Sexual maturity and intraspecific mating success of two sibling species of the Bactrocera dorsalis complex

Bactrocera carambolae Drew & Hancock and B. papayae Drew & Hancock (Diptera: Tephritidae), two closely related sibling species in the B. dorsalis (Hendel) complex were shown to have different rates of sexual maturity. The response of B. carambolae males to methyl eugenol was observed to begin 10 days after emergence and increased with age. The attractancy peaked at 28 days after emergence and above. The males were also found to require a higher dosage of methyl eugenol (1 mg) for optimal response. These results are in contrast with those of B. papayae reported previously. The response to methyl eugenol was also observed to correspond with the age when first mating was performed.After eclosion, both sexes of B. carambolae mated approximately 2 weeks later and showed significantly lower matings/individual when compared with B. papayae in a 60-day observation period. Both sexes of B. papayae and males of B. carambolae were able to remate on the next day. However, B. carambolae females required a minimum refractory period of 8 days in order to be sexually receptive again.During the 60-day period, the mating propensity in B. papayae (100% success) was higher than B. carambolae (71–87% success) (P < 0.05). This observation was substantiated by a higher intraspecific mating success of B. papayae as compared to B. carambolae in a field cage (P < 0.001).     

Piecing together an integrative taxonomic puzzle: microsatellite,wing shape and aedeagus length analyses of Bactrocera dorsalis s.l. (Diptera: Tephritidae) find no evidence of multiple lineages in a proposed contact zone along the Thai/Malay Peninsula

Bactrocera dorsalis (Hendel) and B. papayae Drew & Hancock represent a closely related sibling species pair for which the biological species limits are unclear; i.e. it is uncertain if they are truely two biological species, or one biological species which has been incorrectly split taxonomically. The geographical ranges of the two taxa are thought to abut or overlap on or around the Isthmus of Kra, a recognised biogeographic barrier located on the narrowest portion of the Thai Peninsula. We collected fresh material of B. dorsalis s.l. (i.e. B. dorsalis s.s.+ B. papayae) in a north–south transect down the Thai Peninsula, from areas regarded as being exclusively B. dorsalis s.s., across the Kra Isthmus, and into regions regarded as exclusively B. papayae. We carried out microsatellite analyses and took measurements of male genitalia and wing shape, both used previously to separate the taxa. No significant population structuring was found in the microsatellite analysis, consistent with one, predominantly panmictic population. Both morphological datasets showed consistent, clinal variation along the transect, without disjunction. No evidence supported historical vicariance driven by the Isthmus of Kra, and no dataset supported the current taxonomy of two species. Rather, within and across the area of range overlap or abutment between the two species, only continuous morphological and genetic variation was recorded. Recognition that morphological traits previously used to separate these taxa are continuous, and that there is no genetic evidence for population segregation in the region of suspected species overlap, is consistent with a growing body of literature that reports no evidence of biological differentiation between these taxa.     

One and the same: integrative taxonomic evidence that Bactrocera invadens (Diptera: Tephritidae) is the same species as the Oriental fruit fly Bactrocera dorsalis

The invasive fruit fly Bactrocera invadens Drew, Tsuruta & White, and the Oriental fruit fly Bactrocera dorsalis (Hendel) are highly destructive horticultural pests of global significance. Bactrocera invadens originates from the Indian subcontinent and has recently invaded all of sub‐Saharan Africa, while B. dorsalis principally occurs from the Indian subcontinent towards southern China and South‐east Asia. High morphological and genetic similarity has cast doubt over whether B. invadens is a distinct species from B. dorsalis. Addressing this issue within an integrative taxonomic framework, we sampled from across the geographic distribution of both taxa and: (i) analysed morphological variation, including those characters considered diagnostic (scutum colour, length of aedeagus, width of postsutural lateral vittae, wing size, and wing shape); (ii) sequenced four loci (ITS1, ITS2, cox1 and nad4) for phylogenetic inference; and (iii) generated a cox1 haplotype network to examine population structure. Molecular analyses included the closely related species, Bactrocera kandiensis Drew & Hancock. Scutum colour varies from red‐brown to fully black for individuals from Africa and the Indian subcontinent. All individuals east of the Indian subcontinent are black except for a few red‐brown individuals from China. The postsutural lateral vittae width of B. invadens is narrower than B. dorsalis from eastern Asia, but the variation is clinal, with subcontinent B. dorsalis populations intermediate in size. Aedeagus length, wing shape and wing size cannot discriminate between the two taxa. Phylogenetic analyses failed to resolve B. invadens from B. dorsalis, but did resolve B. kandiensis. Bactrocera dorsalis and B. invadens shared cox1 haplotypes, yet the haplotype network pattern does not reflect current taxonomy or patterns in thoracic colour. Some individuals of B. dorsalis/B. invadens possessed haplotypes more closely related to B. kandiensis than to conspecifics, suggestive of mitochondrial introgression between these species. The combined evidence fails to support the delimitation of B. dorsalis and B. invadens as separate biological species. Consequently, existing biological data for B. dorsalis may be applied to the invasive population in Africa. Our recommendation, in line with other recent publications, is that B. invadens be synonymized with B. dorsalis.     

Integrative taxonomy versus taxonomic authority without peer review: the case of the Oriental fruit fly,Bactrocera dorsalis (Tephritidae)

1. Major global horticultural and food security tephritid fruit fly pests, Bactrocera papayae (papaya fruit fly) and B. invadens (invasive fruit fly), were synonymised with B. dorsalis (Oriental fruit fly) by Schutze et al. (2015a) based on extensive integrative taxonomic evidence from multiple sources. This synonymy was peer reviewed by eight independent experts. 2. Drew & Romig (2016) withdrew B. papayae and B. invadens from synonymy based on opinion drawn primarily from disparate geographical distribution, morphological, and host use information. This reversal was not subjected to peer review. 3. We consider the withdrawal from synonymy as invalid due to significant errors and misrepresentations of the literature provided in the arguments of Drew & Romig (2016) that we propose would not have withstood peer scrutiny. 4. This case reflects a broader issue of individual taxonomic authorities using opinion to challenge extensive evidence generated via scientific hypothesis‐testing methods by discipline specialists. 5. We recommend that taxonomic acts not subjected to peer review, especially of pest species, be actively discouraged by the broader scientific and regulatory community.     

Comparative sensitivity to methyl eugenol of four putative Bactrocera dorsalis complex sibling species – further evidence that they belong to one and the same species B. dorsalis

Males of certain species belonging to the Bactrocera dorsalis complex are strongly attracted to, and readily feed on methyl eugenol (ME), a plant secondary compound that is found in over 480 plant species worldwide. Amongst those species is one of the world’s most severe fruit pests the Oriental fruit fly, Bactrocera dorsalis s.s., and the former taxonomic species Bactrocera invadens, Bactrocera papayae and Bactrocera philippinensis. The latter species have been recently synonymised with Bactrocera dorsalis based on their very similar morphology, mating compatibility, molecular genetics and identical sex pheromones following consumption of ME. Previous studies have shown that male fruit fly responsiveness to lures is a unique phenomenon that is dose species-specific, besides showing a close correlation to sexual maturity attainment. This led us to use ME sensitivity as a behavioural parameter to test if Bactrocera dorsalis and the three former taxonomic species had similar sensitivity towards odours of ME. Using Probit analysis, we estimated the median dose of ME required to elicit species’ positive response in 50% of each population tested (ED₅₀). ED₅₀ values were compared between Bactrocera dorsalis and the former species. Our results showed no significant differences between Bactrocera dorsalis s.s., and the former Bactrocera invadens, Bactrocera papayae and Bactrocera philippinensis in their response to ME. We consider that the Bactrocera males’ sensitivity to ME may be a useful behavioural parameter for species delimitation and, in addition to other integrative taxonomic tools used, provides further supportive evidence that the four taxa belong to one and the same biological species, Bactrocera dorsalis.     

Population dynamics of three Bactrocera spp. fruit flies (Diptera: Tephritidae) and two introduced natural enemies,Fopius arisanus (Sonan) and Diachasmimorpha longicaudata (Ashmead) (Hymenoptera: Braconidae), after an invasion by Bactrocera dorsalis (Hendel) in Tahiti

Oriental fruit fly, Bactrocera dorsalis (Hendel), invaded French Polynesia in 1996. In 2002 a natural enemy, Fopius arisanus (Sonan), was released and established. By 2009 mean (±SD) F. arisanus parasitism for fruit flies infesting Psidium guajava (common guava), Inocarpus fagifer (Polynesian chestnut) and Terminalia catappa (tropical almond) fruits on Tahiti Island was 64.8 ± 2.0%. A second parasitoid, Diachasmimorpha longicaudata (Ashmead), was released and established in 2008. Although widespread, parasitism rates have not been higher than 10%. From 2003 (parasitoid establishment) to 2009 (present survey) numbers of B. dorsalis, Bactrocera tryoni (Froggatt), Queensland fruit fly, and Bactrocera kirki (Froggatt) emerging (per kg of fruit) declined. For example, for P. guajava there was a decline of 92.3%, 96.8%, and 99.6%, respectively. Analysis of co-infestation patterns (1998–2009) of B. dorsalis, B. tryoni, and B. kirki, suggest B. dorsalis is now the most abundant species in many common host fruits. Establishment of F. arisanus is the most successful example of classical biological control of fruit flies in the Pacific outside of Hawaii and can be introduced if B. dorsalis spreads to other French Polynesian islands, as was the recent case when B. dorsalis spread to the Marquesas Islands. These studies support F. arisanus as a prime biological control candidate for introduction into South America and Africa where Bactrocera carambolae Drew and Hancock and Bactrocera invadens Drew, Tsuruta, and White, respectively, have become established.     

A tentative evaluation for population establishment of Bactrocera dorsalis (Diptera: Tephritidae) by its population modeling: Considering the temporal distribution of host plants in a selected area in Jeju,Korea

The Oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae) is a destructive fruit pest in a wide range of cultivated fruit crops and wild plants. This species is a potentially highly invasive fruit fly to Jeju area of Korea. This study was conducted to evaluate the effect of host plants distributed temporally on the population development of B. dorsalis. The temperature-dependent bionomic data for a synonymous group of B. dorsalis, including B. philippinensis, B. papayae, and B. invadens were collected from previous publications and combined to construct a population model of this pest and its thermal constant. We developed a stage-transition model of eggs, larvae and pupae, and an oviposition model for basic population modeling of the four common strains. We investigated the abundance of the host plants of B. dorsalis in a selected site in Jeju and parameterized them in terms of temporal availability to incorporate into the population model. The contribution of host plants for the population growth of B. dorsalis in the selected site was different according to the group of host plants. For example, B. dorsalis populations largely decreased by 93%, when host plants belong to Moraceae (mainly Ficus sp.) were removed in the simulation. Also, we found that the host plants of Prunus persica, Ficus carica, P. mume, Eriobotrya japonica in this order contributed greatly to population abundance of B. dorsalis in the selected area, which was important in terms of mid-season host plants connecting the early adult population of B. dorsalis to citrus plants in the late season. Finally, we discussed a seasonal management strategy against B. dorsalis while considering the availability of host plants and the biology of this fruit fly in an invaded area.     

Ecological significance of male attractant in the defence and mating strategies of the fruit fly, Bactrocera papayae

After being acclimatized to feeding on fruit flies, the Asian house gecko, Hemidactylus frenatus Duméril & Bibron (Gekkonidae:Squamata), consumed fewer methyl eugenol (ME) fed male fruit flies, Bactrocera papayae Drew & Hancock (Tephritidae: Diptera) than when offered ME-deprived males. After one-day exposure to only ME-fed males, the geckos avoided feeding on female flies when in the presence of ME-fed males. When mechanically disturbed, the ME-fed males spontaneously ejaculated a rectal secretion which contains phenyl propanoids that deter the predator.The ME-fed males also competed significantly better than normal (ME-deprived) males for virgin females. Male B. papayae converts ME to three other phenyl propanoids which act in concert as a sex pheromone to attract females during courtship and as an allomone to the gecko.     

Multi‐gene phylogenetic analysis of south‐east Asian pest members of the Bactrocera dorsalis species complex (Diptera: Tephritidae) does not support current taxonomy

Bactrocera dorsalis sensu stricto, B. papayae, B. philippinensis and B. carambolae are serious pest fruit fly species of the B. dorsalis complex that predominantly occur in south‐east Asia and the Pacific. Identifying molecular diagnostics has proven problematic for these four taxa, a situation that cofounds biosecurity and quarantine efforts and which may be the result of at least some of these taxa representing the same biological species. We therefore conducted a phylogenetic study of these four species (and closely related outgroup taxa) based on the individuals collected from a wide geographic range; sequencing six loci (cox1, nad4‐3′, CAD, period, ITS1, ITS2) for approximately 20 individuals from each of 16 sample sites. Data were analysed within maximum likelihood and Bayesian phylogenetic frameworks for individual loci and concatenated data sets for which we applied multiple monophyly and species delimitation tests. Species monophyly was measured by clade support, posterior probability or bootstrap resampling for Bayesian and likelihood analyses respectively, Rosenberg's reciprocal monophyly measure, P(AB), Rodrigo's (P(RD)) and the genealogical sorting index, gsi. We specifically tested whether there was phylogenetic support for the four ‘ingroup’ pest species using a data set of multiple individuals sampled from a number of populations. Based on our combined data set, Bactrocera carambolae emerges as a distinct monophyletic clade, whereas B. dorsalis s.s., B. papayae and B. philippinensis are unresolved. These data add to the growing body of evidence that B. dorsalis s.s., B. papayae and B. philippinensis are the same biological species, which poses consequences for quarantine, trade and pest management.     

Taxonomic Identity of the Invasive Fruit Fly Pest,Bactrocera invadens: Concordance in Morphometry and DNA Barcoding

In 2003, a new fruit fly pest species was recorded for the first time in Kenya and has subsequently been found in 28 countries across tropical Africa. The insect was described as Bactrocera invadens, due to its rapid invasion of the African continent. In this study, the morphometry and DNA Barcoding of different populations of B. invadens distributed across the species range of tropical Africa and a sample from the pest''s putative aboriginal home of Sri Lanka was investigated. Morphometry using wing veins and tibia length was used to separate B. invadens populations from other closely related Bactrocera species. The Principal component analysis yielded 15 components which correspond to the 15 morphometric measurements. The first two principal axes contributed to 90.7% of the total variance and showed partial separation of these populations. Canonical discriminant analysis indicated that only the first five canonical variates were statistically significant. The first two canonical variates contributed a total of 80.9% of the total variance clustering B. invadens with other members of the B. dorsalis complex while distinctly separating B. correcta, B. cucurbitae, B. oleae and B. zonata. The largest Mahalanobis squared distance (D² = 122.9) was found to be between B. cucurbitae and B. zonata, while the lowest was observed between B. invadens populations against B. kandiensis (8.1) and against B. dorsalis s.s (11.4). Evolutionary history inferred by the Neighbor-Joining method clustered the Bactrocera species populations into four clusters. First cluster consisted of the B. dorsalis complex (B. invadens, B. kandiensis and B. dorsalis s. s.), branching from the same node while the second group was paraphyletic clades of B. correcta and B. zonata. The last two are monophyletic clades, consisting of B. cucurbitae and B. oleae, respectively. Principal component analysis using the genetic distances confirmed the clustering inferred by the NJ tree.     

从东南亚进口水果截获桔小实蝇复合种五近缘种的鉴别(双翅目:实蝇科)

介绍了近年从进口东南亚水果中经常截获的、最具经济重要性的桔小实蝇复合种5个近缘种:杨桃实蝇B.carambolae、桔小实蝇B.dorsalis、芒果实蝇B.occipitalis、木瓜实蝇B.papayae及菲律宾实蝇B.philippinensis,分别记述了翅、胸、足、腹及雌虫产卵器主要鉴别特征,并列出桔小实蝇复合种5近缘种鉴别特征检索表。     

Optimizing methyl‐eugenol aromatherapy to maximize posttreatment effects to enhance mating competitiveness of male Bactrocera carambolae (Diptera: Tephritidae)

Methyl‐eugenol (ME) (1,2‐dimethoxy‐4‐(2‐propenyl)benzene), a natural phytochemical, did enhance male Bactrocera carambolae Drew & Hancock (Diptera: Tephritidae) mating competitiveness 3 d after ingestion. Enhanced male mating competitiveness can significantly increase the effectiveness of the sterile insect technique (SIT). ME application to mass reared sterile flies by feeding is infeasible. ME application by aromatherapy however, would be a very practical way of ME application in fly emergence and release facilities. This approach was shown to enhance mating competitiveness of B. carambolae 3 d posttreatment (DPT). Despite this added benefit, every additional day of delaying release will reduce sterile fly quality and will add cost to SIT application. The present study was planned to assess the effects of ME‐aromatherapy on male B. carambolae mating competitiveness 1DPT and 2DPT. ME aromatherapy 1DPT or 2DPT did enhance mating competitiveness of B. carambolae males whereas ME feeding 1DPT and 2DPT did not. Male mating competitiveness was enhanced by the ME aromatherapy irrespective if they received 1DPT, 2DPT or 3DPT. ME aromatherapy, being a viable approach for its application, did enhance mating competitiveness of male B. carambolae 1 d posttreatment as ME feeding did 3 d after ingestion.     

Attraction of feral Bactrocera dorsalis males (Diptera: Tephritidae) to natural versus commercial sources of methyl eugenol

Males of Bactrocera dorsalis (Hendel) are strongly attracted to methyl eugenol (ME), which occurs in over 450 plant species. Given this powerful attraction, ME is commonly used in surveillance and eradication programs against this invasive agricultural pest. Preliminary observations revealed that B. dorsalis males visited ME-bearing flowers of the fruit fly orchid (FFO) Bulbophyllum cheiri subsp. cheiri even when these occurred near traps baited with far greater quantities of ME. Based on this evidence, we undertook field experiments to assess the attraction of feral B. dorsalis males to FFO flowers relative to commercial sources of ME. At the edge of a secondary forest, an FFO flower was placed midway between two ME sources located 20 m apart, and attracted flies were collected over an entire day. When the ME sources were unenclosed (not in traps), the relative attractiveness of FFO flowers to B. dorsalis males varied with the amount of ME placed nearby. The FFO flower (i) attracted a similar proportion of males when 1 g ME was placed at the flanking sites but (ii) captured significantly smaller proportions when the nearby sites had 6 or 10 g commercial ME sources. Similar tests with the commercial sources enclosed in traps showed that (i) 6 g ME sources in Steiner traps attracted significantly more B. dorsalis males than FFO flowers but (ii) 10 g sources in Clear traps (1 L buckets with 4 entrance holes) did not outperform the FFO flowers, presumably owing to limited dispersion of volatiles from the trap. Implications of these results for surveillance programs are discussed.     

Microsatellite markers for the pest fruit fly,Bactrocera papayae (Diptera: Tephritidae) and other Bactrocera species

The dorsalis complex contains some of the most economically important fruit fly pests of the Asia–Pacific regions, including Bactrocera dorsalis, Bactrocera papayae and Bactrocera carambolae. These species are morphologically indistinct and genetically very similar. We describe the development of 12 microsatellite markers isolated from a representative of the dorsalis complex, B. papayae. We show the potential utility of the B. papayae microsatellites and a set of microsatellites isolated from Bactrocera tryoni as population and species markers for the dorsalis complex.     

云南景洪果实蝇属三新种及一新纪录种记述(双翅目,实蝇科)(英文)

记述采自中国云南景洪的果实蝇属3新种和中国1新纪录种:滇黑寡鬃实蝇Bactrocera(Bactrocera)nigrifacia sp.nov.,哈迪氏果实蝇B.(B.)hardyisp.nov.,景洪果实蝇B.(B.)jinghongensis sp.nov.和黑颜面实蝇Bactrocera(Zeugodacus)vultus(Hardy,1973),3新种均符合DrewetHancock(1994)对桔小实蝇复合体的定义。模式标本保存于福建农林大学益虫研究所。滇黑寡鬃实蝇,新种Bactrocera(Bactrocera)nigrifacia sp.nov.(图1～4)新种与黑胫实蝇B.(Bactrocera)nigr of emoralis Whiteet Tsuruta相近,颜均为黑色,与后者的区别在于:2条平行的缝后侧黄色条终止于翅内鬃之前,第2腹背板橙棕色且前缘具黑色横带。正模♂,云南景洪,2010-09-02,Cue-lure引诱,张南南采。副模3♂♂,同正模。词源:新种种名根据颜面黑色而命名。哈迪氏果实蝇,新种Bactrocera(Bactrocera)hardyisp.nov.(图5～7)新种与印尼实蝇Bactrocera(Bactrocera)indonesiae Drewet Hancock相近,与后者的区别为:第3～5腹背板黑褐色,前足腿节黄褐色,且端部具黑褐色斑,中足和后足腿节为黄褐色,且端部具很短的黑褐色条纹。正模♂,云南景洪,2010-09-04,Cue-lure引诱,张南南采。副模3♂♂,同正模。词源:新种种名以双翅目分类专家DilbertE.Hardy的姓氏命名。景洪果实蝇,新种Bactrocera(Bactrocera)jinghongensis sp.nov.(图8～11)新种与基纳巴卢实蝇Bactrocera(Bactrocera)kinabalu Drewet Hancock相近,与后者的区别在于:缝后侧黄色条终止于翅内鬃之前,中足腿节端部1/2黑色。正模♂,云南景洪,2010-09-04,Cue-lure引诱,张南南采。副模4♂♂,同正模。词源:新种种名以模式产地命名。     

Two new species and a new Australian record of Bactrocera Macquart (Diptera: Tephritidae: Dacinae) from northern Queensland, Torres Strait and Papua New Guinea

Abstract  Bactrocera (Bactrocera) speewahensis Fay & Hancock sp. n. is described from northern Queensland and B. (B.) torresiae Huxham & Hancock sp. n. is described from Boigu, Saibai and Dauan islands in Torres Strait and southern Papua New Guinea. Bactrocera (B.) nigrovittata Drew is newly recorded from Australia. All records are of male flies responding to chemical lures.     

Development of a genetic sexing strain in <Emphasis Type="Italic">Bactrocera carambolae</Emphasis> (Diptera: Tephritidae) by introgression of sex sorting components from <Emphasis Type="Italic">B. dorsalis</Emphasis>, Salaya1 strain

Background

The carambola fruit fly, Bactrocera carambolae Drew & Hancock is a high profile key pest that is widely distributed in the southwestern ASEAN region. In addition, it has trans-continentally invaded Suriname, where it has been expanding east and southward since 1975. This fruit fly belongs to Bactrocera dorsalis species complex. The development and application of a genetic sexing strain (Salaya1) of B. dorsalis sensu stricto (s.s.) (Hendel) for the sterile insect technique (SIT) has improved the fruit fly control. However, matings between B. dorsalis s.s. and B. carambolae are incompatible, which hinder the application of the Salaya1 strain to control the carambola fruit fly. To solve this problem, we introduced genetic sexing components from the Salaya1 strain into the B. carambolae genome by interspecific hybridization.

Results

Morphological characteristics, mating competitiveness, male pheromone profiles, and genetic relationships revealed consistencies that helped to distinguish Salaya1 and B. carambolae strains. A Y-autosome translocation linking the dominant wild-type allele of white pupae gene and a free autosome carrying a recessive white pupae homologue from the Salaya1 strain were introgressed into the gene pool of B. carambolae. A panel of Y-pseudo-linked microsatellite loci of the Salaya1 strain served as markers for the introgression experiments. This resulted in a newly derived genetic sexing strain called Salaya5, with morphological characteristics corresponding to B. carambolae. The rectal gland pheromone profile of Salaya5 males also contained a distinctive component of B. carambolae. Microsatellite DNA analyses confirmed the close genetic relationships between the Salaya5 strain and wild B. carambolae populations. Further experiments showed that the sterile males of Salaya5 can compete with wild males for mating with wild females in field cage conditions.

Conclusions

Introgression of sex sorting components from the Salaya1 strain to a closely related B. carambolae strain generated a new genetic sexing strain, Salaya5. Morphology-based taxonomic characteristics, distinctive pheromone components, microsatellite DNA markers, genetic relationships, and mating competitiveness provided parental baseline data and validation tools for the new strain. The Salaya5 strain shows a close similarity with those features in the wild B. carambolae strain. In addition, mating competitiveness tests suggested that Salaya5 has a potential to be used in B. carambolae SIT programs based on male-only releases.

     

Development of allele-specific single-nucleotide polymorphism-based polymerase chain reaction markers in cytochrome oxidase I for the differentiation of Bactrocera papayae and Bactrocera carambolae (Diptera: Tephritidae)

Differentiation of Bactrocera papayae Drew & Hancock and Bactrocera carambolae Drew & Hancock (Diptera: Tephritidae) based on morphological characters has often been problematical. We describe here a single-nucleotide polymorphism (SNP)-based polymerase chain reaction (PCR) assay to differentiate between these two species. For detection of SNPs, fragments derived from each species were amplified using two primer pairs, COIF/COIR and UEA7/UEA10, sequenced, and aligned to obtain a contiguous 1,517-bp segment. Two new sets of primers were designed based on the 11 SNPs identified in the region. Results of the SNP-PCR test using any one of these species-specific primer sets indicate that these two species could be differentiated on basis of presence or absence of a band in the gel profile. We also tested the SNP-PCR primers on Bactrocera umbrosa F., Bactrocera cucurbitae Coquillett, Bactrocera latifrons Hendel, and Bactrocera tau (Walker) but did not detect any band in the gel, indicating the likelihood of a false positive for B. papayae is nil. This SNP-PCR method is efficient and useful, especially for immature life stages or when only adult body parts of the two species are available for identification, as encountered often in quarantine work.     

The <Emphasis Type="Italic">Bactrocera dorsalis</Emphasis> species complex: comparative cytogenetic analysis in support of Sterile Insect Technique applications

Background

The Bactrocera dorsalis species complex currently harbors approximately 90 different members. The species complex has undergone many revisions in the past decades, and there is still an ongoing debate about the species limits. The availability of a variety of tools and approaches, such as molecular-genomic and cytogenetic analyses, are expected to shed light on the rather complicated issues of species complexes and incipient speciation. The clarification of genetic relationships among the different members of this complex is a prerequisite for the rational application of sterile insect technique (SIT) approaches for population control.

Results

Colonies established in the Insect Pest Control Laboratory (IPCL) (Seibersdorf, Vienna), representing five of the main economic important members of the Bactrocera dorsalis complex were cytologically characterized. The taxa under study were B. dorsalis s.s., B. philippinensis, B. papayae, B. invadens and B. carambolae. Mitotic and polytene chromosome analyses did not reveal any chromosomal characteristics that could be used to distinguish between the investigated members of the B. dorsalis complex. Therefore, their polytene chromosomes can be regarded as homosequential with the reference maps of B. dorsalis s.s.. In situ hybridization of six genes further supported the proposed homosequentiallity of the chromosomes of these specific members of the complex.

Conclusions

The present analysis supports that the polytene chromosomes of the five taxa under study are homosequential. Therefore, the use of the available polytene chromosome maps for B. dorsalis s.s. as reference maps for all these five biological entities is proposed. Present data provide important insight in the genetic relationships among the different members of the B. dorsalis complex, and, along with other studies in the field, can facilitate SIT applications targeting this complex. Moreover, the availability of 'universal' reference polytene chromosome maps for members of the complex, along with the documented application of in situ hybridization, can facilitate ongoing and future genome projects in this complex.