Dorsalis Males Research Articles

Less is more: Fewer attract-and-kill sites improve the male annihilation technique against Bactrocera dorsalis (Diptera: Tephritidae).

The Male Annihilation Technique (also termed the Male Attraction Technique; "MAT") is often used to eradicate pestiferous tephritid fruit flies, such as Bactrocera dorsalis (Hendel). MAT involves the application of male-specific attractants combined with an insecticide in spots or stations across an area to reduce the male population to such a low level that suppression or eradication is achieved. Currently, implementations of MAT in California and Florida targeting B. dorsalis utilize the male attractant methyl eugenol (ME) accompanied with a toxicant, such as spinosad, mixed into a waxy, inert emulsion STATIC ME (termed here "SPLAT-MAT-ME"). While highly effective against ME-responding species, such applications are expensive owing largely to the high cost of the carrier matrix and labor for application. Until recently the accepted protocol called for the application of approximately 230 SPLAT-MAT-ME spots per km2; however, findings from Hawaii suggest a lower density may be more effective. The present study adopted the methods of that earlier work and estimated kill rates of released B. dorsalis under varying spot densities in areas of California and Florida that have had recent incursions of this invasive species. Specifically, we directly compared trap captures of sterilized marked B. dorsalis males released in different plots under three experimental SPLAT-MAT-ME densities (50, 110, and 230 per km2) in Huntington Beach, CA; Anaheim, CA; and Sarasota-Bradenton, FL. The plots with a density of 110 sites per km2 had a significantly higher recapture proportion than plots with 50 or 230 sites per km2. This result suggests that large amounts of male attractant may reduce the ability of males to locate the source of the odor, thus lowering kill rates and the effectiveness of eradication efforts. Eradication programs would directly benefit from reduced costs and improved eradication effectiveness by reducing the application density of SPLAT-MAT-ME.

The Discovery of the Potential Attractive Compounds of Bactrocera dorsalis (Hendel)

Bactrocera dorsalis (Hendel) (B. dorsalis) is an important agricultural invasive pest that causes significant economic losses in tropical and subtropical fruit and vegetable crops. In this study, the proteins related to the sense of smell and taste of B. dorsalis, such as OBP, PBP, OR, IR, SNMP and CSP, were screened based on B. dorsalis transcriptome data. By integrating the compounds that were reported to be attractive to B. dorsalis, similar compounds of hydrocarbon compounds were obtained. Molecular docking was used to predict the binding between the similar compounds and the OBP, PBP, OR, IR, SNMP and CSP proteins. Network pharmacology was used to screen the potentially attractive compounds, and ecological experiments with B. dorsalis were finally conducted to verify the effect of these potentially attractive compounds on B. dorsalis. The results showed that the G protein-coupled receptor [BR: KO04030] and ion channel [BR: KO04040] pathways were closely related to the odor tropism of B. dorsalis. A total of 84 compounds, such as mitemcinal, exemestane and midecamycin, have potential binding effects on the B. dorsalis odor receptor proteins. The results of the ecological experiments showed that 1 mg/mL and 0.1 mg/mL 19-norandrostenedione, 1 mg/mL progesterone compounds was significantly attractive to B. dorsalis males, while 0.1 mg/mL exemestane was significantly attractive to B. dorsalis females. In this study, network pharmacology technology was used to discover the potential attractive compounds for B. dorsalis, which is important for the development and subsequent prevention and control of B. dorsalis. It can provide a reference in improving the success rates of clinical trials of new pest control products and in reducing the time and cost of drug development.

Response of some mango-infesting fruit flies to aqueous solutions of the basil plant Ocimum tenuiflorum L

IntroductionHorticulture is an important sub-sector for many African countries. Tephritid fruit flies continue to cause serious direct and indirect damage to the sub-sector. The male annihilation technique (MAT) using methyl eugenol (ME) is among the most revered techniques in fruit fly management. However, ME-based lures are only available to some farmers in Africa. Several basils of the genus Ocimum produce ME.MethodsIn laboratory experiments, we used a dual choice olfactometer to assess the attraction of adult oriental fruit fly Bactrocera dorsalis to intact plants, 100 µL commercial methyl eugenol (ME) (positive control), 10 mg/mL of O. tenuiflorum aqueous extract (Otae), and a negative control (blank). Large arena experiments were conducted to compare the responses of four fruit fly species of economic importance in Africa to Otae-baited traps.ResultsIn dual choice olfactometer assay, more B. dorsalis males (78.6%) than females (23.8%) were attracted to Otae. Most B. dorsalis males were attracted to the positive control (90.5%) and 10 mg/mL Otae (88.5%) compared to the whole plant (84.0%). In large arena experiments, Otae attracted the most B. dorsalis males (47.7%), followed by Zeugodacus cucurbitae males (25.1%), while males of Ceratitis species were the least attracted. The analysis of headspace volatiles from aerial plants, Otae and essential oil using gas chromatography-mass spectrometry detected 97 compounds. The intact plant without flowers, intact plant with flowers, Otae, and the O. tenuiflorum essential oil contributed 76, 62, 33 and 28 compounds, respectively. ME comprised the top three most abundant compounds, especially in the essential oil.DiscussionOur study confirms the potential of O. tenuiflorum as a source of ME for tephritid fruit fly integrated management in Africa. Otae, a readily available alternative to commercial ME, can be used to develop fruit fly-baited traps, particularly for smallholder farmers.

Assessment of non-methyl eugenol-responding lines of Bactrocera dorsalis (Diptera: Tephritidae) males on lure response and mating.

Bactrocera dorsalis (Hendel) (Diptera: Tephritidae), is a major global pest of fruits. Currently, the sequential male annihilation technique, followed by the sterile insect technique has been used to significantly reduce the population of feral males in this species. However, issues with sterile males being killed by going to male annihilation traps have reduced the efficacy of this approach. The availability of males that are non-methyl eugenol-responding would minimize this issue and increase the efficacy of both approaches. For this, we recently established two separate lines of non-methyl eugenol-responding males. These lines were reared for 10 generations and in this paper, we report on the assessment of males from these lines in terms of methyl eugenol response and mating ability. We saw a gradual decrease in non-responders from ca. 35 to 10% after the 7th generation. Despite that, there were still significant differences until the 10th generation in numbers of non-responders over controls using laboratory strain males. We did not attain pure isolines of non-methyl eugenol-responding males, so we used non-responders from the 10th generation of those lines as sires to initiate two reduced-responder lines. Using these reduced responder flies, we found that there was no significant difference in mating competitiveness when compared with control males. Overall, we suggest that it may be possible to establish lines of low or reduced responder males to be used for sterile release programs, that could be applied until the 10th generation of rearing. Our information will contribute to the further development of an increasingly successful management technique incorporating the use of SIT alongside MAT to contain wild populations of B. dorsalis.

Exploration of Clove Bud (Syzygium aromaticum) Essential Oil as a Novel Attractant against Bactrocera dorsalis (Hendel) and Its Safety Evaluation.

Simple SummaryBactrocera dorsalis is among the most economically harmful pests. The lure-and-kill approach is an environmentally friendly and innovative method that offers an opportunity for sustainable surveillance and control of B. dorsalis. However, such a strategy requires highly effective pest attractants. In the current study, we compared the attractive activity of twelve flower essential oils against B. dorsalis adults via the indoor trapping assay. Meanwhile, we studied the attractive features of clove bud essential oil (CBEO) for males under laboratory conditions. Further, we also investigated CBEO’s attractancy to their natural predator, the ladybirds, and its cytotoxicity against non-target organisms’ cells. In particular, sexually mature males were dramatically attracted to the CBEO. Furthermore, the CBEO exhibited no significant attractancy to ladybirds nor cytotoxicity against normal human and mouse cells. The results revealed that CBEO shows potential for development as an eco-friendly and novel attractant agent for the control of B. dorsalis.The oriental fruit fly Bactrocera dorsalis (Hendel) is a destructive polyphagous species that targets many economically important fruits and vegetables. The primary control of B. dorsalis relies mainly on the use of synthetic chemicals, and excessive use of these chemicals has adverse effects on both the environment and human health. Environmentally friendly management of pests involving plant essential oils is useful for controlling the populations of pests responsible for decreasing the yields and quality of crops. In the present study, we demonstrate that clove bud essential oil (CBEO) is strongly attractive to sexually mature males. Mature males responded to the CBEO differently throughout the day; the strongest response was elicited during the day and decreased at dusk. Virgin and mated mature males did not respond differently to CBEO. No obvious response behaviour to the CBEO was observed in two species of beneficial natural predator ladybirds. In addition, a cytotoxicity assessment demonstrated that CBEO is nontoxic to normal human and mouse cells. Based on our laboratory experiments, CBEO may serve as a promising, sustainable, and environmentally friendly attractant for B. dorsalis males; however, field experiments are needed to confirm this hypothesis.

BdorOBP69a is involved in the perception of the phenylpropanoid compound methyl eugenol in oriental fruit fly (Bactrocera dorsalis) males

The oriental fruit fly (Bactrocera dorsalis) is a devastating fruit pest that infests more than 450 plant species. Methyl eugenol (ME) has been used as male attractant to monitor and eradicate B. dorsalis populations for 70 years, but the molecular basis of its activity remains largely unclear. Previously, BdorOBP83b and BdorOBP56f-2 as odorant binding proteins (OBPs) were identified responsible for ME perception. In this study, ME-induced expression profiles and in vitro binding assays revealed that BdorOBP69a is also produced in response to ME and binds directly to it with strong affinity (Kd = 9.54 μM). BdorOBP69a−/− null mutants generated by CRISPR/Cas9 mutagenesis showed significantly lower electroantennogram and behavioral responses to ME than wild-type controls. Molecular docking analysis followed by site-directed mutagenesis showed that residues Leu89 and Phe145 are essential for the interaction between BdorOBP69a and ME. BdorOBP69a is therefore an important component involved in the perception of ME in B. dorsalis and a promising molecular target for the development of new male attractants. The molecular docking and binding assay data also provide an important reference for future OBP gene manipulation and ME chemical engineering to improve the efficiency of male attractants.

Mating Competitiveness of Bactrocera dorsalis (Diptera: Tephritidae) Males From a Genetic Sexing Strain: Effects of Overflooding Ratio and Released Females.

The oriental fruit fly, Bactrocera dorsalis (Hendel), is a global pest that infests a range of fruit and vegetables. Males are attracted to methyl eugenol, and control is often achieved by the Male Annihilation Technique, where methyl eugenol + insecticide dispensers are deployed to eliminate males, preclude matings, and reduce population growth. The Sterile Insect Technique (SIT) has also been used to control B. dorsalis. The SIT involves the release of mass-reared, sterilized males to achieve matings with wild females, who then produce inviable eggs. Two key elements of SIT include the overflooding ratio achieved (sterile: wild males) and the strain type utilized, namely bisexual or genetically sexed (allowing male-only releases). Here, we describe the effects of these two factors on the mating competitiveness of a males from a genetic sexing strain of B. dorsalis, termed DTWP. Mating success was scored for DTWP versus wild males in field cages at ratios of 1:2, 1:1, 2:1, and 10:1 both when DTWP females were or were not concurrently released with DTWP males. Close correspondence was found between observed numbers of matings of particular male-female combinations and expected numbers based on the numbers of flies released of each sex and each strain. As a result, the proportion of total matings achieved by the DTWP across the eight treatments showed a corresponding increase with overflooding ratio. At a given ratio, DTWP males had a higher relative mating success when DTWP females were absent rather than present, although the reason for this was unclear.

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

• Bulbophyllum cheiri flowers contain methyl eugenol (ME) and attract Oriental fruit fly males. • The flower attracts more flies than an equivalent quantity of synthetic ME in traps. • When flanked by traps with higher doses of ME, flowers still attract flies though in lower numbers. 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.

Assessment of 2-allyl-4,5-dimethoxyphenol safety and attractiveness to mature males of Bactrocera dorsalis (Hendel)

Males of the Oriental fruit fly Bactrocera dorsalis (Hendel) are highly attracted to, and compulsively feed, on methyl eugenol (ME). ME is converted into 2-allyl-4,5-dimethoxyphenol (DMP) and (E)-coniferyl alcohol (E-CF), which are temporarily sequestered in the fly’s rectal gland prior to being released at dusk. Previous research initially confirmed that DMP is a relatively strong lure to B. dorsalis males. However, the characteristics of males’ response to DMP and toxicology of DMP remains largely unclear. In our study, we demonstrated that DMP was more attractive to sexually mature males than E-CF tested in laboratory bioassays. Interestingly, the responsiveness of mature males to DMP was not uniform throughout the day, eliciting the highest response during the day and dropping to a low level at night. Furthermore, there were no significant differences between the olfactory responses of virgin and mated mature males to DMP. No obvious signs of toxic symptom and deaths were observed in mice during a 14-day acute oral toxicity testing. Further, toxicologically significant changes were not observed in body weight, water intake, food consumption, and absolute and relative organ weights between control and treated groups, implying DMP could be regarded as nontoxic. Lastly, the cytotoxicity data of DMP on cells showed that it exhibited no significant cytotoxicity to normal human and mouse cells. Taken together, results from both the acute and cellular toxicity experiments demonstrated the nontoxic nature of DMP. In conclusion, DMP shows promise as an effective and eco-friendly lure for B. dorsalis males, and may contribute to controlling B. dorsalis in the flied.

Improvement of protein bait produced from beer yeast waste for controlling Bactrocera dorsalis (Diptera: Tephritidae) in China

• Four preservatives had different inhibition effects to bacteria at varied doses. • The inhibition of all preservatives and antibiotics increased with dose increased. • Kanamycin at all doses was the most effective antibiotics in depressing mixed bacteria. • High-dose addition of guava essence can significantly improve the bait attractiveness. In the present study, preservatives and antibiotics were applied in a variety of doses to assess their effects on the beer waste-based protein bait, a product widely used to control populations of Bactrocera dorsalis (Diptera: Tephritidae). Screening was performed using the inhibition zone method against the dominant bacteria in deteriorated protein bait. Additionally, the attractiveness of the bait was assessed after respectively adding different doses of methyl eugenol, brown sugar solution, ammonium acetate, and guava essence, as determined by bio-cage tests. The results showed that the four selected preservatives had different inhibition effects at different dose levels, and that the level of inhibition increased with dose: at the highest dose of 1:1 (v:v), sodium benzoate can significantly inhibit Staphylococcus spp., potassium sorbate can significantly inhibit Lactobacillus spp., sodium nitrite can significantly inhibit Escherichia spp. and ethyl p-hydroxybenzoate can significantly inhibit Staphylococcus spp. and Xanthomonas spp. Among three antibiotics, kanamycin was the most effective in suppressing a mix of all four bacteria for all tested doses. In terms of lure performance, the addition of four substances in various ratios into the protein bait were found to have varying effects on its attractiveness to B. dorsalis females and males. Specifically, the addition of a high-dose of guava essence could significantly enhance the attractiveness of the bait. Our findings will help to enhance the effectiveness of protein bait applications by prolonging the quality guarantee period and improving its attractiveness toward both female and male B. dorsalis .

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

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. 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. 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.

Quantification and Impact of Cold Storage and Heat Exposure on Mass Rearing Program of Bactrocera dorsalis (Diptera:Tephritidae) Genetic Sexing Strain.

Simple SummaryStoring insects at low temperature has been an effective approach for mass rearing programs, which can increase the shelf-life of bioagents and flexibly manipulate their pre-release periods. However, introducing insects to temperatures outside of their accustomed range can lead to stress and thereby influence their quality and competitiveness in the field. Bactrocera dorsalis is an economically important pest can devastate many fruits and vegetables, and cold storage has been used in storing, packing and shipping of sterile B. dorsalis males to control the wild population, but the impact of cold storage on the quality of B. dorsalis has never been investigated. Here, we examined the impacts of pupal cold storage on developmental parameters and quality of B. dorsalis adults. Overall, we found that pupal cold storage has a negative effect on some biological parameters of B. dorsalis, especially in fecundity. Thus, heat exposure was further conducted on the post-storage adults, and our results show that short-term heat exposure could partially compensate for the loss in fecundity in B. dorsalis adults resulting from the pupal cold storage. Our findings indicate that the flexibility of the B. dorsalis mass rearing program could be improved by utilizing cold storage and heat exposure.Cold storage and heat exposure are crucial components of tephritid fruit fly mass-rearing programs, as they influence the development and fitness traits of produced flies. This work investigated the effects of cold storage on the pupal developmental parameters and quality of Bactrocera dorsalis (Hendel) genetic sexing strain (GSS) adults. Furthermore, the impact of short-term thermal exposure on the fecundity of B. dorsalis (GSS) that also underwent pupal cold storage was examined. Our results show that pupal development time, emergence rate, partial emergence rate, flight ability and fecundity were significantly affected by low temperature and pupal age and their interaction. Pupal cold storage did not pose negative impacts on the mating competition and response to methyl eugenol (ME) in the males. In addition, compared with the adults that were subjected to the same pupal storage protocol (five-day-old pupae stored at 13 °C), adult exposure to 41 °C for 1 h showed significant reparative effects on fecundity. In summary, the cold storage procedure of B. dorsalis (GSS) pupae has the potential to improve the flexibility and efficiency of mass-rearing schedules. Furthermore, short-term thermal exposure showed reparative effects on the fecundity costs induced by pupal cold storage in B. dorsalis (GSS).

Evaluation of a Genetic Sexing Strain of the Oriental Fruit Fly as a Candidate for Simultaneous Application of Male Annihilation and Sterile Insect Techniques (Diptera: Tephritidae).

The oriental fruit fly, Bactrocera dorsalis (Hendel), is an important pest of fruits and vegetables, and many countries operate surveillance programs to detect infestations and, if needed, implement costly control efforts. The Male Annihilation Technique (MAT), which involves deployment of the male lure methyl eugenol (ME) to reduce or eliminate the male population, has been used as a stand-alone strategy or as a precursor to the Sterile Insect Technique (SIT), which involves the release of sterile males to generate sterile male by wild female crosses and the production of inviable progeny. Modeling suggests that simultaneous implementation of MAT and SIT, rather than sequential deployment, increases the probability of successful eradication. Previous research has shown that B. dorsalis males that have fed on ME show reduced tendency to re-visit ME sources. Also, males fed ME gain a mating advantage over nonfed males. The goal of the present study was to evaluate the suitability of a genetic sexing strain of B. dorsalis as a candidate for concurrent implementation of MAT and SIT. Evaluation focused on the timing of prerelease exposure to methyl eugenol to identify the male age at which feeding upon the lure both i) reduces postrelease attraction to ME-baited traps (thus allowing the operation of MAT) and ii) enhances postrelease mating competitiveness (thus increasing the effectiveness of SIT). Results indicate that prerelease ME feeding by 6-d-old males, with release the following day, would allow effective, concurrent implementation of MAT and SIT.

Recaptures of feral Bactrocera dorsalis and B. umbrosa (Diptera: Tephritidae) males after feeding on methyl eugenol.

Two major fruit fly pest species, Bactrocera dorsalis and B. umbrosa, are strongly attracted to methyl eugenol (ME) found in >450 plant species. They are, however, exclusive pollinators of certain daciniphilous (attracting Dacini fruit flies) Bulbophyllum orchids. A comparison between the recaptures of feral males after feeding ad libitum on 0.6 mg ME (simulating an average floral quantity of an orchid flower - Trial 1) and 480 mg in Trial 2 was investigated using the non-invasive capture-mark-release-recapture (CMRR) technique. Based on daily CMRR over a 16-day period, using a different colour enamel paint each day, percentages of B. dorsalis males recaptured in Trial 1 were significantly higher than those in Trial 2. However, for B. umbrosa, percentages of recaptures for different day-specific colours were highly variable due to low fly numbers captured/day. In Trial 1, of 756 B. dorsalis males released, 36.4% were recaptured once, 7.7 twice, 2.4 three times and 0.4 four times. While in Trial 2 of 1157 released males, 6% were recaptured once and 0.3% twice. Of 67 B. umbrosa males released, 28.4% were recaptured once and none more than once in Trial 1. Nevertheless, of 119 flies released in Trial 2, 25.2% were recaptured once and 3.3% twice. Overall, many marked males did return to a single ME-source to 'refuel' ME (a sex pheromone precursor). The results also show that a relatively high number of flies paid multi-visitations to a single 0.6 mg ME-source and indicate that the presence of natural ME-sources may impact area-wide IPM programmes.

A field test on the effectiveness of male annihilation technique against Bactrocera dorsalis (Diptera: Tephritidae) at varying application densities.

Male Annihilation Technique (MAT) is a key tool to suppress or eradicate pestiferous tephritid fruit flies for which there exist powerful male lures. In the case of Bactrocera dorsalis (Hendel), a highly invasive and destructive species, current implementations of MAT utilize a combination of the male attractant methyl eugenol (ME) and a toxicant such as spinosad (“SPLAT-MAT-ME”) applied at a high density with the goal of attracting and killing an extremely high proportion of males. We conducted direct comparisons of trap captures of marked B. dorsalis males released under three experimental SPLAT-MAT-ME site densities (110, 220, and 440 per km2) near Hilo, Hawaii using both fresh and aged traps to evaluate the effectiveness of varying densities and how weathering of the SPLAT-MAT-ME formulation influenced any density effects observed. Counterintuitively, we observed decreasing effectiveness (percent kill) with increasing application density. We also estimated slightly higher average kill for any given density for weathered grids compared with fresh. Spatial analysis of the recapture patterns of the first trap service per replicate x treatment reveals similar positional effects for all grid densities despite differences in overall percent kill. This study suggests that benefits for control and eradication programs would result from reducing the application density of MAT against B. dorsalis through reduced material use, labor costs, and higher effectiveness. Additional research in areas where MAT programs are currently undertaken would be helpful to corroborate this study’s findings.

BdorOR88a Modulates the Responsiveness to Methyl Eugenol in Mature Males of Bactrocera dorsalis (Hendel).

Insect attractants are important prevention tools for managing populations of the Oriental fruit fly, Bactrocera dorsalis (Hendel), which is a highly destructive agricultural pest with health implications in tropical and subtropical countries. Methyl eugenol (ME) is still considered the gold standard of B. dorsalis attractants. Mature male flies use their olfactory system to detect ME, but the molecular mechanism underlying their olfactory detection of ME largely remains unclear. Here, we showed that ME activates the odorant receptors OR63a-1 and OR88a in mature B. dorsalis males antennae by RNA-Seq and qRT-PCR analysis. Interestingly, ME only elicited robust responses in the BdorOR88a/BdorOrco-expressing Xenopus oocytes, thus suggesting that BdorOR88a is necessary for ME reception and tropism in B. dorsalis. Next, our indoor behavioral assays demonstrated that BdorOR63a-1 knockdown had no significant effects on ME detection and tropism. By contrast, reducing the BdorOR88a transcript levels led to a significant decrease in the males’ responsiveness to ME. Taken together, our results gave novel insight in the understanding of the olfactory background to the Oriental fruit fly’s attraction toward ME.

Different methods of methyl eugenol application enhance the mating success of male Oriental fruit fly (Dipera: Tephritidae)

Males of Bactrocera dorsalis (Hendel) (Diptera: Tephritidae) are strongly attracted to methyl eugenol (ME) (1,2-dimethoxy-4-(2-propenyl)benzene), a phenylpropanoid compound occurring in many plant species. Feeding on ME is known to enhance male B. dorsalis mating competitiveness, which can increase the effectiveness of the sterile insect technique (SIT) manifold. However, currently used systems for holding the mass-reared males in fly emergence and release facilities before release, do not allow for application of ME through feeding. Therefore, the current study was designed to evaluate different delivery systems of ME that would be applicable for large-scale application to sterile males held in such facilities. Males of a genetic sexing strain (GSS) of B. dorsalis treated by ME-aromatherapy or ME-airblown-aromatherapy that were competing with ME-fed males achieved a similar level of mating success in walk-in field cages, but the mating success was significantly higher when compared to untreated males. The results confirm the feasibility of developing ME-airblown-aromatherapy as a practical way of large scale ME delivery to enhance the mating competitiveness of sterile B. dorsalis males.

Diversity of the cultivable gut bacterial communities associated with the fruit flies Bactrocera dorsalis and Bactrocera cucurbitae (Diptera: Tephritidae)

Gut microbes play an important role in insect morphogenesis, nutrition, development of resistance against parasitoids and detoxification of toxic compounds. A culture-based approach is therefore an useful tool for the characterization of cultivable microbial communities associated with the insect gut. In the present study an attempt was made to decipher the gender specificity of gut bacterial communities of two major fruit fly species of India viz., Bactrocera dorsalis (Hendel) and Bactrocera cucurbitae (Conquillett) (Diptera: Tephritidae). Based on molecular identification, B. dorsalis females were found to predominantly harbor the bacterial species Enterobacter cloacae, Enterobacter asburiae and Citrobacter freundii, while B. dorsalis males were found to harbor Providencia rettgerii, Klebsiella oxytoca, Enterococcus faecalis and Pseudomonas aeruginosa The cultivable diversity from females of B. cucurbitae comprised mainly of Morganella morganii and Bacillus pumilis while B.cucurbitae males were predominantly colonized by aerobic endospore formers viz., Bacillus cereus, B. licheniformis and B. subtilis. The above findings have thrown light on a distinct pattern of gender specific gut bacterial colonization in fruit flies, which have to be factored in for the formulation of fruit fly management strategies.

Efficacy of trapping systems for monitoring of Afrotropical fruit flies

AbstractThe efficacy of different attractant trap combinations for monitoring of Afrotropical fruit flies was evaluated in commercial fruit production areas and natural areas in the northern parts of South Africa. Five food‐based attractants: three‐component Biolure, a combination of ammonium acetate and trimethylamine, a combination of ammonium acetate and putrescine, torula yeast and Questlure, were evaluated in McPhail‐type traps. Two male lures targeting Ceratitis species: EGO Pherolure and trimedlure, were evaluated in Sensus bucket traps. Three male lures targeting Dacine fruit flies: methyl eugenol, cue lure and zingerone, were evaluated in Moroccan bucket traps. The three‐component Biolure was among the most effective food‐based attractant for females of Ceratitis capitata, C. rosa (R1 and R2), C. cosyra and Bactrocera dorsalis. EGO Pherolure attracted a wider range of Ceratitis species than trimedlure but was equally as effective as trimedlure for males of C. capitata and C. rosa (R1 and R2). Dacine flies were specific in their responses to male lures. Bactrocera dorsalis males responded mainly to methyl eugenol. Males of Dacus species responded to either cue lure or zingerone. Zingerone attracted two cucurbit‐infesting Dacus species: D. frontalis and D. durbanensis. For B. dorsalis, C. capitata and C. cosyra in commercial fruit production areas, patterns of female catches in traps containing food‐based attractants were different to patterns of male catches in male lure‐based traps. Implications of these trapping results are discussed.

Association between changes in reproductive activity and D-glucose metabolism in the tephritid fruit fly, Bactrocera dorsalis (Hendel).

Reproduction is an important life process in insects; however, few studies have attempted to demonstrate the association between reproductive activity and energy metabolism. To address this problem, we focused on the reproductive changes in Bactrocera dorsalis males. We analyzed B. dorsalis male gene expression profiles during mating (DM), 3 h after mating (A3HM) and 12 h after mating (A12HM). Gene annotation and pathway analyses of differentially expressed genes show that galactose metabolism and the starch and sucrose metabolism pathway activities were significantly higher in A12HM group. Moreover, the maltase D gene was the most strongly up-regulated gene. The D-glucose levels were significantly higher in A12HM group. Maltase D expression level was significantly higher in males reared with sucrose. Body weights of the males reared with D-glucose and sucrose were significantly higher than those of the males reared with yeast extract. We observed more mated males from the groups fed sucrose and D-glucose than from those fed yeast extract. The D-glucose levels in individual males were highest at 18:00 h, when flies exhibit the most active mating behavior. This study shows that the maltase D gene and D-glucose are the critical gene and substrate, respectively, in male B. dorsalis mating process.