Addition of Selected Plant-Derived Semiochemicals to Yellow Sticky Traps Does Not Improve Citrus Psyllid Captures.

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.

Efficacy of an existing Ceratitis capitata (Diptera: Tephritidae) cold disinfestation treatment schedule for Ceratitis cosyra.

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.

Larval and adult diet affect phenotypic plasticity in thermal tolerance of the marula fly, Ceratitis cosyra (Walker) (Diptera: Tephritidae).

Introduction: Temperature fluctuations are important for the distribution and survival of insects. Rapid hardening, a type of phenotypic plasticity, is an adaptation that can help individuals better tolerate lethal temperatures because of earlier exposure to a sublethal but stressful temperature. Nutrition and sex are also known to influence a species ability to tolerate thermal stress. This study determined the effects of larval diet, adult diet, sex and hardening on the thermal tolerance of Ceratitis cosyra (Walker) (Diptera: Tephritidae) at lower and upper lethal temperatures. Methods: Larvae were raised on either an 8% torula yeast (high) or a 1% torula yeast (low) larval diet and then introduced to one of three dietary regimes as adults for thermal tolerance and hardening assays: no adult diet, sugar only, or sugar and hydrolysed yeast diet. Flies of known weight were then either heat- or cold-hardened for 2 hours before being exposed to a potentially lethal high or low temperature, respectively. Results: Both nutrition and hardening as well as their interaction affected C. cosyra tolerance of stressful temperatures. However, this interaction was dependent on the type of stress, with nutrient restriction and possible adult dietary compensation resulting in improved cold temperature resistance only. Discussion: The ability of the insect to both compensate for a low protein larval diet and undergo rapid cold hardening after a brief exposure to sublethal cold temperatures even when both the larva and the subsequent adult fed on low protein diets indicates that C. cosyra have a better chance of survival in environments with extreme temperature variability, particularly at low temperatures. However, there appears to be limitations to the ability of C. cosyra to cold harden and the species may be more at risk from long term chronic effects than from any exposure to acute thermal stress.

Utilisation of a mitochondrial intergenic region for species differentiation of fruit flies (Diptera: Tephritidae) in South Africa.

BACKGROUND: 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. RESULTS: 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 tRNAile and tRNAmet. The amplicon consists of a partial segment of tRNAile, intergenic region I (tRNAile - tRNAgln), the complete sequence of tRNAgln, intergenic region II (tRNAgln - tRNAmet), and a partial segment of tRNAmet. 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. CONCLUSION: 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 (tRNAile - tRNAgln) 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.

A multiplex PCR assay for the identification of fruit flies (Diptera: Tephritidae) of economic importance in South Africa.

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.

Cold Tolerance of Immature Stages of Ceratitis capitata and Bactrocera dorsalis (Diptera: Tephritidae).

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.

Τhe complete mitochondrial genomes of Ceratitis rosa and Ceratitis quilicii, members of the Ceratitis FAR species complex (Diptera: Tephritidae).

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).

Effects of male lure dispensers and trap types for monitoring of Ceratitis capitata and Bactrocera dorsalis (Diptera: Tephritidae).

BACKGROUND: Attractant-based trapping is used in the establishment of pest-free areas and areas of low pest prevalence for fruit flies (Diptera: Tephritidae). Male lures are commonly used attractants in fruit fly trapping. In this study, the effects of male lure dispensers, traps and combinations of dispensers and traps on monitoring of two fruit fly pests, Ceratitis capitata (Wiedemann) and Bactrocera dorsalis (Hendel), were investigated in South Africa. RESULTS: In the male-lure-based trapping systems evaluated, trimedlure (TML) for C. capitata and methyl eugenol (ME) for B. dorsalis, the type of dispenser affected catches for both species. Higher catches of B. dorsalis males were recorded in bucket traps baited with a dispenser containing 15 g ME compared with traps baited with dispensers containing either 4 g ME or 2 g ME. Catches of C. capitata males were higher with dispensers containing TML than those with TML plus extender (Capilure®). The type of trap used with TML also influenced catches of C. capitata with higher numbers recorded in yellow Delta trap compared with the Sensus bucket trap. CONCLUSIONS: Dispensers with higher ME loadings are more effective for monitoring of B. dorsalis. The yellow Delta trap baited with TML (without extender) would be an effective monitoring system for C. capitata. Fruit fly prevalence levels as determined by specific trapping systems should be related to their efficiency in terms of catches of the target pests. © 2020 Society of Chemical Industry.

Comparative demography of Bactrocera dorsalis (Hendel) and Ceratitis capitata (Wiedemann) (Diptera: Tephritidae) on deciduous fruit.

Bactrocera dorsalis (Hendel) and Ceratitis capitata (Wiedemann) are highly polyphagous fruit fly species and important pests of commercial fruit in regions of the world where they are present. In South Africa, B. dorsalis is now established in the north and northeastern parts of the country. B. dorsalis is currently absent in other parts of the country including the Western Cape Province which is an important area for the production of deciduous fruit. C. capitata is widespread in South Africa and is the dominant pest of deciduous fruit. The demographic parameters of B. dorsalis and C. capitata on four deciduous fruit types Prunus persica (L.) Batsch, Prunus domestica L., Malus domestica Borkh. and Pyrus communis L. were studied to aid in predicting the potential population establishment and growth of B. dorsalis in a deciduous fruit growing environment. All deciduous fruit types tested were suitable for population persistence of both B. dorsalis and C. capitata. Development was fastest and survival highest on nectarine for both species. B. dorsalis adults generally lived longer than those of C. capitata, irrespective of the fruit types that they developed from. B. dorsalis had a higher net reproductive rate (Ro) on all deciduous fruit tested compared to C. capitata. However, the intrinsic rate of population increase was estimated to be higher for C. capitata than for B. dorsalis on all fruit types tested primarily due to C. capitata's faster generation time. Provided abiotic conditions are optimal, B. dorsalis would be able to establish and grow in deciduous fruit growing areas.

Adult diet does not compensate for impact of a poor larval diet on stress resistance in a tephritid fruit fly.

Adult holometabolous insects may derive metabolic resources from either larval or adult feeding, but little is known of whether adult diets can compensate for deficiencies in the larval diet in terms of stress resistance. We investigated how stress resistance is affected and compensated for by diet across life stages in the marula fruit fly Ceratitis cosyra (Diptera: Tephritidae). Larvae were fed diets containing either 8% torula yeast, the standard diet used to rear this species, or 1% yeast (low protein content similar to known host fruit). At emergence, adults from each larval diet were tested for initial mass, water content, body composition, and desiccation and starvation resistance or they were allocated to one of two adult diet treatments: sucrose only, or sucrose and yeast hydrolysate. The same assays were then repeated after 10 days of adult feeding. Development on a low protein larval diet led to lower body mass and improved desiccation and starvation resistance in newly emerged adults, even though adults from the high protein larval diet had the highest water content. Adult feeding decreased desiccation or starvation resistance, regardless of the diet provided. Irrespective of larval diet history, newly emerged, unfed adults had significantly higher dehydration tolerance than those that were fed. Lipid reserves played a role in starvation resistance. There was no evidence for metabolic water from stored nutrients extending desiccation resistance. Our findings show the possibility of a nutrient-poor larval environment leading to correlated improvement in adult performance, at least in the short term.

An integrative approach to unravel the Ceratitis FAR (Diptera, Tephritidae) cryptic species complex: a review.

This paper reviews all information gathered from different disciplines and studies to resolve the species status within the Ceratitis FAR (Ceratitis fasciventris, Ceratitis anonae, Ceratitis rosa) complex, a group of polyphagous fruit fly pest species (Diptera, Tephritidae) from Africa. It includes information on larval and adult morphology, wing morphometrics, cuticular hydrocarbons, pheromones, microsatellites, developmental physiology and geographic distribution. The general consensus is that the FAR complex comprises Ceratitis anonae, two species within Ceratitis rosa (so-called R1 and R2) and two putatitve species under Ceratitis fasciventris. The information regarding the latter is, however, too limited to draw final conclusions on specific status. Evidence for this recognition is discussed with reference to publications providing further details.

Comparative analysis of development and survival of two Natal fruit fly Ceratitis rosa Karsch (Diptera, Tephritidae) populations from Kenya and South Africa.

Comparative analysis of development and survivorship of two geographically divergent populations of the Natal fruit fly Ceratitis rosa Karsch designated as Ceratitis rosa R1 and Ceratitis rosa R2 from Kenya and South Africa were studied at seven constant temperatures (10, 15, 20, 25, 30, 33, 35 °C). Temperature range for development and survival of both populations was 15-35 °C. The developmental duration was found to significantly decrease with increasing temperature for Ceratitis rosa R1 and Ceratitis rosa R2 from both countries. Survivorship of all the immature stages of Ceratitis rosa R1 and Ceratitis rosa R2 from Kenya was highest over the range of 20-30 °C (87-95%) and lowest at 15 and 35 °C (61-76%). Survivorship of larvae of Ceratitis rosa R1 and Ceratitis rosa R2 from South Africa was lowest at 35 °C (22%) and 33 °C (0.33%), respectively. Results from temperature summation models showed that Ceratitis rosa R2 (egg, larva and pupa) from both countries were better adapted to low temperatures than R1, based on lower developmental threshold. Minimum larval temperature threshold for Kenyan populations were 11.27 °C and 6.34 °C (R1 and R2, respectively) compared to 8.99 °C and 7.74 °C (R1 and R2, respectively) for the South African populations. Total degree-day (DD) accumulation for the Kenyan populations were estimated at 302.75 (Ceratitis rosa R1) and 413.53 (Ceratitis rosa R2) compared to 287.35 (Ceratitis rosa R1) and 344.3 (Ceratitis rosa R2) for the South African populations. These results demonstrate that Ceratitis rosa R1 and Ceratitis rosa R2 from both countries were physiologically distinct in their response to different temperature regimes and support the existence of two genetically distinct populations of Ceratitis rosa. It also suggests the need for taxonomic revision of Ceratitis rosa, however, additional information on morphological characterization of Ceratitis rosa R1 and Ceratitis rosa R2 is needed.

Assessment of fruit fly (Diptera: Tephritidae) management practices in deciduous fruit growing areas in South Africa.

BACKGROUND: Ceratitis capitata (Wiedemann) and Ceratitis rosa Karsch are important fruit fly pests of deciduous fruit in the Western Cape Province, South Africa. The main techniques used for fruit fly control in the Western Cape are the sterile insect technique (SIT) targeting C. capitata and the bait application technique (BAT). We determined the relative success of SIT by comparing adult fly-trap catches and fruit infestation in commercial orchards between three regions under SIT and two regions under BAT in the Western Cape, from 2006 to 2008. RESULTS: Ceratitis capitata was predominant in all regions. In commercial orchards, C. capitata catches peaked towards the end of the fruiting season (March to May) and were low between July and January. During the late season, C. capitata catches were significantly higher in two of the regions under SIT. The sterile to wild male ratio in those regions was found to be mostly <1. CONCLUSION: SIT is not being properly applied in some regions. SIT should be implemented when the pest population is low. The sterile to wild fly ratios should be increased. Alternatively, BAT should be used to lower the pest population before SIT application. Control methods should be more integrated and applied area-wide.

The distribution, relative abundance, and seasonal phenology of Ceratitis capitata, Ceratitis rosa, and Ceratitis cosyra (Diptera: Tephritidae) in South Africa.

Ceratitis capitata (Wiedemann), Ceratitis rosa Karsch, and Ceratitis cosyra (Walker) are fruit fly species (Diptera: Tephritidae) of economic importance in South Africa. These pests cause direct damage to a number of commercially produced fruit and are of phytosanitary concern. A study was conducted to determine the distribution, relative abundance, and seasonal occurrence of the three species in different climatic regions of South Africa. The relative abundance and seasonal phenology of C. capitata and C. rosa were also compared between production areas and home gardens in Stellenbosch, Western Cape. Yellow bucket traps baited with Biolure were used to trap the flies over a 2-yr period in the different sampling areas. Different fruit types were sampled in Stellenbosch to determine fruit fly infestation. C. capitata was found to have a widespread distribution in South Africa, whereas C. rosa were absent from or only present in low numbers in the drier regions. C. cosyra was restricted to the North East and East coast, following a similar pattern to the distribution of marula, Sclerocarrya birrea, an important wild host. Fruit in home gardens provided a breeding ground for C. capitata and C. rosa and a source for infestation of orchards when fruit started to mature, highlighting the need for an area-wide strategy for the control of fruit flies.

Susceptibility of the Mediterranean fruit fly (Ceratitis capitata) and the Natal fruit fly (Ceratitis rosa) to entomopathogenic nematodes.

The potential of entomopathogenic nematodes, Heterorhabditis bacteriophora, Heterorhabditis zealandica and Steinernema khoisanae, to infect pupariating larvae, pupae and adults of Ceratitis capitata and Ceratitis rosa was investigated in laboratory bioassays. Pupariating larvae and adult flies were susceptible to nematode infection, with no infection recorded for the pupae. Pupariating larvae of C. capitata were generally more susceptible to infection than those of C. rosa. Significantly more larvae of C. capitata were infected by H. bacteriophora. For C. rosa, highest infectivity of larvae was obtained with H. zealandica. In contrast, adults of both species were highly infected by S. khoisanae.