Summary
A new species of Phasmarhabditis was isolated from the slug, Polytoxon robustum, from Nairobi, Kenya. The nematode was identified using morphological, morphometric, molecular and phylogenetic ...analyses. Phasmarhabditis kenyaensis n. sp. is characterised by an infective juvenile with the longest body length in the genus, measuring 1232 (1107-1336) μm, by the presence of males with a bursa bearing nine bilateral pairs of genital bursal papillae and one pair of papilliform phasmids flanking the tail, cephalate paired spicules, with an arc length of 71 (57-81) μm, as well as by females with a vulva located at the mid-body region and a conoid tail shape, with two phasmids located at ca 40% of the tail length. The molecular phylogeny of the new species, as inferred from its SSU (small subunit) rRNA gene, places P. kenyaensis n. sp. genetically close to undescribed phasmarhabditids from South Africa, suggesting an African grouping, while the D2-D3 (large ribosomal subunit) and ITS region analyses relate P. kenyaensis n. sp. to P. meridionalis, with weak bootstrap support. This is the third new Phasmarhabditis species described from the African continent, the new species bringing the total known complement of the genus to 14 species. A morphometric compendium to all species cultured in vivo is supplied.
Plant-parasitic nematodes of the genus
Cobb, 1913 comprise a complex group of nematode species, some of which are important vectors of plant viruses. During a field survey to determine the soil ...health of an abandoned honeybush (
) monoculture, a high density of the dagger nematode,
Lamberti & Bleve-Zacheo, 1979 (Nematoda, Dorylaimidae), was observed in soil around the roots of honeybush plants in an abandoned farmland at Bereaville, an old mission station in the Western Cape province of South Africa. Soil samples were taken from the rhizosphere of plants and nematodes were extracted from the soil using a modified extraction tray method. Specimen of the dagger nematodes were processed for scanning electron microscopy, morphological and molecular analysis. Molecular profiling of the nematode species was done in order to give an accurate diagnosis and to effectively discriminate the nematode from other species within the
group. Phylogenetic analysis based on the D2D3 expansion segment of the 28S gene supported a close relationship of species within the
group, however, the protein-coding cytochrome oxidase (
) of the mitochondrial gene provided a useful tool for distinguishing the nematode from other species within the group. This study represents the first report of
from South Africa.
Extensive surveys of entomopathogenic nematodes (EPNs) have been conducted globally to identify native species. In Africa, EPN-related research has gained much attention over the past two decades, ...with several surveys having been undertaken in different countries, including Benin, Cameroon, Egypt, Ethiopia, Kenya, Morocco, Nigeria, Rwanda, South Africa and Tanzania. Such surveys have led to the description of 37 EPN species and 16 species of symbiotically associated bacteria being documented from Africa. Whereas South Africa and Egypt have made significant progress in the discovery and identification of EPN, in terms of their symbiotic bacteria and pathogenicity testing against pest insects, in many other African countries, the research is still in its early stages, or is else non-existent. Most research conducted so far has focused on laboratory bioassays, while research on the use of nematodes in more natural environments is scant. The present review provides a comprehensive overview of EPNs and their associated symbiotic bacteria from the African continent. The biological control potential of local EPN isolates against various economically important insect pests in Africa is also discussed.
One Gram-negative, rod-shaped bacterial strain, isolated from an undescribed
Heterorhabditis
entomopathogenic nematode species was characterized to determine its taxonomic position. The 16S rRNA gene ...sequences indicate that it belongs to the class
Gammaproteobacteria
, to the family
Morganellaceae
, to the genus
Photorhabdus
, and likely represents a novel bacterial species. This strain, designated here as CRI-LC
T
, was therefore molecularly, biochemically, and morphologically characterized to describe the novel bacterial species. Phylogenetic reconstructions using 16S rRNA gene sequences show that CRI-LC
T
is closely related to
P. laumondii
subsp
. laumondii
TT01
T
and to
P. laumondii
subsp
. clarkei
BOJ-47
T
. The 16rRNA gene sequences between CRI-LC
T
and
P. laumondii
subsp
. laumondii
TT01
T
are 99.1% identical, and between CRI-LC
T
and
P. laumondii
subsp
. clarkei
BOJ-47
T
are 99.2% identical. Phylogenetic reconstructions using whole genome sequences show that CRI-LC
T
is closely related to
P. laumondii
subsp
. laumondii
TT01
T
and to
P. laumondii
subsp
. clarkei
BOJ-47
T
. Moreover, digital DNA-DNA hybridization (dDDH) values between CRI-LC
T
and its two relative species
P. laumondii
subsp
. laumondii
TT01
T
and
P. laumondii
subsp
. clarkei
BOJ-47
T
are 65% and 63%, respectively. In addition, we observed that average nucleotide identity (ANI) values between CRI-LC
T
and its two relative species
P. laumondii
subsp
. laumondii
TT01
T
and
P. laumondii
subsp
. clarkei
BOJ-47
T
are 95.8% and 95.5%, respectively. These values are below the 70% dDDH and the 95–96% ANI divergence thresholds that delimits prokaryotic species. Based on these genomic divergence values, and the phylogenomic separation, we conclude that CRI-LC
T
represents a novel bacterial species, for which we propose the name
Photorhabdus africana
sp. nov. with CRI-LC
T
(= CCM 9390
T
= CCOS 2112
T
) as the type strain. The following biochemical tests allow to differentiate
P. africana
sp. nov. CRI-LC
T
from other species of the genus, including its more closely related taxa:
β
-Galactosidase, citrate utilization, urease and tryptophan deaminase activities, indole and acetoin production, and glucose and inositol oxidation. Our study contributes to a better understanding of the taxonomy and biodiversity of this important bacterial group with great biotechnological and agricultural potential.
Change in Planococcus citri appearance (A) before infection, and 48h after infection with (B) Heterorhabditis zealandica and (C) and (D) Steinernema yirgalemense. Display omitted
► Planococcus citri ...highly susceptible to entomopathogenic nematodes. ► Nematodes were found to be 15 times less potent at 80% than at 100% humidity. ► Steinernema yirgalemense was found to be three times more potent than Heterorhabditis zealandica.
Planococcus citri, the citrus mealybug, is the most important species of mealybug known to infest citrus in South Africa. Various laboratory bioassays were conducted to determine the potential of entomopathogenic nematodes to control P. citri. Adult female P. citri were screened for susceptibility to six indigenous nematode species. P. citri was found to be most susceptible to Steinernema yirgalemense and Heterorhabditis zealandica, causing 97% and 91% mortality, respectively. The development of nematodes after infecting adult female P. citri showed both H. zealandica and S. yirgalemense were able to complete their life cycles inside the host. Further bioassays illustrated a linear relationship between mealybug mortality and the concentration of nematodes applied, with the highest level of control using a concentration of 80 infective juveniles (IJs)/insect. As nematodes would be used as an above-ground application to control P. citri in citrus orchards, available water is a major limiting factor. Insecticidal activity proved to be dependent on the available surface moisture after nematode application. The water activity (aw) bioassay indicated that S. yirgalemense to be two times more tolerant to lower levels of free water, with aw50=0.96 and aw90=0.99, compared to H. zealandica with aw50=0.98 and aw90=1.0. After application, nematodes have a limited time frame in which to locate and infect hosts, as the level of available free water gradually decreases, as trees dry out. S. yirgalemense proved able to locate and infect P. citri quicker than H. zealandica. Nematode activity was not significantly affected when exposed to 15°C, 20°C and 25°C. IJs were able to infect P. citri at an exposure time as short as half an hour. Results also showed that the first 2–4h post application is the most decisive time for establishing successful infection of mealybugs. This is the first report on the potential use of nematodes for the control of P. citri.
Entomopathogenic fungi (EPF) are cosmopolitan soil borne pathogens that cause epizootics in various insect
orders. EPF isolates of Metarhizium brunneum and M. pinghaense have shown the potential for ...use as biological
agents of important agricultural insect pests. The aim of the current study was to test for the persistence of
M. brunneum and M. pinghaense on apple bark over a period of three weeks, under laboratory conditions. Apple
bark was sprayed with conidial suspensions of both fungi, at a standard infective conidial concentration of
107 conidia/ml. The persistence, or survival, of the conidia on apple bark was measured using codling moth
larvae (CM) (Cydia pomonella) and females of woolly apple aphid (WAA) (Eriosoma lanigerum) as indicator
species. The results showed that conidia of M. pinghaense can induce mortality of insect pests through contact
with an EPF-treated substrate, with mortality of 39% to 82% for WAA over a period of 10 days post application,
and with mortality of 3% to 68% for CM over a period of 7 days, after application to apple bark. Further
evaluation showed that the conidia of M. pinghaense persisted longer on apple bark, up to 63%, than did
M. brunneum, up to 11%, three weeks post application of the conidial suspensions. The study provides insights
into the potential persistence of fungal isolates on apple bark over time post application. Further evaluation of
the persistence of the isolates on apple bark under both glasshouse and field conditions should be conducted.
Phlyctinus callosus (Schönherr) (Coleoptera: Curculionidae), or the banded fruit weevil (BFW), causes damage to the fruits, leaves and roots of deciduous fruits and grapevines in the Western Cape ...province. The control of the BFW can be improved by means of combining entomopathogenic fungi (EPF) and entomopathogenic nematodes (EPNs). The combination of commercial isolates of Beauveria bassiana (Bb1), B. bassiana (Bb2), Metarhizium anisopliae (Ma1) and a South African isolate M. anisopliae (MaEA2), with Steinernema yirgalemense against BFW adults and larvae were evaluated in laboratory trials. Four treatment regimens were used where BFW were exposed to the EPF and the EPN separately, and to a combination of EPF and S. yirgalemense either immediately, 1 week or 2 weeks apart. The combined application of the different EPF isolates with S. yirgalemense resulted in higher mortality of BFW in the laboratory. With the application of S. yirgalemense 7 or 14 days after application of Bb2 and Bb1, 100% mortality for both larvae and adults, was obtained. Synergy was noted with Bb1, Bb2, Ma1 and MaEA2 when each was combined with S. yirgalemense, when applied 7 or 14 days after application of the EPF. Interactions showed that the EPF and S. yirgalemense have an additive effect when applied simultaneously, and a synergistic effect was obtained when applied 7 or 14 days after the application of the different EPF. The results indicate that the combination of EPF and an EPN show potential as an economically viable control strategy.
Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae) is a major phytosanitary pest of citrus in South Africa. Although several management tools exist, control options registered for use ...against the soil-dwelling life stages are limited. Both entomopathogenic nematodes (EPNs) and entomopathogenic fungi have been investigated previously, but they have not been studied in combination against T. leucotreta. Thus, this study investigated the interaction of an indigenous entomopathogenic fungus, Metarhizium pinghaense (previously anisopliae) FCM Ar 23 B3 with three indigenous EPNs: Steinernema yirgalemense 157-C, S. jeffreyense J194 and Heterorhabditis noenieputensis 158-C for increased late instar T. leucotreta larval mortality. Before interaction experiments, lethal concentration (LC) values for each of these microbial agents were determined through dose-response bioassays. Heterorhabditis noenieputensis recorded the highest LC
50
amongst the nematodes (7.11 IJs/50 µl). Using the pre-determined LC
70
value of M. pinghaense and the LC
50
values for each of the nematode species, interaction experiments were conducted. Combinations of the nematodes either applied simultaneously with the fungus or at 24, 48, 72 or 96 h post-fungal application showed predominantly additive interactions. Synergy between the simultaneous application of S. yirgalemense and M. pinghaense was found, whilst the interaction between H. noenieputensis and M. pinghaense applied simultaneously and S. jeffreyense applied 24 h post-fungal application, recorded antagonistic interactions. The use of these agents in combination may therefore have the potential to increase control of T. leucotreta soil-dwelling life stages in citrus orchards across South Africa and should be further investigated.
Summary
Two isolates of Steinernema bertusi n. sp. were separately recovered from Tito, Mpumalanga, and Port Edward, Kwa Zulu Natal, South Africa. In this paper, we describe the isolates as a new ...entomopathogenic nematode (EPN) species using molecular and morphological methodologies. The new species belongs to the cameroonense-clade, which consists of nematodes only isolated from the African continent. Steinernema bertusi n. sp. is characterised by having the longest infective juvenile (IJ) for this clade at 716 (628-814) μm. The IJ is further characterised by a body diam. of 32 (28-36) μm and the pattern for the arrangement of the lateral ridges from head to tail is 2, 4, 5, 4, 2. The first-generation male spicule and gubernaculum length is 82 (72-88) μm and 63 (54-72) μm, respectively. Only 25% of the second-generation males possess a mucron. The first-generation females of S. bertusi n. sp. have a slightly protruding vulva, with double-flapped epiptygmata and a mucron at the posterior end. The new EPN species is most closely related to S. sacchari and is the sixth species to be included in the cameroonense-clade.
Fungus gnats (sciarids) are among the most important pests in undercover crop production. They cause direct physical damage to plant roots, transfer fungal pathogens and create entry points for ...soil-borne plant pathogens. In 2007, Bradysia impatiens, an important fungus gnat pest was found in association with major tree nursery beds in the Mpumalanga and KwaZulu-Natal Provinces of South Africa and was considered invasive. In this study, eight greenhouses were surveyed in the Western Cape Province and B. impatiens was found to be present in all the greenhouses. Similar to the results of the previous studies, a high haplotype diversity was identified for B. impatiens, which may indicate multiple strain introductions into South Africa. Two other fungus gnat species, Lycoriella sativae and Lycoriella ingenua – globally important sciarid pests of mushroom cultures – were identified as new from South Africa. Through a laboratory culture, the life cycle of B. impatiens was observed to be approximately 21 days at 25 °C. Females laid between 100 and 250 eggs. Possible introduction sources include contaminated vegetative material and growth media, thus there maybe need to revise the importation restrictions on these commodities. The identification of two novel species of sciarid pests that have only previously been identified in the Holarctic region could further emphasise this need. However, the recent discovery of such high sciarid diversity could also be due to only a few studies having been previously done on sciarid pests in South Africa.Significance:• The fungus gnat species Bradysia impatiens is reported as present in several undercover crops in the Western Cape Province of South Africa, including cucumbers, tomatoes, chrysanthemums, mushrooms, blueberries and various herbs.• Lycoriella ingenua and Lycoriella sativae were also found to be present in mushroom gardens – the first report of Lycoriella from the Afro-tropical region.• The three fungus gnat species are some of the most important sciarid pests in undercover crop production worldwide. This study highlights the need for more studies on the distribution of these sciarids and possible invasion history.
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