South Africa is the 13th largest producer and second largest exporter of citrus fruit globally. The false codling moth, Thaumatotibia leucotreta, and the fruit flies, Ceratitis capitata, C. rosa and ...Bactrocera dorsalis, can potentially infest citrus fruit and therefore pose a phytosanitary risk for export markets. Consequently, a wide range of postharvest phytosanitary treatments for disinfestation of citrus fruit from these pests have been investigated. These include cold treatments, irradiation, fumigation, heat treatments, and combinations of some of these. Due to the potential phytotoxic effects of all these treatments, the use of a systems approach that depends on two or more independent measures for acceptable phytosanitary risk mitigation is a preferable option. To date, the only postharvest disinfestation treatments used commercially for T. leucotreta and fruit flies for South African citrus, are stand-alone cold treatments and partial cold treatments, as a component in a multi-tiered systems approach. Research on development of novel and improvement of existing postharvest measures continues as a high priority. This includes postharvest detection technologies, in addition to treatment technologies.
Fruit flies (Diptera: Tephritidae) comprise species of agricultural and economic importance. Five such fruit fly species are known to affect commercial fruit production and export in South Africa: ...Ceratitis capitata, Ceratitis cosyra, Ceratitis rosa, Ceratitis quilicii, and Bactrocera dorsalis. Management practices for these pests include monitoring, application of pest control products, post-harvest disinfestation measures and inspection of consignments both prior to shipment and at ports of entry. In activities relating to monitoring and inspection, accurate identification of these pests to species level is required. While morphological keys for adult stages of these fruit fly species have been well developed, morphological keys for earlier life stages remain problematic. In instances where closely related species cannot be reliably distinguished morphologically, there is a need for molecular tools to assist in identifying these five fruit fly species during surveillance practices, where sequencing-based approaches would be beneficial. Two complete mitochondrial genomes were assembled for each fruit fly species investigated using high throughput sequencing data generated in this study. A single primer set was designed to amplify a region between tRNA.sup.ile and tRNA.sup.met. The amplicon consists of a partial segment of tRNA.sup.ile, intergenic region I (tRNA.sup.ile - tRNA.sup.gln), the complete sequence of tRNA.sup.gln, intergenic region II (tRNA.sup.gln - tRNA.sup.met), and a partial segment of tRNA.sup.met. PCR amplicons were generated for 20 specimens of each species, five of which were colony adult males, five colony larvae, and 10 wild, trap-collected specimens. Upon analysis of the amplicon, intergenic region I was identified as the most informative region, allowing for unambiguous identification of the five fruit fly species. The similarity in intergenic region II was too high between C. rosa and C. quilicii for accurate differentiation of these species. The identity of all five fruit flies investigated in this study can be determined through sequence analysis of the mitochondrial intergenic regions. Within the target amplicon, intergenic region I (tRNA.sup.ile - tRNA.sup.gln) shows interspecific variation sufficient for species differentiation based on multiple sequence alignment. The variation in the length of intergenic region I is proposed as a potential tool for accurately identifying these five fruit flies in South Africa.
Abstract
The fruit fly (Diptera: Tephritidae) species,
Ceratitis capitata
,
Ceratitis cosyra
,
Ceratitis rosa
,
Ceratitis quilicii
, and
Bactrocera dorsalis
are of economic importance in South ...Africa. These agricultural pests cause extensive damage to a range of commercially produced fruit, primarily for export. These pests are of phytosanitary significance, and their presence in fruit-producing regions in South Africa has led to restrictions in export trade of fresh produce. Accurate identification of these flies, particularly at immature stages intercepted in fruit consignments originating from South Africa, is essential but remains an ongoing challenge. A rapid and accurate identification assay to differentiate these five species is needed for inspection and pest surveillance. High throughput sequencing data were generated for each of the five fruit fly species, and five sets of species-specific primers were designed for use in a multiplex PCR. Each primer set amplifies an amplicon of a different size for each species allowing for accurate identification. PCR sensitivity tests demonstrate that the limit of detection for this assay is 10 ng and 4 ng of DNA when extracted from larvae and adult specimens, respectively. The assay developed can be applied in fruit inspection and survey activities within the country and at ports of entry.
Ceratitis FAR is an African species complex comprising insect pests of great economic interest and obscure species limits. Here, we report the mitochondrial genomes of two members of the FAR complex, ...namely Ceratitis rosa and the recently characterized Ceratitis quilicii. A phylogenetic analysis based on PCGs of available Tephritidae mitogenomes is presented. The current mitochondrial sequences from the FAR complex could contribute toward the resolution of phylogenetic relationships and species limits within this taxonomically challenging group, which is also an important issue for the development of environment-friendly and species-specific control methods, such as the sterile insect technique (SIT).
Bactrocera dorsalis (Hendel) is a new fruit fly pest of some fruit types in the north and north eastern areas of South Africa. In order to determine whether existing cold disinfestation treatment ...schedules for an indigenous fruit fly pest: Ceratitis capitata (Wiedemann) would be effective for B. dorsalis, cold tolerances of four immature stages of the two species were compared. Studies were done in an artificial carrot-based larval diet. The developmental rates of the immature stages of the two species in the carrot-based larval diet were first determined at a constant temperature of 26°C. The developmental times for eggs and three larval stages were found to be similar for the two species. Incubation times of both species after egg inoculation were determined to be 0, 3, 4, and 6 d for obtaining egg, first larval, second larval, and third larval stages respectively for the cold treatment. At a test temperature of –0.6°C, mortality rates of C. capitata eggs, first instars, second instars, and third instars were lower than those of B. dorsalis. These results demonstrate that the current cold treatment schedules for disinfestation of C. capitata can be used as equally or more efficacious treatments for B. dorsalis.
The efficacy of an existing cold disinfestation postharvest treatment targeting Ceratitis capitata (Wiedemann) in citrus was determined for the marula fly, Ceratitis cosyra (Walker). The cold ...tolerances of C. capitata and C. cosyra were first quantified in artificial diet at 3.5 °C at different exposure periods for up to 18 days. Ceratitis capitata was found to be more cold tolerant than C. cosyra. At 3.5 °C, the duration to achieve 99.9968% mortality was calculated to be 11.57 days for C. capitata and 9.10 days for C. cosyra. Under an existing C. capitata cold treatment schedule at 1 °C for 14 days, the conditions required for complete mortality of the third larval stage of C. cosyra in orange, Citrus sinensis (L.) Osbeck cv. Valencia, were then determined. No survivors of C. cosyra in oranges were recorded beyond 11 days of cold treatment at 1 °C. The efficacy of this C. capitata treatment for disinfestation of C. cosyra was thereafter confirmed in large scale trials in Valencia oranges. In the large-scale trial at the lowest mean temperature of 1.19 °C for 14 days, there were no survivors from a total of 85 490 treated C. cosyra third instars in oranges. Since C. capitata was shown to be more cold tolerant than C. cosyra and a large scale test demonstrated at least 99.9965% efficacy after 14 days at 1.19 °C, compared with the established effective C. capitata cold treatment of 14 days at 1.11 °C, cold disinfestation treatments for C. capitata should be at least equally effective against C. cosyra.
Fast and effective monitoring and surveillance techniques are crucial for the swift implementation of control methods to prevent the spread of Huanglongbing, a devastating citrus disease, and its ...invasive psyllid vector, Asian citrus psyllid, Diaphorina citri, into South Africa, as well as to control the native vector, African citrus triozid, Trioza erytreae. Monitoring for citrus psyllid pests can be improved by using semiochemical odorants to augment already visually attractive yellow sticky traps. However, environmental variables such as temperature and humidity could influence odorant release rates. Five field cages were used to test the ability of a selection of odorants to improve yellow sticky trap efficacy in capturing citrus psyllids. Environmental effects on odorant loss from the dispensers were also investigated. The odorants that most improved yellow sticky trap captures in field cages were then tested under open field conditions alongside lower concentrations of those same lures. Gas chromatography-mass spectrometry was used to calculate odorant release rates as well as to determine if any contamination occurred under field conditions. None of the odorants under field cage or field conditions significantly improved psyllid capture on yellow sticky traps. Temperature influenced odorant loss, and release rate from polyethylene bulbs decreased over time. Based on these results, the use of unbaited yellow sticky traps seems to be the most effective method for monitoring of Huanglongbing vectors.
Frugivorous insects use visual, chemical and tactile cues to find a suitable host for oviposition. However, these cues can vary greatly among fruit cultivars and condition, changing their ...susceptibility to fruit fly oviposition. The aims of this study were to (1) determine the effects of ripeness stage and damage on oviposition propensity by sexually mature, mated female oriental fruit flies, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae), on five citrus types (species and cultivars) under choice and no‐choice conditions and (2) describe the oviposition behaviour of B. dorsalis on ripe fruit of the same five citrus types that were either damaged or undamaged under no‐choice conditions. All tests were conducted in the laboratory. The citrus types tested were Citrus sinensis (L.) Osbeck cv Delta Valencia orange, Citrus sinensis (L.) Osbeck cv Glen Ora Late navel orange, Citrus limon (L) (Burm.f.) cv Eureka lemon, Citrus paradisi (Macfad.) cv Star Ruby grapefruit and Citrus reticulata (Blanco) cv Nadorcott mandarin. Peel physical properties and essential oil composition were determined for each citrus type and stage. Oviposition propensity of B. dorsalis was significantly greater on damaged citrus but was not correlated with fruit diameter, peel thickness, oil gland density or oil gland size. A total of 45 aromatic compounds were found to be significant between the five cultivars investigated, and 6 of 11 compounds were significantly associated with over‐ripe fruits. Bactrocera dorsalis spent a significantly greater proportion of time ovipositing in damaged citrus and showed higher aggression when oviposition occurred in undamaged citrus. These results suggest that the removal of damaged and fallen fruit is important for controlling this pest in citrus orchards.
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