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Papers by Tshima Ramakuwela
Journal of Nematology, 2021
Soil pH affects the availability of nutrients, which impacts plant growth and development. Simila... more Soil pH affects the availability of nutrients, which impacts plant growth and development. Similarly, soil pH may also influence microorganisms in the soil, either beneficial or nonbeneficial. One such group of beneficial microorganisms is entomopathogenic nematodes (EPN), parasites of soil-inhabiting insects. Entomopathogenic nematodes have a number of attributes that make them good alternatives to chemical insecticides. The objective of this study was to investigate pH tolerance of 11 steinernematids and six heterorhabditids post exposure to different pH levels. Entomopathogenic nematode populations were exposed to varying pH levels (pH2 to pH11) made up from two different chemical solutions (ammonium-acetate and citrate-phosphate). Entomopathogenic nematode populations are expected to have varying tolerance to different pH levels. The highest infective juvenile survival was obtained from pH3 to pH10 in citrate-phosphate, where all populations displayed >50% survival. Steinerne...
Journal of Applied and Natural Science, 2015
Experiment was conducted to study the effect of different treatments on preservation of strawberr... more Experiment was conducted to study the effect of different treatments on preservation of strawberry pulp at ambient and low storage temperature condition. The samples were pasteurized at 100°C for 15 minutes (T1), sodium benzoate 250 ppm (T2) and sodium benzoate 500 ppm (T3). The respective samples were stored for two months at room (25±5°C) and low (7±2°C) temperature conditions and reducing sugars; total sugar and sensory evaluation were recorded at three days of interval period. The results showed that the total sugar (%) increased in pulp sample maximum in T6 (5.9%) and minimum in T1 (4.8%), the maximum value regarding reducing sugars was recorded in T6 (4.9%) and minimum in T1 (1.4%) after 60th days of storage. However, reducing sugars and total sugar decreased in the stored pulp at room temperature and spoiled completely on 18th day of storage. The acceptability of organoleptic score decrease with the duration of storage in both ambient and low temperature. Among different trea...
Biological Control, 2019
Pecan (Carya illinoinensis) is an important crop in the USA, which produces approximately 55% of ... more Pecan (Carya illinoinensis) is an important crop in the USA, which produces approximately 55% of the world's pecans. Several insect pests and various plant diseases reduce crop yield directly destroying nutmeats, or indirectly through effects on foliage and shucks, reducing photosynthesis. Beauveria bassiana is a well-studied, commercialized fungal entomopathogen that when applied inundatively is an effective biocontrol agent against certain pecan pests. In addition to being used in inundative biocontrol, B. bassiana can exist as an endophyte in many plant species and has been shown in some cases to reduce pest damage when present as an endophyte. The potential for B. bassiana to exist as an endophyte in pecan had not been explored previously. We tested whether B. bassiana could endophytically colonize pecan seedlings by seed soaking, seed coating and soil drenching. Results indicated that B. bassiana became established in the roots, leaves and stems of pecan seedlings. Establishment was verified using molecular techniques as well as completing Koch's postulates on the re-isolated fungus, infecting two susceptible insect hosts (Galleria mellonella and Tenebrio molitor) and a target pest (Curculio caryae). Subsequently we explored whether the established endophytic fungus suppressed two pecan aphid species. In a leaf-disc assay, populations of two pecan aphids (Melanocallis caryaefoliae and Monellia caryella) were reduced when placed on leaves of pecan that were colonized endophytically with B. bassiana, relative to control leaves. Our study demonstrates the ability to establish endophytic B. bassiana in pecan and the potential to apply this capability in pecan pest management. Additional research is needed to determine the utility of the endophytic approach against various insect and plant pathogens and to measure efficacy under field conditions.
Nematology, 2016
Steinernema beitlechemi n. sp. is a new species of entomopathogenic nematode isolated from soil s... more Steinernema beitlechemi n. sp. is a new species of entomopathogenic nematode isolated from soil samples collected in Bethlehem, Free State province, South Africa. The infective juveniles of S. beitlechemi n. sp. are characterised by a body length of 696 (606-768) μm, position of nerve ring of 96 (86-105) μm from the head and lateral fields with six ridges (i.e., seven lines) in mid-body. First-generation males of S. beitlechemi n. sp. can be distinguished by a spicule length of 93 (88-100) μm and 12 pairs of genital papillae. First-generation females have a moderately protruding vulva and a rounded tail tip bearing one spine-like projection. The new species is further characterised by sequences of the ITS and partial 28S regions of the ribosomal DNA. Phylogenetic analyses show S. beitlechemi n. sp. as a member of a strongly supported monophyletic clade with three other African species: S. sacchari, S. cameroonense and S. nyetense.
Low-cost mass production of entomopathogenic nematodes (EPNs) is an important prerequisite toward... more Low-cost mass production of entomopathogenic nematodes (EPNs) is an important prerequisite towards their successful commercialisation. This study evaluated six low-cost solid substrate media for in vitro mass production of Steinernema innovationi. Cost analysis was undertaken and an estimated retail price was calculated. This was then compared to the costs of commercial EPN products currently on the market. The highest yield of infective juveniles (IJs) was obtained from a medium containing a puree of house fly, Musca domestica, larvae + 0.15 g canola oil, (781,678 ± 221 IJs/5 g medium). This medium also had the lowest number of adults remaining in the medium and dead IJs (<10%) at the time of harvest (Day 28). The estimated retail price (R243.27 per 50 million IJs) for S. innovationi produced with our solid culture system was considerably lower than the market price for other Steinernema species products sold by E∼nema, BASF corporation, Koppert, BioBest and Natural Insect Contr...
Biological Control
Pecan (Carya illinoinensis) is an important crop in the USA, which produces approximately 55% of ... more Pecan (Carya illinoinensis) is an important crop in the USA, which produces approximately 55% of the world's pecans. Several insect pests and various plant diseases reduce crop yield directly destroying nutmeats, or indirectly through effects on foliage and shucks, reducing photosynthesis. Beauveria bassiana is a well-studied, commercialized fungal entomopathogen that when applied inundatively is an effective biocontrol agent against certain pecan pests. In addition to being used in inundative biocontrol, B. bassiana can exist as an endophyte in many plant species and has been shown in some cases to reduce pest damage when present as an endophyte. The potential for B. bassiana to exist as an endophyte in pecan had not been explored previously. We tested whether B. bassiana could endophytically colonize pecan seedlings by seed soaking, seed coating and soil drenching. Results indicated that B. bassiana became established in the roots, leaves and stems of pecan seedlings. Establishment was verified using molecular techniques as well as completing Koch's postulates on the re-isolated fungus, infecting two susceptible insect hosts (Galleria mellonella and Tenebrio molitor) and a target pest (Curculio caryae). Subsequently we explored whether the established endophytic fungus suppressed two pecan aphid species. In a leaf-disc assay, populations of two pecan aphids (Melanocallis caryaefoliae and Monellia caryella) were reduced when placed on leaves of pecan that were colonized endophytically with B. bassiana, relative to control leaves. Our study demonstrates the ability to establish endophytic B. bassiana in pecan and the potential to apply this capability in pecan pest management. Additional research is needed to determine the utility of the endophytic approach against various insect and plant pathogens and to measure efficacy under field conditions.
Journal of Nematology
Soil pH affects the availability of nutrients, which impacts plant growth and development. Simila... more Soil pH affects the availability of nutrients, which impacts plant growth and development. Similarly, soil pH may also influence microorganisms in the soil, either beneficial or nonbeneficial. One such group of beneficial microorganisms is entomopathogenic nematodes (EPN), parasites of soil-inhabiting insects. Entomopathogenic nematodes have a number of attributes that make them good alternatives to chemical insecticides. The objective of this study was to investigate pH tolerance of 11 steinernematids and six heterorhabditids post exposure to different pH levels. Entomopathogenic nematode populations were exposed to varying pH levels (pH2 to pH11) made up from two different chemical solutions (ammonium-acetate and citrate-phosphate). Entomopathogenic nematode populations are expected to have varying tolerance to different pH levels. The highest infective juvenile survival was obtained from pH3 to pH10 in citrate-phosphate, where all populations displayed >50% survival. Steinernema carpocapsae populations had >90% survival at pH3 to pH11 in citrate-phosphate solutions. Overall, the steinernematids had a higher survival range in ammonium-acetate pH solutions compared with the heterorhabditids. Moreover, Steinernema spp., S. carpocapsae (ScCxrd, ScAll, and ScItalian) and S. riobrave showed consistently higher survival in both acidic and alkaline solutions, when compared to the other steinernematids, suggesting that they may be applied in both acidic and alkaline soils. These findings can be of use when selecting EPNs for biological control purposes in the two countries, respectively.
Journal of Nematology
Entomopathogenic nematode species perform differently under different environmental conditions; t... more Entomopathogenic nematode species perform differently under different environmental conditions; therefore, the authors investigated the biological and environmental characteristics that could optimize performance of Steinernema innovationi. The authors studied the effect of temperature on infectivity and reproduction, the foraging behavior and host range. Thermal activity was optimal between 22 and 25°C. Highest infective juvenile (IJ) yields in last instar Galleria mellonella were observed at 22°C (333,014 IJs/g) and 25°C (354,165 IJs/g). An average of 26% of the IJs infected G. mellonella larvae at depths of 15 cm within 24 hr. Steinernema innovationi IJs raised greater than 95% of their body off the substrate and moved in a circular pattern, but did not jump. The hosts, Acheta domesticus, Chilo partellus, and Plutella xylostella showed the least susceptibility. All other hosts, [Eldana saccharina, Sesamia calamistis, Tenebrio molitor, G. mellonella, Cydia pomonella] suffered 100% larval mortality. Pupal mortality ranged from 47 to 68%. An LC50 and LC70 of 3 and 31 IJs/larva, respectively, were calculated for Agrotis ipsilon. The results indicate that S. innovationi is adapted to moderate temperatures. Furthermore, to the author's knowledge this is the first report of a nematode (particularly from 'glaseri group') that shows cruiser-type behavior in movement, but also nictates.
Indian Journal of Entomology, 2012
Journal of Nematology
A new species of entomopathogenic nematode (EPN), Steinernema biddulphi n. sp., was isolated from... more A new species of entomopathogenic nematode (EPN), Steinernema biddulphi n. sp., was isolated from a maize field in Senekal, Free State Province of South Africa. Morphological and molecular studies indicated the distinctness of S. biddulphi n. sp. from other Steinernema species. Steinernema biddulphi n. sp. is characterized IJs with average body length of 663 mm (606-778 mm), lateral fields with six ridges in mid-body region forming the formula 2,6,2. Excretory pore located anterior to mid-pharynx (D% = 46). Hyaline layer occupies approximately half of tail length. Male spicules slightly to moderately curved, with a sharp tip and golden brown in color. The first generation of males lacking a mucron on the tail tip while the second generation males with a short filamentous mucron. Genital papillae with 11 pairs and one unpaired preanal papilla. The new species is further characterized by sequences of the internal transcribed spacer (ITS) and partial 28S regions (D2-D3) of the ribosomal DNA (rDNA). Phylogenetic data show that S. biddulphi n. sp. belongs to the ''bicornutum'' clade within the Steinernematidae family.
Journal of Nematology, 2021
Soil pH affects the availability of nutrients, which impacts plant growth and development. Simila... more Soil pH affects the availability of nutrients, which impacts plant growth and development. Similarly, soil pH may also influence microorganisms in the soil, either beneficial or nonbeneficial. One such group of beneficial microorganisms is entomopathogenic nematodes (EPN), parasites of soil-inhabiting insects. Entomopathogenic nematodes have a number of attributes that make them good alternatives to chemical insecticides. The objective of this study was to investigate pH tolerance of 11 steinernematids and six heterorhabditids post exposure to different pH levels. Entomopathogenic nematode populations were exposed to varying pH levels (pH2 to pH11) made up from two different chemical solutions (ammonium-acetate and citrate-phosphate). Entomopathogenic nematode populations are expected to have varying tolerance to different pH levels. The highest infective juvenile survival was obtained from pH3 to pH10 in citrate-phosphate, where all populations displayed >50% survival. Steinerne...
Journal of Applied and Natural Science, 2015
Experiment was conducted to study the effect of different treatments on preservation of strawberr... more Experiment was conducted to study the effect of different treatments on preservation of strawberry pulp at ambient and low storage temperature condition. The samples were pasteurized at 100°C for 15 minutes (T1), sodium benzoate 250 ppm (T2) and sodium benzoate 500 ppm (T3). The respective samples were stored for two months at room (25±5°C) and low (7±2°C) temperature conditions and reducing sugars; total sugar and sensory evaluation were recorded at three days of interval period. The results showed that the total sugar (%) increased in pulp sample maximum in T6 (5.9%) and minimum in T1 (4.8%), the maximum value regarding reducing sugars was recorded in T6 (4.9%) and minimum in T1 (1.4%) after 60th days of storage. However, reducing sugars and total sugar decreased in the stored pulp at room temperature and spoiled completely on 18th day of storage. The acceptability of organoleptic score decrease with the duration of storage in both ambient and low temperature. Among different trea...
Biological Control, 2019
Pecan (Carya illinoinensis) is an important crop in the USA, which produces approximately 55% of ... more Pecan (Carya illinoinensis) is an important crop in the USA, which produces approximately 55% of the world's pecans. Several insect pests and various plant diseases reduce crop yield directly destroying nutmeats, or indirectly through effects on foliage and shucks, reducing photosynthesis. Beauveria bassiana is a well-studied, commercialized fungal entomopathogen that when applied inundatively is an effective biocontrol agent against certain pecan pests. In addition to being used in inundative biocontrol, B. bassiana can exist as an endophyte in many plant species and has been shown in some cases to reduce pest damage when present as an endophyte. The potential for B. bassiana to exist as an endophyte in pecan had not been explored previously. We tested whether B. bassiana could endophytically colonize pecan seedlings by seed soaking, seed coating and soil drenching. Results indicated that B. bassiana became established in the roots, leaves and stems of pecan seedlings. Establishment was verified using molecular techniques as well as completing Koch's postulates on the re-isolated fungus, infecting two susceptible insect hosts (Galleria mellonella and Tenebrio molitor) and a target pest (Curculio caryae). Subsequently we explored whether the established endophytic fungus suppressed two pecan aphid species. In a leaf-disc assay, populations of two pecan aphids (Melanocallis caryaefoliae and Monellia caryella) were reduced when placed on leaves of pecan that were colonized endophytically with B. bassiana, relative to control leaves. Our study demonstrates the ability to establish endophytic B. bassiana in pecan and the potential to apply this capability in pecan pest management. Additional research is needed to determine the utility of the endophytic approach against various insect and plant pathogens and to measure efficacy under field conditions.
Nematology, 2016
Steinernema beitlechemi n. sp. is a new species of entomopathogenic nematode isolated from soil s... more Steinernema beitlechemi n. sp. is a new species of entomopathogenic nematode isolated from soil samples collected in Bethlehem, Free State province, South Africa. The infective juveniles of S. beitlechemi n. sp. are characterised by a body length of 696 (606-768) μm, position of nerve ring of 96 (86-105) μm from the head and lateral fields with six ridges (i.e., seven lines) in mid-body. First-generation males of S. beitlechemi n. sp. can be distinguished by a spicule length of 93 (88-100) μm and 12 pairs of genital papillae. First-generation females have a moderately protruding vulva and a rounded tail tip bearing one spine-like projection. The new species is further characterised by sequences of the ITS and partial 28S regions of the ribosomal DNA. Phylogenetic analyses show S. beitlechemi n. sp. as a member of a strongly supported monophyletic clade with three other African species: S. sacchari, S. cameroonense and S. nyetense.
Low-cost mass production of entomopathogenic nematodes (EPNs) is an important prerequisite toward... more Low-cost mass production of entomopathogenic nematodes (EPNs) is an important prerequisite towards their successful commercialisation. This study evaluated six low-cost solid substrate media for in vitro mass production of Steinernema innovationi. Cost analysis was undertaken and an estimated retail price was calculated. This was then compared to the costs of commercial EPN products currently on the market. The highest yield of infective juveniles (IJs) was obtained from a medium containing a puree of house fly, Musca domestica, larvae + 0.15 g canola oil, (781,678 ± 221 IJs/5 g medium). This medium also had the lowest number of adults remaining in the medium and dead IJs (<10%) at the time of harvest (Day 28). The estimated retail price (R243.27 per 50 million IJs) for S. innovationi produced with our solid culture system was considerably lower than the market price for other Steinernema species products sold by E∼nema, BASF corporation, Koppert, BioBest and Natural Insect Contr...
Biological Control
Pecan (Carya illinoinensis) is an important crop in the USA, which produces approximately 55% of ... more Pecan (Carya illinoinensis) is an important crop in the USA, which produces approximately 55% of the world's pecans. Several insect pests and various plant diseases reduce crop yield directly destroying nutmeats, or indirectly through effects on foliage and shucks, reducing photosynthesis. Beauveria bassiana is a well-studied, commercialized fungal entomopathogen that when applied inundatively is an effective biocontrol agent against certain pecan pests. In addition to being used in inundative biocontrol, B. bassiana can exist as an endophyte in many plant species and has been shown in some cases to reduce pest damage when present as an endophyte. The potential for B. bassiana to exist as an endophyte in pecan had not been explored previously. We tested whether B. bassiana could endophytically colonize pecan seedlings by seed soaking, seed coating and soil drenching. Results indicated that B. bassiana became established in the roots, leaves and stems of pecan seedlings. Establishment was verified using molecular techniques as well as completing Koch's postulates on the re-isolated fungus, infecting two susceptible insect hosts (Galleria mellonella and Tenebrio molitor) and a target pest (Curculio caryae). Subsequently we explored whether the established endophytic fungus suppressed two pecan aphid species. In a leaf-disc assay, populations of two pecan aphids (Melanocallis caryaefoliae and Monellia caryella) were reduced when placed on leaves of pecan that were colonized endophytically with B. bassiana, relative to control leaves. Our study demonstrates the ability to establish endophytic B. bassiana in pecan and the potential to apply this capability in pecan pest management. Additional research is needed to determine the utility of the endophytic approach against various insect and plant pathogens and to measure efficacy under field conditions.
Journal of Nematology
Soil pH affects the availability of nutrients, which impacts plant growth and development. Simila... more Soil pH affects the availability of nutrients, which impacts plant growth and development. Similarly, soil pH may also influence microorganisms in the soil, either beneficial or nonbeneficial. One such group of beneficial microorganisms is entomopathogenic nematodes (EPN), parasites of soil-inhabiting insects. Entomopathogenic nematodes have a number of attributes that make them good alternatives to chemical insecticides. The objective of this study was to investigate pH tolerance of 11 steinernematids and six heterorhabditids post exposure to different pH levels. Entomopathogenic nematode populations were exposed to varying pH levels (pH2 to pH11) made up from two different chemical solutions (ammonium-acetate and citrate-phosphate). Entomopathogenic nematode populations are expected to have varying tolerance to different pH levels. The highest infective juvenile survival was obtained from pH3 to pH10 in citrate-phosphate, where all populations displayed >50% survival. Steinernema carpocapsae populations had >90% survival at pH3 to pH11 in citrate-phosphate solutions. Overall, the steinernematids had a higher survival range in ammonium-acetate pH solutions compared with the heterorhabditids. Moreover, Steinernema spp., S. carpocapsae (ScCxrd, ScAll, and ScItalian) and S. riobrave showed consistently higher survival in both acidic and alkaline solutions, when compared to the other steinernematids, suggesting that they may be applied in both acidic and alkaline soils. These findings can be of use when selecting EPNs for biological control purposes in the two countries, respectively.
Journal of Nematology
Entomopathogenic nematode species perform differently under different environmental conditions; t... more Entomopathogenic nematode species perform differently under different environmental conditions; therefore, the authors investigated the biological and environmental characteristics that could optimize performance of Steinernema innovationi. The authors studied the effect of temperature on infectivity and reproduction, the foraging behavior and host range. Thermal activity was optimal between 22 and 25°C. Highest infective juvenile (IJ) yields in last instar Galleria mellonella were observed at 22°C (333,014 IJs/g) and 25°C (354,165 IJs/g). An average of 26% of the IJs infected G. mellonella larvae at depths of 15 cm within 24 hr. Steinernema innovationi IJs raised greater than 95% of their body off the substrate and moved in a circular pattern, but did not jump. The hosts, Acheta domesticus, Chilo partellus, and Plutella xylostella showed the least susceptibility. All other hosts, [Eldana saccharina, Sesamia calamistis, Tenebrio molitor, G. mellonella, Cydia pomonella] suffered 100% larval mortality. Pupal mortality ranged from 47 to 68%. An LC50 and LC70 of 3 and 31 IJs/larva, respectively, were calculated for Agrotis ipsilon. The results indicate that S. innovationi is adapted to moderate temperatures. Furthermore, to the author's knowledge this is the first report of a nematode (particularly from 'glaseri group') that shows cruiser-type behavior in movement, but also nictates.
Indian Journal of Entomology, 2012
Journal of Nematology
A new species of entomopathogenic nematode (EPN), Steinernema biddulphi n. sp., was isolated from... more A new species of entomopathogenic nematode (EPN), Steinernema biddulphi n. sp., was isolated from a maize field in Senekal, Free State Province of South Africa. Morphological and molecular studies indicated the distinctness of S. biddulphi n. sp. from other Steinernema species. Steinernema biddulphi n. sp. is characterized IJs with average body length of 663 mm (606-778 mm), lateral fields with six ridges in mid-body region forming the formula 2,6,2. Excretory pore located anterior to mid-pharynx (D% = 46). Hyaline layer occupies approximately half of tail length. Male spicules slightly to moderately curved, with a sharp tip and golden brown in color. The first generation of males lacking a mucron on the tail tip while the second generation males with a short filamentous mucron. Genital papillae with 11 pairs and one unpaired preanal papilla. The new species is further characterized by sequences of the internal transcribed spacer (ITS) and partial 28S regions (D2-D3) of the ribosomal DNA (rDNA). Phylogenetic data show that S. biddulphi n. sp. belongs to the ''bicornutum'' clade within the Steinernematidae family.