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Sean D Moore - One of the best experts on this subject based on the ideXlab platform.
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biological control of a phytosanitary pest Thaumatotibia leucotreta a case study
International Journal of Environmental Research and Public Health, 2021Co-Authors: Sean D MooreAbstract:Thaumatotibia leucotreta, known as the false codling moth, is a pest of citrus and other crops in sub-Saharan Africa. As it is endemic to this region and as South Africa exports most of its citrus around the world, T. leucotreta has phytosanitary status for most markets. This means that there is zero tolerance for any infestation with live larvae in the market. Consequently, control measures prior to exporting must be exemplary. Certain markets require a standalone postharvest disinfestation treatment for T. leucotreta. However, the European Union accepts a systems approach, consisting of three measures and numerous components within these measures. Although effective preharvest control measures are important under all circumstances, they are most critical where a standalone postharvest disinfestation treatment is not applied, such as within a systems approach. Conventional wisdom may lead a belief that effective chemical control tools are imperative to achieve this end. However, we demonstrate that it is possible to effectively control T. leucotreta to a level acceptable for a phytosanitary market, using only biological control tools. This includes parasitoids, predators, microbial control, semiochemicals, and sterile insects. Simultaneously, on-farm and environmental safety is improved and compliance with the increasing stringency of chemical residue requirements imposed by markets is achieved.
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The role of abiotic factors in the pupation of Thaumatotibia leucotreta Meyrick (Lepidoptera: Tortricidae) in the soil
Agricultural and Forest Entomology, 2018Co-Authors: Claire N. Love, Sean D Moore, Martin HillAbstract:A key focus area of the South African citrus industry is the improved control of the phytosanitary citrus pest Thaumatotibia leucotreta (Lepidoptera: Tortricidae). New methods of control for this pest are continually being sought and the use of entomopathogens as biological control agents of the soil-dwelling life stages of T. leucotreta has shown great promise. Current understanding of T. leucotreta pupation biology, behaviour and survival is limited; thus, improving upon this knowledge would be useful for the biological control of this life stage. Abiotic factors, namely soil texture class, ground cover, soil compaction and soil moisture, were investigated in the laboratory, aiming to determine the effects of these on T. leucotreta pupation variables. The investigations consisted of an examination of the wandering behaviour of larvae prior to pupation site selection, the pupation behaviour after selecting a pupation site, and eclosion biology and success. These abiotic factors often had a limited influence on T. leucotreta pupation. Interesting consistencies included limited wandering behaviour, the shallowness of T. leucotreta pupation and a high eclosion success in sandy loam soils in certain cases. These factors are likely to have both positive and negative implications for entomopathogenic biological control programmes.
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Development of an improved postharvest cold treatment for Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae)
Postharvest Biology and Technology, 2017Co-Authors: Sean D Moore, C. N. Love, Wayne Kirkman, P R Stephen, T. G. Grout, S. Albertyn, V. HattinghAbstract:Abstract Some of South Africa’s fresh produce export markets require postharvest cold treatment of fruit as a phytosanitary risk mitigation treatment for Thaumatotibia leucotreta. Currently, the most widely used treatment entails a 22-d exposure to sub-zero temperatures. This treatment has been primarily based on studies conducted in the 1950s and 1960s. Given the age of the data and subsequent indications that a reduced duration treatment may be effective, a new set of cold treatment efficacy data was generated in this study. The treatments were tested at the probit 9 level, using fourth and fifth instar T. leucotreta , these instars having previously been shown to be the most cold-tolerant. Three time-temperature combinations using sub-zero temperatures were initially evaluated: 20 d, 18 d and 16 d at average temperatures in the range of −0.16 °C to −0.44 °C; and thereafter a time-temperature combination using an above-zero temperature was evaluated: 19 d at an average temperature of 1.05 °C. All treatments were shown to cause mortality at or in excess of the probit 9 level (99.9968% efficacy at the 95% confidence level). These results demonstrate the efficacy of the following potential postharvest cold treatments for T. leucotreta for phytosanitary treatment purposes: 16 d at −0.2 °C, 18 d at −0.4 °C, 20 d at −0.4 °C and 19 d at 1.0 °C, which are recommended for conversion into the following treatment protocols: 16 d at or below −0.1 °C, 18 d at or below −0.3 °C, 20 d at or below −0.3 °C and 19 d at or below 1.2 °C, commencing once all probe readings are at or below: −0.2 °C, −0.4 °C, −0.4 °C and 1.0 °C respectively. Relative to the cold treatments currently in use for T. leucotreta , the shorter duration and in some cases higher temperatures will be less costly and logistically easier to apply with reduced adverse effects in the form of fruit chilling injury and hence trade restriction.
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Partial Cold Treatment of Citrus Fruit for Export Risk Mitigation for Thaumatotibia leucotreta (Lepidoptera: Tortricidae) as Part of a Systems Approach.
Journal of economic entomology, 2016Co-Authors: Sean D Moore, C. N. Love, Wayne Kirkman, S. Albertyn, Julie A. Coetzee, V. HattinghAbstract:Some of South Africa's citrus export markets require mandatory postharvest cold treatment of citrus fruit as a phytosanitary risk mitigation treatment for Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae). An alternative to this may be partial cold treatment as one of the final steps in a systems approach to mitigate phytosanitary risk. Consequently, the efficacy of such partial cold treatments was evaluated. It was first determined that a 2°C cold treatment was significantly more effective against fourth and fifth instars (the most cold-tolerant instars) than treatments at 3°C and 4°C for a duration of 18 d. Secondly, it was determined that 2°C for 18 d and 1°C for 16 d were similarly effective, but both treatments were significantly more effective than 1°C for 14 d. Mean mortality of fourth and fifth instars treated with 2°C for 18 d in seven replicates from four trials was 99.94%. Finally, it was determined that the inability of the majority of surviving larvae to develop to adulthood would further increase the efficacy of a 2°C for 18 d treatment to 99.96%. Inclusion of reproductive nonviability of survivors increased mortality to 99.99%.
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Comparing the Use of Laboratory-Reared and Field-Collected Thaumatotibia leucotreta (Lepidoptera: Tortricidae) Larvae for Demonstrating Efficacy of Postharvest Cold Treatments in Citrus Fruit.
Journal of economic entomology, 2016Co-Authors: Sean D Moore, Wayne Kirkman, S. Albertyn, V. HattinghAbstract:Some of South Africa's export markets require postharvest cold treatment of citrus fruit for phytosanitary risk mitigation for Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae). An alternative to a standalone cold treatment may be a reduced intensity cold treatment as a step in a systems approach. For cold treatment trials, large numbers of larvae are required. Due to recent dramatic improvement of T. leucotreta control in the field, sufficient naturally infested citrus fruit are no longer available. Artificial infestation of fruit is not viable due to rapid decay of the fruit. Consequently, it is necessary to use laboratory-reared T. leucotreta larvae in artificial diet. In trials, field-collected larvae from the Eastern Cape were at least as cold-tolerant as those from other regions. Larvae in Navel oranges showed the median level of susceptibility in a range of citrus types evaluated at 6°C, and their use in trials was considered acceptable due to their greater natural susceptibility to T. leucotreta infestation. We demonstrated that larvae at high density in artificial diet were at least as cold-tolerant as larvae at lower densities. When exposed to 2°C for 18 d or longer, larvae in artificial diet as used in the trials were at least as cold-tolerant as larvae in fruit. Very few surviving larvae from fruit completed development, with no subsequent generation. Consequently, it is considered justifiable to conduct cold-treatment trials with laboratory-reared T. leucotreta larvae in artificial diet without risk of overestimating the effect of cold on feral larvae in citrus fruit. [corrected]
S D Moore - One of the best experts on this subject based on the ideXlab platform.
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an improved systems approach as a phytosanitary measure for Thaumatotibia leucotreta lepidoptera tortricidae in export citrus fruit from south africa
Journal of Economic Entomology, 2020Co-Authors: V. Hattingh, S D Moore, Wayne Kirkman, Sean R. Thackeray, Mat Goddard, Mellissa Peyper, Gary Sharp, Paul J R Cronje, K L PringleAbstract:A systems approach was previously developed for mitigating phytosanitary risk of Thaumatotibia leucotreta (Meyrick) in citrus fruit exported from South Africa, as an alternative to a standalone cold disinfestation treatment. The present study first tested the original systems approach by applying it on a semicommercial scale in 10 Nova mandarin orchards. Fruit were inspected at points in the production, packing, and simulated shipping process, to assess performance of the systems approach. Additional data were obtained from 17 Valencia orange orchards and six packinghouses. In the second part of this study, the systems approach was accordingly revised and improved, consisting of three measures: 1) preharvest controls and measurements and postpicking sampling, inspection, and packinghouse procedures; 2) postpacking sampling and inspection; and 3) shipping conditions. The model quantifying the effectiveness of the systems approach was improved by correcting errors in the original version, updating parameter values and adding a component that provides for comparison with the risk mitigation provided by a standalone disinfestation treatment. Consequently, the maximum potential proportion of fruit that may be infested with live T. leucotreta after application of the improved systems approach is no greater than the proportion of fruit that may be infested after application of a Probit 9 efficacy postharvest disinfestation treatment to fruit with a 2% pretreatment infestation. The probability of a mating pair surviving is also determined. The model enables a priori determination of the required threshold levels for any of the three measures, based on quantification of the other two measures.
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control options for false codling moth Thaumatotibia leucotreta lepidoptera tortricidae in south africa with emphasis on the potential use of entomopathogenic nematodes and fungi
African Entomology, 2018Co-Authors: Antoinette P. Malan, S D Moore, J I Von Diest, Pia AddisonAbstract:False codling moth (FCM), Thaumatotibia leucotreta (Lepidoptera: Tortricidae) is an important pest of various fruit crops in South Africa. Current FCM control strategies include the use of chemical insecticides. However, FCM has developed resistance to some of the insecticides, and stringent chemical residue restrictions have been imposed by some foreign markets. Thus, the demand for high-quality fruit has translated into a need for new, efficient and effective integrated pest management (IPM) strategies. One such strategy is the control of the soil-dwelling life stages of FCM, using entomopathogenic nematodes (EPNs) and entomopathogenic fungi (EPF). Both of the biocontrol agents concerned have individually been shown to be effective against FCM. However, it is possible that, if they are applied simultaneously, a synergistic relationship might be observed between EPNs and EPF that could serve to enhance their efficacy against the target pest. In addition to reviewing previous and current control options against FCM in South African fruit crops, this study investigates the potential for using EPNs and EPF individually, and in combination, as biological control agents against FCM within an IPM system.
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genome analysis and genetic stability of the cryptophlebia leucotreta granulovirus crlegv sa after 15 years of commercial use as a biopesticide
International Journal of Molecular Sciences, 2017Co-Authors: Marcel Van Der Merwe, S D Moore, Caroline Knox, John K Opokudebrah, Michael D Jukes, Martyna Krejmerrabalska, Boguslaw Szewczyk, Lukasz Rabalski, Martin HillAbstract:Thaumatotibia leucotreta Meyrick (Lepidoptera: Tortricidae) is an indigenous pest in southern Africa which attacks citrus fruits and other crops. To control T. leucotreta in South Africa, an integrated pest management (IPM) programme incorporating the baculovirus Cryptophlebia leucotreta granulovirus (CrleGV-SA) as a biopesticide has been implemented. This study investigated the genetic stability of a commercially produced CrleGV-SA product that has been applied in the field since 2000. Seven representative full-genome sequences of the CrleGV-SA isolate spanning a 15-year period were generated and compared with one another. Several open reading frames (ORFs) were identified to have acquired single nucleotide polymorphisms (SNPs) during the 15-year period, with three patterns observed and referred to as “stable”, “reversion”, and “unstable switching”. Three insertion events were also identified, two of which occurred within ORFs. Pairwise multiple alignments of these sequences showed an identity ranging from 99.98% to 99.99%. Concentration-response bioassays comparing samples of CrleGV-SA from 2000 and 2015 showed an increase in virulence toward neonate T. leucotreta larvae. The CrleGV-SA genome sequence generated from the 2015 sample was compared to the Cape Verde reference genome, CrleGV-CV3. Several fusion events were identified between ORFs within these genomes. These sequences shared 96.7% pairwise identity, confirming that CrleGV-SA is a genetically distinct isolate. The results of this study indicate that the genome of CrleGV-SA has remained stable over many years, with implications for its continued use as a biopesticide in the field. Furthermore, the study describes the first complete baculovirus genome to be sequenced with the MinION (Oxford Nanopore, Oxford, UK) platform and the first complete genome sequence of the South African CrleGV isolate.
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Entomopathogenic fungi as control agents of Thaumatotibia leucotreta in citrus orchards: field efficacy and persistence
BioControl, 2016Co-Authors: C. A. Coombes, S D Moore, M. P. Hill, J. F. DamesAbstract:Entomopathogenic fungal isolates Beauveria bassiana (Balsamo) Vuillemin (Hypocreales: Cordycipitaceae) strain G Ar 17 B3 and Metarhizium anisopliae (Metchnikoff) Sorokin (Hypocreales: Clavicipitaceae) strain FCM Ar 23 B3 have been identified as effective control agents of the important citrus pest Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae) wandering fifth instars under laboratory conditions. This study is the first report on the ability of these isolates to persist and reduce T. leucotreta infestation in commercial citrus orchards in South Africa. A reduction in pest infestation of between 28 and 82 % upon trial completion was reported. Both isolates were recovered from soil samples collected five months post-application with high host density and moderate to high soil moisture favouring recovery. Low soil moisture negatively influenced the persistence of both isolates and the control efficiency of B. bassiana . These results provide evidence and support for the future use of these isolates against T. leucotreta thus warranting further investigation.
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host searching and oviposition behaviour of agathis bishopi hymenoptera braconidae a larval parasitoid of false codling moth Thaumatotibia leucotreta lepidoptera tortricidae a potential proxy indicator for fruit infestation
African Entomology, 2016Co-Authors: K Zimba, S D Moore, U Heshula, M. P. HillAbstract:Agathis bishopi (Nixon) (Hymenoptera: Braconidae)is an arrhenotokous larval endoparasitoid of Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae) (Gendall 2007; Hofmeyr et al. 2015) commonly known as false codling moth (FCM), a major pest of citrus in South Africa (Moore et al. 2004; Malan et al. 2011). Under field conditions, A. bishopi was identified attacking more than 34% of FCM larvae in fruit, showing good biocontrol potential (Gendall 2007). Preference by A. bishopi for parasitising the early instars of its concealed host suggests that the parasitoid has strong natural host location ability (Sishuba 2003; Gendall 2007).
P R Stephen - One of the best experts on this subject based on the ideXlab platform.
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Development of an improved postharvest cold treatment for Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae)
Postharvest Biology and Technology, 2017Co-Authors: Sean D Moore, C. N. Love, Wayne Kirkman, P R Stephen, T. G. Grout, S. Albertyn, V. HattinghAbstract:Abstract Some of South Africa’s fresh produce export markets require postharvest cold treatment of fruit as a phytosanitary risk mitigation treatment for Thaumatotibia leucotreta. Currently, the most widely used treatment entails a 22-d exposure to sub-zero temperatures. This treatment has been primarily based on studies conducted in the 1950s and 1960s. Given the age of the data and subsequent indications that a reduced duration treatment may be effective, a new set of cold treatment efficacy data was generated in this study. The treatments were tested at the probit 9 level, using fourth and fifth instar T. leucotreta , these instars having previously been shown to be the most cold-tolerant. Three time-temperature combinations using sub-zero temperatures were initially evaluated: 20 d, 18 d and 16 d at average temperatures in the range of −0.16 °C to −0.44 °C; and thereafter a time-temperature combination using an above-zero temperature was evaluated: 19 d at an average temperature of 1.05 °C. All treatments were shown to cause mortality at or in excess of the probit 9 level (99.9968% efficacy at the 95% confidence level). These results demonstrate the efficacy of the following potential postharvest cold treatments for T. leucotreta for phytosanitary treatment purposes: 16 d at −0.2 °C, 18 d at −0.4 °C, 20 d at −0.4 °C and 19 d at 1.0 °C, which are recommended for conversion into the following treatment protocols: 16 d at or below −0.1 °C, 18 d at or below −0.3 °C, 20 d at or below −0.3 °C and 19 d at or below 1.2 °C, commencing once all probe readings are at or below: −0.2 °C, −0.4 °C, −0.4 °C and 1.0 °C respectively. Relative to the cold treatments currently in use for T. leucotreta , the shorter duration and in some cases higher temperatures will be less costly and logistically easier to apply with reduced adverse effects in the form of fruit chilling injury and hence trade restriction.
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the cryptophlebia leucotreta granulovirus 10 years of commercial field use
Viruses, 2015Co-Authors: S D Moore, Wayne Kirkman, Garth I Richards, P R StephenAbstract:In the last 15 years, extensive work on the Cryptophlebia leucotreta granulovirus (CrleGV) has been conducted in South Africa, initially in the laboratory, but subsequently also in the field. This culminated in the registration of the first CrleGV-based biopesticide in 2004 (hence, the 10 years of commercial use in the field) and the second one three years later. Since 2000, more than 50 field trials have been conducted with CrleGV against the false codling moth, Thaumatotibia leucotreta, on citrus in South Africa. In a representative sample of 13 field trials reported over this period, efficacy (measured by reduction in larval infestation of fruit) ranged between 30% and 92%. Efficacy was shown to persist at a level of 70% for up to 17 weeks after application of CrleGV. This only occurred where the virus was applied in blocks rather than to single trees. The addition of molasses substantially and sometimes significantly enhanced efficacy. It was also established that CrleGV should not be applied at less than ~2 × 1013 OBs per ha in order to avoid compromised efficacy. As CrleGV-based products were shown to be at least as effective as chemical alternatives, persistent and compatible with natural enemies, their use is recommended within an integrated program for control of T. leucotreta on citrus and other crops.
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The Cryptophlebia leucotreta Granulovirus—10 Years of Commercial Field Use
Viruses, 2015Co-Authors: Sean D Moore, G I Richards, Wayne Kirkman, P R StephenAbstract:In the last 15 years, extensive work on the Cryptophlebia leucotreta granulovirus (CrleGV) has been conducted in South Africa, initially in the laboratory, but subsequently also in the field. This culminated in the registration of the first CrleGV-based biopesticide in 2004 (hence, the 10 years of commercial use in the field) and the second one three years later. Since 2000, more than 50 field trials have been conducted with CrleGV against the false codling moth, Thaumatotibia leucotreta, on citrus in South Africa. In a representative sample of 13 field trials reported over this period, efficacy (measured by reduction in larval infestation of fruit) ranged between 30% and 92%. Efficacy was shown to persist at a level of 70% for up to 17 weeks after application of CrleGV. This only occurred where the virus was applied in blocks rather than to single trees. The addition of molasses substantially and sometimes significantly enhanced efficacy. It was also established that CrleGV should not be applied at less than ~2 × 1013 OBs per ha in order to avoid compromised efficacy. As CrleGV-based products were shown to be at least as effective as chemical alternatives, persistent and compatible with natural enemies, their use is recommended within an integrated program for control of T. leucotreta on citrus and other crops.
Ochou Germain Ochou - One of the best experts on this subject based on the ideXlab platform.
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caracteristiques de l evolution spatio temporelle de Thaumatotibia leucotreta meyrick lepidoptera tortricidae dans les zones de production cotonniere de cote d ivoire
European Scientific Journal ESJ, 2018Co-Authors: Germain Ochou Ochou, Pitou Woklin Euloge Kone, Malanno Kouakou, Kouadio Kra Norbert Bini, Dagnogo Mamadou, Koffi Christophe Kobenan, Charles Sekpa Dekoula, Roland Didi, Acka Emmanuel Dick, Ochou Germain OchouAbstract:In order to update knowledge on the spatio-temporal evolution of Thaumatotibia leucotreta, the geographical areas and seasons of predilection of adult and larval populations have been studied in the last six years from 2012 to 2017. Monitoring of natural adult populations revealed that populations were more abundant in the southern cotton production area as compared to the north. A Monitoring of larval infestations showed that infestations occurred on cotton at the end of august (0.10 larvae/100 bolls) and increased gradually during october-november (0.31 to 0.93 larvae/100 bolls), indicating a strong relationship between evolution of adult and larval populations and cotton phenology. Early sowings exhibited higher infestation levels (0.87 larvae/100 bolls). Annual variations of pest infestation levels increased from years to years, from 0.23 to 0.49 larvae/100 bolls over the study period. Mapping the geographic distribution of infestations showed highest pest densities in the southern zone, mostly in surrounding areas of Boron (1.52 larvae/100 bolls). With regard to the emerging status of T. leucotreta over recent years, the current pyrethroid resistance management strategy deserves to be improved on the basis of the pest geographic and seasonal profiles.
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efficacite de la confusion sexuelle contre Thaumatotibia cryptophlebia leucotreta lepidoptera tortricidae dans les exploitations cotonnieres en cote d ivoire
International Journal of Biological and Chemical Sciences, 2017Co-Authors: Germain Ochou Ochou, Pitou Woklin Euloge Kone, Gouzou Juste Roland Didi, Malanno Kouakou, Kouadio Kra Norbert Bini, Dagnogo Mamadou, Ochou Germain OchouAbstract:Le faux ver rose Thaumatotibia leucotreta (Lepidoptera : Tortricidae) est une espece carpophage du cotonnier. En Cote d’Ivoire, elle est difficilement controlee par les traitements insecticides et ses infestations sont en forte croissance au cours de ces dix dernieres annees. En vue de mettre en place une strategie de gestion efficace, il a ete evalue une methode de confusion sexuelle contre le ravageur a l’aide d’une formulation de pheromone composee de 240 mg de matieres actives (166,8 mg de E-8 - dodecenyl acetate + 70,8 mg de Z-8 - dodecenyl acetate + 2,4 mg de E/Z-8 – dodecenol) par diffuseur. Un dispositif en milieu paysan a mis en comparaison des parcelles paysannes non traitees et des parcelles traitees a differentes doses de pheromone de confusion. Les doses minimales de 24 a 48 g m.a/ha ont permis de reduire de facon significative sur une duree de plus de 4 mois l’abondance des populations mâles naturelles de T. leucotreta ainsi que les taux d’attaques sur les capsules vertes et les niveaux d’infestations larvaires. Aussi les parcelles paysannes ayant recu la confusion sexuelle ont-elles assure un meilleur rendement coton graine que les parcelles non traitees. La presente etude a permis de definir les modalites d'application de la confusion sexuelle contre T. leucotreta dans un contexte de petites exploitations cotonnieres. Cette methode constitue donc un recours pour ameliorer le programme de protection phytosanitaire en vigueur en Cote d’Ivoire. Mots cles : Confusion sexuelle, cotonnier, Cote d’Ivoire, gestion integree, Thaumatotibia leucotreta.
Martin Hill - One of the best experts on this subject based on the ideXlab platform.
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The role of abiotic factors in the pupation of Thaumatotibia leucotreta Meyrick (Lepidoptera: Tortricidae) in the soil
Agricultural and Forest Entomology, 2018Co-Authors: Claire N. Love, Sean D Moore, Martin HillAbstract:A key focus area of the South African citrus industry is the improved control of the phytosanitary citrus pest Thaumatotibia leucotreta (Lepidoptera: Tortricidae). New methods of control for this pest are continually being sought and the use of entomopathogens as biological control agents of the soil-dwelling life stages of T. leucotreta has shown great promise. Current understanding of T. leucotreta pupation biology, behaviour and survival is limited; thus, improving upon this knowledge would be useful for the biological control of this life stage. Abiotic factors, namely soil texture class, ground cover, soil compaction and soil moisture, were investigated in the laboratory, aiming to determine the effects of these on T. leucotreta pupation variables. The investigations consisted of an examination of the wandering behaviour of larvae prior to pupation site selection, the pupation behaviour after selecting a pupation site, and eclosion biology and success. These abiotic factors often had a limited influence on T. leucotreta pupation. Interesting consistencies included limited wandering behaviour, the shallowness of T. leucotreta pupation and a high eclosion success in sandy loam soils in certain cases. These factors are likely to have both positive and negative implications for entomopathogenic biological control programmes.
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genome analysis and genetic stability of the cryptophlebia leucotreta granulovirus crlegv sa after 15 years of commercial use as a biopesticide
International Journal of Molecular Sciences, 2017Co-Authors: Marcel Van Der Merwe, S D Moore, Caroline Knox, John K Opokudebrah, Michael D Jukes, Martyna Krejmerrabalska, Boguslaw Szewczyk, Lukasz Rabalski, Martin HillAbstract:Thaumatotibia leucotreta Meyrick (Lepidoptera: Tortricidae) is an indigenous pest in southern Africa which attacks citrus fruits and other crops. To control T. leucotreta in South Africa, an integrated pest management (IPM) programme incorporating the baculovirus Cryptophlebia leucotreta granulovirus (CrleGV-SA) as a biopesticide has been implemented. This study investigated the genetic stability of a commercially produced CrleGV-SA product that has been applied in the field since 2000. Seven representative full-genome sequences of the CrleGV-SA isolate spanning a 15-year period were generated and compared with one another. Several open reading frames (ORFs) were identified to have acquired single nucleotide polymorphisms (SNPs) during the 15-year period, with three patterns observed and referred to as “stable”, “reversion”, and “unstable switching”. Three insertion events were also identified, two of which occurred within ORFs. Pairwise multiple alignments of these sequences showed an identity ranging from 99.98% to 99.99%. Concentration-response bioassays comparing samples of CrleGV-SA from 2000 and 2015 showed an increase in virulence toward neonate T. leucotreta larvae. The CrleGV-SA genome sequence generated from the 2015 sample was compared to the Cape Verde reference genome, CrleGV-CV3. Several fusion events were identified between ORFs within these genomes. These sequences shared 96.7% pairwise identity, confirming that CrleGV-SA is a genetically distinct isolate. The results of this study indicate that the genome of CrleGV-SA has remained stable over many years, with implications for its continued use as a biopesticide in the field. Furthermore, the study describes the first complete baculovirus genome to be sequenced with the MinION (Oxford Nanopore, Oxford, UK) platform and the first complete genome sequence of the South African CrleGV isolate.
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Citrus thrips, Scirtothrips aurantii (Thysanoptera: Thripidae), damage and infestation in the presence of molasses
Crop Protection, 2015Co-Authors: Sean R. Thackeray, Matthew C. Parkinson, Sean D Moore, Martin HillAbstract:Abstract The Cryptophlebia leucotreta granulovirus (CrleGV) is used for control of false codling moth (FCM), Thaumatotibia leucotreta (Lepidoptera: Tortricidae), on citrus in South Africa. The virus is applied with molasses, which has been shown to improve its efficacy against FCM. However, little is known about the influence of molasses used as a spray additive on citrus thrips, Scirtothrips aurantii , a major cosmetic pest of citrus fruit. The aim of this study was to determine if molasses influences the occurrence of, and damage to fruit, caused by Scitothrips aurantii . A field trial was conducted that included trees sprayed with different molasses concentrations and control trees at four sites in the Eastern Cape Province of South Africa. Scirtothrips aurantii population sizes were quantified through monitoring with yellow sticky traps, a scouting protocol and a damage assessment after application of the respective treatments. Numbers of adult S. aurantii caught with yellow sticky traps were high for all study sites but there was no significant difference among treatments within sites (P > 0.05). Scouting also revealed high S. aurantii numbers combined with low numbers of predatory mites. However, there was no significant difference in the number of adult or larval S. aurantii present on fruit among treatments within sites (P > 0.05). A damage evaluation, conducted one month after the study, showed no significant difference among treatments (P > 0.05). This study has shown that the inclusion of molasses, applied as a medium cover spray, does not result in increased S. aurantii infestation or damage and can thus be included in the CrleGV applications.
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Comparison of the Biology of Geographically Distinct Populations of the Citrus Pest, Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae), in South Africa
African Entomology, 2014Co-Authors: John K. Opoku-debrah, Caroline Knox, Martin Hill, Sean D MooreAbstract:Baculovirus biopesticides are an important component of integrated pest management programmes worldwide. One such example is the Cryptophlebia leucotreta granulovirus (CrleGV) which is used for the control of false codling moth, Thaumatotibia (= Cryptophlebia) leucotreta (Meyrick) (Lepidoptera: Tortricidae), a pest of citrus and other crops in South Africa. A potential problem associated with constant application of viral biopesticides is the differing susceptibility to the virus observed between different geographic populations of the insect host. This could be related to a number of factors, including biological performance and fitness of the target insect population. This study compared a variety of phenotypic traits between geographically distinct T. leucotreta populations collected from the Addo, Marble Hall, Citrusdal and Nelspruit regions of South Africa, and reared under laboratory conditions for several generations. Traits including pupal mass, female fecundity, egg hatch, pupal survival, adult eclosion and developmental time were used as parameters to measure biological performance and fitness. Insects from the Citrusdal region of the Western Cape exhibited significantly lower pupal mass, female fecundity, egg hatch, pupal survival, adult eclosion and the longest duration in larval and pupal development compared to the other colonies investigated. This is the first study to report differences in the performance of laboratory reared T. leucotreta from different geographic locations, and the findings may have important implications for the application of viral biopesticides for the control of this pest in South Africa.
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Thaumatotibia leucotreta and the Navel orange: ovipositional preferences and host susceptibility
Journal of Applied Entomology, 2014Co-Authors: C. N. Love, Martin Hill, Sean D MooreAbstract:False codling moth, Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae), presents a significant threat to the South African citrus industry. To limit income loss due to direct larval damage or from fruit rejection due to the phytosanitary status of this pest, additional pre-harvest control techniques are required for Navel oranges, which are known to be susceptible to T. leucotreta damage. A number of Navel orange cultivars have been developed, and differences in female T. leucotreta ovipositional preference and susceptibility of cultivars to larval penetration are known to exist. Navel orange cultivars were grouped according to time of maturity (early, mid- and late season). Female T. leucotreta were subjected to choice and no-choice tests with these cultivars, measured by oviposition. Host susceptibility was tested by allowing neonate T. leucotreta larvae to penetrate the different Navel cultivars. In the early maturing group, Fischer Navels were least preferred for oviposition and the least susceptible to larval penetration. The mid- and late season maturing groupings showed limited differences in oviposition preference, although host susceptibility did appear to be an important factor in assessing the vulnerability of fruit to T. leucotreta. Despite being widely planted in South Africa, the mid-season Palmer Navels were highly susceptible to larval penetration, while for the late season cultivars, Cambria and Glen Ora Late were the least susceptible to T. leucotreta. As a result of these laboratory trials, it is recommended that farmers increase cultivation of Fischer Navels as the principal early season cultivar, avoid Palmer Navels in favour of other mid-season maturing cultivars and give preference to the late maturing Cambria and Glen Ora Late cultivars, to limit T. leucotreta damage.