Bactrocera Invadens Research Articles

Cannibalism among adult bush crickets (Ruspolia differens) when fed on different insect preys and artificial diets

Edible bush cricketsRuspolia differens have received considerable interest in recent years primarily due to their widespread consumption across Sub Sahara Africa. Currently, these pseudo grasshoppers are only available in large quantities twice a year during the rainy seasons. Therefore, there is great research interest in studying their farming potential for possible mass rearing. However, due to their cannibalistic behaviours, such attempts have proven an uphill task. This study evaluated measures that may reduce cannibalism by providing alternative prey to rearedR. differens. Ten young adults of either females or malesR. differens were kept separately in well-aerated cages (50×50×50 cm). Then, two sets of experiment were set up as follows: in the no-choice set-up, twenty live or dead second instar (L2) larvae each ofHermetia illucens,Chilo partellus,Bactrocera invadens, andSchistocerca gregaria were administered separately to both male and female cages for six successive days. In the choice set-up, a mixture of twenty live or dead L2 larvae of the insects mentioned above was fed for twelve consecutive days. The control diets included an artificial diet only or artificial diet + corn leaves and were provided for six days consecutively to both males and females separately. In each case, the proportion of cannibalism and the possibility of hunting behaviour byR. differens was recorded. Cannibalism was significantly reduced in both male and femaleR. differens cages where prey was administered compared to the control diets. Besides, cannibalism was significantly reduced in both male and femaleR. differens cages when live insect prey was provided compared to dead insect prey. There were indications of a hunting behaviour exhibited byR. differens as they tended to feed more on living than on dead insect prey. Our findings show that the addition of live insect prey could reduce the prevalence of cannibalism duringR. differens, thus preventing colony collapse due to cannibalism and also providing a safe means to eliminate insect pests, which could serve as prey.

Assessment of the major insect pests associated with kola nuts in Ghana

ABSTRACT Cola nitida (Kola) is an important cash crop cultivated in the forest areas of West Africa. The crop is attacked by a lot of insect pests, chief among them are the kola seed weevil, Balanogastris kolae, and some Sophrorhinus pest species. Not much is known about the pest status of fruit fly species on the crop, especially Bactrocera invadens and Ceratitis colae which is known to feed exclusively on the crop. This study seeks to assess the incidence, population dynamics and damage caused by insect pests on kola in the middle belt of Ghana to inform pest management decisions. The major insect pests identified on kola in the study include the kola seed weevils Balanogastris kolae, Sophrorhinus spp and fruit fly species Bactrocera invadens, Ceratitis colae and other Ceratitis spp. There was a significant locational effect on the number of fruit fly species trapped. The kola nut weevils (Balanogastris kolae and the Sophrorhinus species) remain the most important kola pests accounting for 81.4% of the sampled damaged pods. Information obtained from the population dynamics of these kola insect pests could aid in the development of an integrated strategy for managing these pests on the crop.

Biogeography, Speciation and Taxonomy within the genus Bactrocera Macquart with application to the Bactrocera dorsalis (Hendel) complex of fruit flies (Diptera: Tephritidae: Dacinae)

The genus Bactrocera Macquart comprises a large group of some 750 species distributed across the Asia-Pacific and Afrotropical regions. Most of these have been described and revised by Drew (1989), Drew & Hancock (1994) and Drew & Romig (2013, 2022). A taxonomic study of such a large and diverse group of species provides valuable information that can be used in the elucidation of concepts on biogeography and evolution that are presented in this paper. While a wider discussion of this genus and its many complexes of sibling species awaits a future publication, in this paper we discuss the Bactrocera dorsalis (Hendel) complex in light of current knowledge of biogeography and evolution in the Asia-Pacific region. Within the dorsalis complex, 70 species were recognized in South-East Asia by Drew & Romig (2013) and eight listed for Papua New Guinea and Australia by Drew (1989). Seventy-nine species are now included in this paper. Within this complex, two major groups occur, one with species responding to methyl eugenol and the other to cue lure. The 34 non-cue lure responding group of species are discussed, most of which respond to methyl eugenol and seven of which are recognized as having pest status, namely, B. carambolae Drew & Hancock, B. caryeae (Kapoor), B. dorsalis (Hendel), B. kandiensis Drew & Hancock, B. occipitalis (Bezzi), B. ochroma Drew & Romig and B. papayae Drew & Hancock. An eighth species, Bactrocera invadens Drew, Tsuruta & White is included in this discussion on the basis of its molecular similarity to B. dorsalis. The remaining group of 45 species, mostly cue lure-responding and including the pest species B. pyrifoliae Drew & Hancock and B. syzygii White & Tsuruta, are also discussed. Morphological and ecological data are presented for each pest species and their biosecurity risks assessed. In addition, new data based on further research on the male aedeagus have demonstrated that B. carambolae, B. occipitalis, B. papayae and B. invadens are markedly different from B. dorsalis in the dimensions and shape of the glans and preglans appendix. Based on this evidence, and that presented by Drew & Romig (2016), the withdrawal of B. papayae and B. invadens from synonymy with B. dorsalis by Drew & Romig (2016) remains valid, while the similarity in aedeagus characters between B. papayae and B. philippinensis further supports the synonymisation of these two species. The remainder of the 34 non-cue lure responding species are distributed from the Indian subcontinent, across South-East Asia, Papua New Guinea and north-eastern Australia, some with restricted geographic distributions and specific host plant species. Comments on the reliability of molecular phylogenies in the Dacini are included, with the published mitogenome of 'Dacus longicornis' regarded, on morphological evidence, as data based on a misidentification of Dacus (Mellesis) polistiformis (Senior-White), and the recent synonymy of B. albistrigata (de Meijere) with B. frauenfeldi (Schiner) considered to be based on insufficient evidence.

Acute and residual concentration-dependent toxicities of some selected insecticides to adult Bactrocera invadens Drew, Tsuruta and White (Diptera: Tephritidae)

BackgroundThe high yield loss reported from the infestations of fruits by Bactrocera invadens Drew, Tsuruta and White in West Africa can impact negatively on the growth of horticulture in the region. Similarly, the shortage of insecticides specifically registered for the control of this pest in Ghana makes decision by farmers on which insecticide to use against this pest uncertain and risky.ResultsThe result for the acute lethal toxicity shows that the lethal concentration (LC) values of the tested insecticides are 0.59 (diazinon (Diazol)), 0.81 (chlorpyrifos (Pyrinex)), 1.21 (cypermethrin+dimethoate (Cydim super)), and 3.12 (deltamethrin (Deltapaz)) ml L−1 of water. The result for the residual toxicities of three concentrations for each of the tested insecticides shows that the lethal times LT (LT50 and 90) for the adult B. invadens differed significantly for all the ages of the residues. Some insecticides exhibited low lethal time even on panels that are up to 6 days old after treatment.ConclusionWe concluded that the acute lethal toxicity of the insecticides from most-to-least toxic are diazinon (Diazol) > chlorpyrifos (Pyrinex) > cypermethrin + dimethoate (Cydim super) > deltamethrin (Deltapaz). The residual toxicity of the label rates of all the insecticides are equal to those of the higher doses but better than those of the least doses. The implication of these findings for the management of B. invadens has been discussed.

Identification and Abundance of Fruit Fly Species Responsible for Fruit Drop of Sweet Orange (Citrus sinensis L. Osbeck) in Benue State, Nigeria

Background and Objective: Citrus is one of the most important and among the top ten widely cultivated fruits in Nigeria. It is produced more in the Guinea and Sudan Savanna zones of the country with Benue State having the highest annual production. In the South of Savanna region of Africa, particularly in Nigeria; despite the economic, nutritional and health benefits of citrus, limited research work has been carried out on the identification and control of fruit flies of economic importance to the crop. The objectives of this study are to identify and determine the abundance of the fruit fly species responsible for fruit drop of citrus in Benue State, Nigeria.
 Materials and Methods: Fruit fly identification was done through fruit culture experiment carried out in the College of Agronomy Teaching and Research Farm, Federal University of Agriculture, Makurdi in October 2014 and October 2015.The experiment was a 2 x 3 factorial in a completely randomized design with four replications. The two factors were Zones (Zone A and B) and Varieties (Ibadan Sweet, Valencia and Washington Navel). Ten naturally infested orange fruits from four randomly selected citrus trees of each variety in each zone were weighed and placed in each plastic rearing box with dimension 39 x 27 x 26 cm containing sterilized moist soil securely covered with 1 mm mesh net for pupation and adult insect emergence. Emerged adults were killed using Mobil insecticide (Cyphenothrin), counted, sexed and stored in specimen bottles with 70% alcohol for preservation and later identification.
 Results: Fruit fly species identified from citrus fruit culture were: Bactrocera invadens (Drew), Ceratitis capitata (Weid) and Dacus bivittata (Biggot). Bactrocera invadens were the most abundant species and accounted for 63.70% in Washington navel and 63.10% in Valencia in 2014 and 2015 respectively. The varieties showed no significant differences (p>0.05) on the abundance of Ceratitis capitata and Dacus bivittata in 2014. In 2015 however, Ibadan Sweet variety showed significant difference (p < 0.05) on the abundance of Ceratitis capitata (28.30%) when compared with other varieties (15.8%) each.
 Conclusion: Fruit fly species responsible for citrus fruit drop in Benue State were Bactrocera invadens (Drew), Ceratitis capitata (Weid) and Dacus bivittata (Biggot) with Bactrocera invadens (Drew) recorded as the most abundant species.

Oriental Fruit fly distribution within Kandara sub county, Murang’a, Kenya

The Oriental fruit fly (Bactrocera dorsalis (Hendel) (Diptera: Tephritidae), previously recognized as Bactrocera invadens, presence in Kenya dates since 2003, the first record of this pest in Africa. Its phytosanitary importance resulted to avocado export ban to South Africa in 2008 and later to Seychelles, to prevent possible entry of this pest into these markets through fruit trade. To regain these markets and avoid more external market loss, this study was carried out to facilitate creation of a pest free area for fruit flies as required by the International Standards for Phytosanitary Measures (ISPM) number 26. Detection survey for the pest was conducted using 110 methyl eugenol lure-based traps laced with malathion insecticide, placed throughout Kandara Sub-County, at a density of 5 traps/km2 in June 2013. The sub county has the highest concentration of small-scale farmers of avocados for export markets in Kenya. The traps were examined after 2 weeks of placement. Data on host plants was also collected. The results showed that traps captured the pest in all agroecological zones (Lower highland (LH)1, Upper midland (UM) 1, Upper midland (UM) 2 and Upper midland (UM) 3). Possible host plants observed in the farms included avocado, mango, pawpaw, guava, coffee, passion fruit, loquats, banana, citrus, and tree tomato. The pest density was highest in UM 3, which has the lowest elevation and the highest concentration of mango orchards. High trap catches recorded in market centres was associated with poor disposal of fruits. The lowest pest density was recorded at LH 1, which has the highest elevation in the sub-county. Therefore, creation of a pest free area in the Sub County will rely on effective mass trapping exercise for more than six months in order to remove all the flies, followed by protection of the area from emerging flies using strategically placed traps and various cultural practices, accompanied by strong farmer participation and stakeholder partnership to ensure integrity of exported fruit sources. Keywords: Asian invasive fruit fly, pest free area, fence traps, Agro ecological zones

Evaluation of traps and attractants for mass trapping of African Invader Fly, <i>Bactrocera invadens</i> on mango in south west Nigeria

Mass trapping has demonstrated to be a powerful tool in the control of fruit flies, its use in African countries has currently increased remarkably as a control method. This study evaluated the efficacy of two traps; Lynfield Trap (LT) and Modified Lynfield Trap(MLT) and two lures (Methyl Eugenol (ME) and Protein Bait from Brewery Waste (PBBW)) for mass trapping of Bactrocera invadens Drew, Tsuruta, & White (Diptera: Tephritidae) on mango during 2014 and 2015 fruiting seasons. Traps containing attractants were randomly set on mango homestead trees in three replicates at three selected locations in Ibadan Southwest Nigeria. Results showed no significant difference (p > 0.01) between the trap types baited with ME attractant, although the MLT recorded higher catches of B. invadens during the two seasons. Methyl eugenol was significantly (p < 0.01) more effective than hydrolyzed protein bait from brewery waste in mass trapping B. invadens in the three locations of study. However, ME trapped only male B invadens while PBBW trapped both male and female. B. invadens population was highest at the peak of mango ripening (June) and the density of flies trapped in 2015 was significantly (p < 0.05) higher than 2014 in all the locations. Suitable choice of traps, lures and season enhances the mass trapping results. The use of Protein bait from brewery waste and modified lynfield trap for monitoring B. invadens and population suppression is promising and should be encouraged since they attract both sexes and less cost effective.Keywords: trapping, mango, lures, fruit fly, control

Efficacy of Two Food-based Attractants and Methyl eugenol for Mass trapping of African invader fly, Bactrocera invadens (Diptera:Tephritidae) on Bush mango in Ibadan, Southwest Nigeria

Efficacy of Two Food-based Attractants and Methyl eugenol for Mass trapping of African invader fly, Bactrocera invadens (Diptera:Tephritidae) on Bush mango in Ibadan, Southwest Nigeria

COATING OF GUAVA (PSIDIUM GUAJAVA L.) FRUITS WITH BOTANICAL EDIBLE OILS FOR SHELF LIFE AND FRUIT FLIES

Guava (Psidium guajava L.) fruit is a popular nutritious dessert in Sudan. It is famous for its medicinal values as a prompt cure for digestive disorders and respiratory ailness this besides being a rich source of C vitamin. This fruit is highly amenable to fruit fly attack and it is a harbor of eggs of five different species [Ceratitis capitata Wied.; Ceratitis quinaria Bez.; Ceratitis cosyra Wlk.; Bactrocera invadens De Trusta and White and Bactrocera zonata (Saunders)] in Sudan. This is stimulating to a chain of endless research to combat these notorious pests which account for huge losses in this crop that reach up to 80% or even more. This research aimed at evaluating the effect of oil coating on fruit fly infestation and the quality indexes in guava fruit using five different botanical edible oils. The results showed that groundnut (Arachis hypogaea L.) (GNO), sesame (Sesamum indicum L.) (SO), baobab (Adansonia digitata L.) (BO), olive (Olea europaea L.) (OO) and neem (Azadirachta indica A. Juss) (NO) oils effected a corrected disinfestation of 80, 72, 56, 52 and 28% in test fruits brought from Kadaro orchards North Khartoum, respectively. The corresponding average readings of maggots in infested fruits were 4, 17, 11, 5, 7 and [10 (for the first 4) and 26 for NO] in the control. Two essential quality indexes were checked in test fruits which included fruit color (FC) and firmness (FF). The corrected test readings reflected 64, 80, 44, 52,-4 and [8 (for the first 4) and 20 for NO] in the control sustained FC for GNO, SO, BO, OO, NO and the control, respectively. However, the corresponding readings for FF were 3 (medium) for all oils and 4 (soft) for the controls. These results reflect a potent and the best efficacy of peanut and sesame oils, of the five test oils, in controlling fruit flies in guava and extending its shelf life.

Epicuticular chemistry reinforces the new taxonomic classification of the Bactrocera dorsalis species complex (Diptera: Tephritidae, Dacinae).

Bactrocera invadens Drew, Tsuruta & White, Bactrocera papayae Drew & Hancock, and Bactrocera philippinensis Drew & Hancock, key pest species within the Bactrocera dorsalis species complex, have been recently synonymized under the name Bactrocera dorsalis (Hendel). The closely related Bactrocera carambolae Drew & Hancock remains as a discrete taxonomic entity. Although the synonymizations have been accepted by most researchers, debate about the species limits remains. Because of the economic importance of this group of taxa, any new information available to support or deny the synonymizations is valuable. We investigated the chemical epicuticle composition of males and females of B. dorsalis, B. invadens, B. papayae, B. philippinensis, and B. carambolae by means of one- and two-dimensional gas chromatography–mass spectrometry, followed by multiple factor analyses and principal component analysis. Clear segregation of complex cuticule profiles of both B. carambolae sexes from B. dorsalis (Hendel) was observed. In addition to cuticular hydrocarbons, abundant complex mixtures of sex-specific oxygenated lipids (three fatty acids and 22 fatty acid esters) with so far unknown function were identified in epicuticle extracts from females of all species. The data obtained supports both taxonomic synonymization of B. invadens, B. papayae, and B. philippinensis with B. dorsalis, as well as the exclusion of B. carambolae from B. dorsalis.

Activity Pattern and Distribution of African Invader Fly, Bactrocera invadens (Drew, Tsuruta and White) [Diprera: Tephritidae] in Ondo State, Southwestern Nigeria

Activity Pattern and Distribution of African Invader Fly, Bactrocera invadens (Drew, Tsuruta and White) [Diprera: Tephritidae] in Ondo State, Southwestern Nigeria

Diversity of Frugivore Fruit Fly Species (Diptera: Tephritidae) in Niger State, Southern Guinea Savannah Zone of Nigeria

The diversity of frugivore fruit fly (Diptera: Tephritidae) species was studied from May-October, 2014 in orchards of mango, cashew, guava and water melon situated in Paikoro and Lapai Local Government Areas of Niger State, Nigeria, The flies were trapped using Ball and Steiner traps baited with torula yeast and a para-pheromone, methyl eugenol, respectively. Traps were cleared at 7-day intervals and serviced monthly. Trapped flies were collected in zip-packs, transferred into 75% alcohol and identified in the laboratory. Twenty-three fly species within the genera Bactrocera, Ceratitis, Dacus, Perilampsis and Trirhithrum were collected, with Ceratitis species being the richest. The trap with para-pheromone trapped higher number of species than that with torula yeast bait. Bactrocera invadens was the most abundant species at all sites. Alpha diversity index showed that the mango orchard was richer in species than other sites while Beta diversity index revealed high similarities among sampling sites.

Abundance of African invader fly, Bactrocera invadens drew, tsuruta and white (diptera: tephritidae) and influence of weather parameters on trap catches in mango in the Volta region of Ghana.

The seasonal abundance of African Invader fly, Bactrocerainvadens and the influence of temperature and rainfall on fly catches was determined in two agro ecological zones; moist semi-deciduous forest area and the coastal grassland area of the Volta Region of Ghana for year of mango production. Traps containing methyl eugenol were used in monitoring the abundance of the Africa invader fly, Bactrocera invadens where data on both temperature and rainfall were collected from Meteorological Services of Ghana in Volta region. A total of 49,322 organisms captured, 45,829 were identified as Bactrocerainvadens and 3493 were non-fruit fly. There were significant differences (p < 0.05) in the number of Bactrocerainvadens captured between the agro ecological zones with relative fly densities of 5.06 F/T/D in moist semi deciduous forest area and 2.38 F/T/D in the coastal grassland zone. The result shows that climatic factors affected Bactrocerainvadens differently in different agro ecological area. There was negative correlation and highly significant (p < 0.001) correlation between fruit flies and temperature whereas there was negative correlation and high significant (p < 0.01) difference between rainfall in the moist semi deciduous forest area. In the coastal grassland area, there was negative correlation and highly significant (p < 0.001) between Bactrocerainvadens for both rainfall and temperature. Bactrocerainvadens activities peaked differently during the study period due to favourable climatic conditions. The activities of Bactrocerainvadens peaked during weeks 7 and 29 in the moist semi deciduous forest area while their activities peaked during weeks 3 and 24 for the coastal grassland areas. Both agro ecological zones recorded the presence of Bactrocerainvadens, their number and proportion varied considerably with associated effects of the weather parameters on their abundance. The effect of weather parameters on the abundance of bactrocera invadens requires the development of degree day models to manage them.

Preliminary inventory of hymenopteran parasitoids associated with fruit-infesting flies (Diptera: Tephritidae) in Northern Ghana

ABSTRACTBaseline studies were conducted to determine the parasitoids associated with fruit flies in the northern savanna ecology of Ghana. Fruit fly puparia obtained from incubation of 17 host fruit species were maintained in rearing cages for the emergence of parasitoid wasps. Four species of braconid parasitoids namely, Fopius caudatus (Szépligeti), Psyttalia cosyrae (Wilkinson), Psyttalia concolor (Szépligeti) and Diachasmimorpha fullawayi (Silvestri) were recovered. F. caudatus was the most abundant parasitoid (61.0%) reared from most host fruits while D. fullawayi was the least abundant (7.7%). The overall mean parasitism rate was 7.1% with the highest record in Annona senegalensis Pers., Sarcocepholus latifolium S. Bruce and Icacina senegalensis Juss. Ceratitis cosyra and Bactrocera invadens were the fruit fly species most commonly reared that produced F. caudatus, and to a lesser extent, P. cosyrae. The peak occurrence of the parasitoids coincided with the peak of the rains and the maturity period of many of the host fruits. This first inventory of tephritid parasitoids in Ghana provides critical baseline data for biological control efforts in the future.

Future Risks of Pest Species under Changing Climatic Conditions.

Most agricultural pests are poikilothermic species expected to respond to climate change. Currently, they are a tremendous burden because of the high losses they inflict on crops and livestock. Smallholder farmers in developing countries of Africa are likely to suffer more under these changes than farmers in the developed world because more severe climatic changes are projected in these areas. African countries further have a lower ability to cope with impacts of climate change through the lack of suitable adapted management strategies and financial constraints. In this study we are predicting current and future habitat suitability under changing climatic conditions for Tuta absoluta, Ceratitis cosyra, and Bactrocera invadens, three important insect pests that are common across some parts of Africa and responsible for immense agricultural losses. We use presence records from different sources and bioclimatic variables to predict their habitat suitability using the maximum entropy modelling approach. We find that habitat suitability for B. invadens, C. cosyra and T. absoluta is partially increasing across the continent, especially in those areas already overlapping with or close to most suitable sites under current climate conditions. Assuming a habitat suitability at three different threshold levels we assessed where each species is likely to be present under future climatic conditions and if this is likely to have an impact on productive agricultural areas. Our results can be used by African policy makers, extensionists and farmers for agricultural adaptation measures to cope with the impacts of climate change.

The status of Bactrocera invadens Drew, Tsuruta & White (Diptera: tephritidae) inferred from complete mitochondrial genome analysis

In this study, the complete 15,911 bp mitochondrial genome (mitogenome) of Bactrocera invadens was sequenced. To estimate the status of B. invadens, all available mitogenomes of Bactrocera were downloaded from GenBank for phylogenetic analysis. Phylogenetic analyses showed that B. invadens, B. philippinensis, B. papayae, and three B. dorsalis sequences formed a well-supported clade with very short terminal branch lengths, indicting the relatively close evolutionary relationships of these taxa. The results further supported that B. invadens, the same as B. philippinensis and B. papayae, belongs to the same species as B. dorsalis.

Historical perspective on the synonymization of the four major pest species belonging to the Bactrocera dorsalis species complex (Diptera, Tephritidae).

An FAO/IAEA-sponsored coordinated research project on integrative taxonomy, involving close to 50 researchers from at least 20 countries, culminated in a significant breakthrough in the recognition that four major pest species, Bactrocera dorsalis, Bactrocera philippinensis, Bactrocera papayae and Bactrocera invadens, belong to the same biological species, Bactrocera dorsalis. The successful conclusion of this initiative is expected to significantly facilitate global agricultural trade, primarily through the lifting of quarantine restrictions that have long affected many countries, especially those in regions such as Asia and Africa that have large potential for fresh fruit and vegetable commodity exports. This work stems from two taxonomic studies: a revision in 1994 that significantly increased the number of described species in the Bactrocera dorsalis species complex; and the description in 2005 of Bactrocera invadens, then newly incursive in Africa. While taxonomically valid species, many biologists considered that these were different names for one biological species. Many disagreements confounded attempts to develop a solution for resolving this taxonomic issue, before the FAO/IAEA project commenced. Crucial to understanding the success of that initiative is an accounting of the historical events and perspectives leading up to the international, multidisciplinary collaborative efforts that successfully achieved the final synonymization. This review highlights the 21 year journey taken to achieve this outcome.

Cytogenetic and symbiont analysis of five members of the B. dorsalis complex (Diptera, Tephritidae): no evidence of chromosomal or symbiont-based speciation events.

The Bactrocera dorsalis species complex, currently comprising about 90 entities has received much attention. During the last decades, considerable effort has been devoted to delimiting the species of the complex. This information is of great importance for agriculture and world trade, since the complex harbours several pest species of major economic importance and other species that could evolve into global threats. Speciation in Diptera is usually accompanied by chromosomal rearrangements, particularly inversions that are assumed to reduce/eliminate gene flow. Other candidates currently receiving much attention regarding their possible involvement in speciation are reproductive symbionts, such as Wolbachia, Spiroplasma, Arsenophonus, Rickettsia and Cardinium. Such symbionts tend to spread quickly through natural populations and can cause a variety of phenotypes that promote pre-mating and/or post-mating isolation and, in addition, can affect the biology, physiology, ecology and evolution of their insect hosts in various ways. Considering all these aspects, we present: (a) a summary of the recently gained knowledge on the cytogenetics of five members of the Bactrocera dorsalis complex, namely Bactrocera dorsalis s.s., Bactrocera invadens, Bactrocera philippinensis, Bactrocera papayae and Bactrocera carambolae, supplemented by additional data from a Bactrocera dorsalis s.s. colony from China, as well as by a cytogenetic comparison between the dorsalis complex and the genetically close species, Bactrocera tryoni, and, (b) a reproductive symbiont screening of 18 different colonized populations of these five taxa. Our analysis did not reveal any chromosomal rearrangements that could differentiate among them. Moreover, screening for reproductive symbionts was negative for all colonies derived from different geographic origins and/or hosts. There are many different factors that can lead to speciation, and our data do not support chromosomal and/or symbiotic-based speciation phenomena in the taxa under study.

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.

Resolving cryptic species complexes of major tephritid pests.

An FAO/IAEA Co-ordinated Research Project (CRP) on “Resolution of Cryptic Species Complexes of Tephritid Pests to Overcome Constraints to SIT Application and International Trade” was conducted from 2010 to 2015. As captured in the CRP title, the objective was to undertake targeted research into the systematics and diagnostics of taxonomically challenging fruit fly groups of economic importance. The scientific output was the accurate alignment of biological species with taxonomic names; which led to the applied outcome of assisting FAO and IAEA Member States in overcoming technical constraints to the application of the Sterile Insect Technique (SIT) against pest fruit flies and the facilitation of international agricultural trade. Close to 50 researchers from over 20 countries participated in the CRP, using coordinated, multidisciplinary research to address, within an integrative taxonomic framework, cryptic species complexes of major tephritid pests. The following progress was made for the four complexes selected and studied:Anastrepha fraterculus complex – Eight morphotypes and their geographic and ecological distributions in Latin America were defined. The morphotypes can be considered as distinct biological species on the basis of differences in karyotype, sexual incompatibility, post-mating isolation, cuticular hydrocarbon, pheromone, and molecular analyses. Discriminative taxonomic tools using linear and geometric morphometrics of both adult and larval morphology were developed for this complex.Bactrocera dorsalis complex – Based on genetic, cytogenetic, pheromonal, morphometric, and behavioural data, which showed no or only minor variation between the Asian/African pest fruit flies Bactrocera dorsalis, Bactrocera papayae, Bactrocera philippinensis and Bactrocera invadens, the latter three species were synonymized with Bactrocera dorsalis. Of the five target pest taxa studied, only Bactrocera dorsalis and Bactrocera carambolae remain as scientifically valid names. Molecular and pheromone markers are now available to distinguish Bactrocera dorsalis from Bactrocera carambolae.Ceratitis FAR Complex (Ceratitis fasciventris, Ceratitis anonae, Ceratitis rosa) – Morphology, morphometry, genetic, genomic, pheromone, cuticular hydrocarbon, ecology, behaviour, and developmental physiology data provide evidence for the existence of five different entities within this fruit fly complex from the African region. These are currently recognised as Ceratitis anonae, Ceratitis fasciventris (F1 and F2), Ceratitis rosa and a new species related to Ceratitis rosa (R2). The biological limits within Ceratitis fasciventris (i.e. F1 and F2) are not fully resolved. Microsatellites markers and morphological identification tools for the adult males of the five different FAR entities were developed based on male leg structures.Zeugodacus cucurbitae (formerly Bactrocera (Zeugodacus) cucurbitae) – Genetic variability was studied among melon fly populations throughout its geographic range in Africa and the Asia/Pacific region and found to be limited. Cross-mating studies indicated no incompatibility or sexual isolation. Host preference and genetic studies showed no evidence for the existence of host races. It was concluded that the melon fly does not represent a cryptic species complex, neither with regard to geographic distribution nor to host range. Nevertheless, the higher taxonomic classification under which this species had been placed, by the time the CRP was started, was found to be paraphyletic; as a result the subgenus Zeugodacus was elevated to genus level.