found in the percentage of parasitoids entering diapause and in the sex ratio of emerging parasitoids. Percentage diapause appears to be influenced by host species (more parasitoids enter diapause inD. melanogaster Meigen than inD. subobscura Collin) and temperature. It is not correlated with any of the abiotic factors investigated, but is correlated with survival probability inD. melanogaster larvae and with the time of year in which the experiment was conducted (even though none of the parasitoids experienced natural day light). Sex ratio was only found to correlate with percentage diapause, suggesting that males enter diapause more frequently than females. It is concluded thatA. tabida uses diapause to survive both unfavourable abiotic and biotic circumstances.     

Host plant use in sympatric closely related flea beetles

Studies on strategies of host plant use in sympatric-related species are significant to the theory of sympatric speciation. Altica fragariae Nakane and Altica koreana Ogloblin are sympatric closely related flea beetles found in Beijing, northern China. All their recorded host plants are in the subfamily Rosoideae of the Rosaceae, so we regard them as a model system to study interactions between herbivorous insects and plant-insect co-evolution. We conducted a set of experiments on the host preference and performance of these flea beetles to study whether these closely related species have the ability to use sympatric novel host plants and whether monophagous and oligophagous flea beetles use the same strategy in host plant use. Oviposition preference experiments showed that A. koreana, a monophagous flea beetle, displayed high host fidelity. However, A. fragariae, which is oligophagous, often made "oviposition mistakes," ovipositing on nonhost plants such as Potentilla chinensis, the host plant of A. koreana, although normal host plants were preferred over novel ones. Larval performance studies suggested that A. fragariae was able to develop successfully on P. chinensis. Feeding experiences of larvae had no effect on feeding preference, oviposition preference, and fecundity of adults. However, females were impaired in their reproductive ability when fed on nonhost plants. Therefore, A. fragariae finished their development of larval stages on P. chinensis and came back to their primary host plant, Duchesnea indica, for feeding and reproduction after eclosion.     

Phylogenetics of Stelis and closely related genera (Orchidaceae: Pleurothallidinae)

Stelis, one of the largest genera within Pleurothallidinae, was recently recircumscribed to include a few hundred more species, most of which had previously been assigned to Pleurothallis. Here, a new phylogenetic analysis of Stelis and closely related genera based on DNA sequences from nuclear ITS and chloroplast matK, based on a much larger sample, is presented; it includes more than 100 species assigned to Stelis and covers all proposed groupings within the genus, many of which have not previously been represented. Clades are proposed to enable easier discussion of groups of closely related species; each clade is characterized morphologically, ecologically, and geographically to explain the evidence found in the molecular analysis. Discussion of the evolutionary trends of character states found in the genus in its broad sense is given. The current taxonomy of the group is given and the possible taxonomical implications of the findings presented here are discussed.     

Flavonoid chemistry of the endemic species of Myrceugenia (Myrtaceae) of the Juan Fernandez Islands and relatives in continental South America

Twenty-one flavonoids were isolated from the leaves of two endemic species ofMyrceugenia on the Juan Fernandez Islands,M. fernandeziana andM. schulzei, from two related species from Brazil,M. campestris andM. rufescens, and from five species from continental Chile,M. colchaguensis, M. exsucca, M. lanceolata, M. pinifolia, andM. rufa. A phenetic analysis was used to evaluate chemical similarities.Myrceugenia campestris andM. rufescens appear most closely related to each other based on flavonoid profiles, and they are also different from the other seven species. The two endemic species in the Juan Fernandez Islands,M. fernandeziana andM. schulzei, group with the continental Chilean species. The former is most closely related toM. lanceolata, and the latter clusters withM. exsucca, although somewhat distantly. The results suggest that the two Juan Fernandez endemics are derived from two introductions from the Chilean continent and not from immigrants from the eastern side of the Andes.     

Phenology, synchrony and host range of the Tasmanian population of Cotesia urabae introduced into New Zealand for the biocontrol of Uraba lugens

The population dynamics of Cotesia urabae (Austin and Allen) (Braconidae: Microgastrinae), a biological control agent from Tasmania, and its eucalypt feeding host, Uraba lugens (Walker) (Lepidoptera: Nolidae) was investigated prior to its introduction to New Zealand in 2011. Previous host range testing on potential New Zealand non-targets determined C. urabae had some potential to attack an endemic species, Nyctemera annulata (Boisduval) (Lepidoptera: Arctiidae). A closely related species in Tasmania, Nyctemera amica, was thus investigated as a potential host along with the native host U. lugens, to better understand the host range of C. urabae and the synchrony with its host in Tasmania. Adult C. urabae emerged from pupal cocoons in the field during January which confirmed a five month window in which its host, the larvae of U. lugens, was absent in the field. Experiments using sentinel N. amica and U. lugens larvae, field collections of N. amica and of larvae of other Lepidopteran species during this five month time window detected no parasitism by C. urabae. In the laboratory, host specificity testing showed reduced attack rates and no resultant C. urabae eggs or developing larvae or any successful pupation of C. urabae larvae from attacked N. amica larvae. It was concluded that N. amica is most unlikely to be a host for C. urabae in Tasmania and no evidence of any other alternative host was found.     

Inter- and intra-specific host discrimination in gregarious and solitary endoparasitoid wasps

In nature, most species of Lepidoptera are attacked by parasitoids, and some species may be hosts for several parasitoid species. When hosts are parasitized by more than one female of the same species (=superparasitism) or females of different species (=multiparasitism), then intrinsic competition occurs for control of host resources. To reduce competition, some parasitoids are able to recognize the difference between parasitized and unparasitized hosts. Inter- and intra-specific host discrimination were investigated in the two sympatric species, the gregarious Cotesia kariyai (Watanabe) and solitary Meteorus pulchricornis (Wesmael), endoparasitoids of the Oriental armyworm Mythimna separata (Walker). To measure host discrimination, choice experiments were conducted in which females of both species foraged and chose between healthy host larvae and hosts initially parasitized by either C. kariyai or M. pulchricornis. An olfactory test was also performed to examine the discrimination behavior of the two parasitoids. Our results showed that, in oviposition choice tests, both braconid female wasps were able to discriminate between unparasitized hosts and from four to seven day-old hosts previously attacked by conspecific and heterospecific wasps. On the other hand, superparasitism and multiparasitism occurred even in host larvae that were parasitized two days earlier. However, once the immature parasitoids hosts are at larval stage (1st and 2nd instar), super- and multiparasitism were avoided in the two-choice test, but the latter often occurred in the multiple-choice experiment. Host discrimination abilities may have been based on plant volatile signals incurred from damaged plants and internal mechanisms from four to seven post-parasitized hosts.     

Absence of Complementary Sex Determination in the Parasitoid Wasp Genus Asobara (Hymenoptera: Braconidae)

An attractive way to improve our understanding of sex determination evolution is to study the underlying mechanisms in closely related species and in a phylogenetic perspective. Hymenopterans are well suited owing to the diverse sex determination mechanisms, including different types of Complementary Sex Determination (CSD) and maternal control sex determination. We investigated different types of CSD in four species within the braconid wasp genus Asobara that exhibit diverse life-history traits. Nine to thirteen generations of inbreeding were monitored for diploid male production, brood size, offspring sex ratio, and pupal mortality as indicators for CSD. In addition, simulation models were developed to compare these observations to predicted patterns for multilocus CSD with up to ten loci. The inbreeding regime did not result in diploid male production, decreased brood sizes, substantially increased offspring sex ratios nor in increased pupal mortality. The simulations further allowed us to reject CSD with up to ten loci, which is a strong refutation of the multilocus CSD model. We discuss how the absence of CSD can be reconciled with the variation in life-history traits among Asobara species, and the ramifications for the phylogenetic distribution of sex determination mechanisms in the Hymenoptera.     

An improved method of genomic in situ hybridization (GISH) for distinguishing closely related genomes of tetraploid and hexaploid wheat species

An improved modification of genomic in situ hybridization (GISH) was proposed. It allows clear and reproducible discrimination between closely related genomes of both tetraploid and hexaploid wheat species due to preannealing of labeled DNA probes and prehybridization of chromosomal samples with blocking DNA. The method was applied to analyze intergenomic translocations 6A:6B and 1A:6B identified in the IG46147 and IG116188 samples of tetraploid wheat Triticum dicoccoides by C-banding. The structure of the rearranged chromosomes was defined for two translocation variants, and the breakpoints were identified on the chromosome arms. Possible application of the developed GISH variant to study genome reorganizations during speciation of allopolyploid plants in evolution is discussed.     

Can spectral cues contribute to species separation in closely related grasshoppers?

 The acridid grasshoppers Chorthippus biguttulus and Ch. mollis, which are closely related and often sympatric species, were compared intra- and interspecifically with regard to the spectra of their calling and courtship songs and of the sound-induced vibrations of the tympanal membrane, as well as the threshold curves of the tympanal nerve. In the low-frequency range but not in the ultrasound region, the maxima of these various curves fall at distinctly different frequencies in the two species. It is shown that the low-frequency sensitivity of the auditory system in both species, especially in females, is well matched to the conspecific song spectra but not to those of the heterospecific songs. Whether these characteristics actually contribute to species discrimination remains to be determined by behavioural tests. Accepted: 23 August 1996     

Host–parasitoid interaction as affected by interkingdom competition

Although still underrepresented in ecological research, competitive interactions between distantly related organisms (so-called “interkingdom competition”) are expected to be widespread in various ecosystems, with yet unknown consequences for, e.g. trophic interactions. In the model host–parasitoid system Drosophila melanogaster–Asobara tabida, toxic filamentous fungi have been shown to be serious competitors that critically affect the density-dependent survival of host Drosophila larvae. This study investigates the extent to which the competing mould Aspergillus niger affects key properties of the well-studied Drosophila–parasitoid system and how the host–parasitoid interaction influences the microbial competitor. In contrast to slightly positive density-dependent host mortality under mould-free conditions, competing A. niger mediated a strong Allee effect for parasitised larvae, i.e. mortality decreased with increasing larval density. It was found that the common toxic fungal metabolite kojic acid is not responsible for higher death rates in parasitised larvae. Single parasitised Drosophila larvae were less harmful to fungal reproduction than unparasitised larvae, but this effect vanished with an increase in larval density. As predicted from the negative effect of fungi on host survival and thus on parasitoid fitness at low larval densities, A. tabida females spent less time foraging in fungus-infested patches. Interestingly, even though high host larval densities increased host survival, parasitoids still reduced their search efforts in fungus-infested patches, indicating a benefit for host larvae from feeding in the presence of noxious mould. Thus, this experimental study provides evidence of the potentially important role of interkingdom competition in determining trophic interactions in saprophagous animal communities and the dynamics of both host–parasitoid and microbial populations.