An assessment of the status of psylloid species (Hemiptera: Psylloidea) as potential pests of commercial citrus in southern Africa: implications for pest management
- Authors: Moagi, Raynold
- Date: 2024-10-11
- Subjects: Citrus Diseases and pests South Africa , Candidatus Liberibacter , Psylloidea , Polymerase chain reaction , Insect trapping Equipment and supplies , Pests Control
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/464417 , vital:76509
- Description: Psylloids (Hemiptera: Psylloidea), constitute a group of plant sap-sucking insects, some of which are economically significant pests in different ecosystems due to their potential to transmit Gram-negative bacteria, such as the Candidatus Liberibacter species. The African citrus triozid (ACT), Trioza erytreae (Del Guercio), which transmits African citrus greening and the Asian citrus psyllid (ACP), Diaphorina citri Kuwayama, which transmits Asian citrus greening are significant threats to citrus. Asian citrus psyllid poses a global economic threat due to its ability to vector “Candidatus Liberibacter asiaticus” (CLas), which can rapidly kill citrus trees. However, both ACP and CLas are currently not present in southern Africa but are present in East and West Africa. In the Afrotropical region, 71 triozid species are known to occur and approximately 41 described Diaphorina species in southern Africa. Currently, two indigenous Diaphorina species, Diaphorina punctulata and Diaphorina zebrana have been documented to feed on citrus. There is a significant knowledge gap regarding the ecological roles of other indigenous psylloid species occurring within the citrus environments. Therefore, this study aimed to: (i) determine the diversity and community structure of psylloid species in citrus environments, and (ii) their host ranges through DNA analysis of gut contents to determine if they fed on citrus. Field surveys were carried out across 12 distinct commercial citrus environments across Limpopo and Mpumalanga provinces between 2022 and 2023. Psylloids were collected using yellow sticky traps and an insect sweep-net. Collected psylloid specimens were preserved in 70% ethanol vials and identified to the lowest possible taxonomic level (i.e. genus or species) using both published and unpublished dichotomous identification keys. Furthermore, citrus leaf samples were collected from the same plants on which psylloids were found in the orchards. Genomic DNA (gDNA) was extracted from both leaf and psylloid samples using two different DNA extraction methods. To confirm if citrus DNA could be detected in the psylloid guts, all leaf gDNA samples were initially amplified using the rbcLaF/R primer pair, targeting a 530-bp region of the chloroplast rbcL gene through the polymerase chain reaction (PCR). Lastly, gut content analysis was performed on 11 psylloid species using the same primer pair through PCR to detect citrus DNA. A total of 4,900 psylloids belonging to five families (i.e. Aphalaridae, Carsidaridae, Liviidae, Psyllidae and Triozidae), 19 genera and 47 species, were collected in citrus environments. More psylloids were recorded in Limpopo (3,754) than in Mpumalanga (1,146). The most abundant species were Pauropsylla trichaeta (1,680), followed by Diaphorina punctulata (466), Trioza erytreae (426), Diaphorina virgata (371), Euryconus sp. (358), Cacopsylla sp. (311), Retroacizzia mopanei (263), Acizzia russellae-group (240), Acizzia sp.3 (216) and Acizzia sp.2 (140). Yellow sticky traps captured 3,265 psylloids in citrus orchards, while an insect sweep-net collected 1,635 psylloids (477 from citrus orchards and 1,158 from adjacent natural vegetation). Data from the insect sweep-net revealed that 22 psylloid species were recorded on citrus. In comparison, nine psylloid species were found on Vachellia spp. and unidentified plant species separately, whereas six, three and two psylloid species were recorded on marula, Ficus sp. and mopane, respectively. The abundance, richness and community structure of psylloids differed significantly between the collection methods, provinces and among plant species. The rbcLaF/R primer pair amplified all citrus leaf gDNA samples, producing amplicons of the targeted 530-bp size. The PCR analysis of 11 psylloid species showed that the rbcLaF/R primer pair amplified plant DNA, with PCR-amplified plant DNA samples producing amplicons between 500-bp and 750-bp in the gut contents of five psyllid species: Diaphorina punctulata, Diaphorina virgata, Diaphorina zebrana, Euryconus sp. and Trioza erytreae. However, the targeted 530-bp plant DNA region was only amplified from the gut contents of Euryconus sp. and Diaphorina punctulata. This study documented psylloid diversity and community structure within commercial citrus environments. The findings indicate that the community of psylloids was diverse in citrus environments, with yellow sticky traps being more effective in monitoring different psyllid species within these environments. Furthermore, the PCR analysis detected citrus DNA in the gut contents of Euryconus sp. and Diaphorina punctulata, suggesting that they could be nibbling on citrus when their specific or main host-plants adjacent to citrus orchards are depleted. However, these insects do not lay their eggs or complete their life cycle on citrus, further confirming that citrus is not their host-plant. Thus, further studies, including Sanger sequencing of PCR-amplified plant DNA, are recommended to confirm the ingested plant species, and host-specific testing including infection trials needs to be conducted. , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2024
- Full Text:
- Date Issued: 2024-10-11
- Authors: Moagi, Raynold
- Date: 2024-10-11
- Subjects: Citrus Diseases and pests South Africa , Candidatus Liberibacter , Psylloidea , Polymerase chain reaction , Insect trapping Equipment and supplies , Pests Control
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/464417 , vital:76509
- Description: Psylloids (Hemiptera: Psylloidea), constitute a group of plant sap-sucking insects, some of which are economically significant pests in different ecosystems due to their potential to transmit Gram-negative bacteria, such as the Candidatus Liberibacter species. The African citrus triozid (ACT), Trioza erytreae (Del Guercio), which transmits African citrus greening and the Asian citrus psyllid (ACP), Diaphorina citri Kuwayama, which transmits Asian citrus greening are significant threats to citrus. Asian citrus psyllid poses a global economic threat due to its ability to vector “Candidatus Liberibacter asiaticus” (CLas), which can rapidly kill citrus trees. However, both ACP and CLas are currently not present in southern Africa but are present in East and West Africa. In the Afrotropical region, 71 triozid species are known to occur and approximately 41 described Diaphorina species in southern Africa. Currently, two indigenous Diaphorina species, Diaphorina punctulata and Diaphorina zebrana have been documented to feed on citrus. There is a significant knowledge gap regarding the ecological roles of other indigenous psylloid species occurring within the citrus environments. Therefore, this study aimed to: (i) determine the diversity and community structure of psylloid species in citrus environments, and (ii) their host ranges through DNA analysis of gut contents to determine if they fed on citrus. Field surveys were carried out across 12 distinct commercial citrus environments across Limpopo and Mpumalanga provinces between 2022 and 2023. Psylloids were collected using yellow sticky traps and an insect sweep-net. Collected psylloid specimens were preserved in 70% ethanol vials and identified to the lowest possible taxonomic level (i.e. genus or species) using both published and unpublished dichotomous identification keys. Furthermore, citrus leaf samples were collected from the same plants on which psylloids were found in the orchards. Genomic DNA (gDNA) was extracted from both leaf and psylloid samples using two different DNA extraction methods. To confirm if citrus DNA could be detected in the psylloid guts, all leaf gDNA samples were initially amplified using the rbcLaF/R primer pair, targeting a 530-bp region of the chloroplast rbcL gene through the polymerase chain reaction (PCR). Lastly, gut content analysis was performed on 11 psylloid species using the same primer pair through PCR to detect citrus DNA. A total of 4,900 psylloids belonging to five families (i.e. Aphalaridae, Carsidaridae, Liviidae, Psyllidae and Triozidae), 19 genera and 47 species, were collected in citrus environments. More psylloids were recorded in Limpopo (3,754) than in Mpumalanga (1,146). The most abundant species were Pauropsylla trichaeta (1,680), followed by Diaphorina punctulata (466), Trioza erytreae (426), Diaphorina virgata (371), Euryconus sp. (358), Cacopsylla sp. (311), Retroacizzia mopanei (263), Acizzia russellae-group (240), Acizzia sp.3 (216) and Acizzia sp.2 (140). Yellow sticky traps captured 3,265 psylloids in citrus orchards, while an insect sweep-net collected 1,635 psylloids (477 from citrus orchards and 1,158 from adjacent natural vegetation). Data from the insect sweep-net revealed that 22 psylloid species were recorded on citrus. In comparison, nine psylloid species were found on Vachellia spp. and unidentified plant species separately, whereas six, three and two psylloid species were recorded on marula, Ficus sp. and mopane, respectively. The abundance, richness and community structure of psylloids differed significantly between the collection methods, provinces and among plant species. The rbcLaF/R primer pair amplified all citrus leaf gDNA samples, producing amplicons of the targeted 530-bp size. The PCR analysis of 11 psylloid species showed that the rbcLaF/R primer pair amplified plant DNA, with PCR-amplified plant DNA samples producing amplicons between 500-bp and 750-bp in the gut contents of five psyllid species: Diaphorina punctulata, Diaphorina virgata, Diaphorina zebrana, Euryconus sp. and Trioza erytreae. However, the targeted 530-bp plant DNA region was only amplified from the gut contents of Euryconus sp. and Diaphorina punctulata. This study documented psylloid diversity and community structure within commercial citrus environments. The findings indicate that the community of psylloids was diverse in citrus environments, with yellow sticky traps being more effective in monitoring different psyllid species within these environments. Furthermore, the PCR analysis detected citrus DNA in the gut contents of Euryconus sp. and Diaphorina punctulata, suggesting that they could be nibbling on citrus when their specific or main host-plants adjacent to citrus orchards are depleted. However, these insects do not lay their eggs or complete their life cycle on citrus, further confirming that citrus is not their host-plant. Thus, further studies, including Sanger sequencing of PCR-amplified plant DNA, are recommended to confirm the ingested plant species, and host-specific testing including infection trials needs to be conducted. , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2024
- Full Text:
- Date Issued: 2024-10-11
Biology and management of the fruit piercing moth Serrodes partita in citrus orchards
- Authors: Mushore, Tapiwa Gift
- Date: 2024-10-11
- Subjects: Baculoviruses , Moths Monitoring , Pests Control , Insect traps , Citrus Diseases and pests South Africa Kat River Valley , Catapult moth
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/466792 , vital:76779 , DOI https://doi.org/10.21504/10962/466792
- Description: The fruit-piercing moth, Serrodes partita (Fabricius) (Lepidoptera: Erebidae), is a polyphagous, multivoltine pest of citrus. This insect has a distinct geographical separation between its larval and adult stages, each with different feeding patterns. During the larval stage, it primarily acts as a forest defoliator, feeding mostly on Jacket plum, Pappea capensis Eckl. & Zeyh. (Sapindaceae). In contrast, the adult stage of this moth feeds on both tropical and subtropical fruit, including citrus and can cause serious economic losses. The adult moth uses its sclerotised proboscis to pierce the skin of ripening or ripe fruit, from which it extracts the juice. This piercing action initiates a fermentation process within the fruit, attracting other secondary-feeding moths, commonly referred to as fruit-sucking moths. As a result of the feeding activity, the affected fruit eventually rot, drop to the ground, and become unsuitable for the market. Serrodes partita exhibits an outbreak life strategy, reoccurring every 5 to 10 years. In South Africa's Eastern Cape Province, specifically in the Upper Kat River Valley, citrus growers have expressed concerns about the impact of this moth on soft citrus (Satsumas and Clementines). This raises the possibility of a shift in the population dynamics of S. partita, where these occurrences become more frequent and less sporadic. Such a trend poses a significant threat to fruit arboriculture in the Eastern Cape region. Currently, there are limited management strategies available for managing fruit-piecing moths. The use of pesticides is not a feasible option for ripe or nearly ripe fruit, and is ineffective against the adult moth. Alternative control methods, such as orchard netting and light barriers, either come with high costs or are impractical for large-scale citrus production. Given the limited range of management options, combined with the moth's tendency for sudden outbreaks, citrus growers find themselves without effective means to manage this pest. The objective of this study was, therefore, to investigate the biology of S. partita and explore various control options to effectively manage this pest. Research focused on the biology and laboratory rearing of larval stages of S. partita. The flight behaviour, feeding patterns, and preferences of adult S. partita within citrus orchards were also explored. The aim was to elucidate key fundamental aspects, including whether the same population frequents a particular orchard, and if infestations within orchards exhibit a specific direction. Lure type and lure presentation method trials were conducted to determine the most effective lure and trap design. Seasonal monitoring of S. partita in soft citrus orchards was conducted over three years to determine its outbreak status in the Committee’s Drift area and the role of weather variables in the activity of the moth. Damage assessments were also conducted alongside monitoring to determine the level of damage inflicted by S. partita. Natural enemies associated with S. partita were explored to determine the prevalence and causes of mortality in late instars during laboratory rearing. Rearing S. partita on an artificial diet was unsuccessful despite several modifications. The moth, however, completed its entire life cycle on its natural host, P. capensis in the laboratory. The total life cycle from egg to adult took 80.7 ± 3.6 days, the larval stage lasted 52.3 ± 2.8 days, and the pupal stage lasted 25.8 ± 3.6 days at 21°C. The investigation into the biology of S. partita also brought attention to the most susceptible stages of its growth, with high mortality rates recorded among neonates and late instars. The findings of the study revealed directional patterns of moth infestations, with higher numbers observed at the orchard's periphery leading towards natural vegetation. This raises the prospect of using sacrificial rows on the edge of a citrus orchard to concentrate moth feeding damage during outbreak years. Using a mark and recapture technique, the study showed that a relatively small proportion (4.5 %) of moths tended to revisit the same orchard. The moths strongly preferred damaged fruit (85 %) over undamaged fruit. Visible damage (rotting symptoms) typically became apparent within 3 to 5 days. Satsumas had a higher number of feeding scars (2.1) than Clementines (1.08), highlighting their susceptibility. The study also established that, on average, pierced soft citrus fruit takes about four days to display symptoms of decay. Synthetic proprietary Australian lures were ineffective at attracting the moth, whereas fresh bananas proved to be a successful lure. Furthermore, the addition of both Agar and Super absorbent polymer showed promise as thickening agents to enhance the longevity of fresh bananas in traps. The effectiveness of various trap designs was compared, including the funnel trap, delta trap, bucket trap, and circular trap, in capturing fruit-feeding moths. The funnel trap performed best as it captured the most moths, followed by the delta trap, Lynfield trap and disc trap, respectively. Additionally, an electronic enhancement to the funnel trap, incorporating a zapper element, improved efficiency. However, efforts to exploit both visual and olfactory cues through the inclusion of an Ultraviolet (UV) light component did not improve its effectiveness. No extensive outbreaks were recorded during the study; however, population variations of S. partita populations were recorded. Annual trends showed two population peaks, with the first peak recorded from December to March, while the second peak was recorded from April to July. The activity of the moths also differed across different months, with the highest peaks recorded in May, while no moths were recorded from August to November. Both cultivar type and farm location did not influence the occurrence of the moth. Meanwhile cumulative weather parameters (rainfall, temperature and humidity) from the four months prior to occurrence influenced the activity of S. partita. Temperature determined the timing of the outbreak, while rainfall determined the magnitude of the outbreak. Damage assessment showed very low fruit damage by S. partita throughout the monitoring period. Varying levels of infestation by a tachinid fly, 4 % and 35 %, were recorded for 2021 and 2022, respectively. The tachinid parasitoid could not be identified at the species level. A novel baculovirus, tentatively classified as S. partita NPV (SepaNPV), was identified as the larval mortality causative agent. This study enhanced our understanding of S. partita's biology and population dynamics, providing valuable insights for developing effective management strategies against this economically impactful citrus pest. Future research should focus on refining control measures and addressing the challenges of the adult moth's elusive nature. , Thesis (PhD) -- Faculty of Science, Zoology and Entomology, 2024
- Full Text:
- Date Issued: 2024-10-11
- Authors: Mushore, Tapiwa Gift
- Date: 2024-10-11
- Subjects: Baculoviruses , Moths Monitoring , Pests Control , Insect traps , Citrus Diseases and pests South Africa Kat River Valley , Catapult moth
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/466792 , vital:76779 , DOI https://doi.org/10.21504/10962/466792
- Description: The fruit-piercing moth, Serrodes partita (Fabricius) (Lepidoptera: Erebidae), is a polyphagous, multivoltine pest of citrus. This insect has a distinct geographical separation between its larval and adult stages, each with different feeding patterns. During the larval stage, it primarily acts as a forest defoliator, feeding mostly on Jacket plum, Pappea capensis Eckl. & Zeyh. (Sapindaceae). In contrast, the adult stage of this moth feeds on both tropical and subtropical fruit, including citrus and can cause serious economic losses. The adult moth uses its sclerotised proboscis to pierce the skin of ripening or ripe fruit, from which it extracts the juice. This piercing action initiates a fermentation process within the fruit, attracting other secondary-feeding moths, commonly referred to as fruit-sucking moths. As a result of the feeding activity, the affected fruit eventually rot, drop to the ground, and become unsuitable for the market. Serrodes partita exhibits an outbreak life strategy, reoccurring every 5 to 10 years. In South Africa's Eastern Cape Province, specifically in the Upper Kat River Valley, citrus growers have expressed concerns about the impact of this moth on soft citrus (Satsumas and Clementines). This raises the possibility of a shift in the population dynamics of S. partita, where these occurrences become more frequent and less sporadic. Such a trend poses a significant threat to fruit arboriculture in the Eastern Cape region. Currently, there are limited management strategies available for managing fruit-piecing moths. The use of pesticides is not a feasible option for ripe or nearly ripe fruit, and is ineffective against the adult moth. Alternative control methods, such as orchard netting and light barriers, either come with high costs or are impractical for large-scale citrus production. Given the limited range of management options, combined with the moth's tendency for sudden outbreaks, citrus growers find themselves without effective means to manage this pest. The objective of this study was, therefore, to investigate the biology of S. partita and explore various control options to effectively manage this pest. Research focused on the biology and laboratory rearing of larval stages of S. partita. The flight behaviour, feeding patterns, and preferences of adult S. partita within citrus orchards were also explored. The aim was to elucidate key fundamental aspects, including whether the same population frequents a particular orchard, and if infestations within orchards exhibit a specific direction. Lure type and lure presentation method trials were conducted to determine the most effective lure and trap design. Seasonal monitoring of S. partita in soft citrus orchards was conducted over three years to determine its outbreak status in the Committee’s Drift area and the role of weather variables in the activity of the moth. Damage assessments were also conducted alongside monitoring to determine the level of damage inflicted by S. partita. Natural enemies associated with S. partita were explored to determine the prevalence and causes of mortality in late instars during laboratory rearing. Rearing S. partita on an artificial diet was unsuccessful despite several modifications. The moth, however, completed its entire life cycle on its natural host, P. capensis in the laboratory. The total life cycle from egg to adult took 80.7 ± 3.6 days, the larval stage lasted 52.3 ± 2.8 days, and the pupal stage lasted 25.8 ± 3.6 days at 21°C. The investigation into the biology of S. partita also brought attention to the most susceptible stages of its growth, with high mortality rates recorded among neonates and late instars. The findings of the study revealed directional patterns of moth infestations, with higher numbers observed at the orchard's periphery leading towards natural vegetation. This raises the prospect of using sacrificial rows on the edge of a citrus orchard to concentrate moth feeding damage during outbreak years. Using a mark and recapture technique, the study showed that a relatively small proportion (4.5 %) of moths tended to revisit the same orchard. The moths strongly preferred damaged fruit (85 %) over undamaged fruit. Visible damage (rotting symptoms) typically became apparent within 3 to 5 days. Satsumas had a higher number of feeding scars (2.1) than Clementines (1.08), highlighting their susceptibility. The study also established that, on average, pierced soft citrus fruit takes about four days to display symptoms of decay. Synthetic proprietary Australian lures were ineffective at attracting the moth, whereas fresh bananas proved to be a successful lure. Furthermore, the addition of both Agar and Super absorbent polymer showed promise as thickening agents to enhance the longevity of fresh bananas in traps. The effectiveness of various trap designs was compared, including the funnel trap, delta trap, bucket trap, and circular trap, in capturing fruit-feeding moths. The funnel trap performed best as it captured the most moths, followed by the delta trap, Lynfield trap and disc trap, respectively. Additionally, an electronic enhancement to the funnel trap, incorporating a zapper element, improved efficiency. However, efforts to exploit both visual and olfactory cues through the inclusion of an Ultraviolet (UV) light component did not improve its effectiveness. No extensive outbreaks were recorded during the study; however, population variations of S. partita populations were recorded. Annual trends showed two population peaks, with the first peak recorded from December to March, while the second peak was recorded from April to July. The activity of the moths also differed across different months, with the highest peaks recorded in May, while no moths were recorded from August to November. Both cultivar type and farm location did not influence the occurrence of the moth. Meanwhile cumulative weather parameters (rainfall, temperature and humidity) from the four months prior to occurrence influenced the activity of S. partita. Temperature determined the timing of the outbreak, while rainfall determined the magnitude of the outbreak. Damage assessment showed very low fruit damage by S. partita throughout the monitoring period. Varying levels of infestation by a tachinid fly, 4 % and 35 %, were recorded for 2021 and 2022, respectively. The tachinid parasitoid could not be identified at the species level. A novel baculovirus, tentatively classified as S. partita NPV (SepaNPV), was identified as the larval mortality causative agent. This study enhanced our understanding of S. partita's biology and population dynamics, providing valuable insights for developing effective management strategies against this economically impactful citrus pest. Future research should focus on refining control measures and addressing the challenges of the adult moth's elusive nature. , Thesis (PhD) -- Faculty of Science, Zoology and Entomology, 2024
- Full Text:
- Date Issued: 2024-10-11
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