Discoideus Gyllenhal Research Articles

Olfactory Receptor Neurons for Plant Volatiles and Pheromone Compounds in the Lucerne Weevil, Sitona discoideus

Antennal olfactory receptor neurons (ORNs) for pheromone-related and plant volatile compounds were identified and characterized in the lucerne weevil, Sitona discoideus (Gyllenhal), using the single sensillum recording technique. Our study using five pheromone-related compounds and 42 plant volatile compounds indicates that S. discoideus have highly specialized ORNs for pheromone and plant volatile compounds. Different groups of ORNs present in both males and females of S. discoideus were highly sensitive to 4-methylheptane-3,5-dione (diketone) and four isomers (RR, RS, SR and SS) of 5-hydroxy-4-methylheptan-3-one, respectively. Our results also indicate that male S. discoideus, using the sensory input from antennal ORNs, can distinguish both diketone and the RR-isomer from others, and RS- and SS-isomers from others, although it was unclear if they can distinguish between RS-isomer and SS-isomer, or between diketone and the SR-isomer. It also appeared that female S. discoideus could distinguish between RS-isomer and SS-isomers. The antennae of S. discoideus thus contain sex-specific sets of ORNs for host- and non-host plant volatile compounds. Both sexes of S. discoideus have highly sensitive and selective ORNs for some green-leaf volatiles, such as (Z)-3-hexenol and (E)-2-hexenal. In contrast, male antennae of S. discoideus house three distinct groups of ORNs specialized for myrcene and (E)-β-ocimene, 2-phenylethanol, and phenylacetaldehyde, respectively, whereas female antennae contain three groups of ORNs specialized for (±)-linalool and (±)-α-terpineol, myrcene and (E)-β-ocimene, (±)-1-octen-3-ol, and 3-octanone. Our results suggest that S. discoideus use a multi-component pheromone communication system, and a sex-specific set of ORNs with a narrow range of response spectra for host-plant location.

First record of the exotic pest Sitona discoideus Gyllenhal 1834 (Coleoptera: Curculionidae) in Argentina

Fil: del Rio, Maria Guadalupe. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Division Entomologia; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - La Plata; Argentina

Selecting non-target species for arthropod biological control agent host range testing: Evaluation of a novel method

Regulators often require risk assessment to ascertain biosafety of biocontrol agents before approval for release. Selecting the most informative non-target species for host range testing can be challenging. Here we compare traditional test list selection with a more objective method that selects species from a dataset of invertebrates from the receiving environment. A model, PRONTI (priority ranking of non-target invertebrates) ranks species using five criteria: hazard, exposure, potential ecological impacts from exposure, anthropocentric value and testability. For a case study, we used the braconid parasitoid Microctonus aethiopoides Loan released in New Zealand in 1982 for biocontrol of the pest weevil Sitona discoideus Gyllenhal. We compared species prioritised by PRONTI as worthy of testing with those selected prior to release. Several species which have been attacked in the field by M. aethiopoides since its release ranked highly suggesting that if PRONTI had been available pre-release, better predictions of non-target attack might have been made. The investment in time needed to adopt PRONTI needs to be balanced against its objectivity when comparing it with current conventional methods.

Could research in the native range, and non-target host range in Australia, have helped predict host range of the parasitoid Microctonus aethiopoides Loan (Hymenoptera: Braconidae), a biological control agent introduced for Sitona discoideus Gyllenhal (Coleoptera: Curculionidae) in New Zealand?

It is generally accepted that knowledge of the natural and novel host range of proposed biological control agents can help to inform predictions of potential host range in new areas of introduction. To test this hypothesis, this paper describes a retrospective study conducted to contrast and compare the natural host range of Microctonus aethiopoides Loan (Hymenoptera: Braconidae) with its novel host range found in Australia and New Zealand, where it has been introduced to control the adult stage of the weevil Sitona discoideus Gyllenhal (Coleoptera: Curculionidae), a pest of lucerne. Surveys carried out in and near lucerne crops in Morocco and Australia each resulted in collections of over 3,000 weevils, of which respectively 84 % and 93 % were S. discoideus. The host ranges determined from these surveys for each M. aethiopoides population were then compared with information already available for field host range in New Zealand. In Morocco, species in the genera Sitona and Charagmus (Curculionidae: Entiminae: Sitonini) and Hypera (Curculionidae: Hyperinae: Hyperini) were found to be parasitised by M. aethiopoides. In Australia, an earlier record of non-target parasitism of ‘Prosayleus’ sp. 2 (Curculionidae: Entiminae: Leptopiini) is still the only known instance of non-target parasitism by M. aethiopoides. The known non-target field host range in New Zealand is much greater, comprising 19 native and introduced weevil species mainly in the subfamily Entiminae (tribe Leptopiini) but also in Curculioninae, Cyclominae and Lixinae. This is discussed in the context of predictions that could have been made at the time of introduction 30 years ago had the Moroccan and Australian data, modern molecular technologies and current understanding of weevil classification been available. The absence of Leptopiini in Morocco and the record of a native Australian leptopiine host could have indicated that native weevils in this tribe in New Zealand might be at risk of attack by M. aethiopoides.

Field Parasitism of Nontarget Weevil Species (Coleoptera: Curculionidae) by the Introduced Biological Control Agent <I>Microctonus aethiopoides</I> Loan (Hymenoptera: Braconidae) over an Altitude Gradient

The parasitoid, Microctonus aethiopoides Loan (Hymenoptera: Braconidae) was introduced into New Zealand in 1982 to control the alfalfa pest, Sitona discoideus Gyllenhal (Coleoptera: Curculionidae). Studies have shown that a number of nontarget weevil species are attacked in the field by this parasitoid. A field study was carried out to investigate nontarget parasitism by M. aethiopoides over an altitudinal sequence from the target host habitat (alfalfa) into native grassland. Three locations were selected for the study, and at each, the alfalfa growing in the valley floor was sampled annually for parasitism of the target pest that ranged between 17 and 78%. At progressively higher altitudes, three further grassland sites at each location were sampled monthly during spring to autumn for up to 6 yr. Weevil densities were estimated, species identified, and dissections carried out to determine reproductive status and parasitism. Almost 12,000 weevils were collected during the study, which were identified as 36 species in total from the three locations. Eight weevil species were found to be parasitized, including S. discoideus, the target host that was found at all sites. Parasitism of nontarget species was approximately 2% overall but varied with location, site, and season. Substantial nontarget parasitism was found at only one of the locations, with up to 24% parasitism of a native weevil, Nicaeana fraudator Broun (Coleoptera: Curculionidae), recorded. Another species, Irenimus egens (Broun) (Coleoptera: Curculionidae), was also found at this location at similar population densities but was attacked far less by M. aethiopoides. Results are discussed in relation to weevil phenology.

Virus-like particles in the ovaries of Microctonus aethiopoides Loan (Hymenoptera: Braconidae): Comparison of biotypes from Morocco and Europe

Virus-like particles (MaVLP) have been discovered in the ovarial epithelial cells of the solitary, koinobiont, endoparasitoid, Microctonus aethiopoides Loan (Hymenoptera: Braconidae) introduced to New Zealand originally from Morocco to control the lucerne pest Sitona discoideus Gyllenhal (Coleoptera: Curculionidae). MaVLP have been found in all females examined. It has been suggested, although not demonstrated, that like many other such VLP found in parasitoids, MaVLP might play a role in host immunosuppression. Since another biotype of M. aethiopoides from Ireland has been proposed for introduction to control the white clover pest, Sitona lepidus Gyllenhal, in New Zealand, it was considered that females from this biotype warranted transmission electron microscope examination for VLP. No VLP were observed in ovarian tissues of specimens collected from three different locations in Ireland. Similarly, none were found in M. aethiopoides sourced from France, Wales, and Norway. These observations are discussed in relation to quarantine host specificity tests with the Irish biotype, which found that the host range of the Irish biotype is likely to be less extensive than that of the Moroccan biotype already in New Zealand.

Parasitism of the lucerne pest Sitona discoideus Gyllenhal (Coleoptera: Curculionidae) and non‐target weevils by Microctonus aethiopoides Loan (Hymenoptera: Braconidae) in south‐eastern Australia, with an assessment of the taxonomic affinities of non‐target hosts of M. aethiopoides recorded from Australia and New Zealand

Abstract The braconid parasitoid Microctonus aethiopoides Loan has been released in Australia and New Zealand for biological control of the lucerne pest Sitona discoideus Gyllenhal. In New Zealand, the parasitoid attacks a number of endemic weevil species. A survey of Curculionoidea found in and near lucerne in south‐eastern Australia was carried out to investigate whether similar non‐target parasitism was occurring, and to relate this to levels of parasitism found in the target host, S. discoideus. Some of the original M. aethiopoides release sites were particularly targeted in the survey of 25 sites in Victoria, New South Wales and South Australia. Almost 2500 weevils were collected, of which over 90% were S. discoideus, with the remaining 197 other weevils comprising 29 species found at 15 of the 25 sites. Parasitism of S. discoideus by M. aethiopoides occurred at 12 lucerne sites, with levels ranging from 0 to 25%. A single incidence of parasitism of a species of an Australian native weevil Prosayleus sp. by M. aethiopoides was recorded. No parasitism of any other weevil species was observed. The taxonomic affinities between Sitona and native Australian and New Zealand weevils are discussed, concluding that non‐target host range in M. aethiopoides may be determined more by ecological factors than by taxonomic affinities among its hosts.

Using Models to Estimate Parasitoid Impacts on Nontarget Host Abundance

A method is described for estimating the impact of a parasitoid on the abundance of a nontarget host, using the intrinsic rate of host increase, the average abundance of the host in the presence of parasitism, and the estimated mortality caused by the parasitoid. The method is applied to the braconid Microctonus aethiopoides Loan, introduced to New Zealand to control Sitona discoideus Gyllenhal in lucerne but also attacking native weevils Irenimus spp. and Nicaeana spp. The nontarget host population was modeled using discrete Ricker or continuous logistic models, tuning the models to host population data in the presence of parasitism, then removing parasitism and determining the increase in predicted equilibrium host density. In an area where up to 30% parasitism of a nontarget host population has been recorded, the model estimated an 8% reduction of the nontarget host. In another area, where the parasitoid has not established, the method was applied in reverse to predict the parasitoid’s impact if it did establish. In this case, the model predicted a 30% suppression of population density. The host’s intrinsic rate of increase, rm, accounts for this difference in predicted impact, which was small in the low altitude area where rm was high, and the impact was larger in the higher altitude site where rm was smaller.

Factors affecting parasitism by Microctonus aethiopoides (Hymenoptera: Braconidae) and parasitoid development in natural and novel host species.

A laboratory study of aspects of parasitoid host acceptance, suitability and physiological regulation in natural and novel host species was carried out to investigate the degree of variability encountered with different hosts and to determine the value of such observations in host range determination. The parasitoid Microctonus aethiopoides Loan was exposed to a natural host, Sitona discoideus Gyllenhal (Coleoptera: Curculionidae) and three novel hosts, the New Zealand native Nicaeana cervina Broun, the introduced weed biological control agent Rhinocyllus conicus (Froehlich), and a congeneric pest species, Sitona lepidus Gyllenhal (all Coleoptera: Curculionidae). Per cent parasitism of these species was 54%, 43%, 39% and 0%, respectively. The results indicated that for both S. discoideus and R. conicus more males than females were parasitized (69% cf. 45%, and 49% cf. 32% respectively) but host size was not a significant factor. Overall, superparasitism was recorded in about 29% of parasitized weevils and there was evidence that host discrimination to avoid superparasitism occurred in the natural host. Conversely, superparasitism occurred more frequently than would be expected in N. cervina (42%) coupled with higher survival of larvae in superparasitized hosts in this species. The frequency distribution of attack of R. conicus by M. aethiopoides was not different from random. Parasitoid development was more rapid in the natural host, S. discoideus, and parasitoid size was positively correlated with host size. There was a strong positive relationship between parasitoid larval survival and the presence of teratocytes in all hosts. Host fecundity and fertility were reduced by parasitism for most species, and in some cases, by exposure to parasitoids in the absence of detectable parasitism. It was concluded that laboratory observations can provide useful information on the compatibility between host and parasitoid which can complement traditional host range tests to predict field host range.

Host selection and reproductive success of French and Moroccan populations of the parasitoid, Microctonus aethiopoides (Hymenoptera: Braconidae)

French and Moroccan populations of the parasitoid Microctonus aethiopoides Loan were studied in the laboratory for their host selection, mating behavior, and reproductive success. The French strain, collected on Hypera postica (Gyllenhal), although capable of parasitizing and producing viable offspring on Sitona weevils, preferred Hypera weevils, its known target host. The Moroccan strain, collected on Sitona discoideus Gyllenhal, exhibited host specificity for Sitona. A partial reproductive isolation was observed between the two strains. Moroccan females mated more frequently with French males than did French females with Moroccan males. The pre-copulation time for mating pairs of opposite strains was significantly longer than that for mating pairs of the same strain. There was no significant difference in copulation time nor in larval and pupal duration between French and Moroccan strains. In summary, the French and Moroccan strains of M. aethiopoides are clearly separable by biological, behavioral, and morphometric traits and the preferred host for Hypera is the French strain and Sitona for the Moroccan strain. Consequently, geographic location and host source become important when considering this parasitoid as a potential biological control agent.

Development of teratocytes associated with Microctonus aethiopoides Loan (Hymenoptera: Braconidae) in natural and novel host species

A laboratory study investigated development of teratocytes derived from the parasitoid Microctonus aethiopoides Loan in the natural host, Sitona discoideus Gyllenhal, and in three novel hosts, the introduced weed biological control agent Rhinocyllus conicus (Froehlich), and two New Zealand native species Nicaeana cervina Broun and Irenimus stolidus Broun. Weevils were exposed to parasitoids and then examined 6, 10 and 15 days post-parasitism for parasitoid stage and size, and teratocyte number and size. In all hosts, teratocyte numbers decreased and size increased as parasitoid development progressed, although 6 days after parasitism, fewer, larger teratocytes were found in I. stolidus than S. discoideus or N. cervina. In weevils containing second-third instar parasitoid larvae, the most permissive hosts, S. discoideus and N. cervina contained more teratocytes than the least permissive hosts I. stolidus and R. conicus. Host gender influenced some aspects of parasitoid and teratocyte development. Total teratocyte volume was greater in female than male S. discoideus at all sampling times, and at 10 days post-parasitism in N. cervina. A possible relationship between host suitability and teratocyte development is discussed.

Behavioural Acceptability of Sitona lepidus (Coleoptera: Curculionidae) to the Parasitoid Microctonus aethiopoides (Hymenoptera: Braconidae) Using the Pathogenic Bacterium Serratia marcescens Bizio

Microctonous aethiopoides Loan has been introduced into New Zealand to control the lucerne pest Sitona discoideus Gyllenhal (Coleoptera: Curculionidae). Sitona lepidus Gyllenhal (Coleoptera: Curculionidae) a pest of clover ( Trifolium spp.), has recently established in New Zealand. Laboratory experiments to test the potential of M. aethiopoides to parasitize S. lepidus has resulted in very low levels of parasitism. To investigate whether there were behavioural or physiological barriers to successful parasitism, two experiments were conducted using the insect pathogenic bacterium. Serratia marcescens Bizio as a marker for parasitoid ovipositor penetration. Firstly, M. aethiopoides 'treated' with S. marcescens were exposed to weevils and rapid weevil mortality was used to indicate ovipositor penetration. Up to 50% mortality of S. lepidus occurred, which was comparable with mortality observed in the permissive host Listronotus bonariensis . Dissection of S. lepidus exposed to parasitoids treated with distilled water showed that ca. 21% contained parasitoid eggs of which 98% were nonviable. In the second experiment, exposure periods of 24, 48 and 72 h to S. marcescens -treated parasitoids produced an increase in S. lepidus mortality of 14, 28 and 38%, respectively. There was 3% successful parasitoid development in weevils exposed for 72 h to parasitoids treated with distilled water. M. aethiopoides has been shown to develop successfully in a wide range of non-target weevil species both in the laboratory and field. Possible reasons for poor survival of M. aethiopoides immature stages in S. lepidus are discussed.

Feeding by Sitona discoideus after exposure to the parasitoid Microctonus aethiopoides

The impact of the parasitoid Microctonus aethiopoides Loan (Hymenoptera: Braconidae) on the feeding activity of its adult weevil host Sitona discoideus Gyllenhal (Coleoptera: Curculionidae) was studied in the laboratory. Feeding by parasitised S. discoideus showed a distinct pattern with no significant feeding during the first two days after exposure to the parasitoids, peak feeding six days before parasitoid emergence and no feeding on the day of parasitoid emergence. Reproductive female S. discoideus consumed significantly more lucerne than parasitised weevils, unparasitised males, or non-reproductive females.

The potential of parasitoid strains in biological control: Observations to date on Microctonus spp. intraspecific variation in New Zealand

Over the last 15 years New Zealand researchers have been actively involved in the classical biological control of forage weevil pests. In the 1980s, the lucerne pest Sitona discoideus Gyllenhal (Coleoptera: Curculionidae) was successfully suppressed by the parasitoid Microctonus aethiopoides Loan (Hymenoptera: Braconidae). Since 1990, an additional programme has been developed to examine the impact of the recently introduced parasitoid Microctonus hyperodae (Hymenoptera: Braconidae) on New Zealand's worst ryegrass pest, the Argentine stem weevil ( Listronotus bonariensis (Kuschel)). The imported M. hyperodae founder populations were collected from a wide range of ecoclimatic zones. During both of the programmes, the importance of ecotypes has become increasingly apparent. The New Zealand M. aethiopoides population revealed phenological patterns quite different from those observed in Mediterranean Europe, North America and Australia. As a result of these observations, part of the current research into M. hyperodae has been developed specifically to explore ecotypic variation and its implications. This contribution reviews progress to date in researching ecotypic differences and comments on the potential of ecotypes in classical biological control, with particular reference to recently developed DNA-based techniques.

Sitona lepidusGyllenhal (Coleoptera: Curculionidae), a potential clover pest new to New Zealand

Sitona lepidus Gyllenhal (syn. S. flavescens (Marsham)) (Coleoptera: Curculionidae), a potential legume pest species new to New Zealand, is reported from near Hamilton. A key is provided to distinguish S. lepidus from S. discoideus Gyllenhal, a lucerne pest already established in New Zealand. Information is given on the distribution of S. lepidus in New Zealand and overseas, the biology and life cycle, mostly derived from the literature, and potential pest status and control.

Diagnostic characteristics and biology of threeMicroctonusspp. (Hymenoptera: Braconidae, Euphorinae) parasitoids of weevils (Coleoptera: Curculionidae) in New Zealand pasture and lucerne.

Two species of Microctonus have been introduced to control 2 weevil pests found in the pastoral habitat. M. aethiopoides Loan was introduced and successfully controlled Sitona discoideus (Gyllenhal) while M. hyperodae Loan has been recently released to control Listronotus bonariensis (Kuschel). The third species, M. zealandicus Shaw, is indigenous to New Zealand and is associated with a native Curculionidae Irenimus aequalis Broun. Microctonus aethiopoides has been found to parasitise field populations of L. bonariesis and I. aequalis, while laboratory observations have suggested that I. aequalis may be a target for opportunist parasitism by M. hyperodae. As the 3 weevil species may be found co-existing in the pastoral habitat, a diagnostic key and brief description of the biology is provided to discriminate between the 3 parasitoid species.

A Modelling Analysis of the Successful Biological Control of Sitona discoideus (Coleoptera: Curculionidae) by Microctonus aethiopoides (Hymenoptera: Braconidae) in New Zealand

Simple models were developed to explore the interaction between the lucerne (Medicago sativa L.) pest Sitona discoideus Gyllenhal and its introduced braconid parasite Microctonus aethiopoides Loan in New Zealand. A model for the population dynamics of S. discoideus demonstrated that observed levels of parasitism account for a decline in pest abundance, in spite of strong density-dependent mortality in the host. An empirical model for changes in parasitism from year to year, spanning five to six parasitoid generations each year, suggested that control is likely to be maintained in the long term and that the interaction is stable

Use of an electric blanket for winter field collection of Argentine stem weevil,Listronotus bonariensis(Kuschel) (Coleoptera: Curculionidae)

Maintenance of large populations of the parasitoid Microctonus hyperodae Loan demanded high numbers of its host the Argentine stem weevil Listronotus bonariensis (Kuschel). To fulfil this requirement under winter conditions a very effective technique using an electric blanket was devised to collect up to 450 weevils day - 1 irrespective of weather conditions. Under warmer spring conditions fewer weevils were trapped and there were indications that the method may have biased catches towards weevils that had been opportunistically parasitised by the Sitona discoideus Gyllenhal parasitoid, Microctonus aethiopoides Loan. Possible reasons for these results are discussed, as is the potential of the method as a surveying tool.

Inter-seasonal variation inSitona discoideusGyllenhal (Coleoptera: Curculionidae) larval damage to lucerne in Canterbury and the economics of insecticidal control

Abstract In four out of five seasons at Darfield, Canterbury, Sitona discoideus Gyllenhal larval damage significantly reduced lucerne ( < 5 years old) production in at least one cut. Of all the yield losses, a maximum of 46.5% was measured at the time of the second cut in a 1-year-old stand during the 1986 – 87 season. Levels of damage similar to those at Darfield were also recorded in Marlborough and North Canterbury in the 1985 – 86 season and were observed qualitatively in the Timaru and Ashburton areas. An economic analysis using 85% dry matter (DM) 25 kg bales valued at either $2.50 or $4.50 each showed that in four out of five seasons, there was distinct economic benefit derived from applying insecticide. Recommended insecticide use did not incur a significant economic loss on any occasion. Such results indicate that prophylactic sprays are justifiable, at least in areas comparable to Darfield. Each season's maximum percent yield loss correlated significantly with a rainfall index. Data collected al...

Population Dynamics and Larval Establishment of Sitona discoideus (Coleoptera: curculionidae) in New Zealand Lucerne

(1) Sitona discoideus Gyllenhal population data collected from young lucerne (Medicago sativa L.) in Canterbury, New Zealand in 1982-86 were analysed using life tables. Manipulated weevil densities in 1983-84 allowed intra-seasonal and inter-seasonal relationships to be studied. (2) In general, there was a high degree of density-dependent mortality, probably amongst the neonate larvae during their establishment in the root nodules. (3) There was considerable variation in the pattern of larval survival in wet compared with dry seasons. In the latter, density-dependent effects occurred after little cumulative egg laying (750-2400 eggs m-2) compared with higher levels (11 770 m-2) in the wet season. Under wet conditions, there was greater mortality amongst the later instars. (4) Egg laying in the field was modelled on laboratory-derived temperature/rate relationships and field air temperatures. Model predictions suggested that 30-50% of the maximum fecundity was reached, indicating some maladaptation. (5) The range of feeding habits of Sitona spp. is reviewed with regard to the degree of dependence of the genus on root nodules.