Bactrocera Dorsalis Research Articles

Addition of ammonium acetate to torula yeast borax and its effect on captures of three species of economically important fruit flies (Diptera: Tephritidae).

Many countries operate continuous trapping programs to detect invasive fruit flies (Diptera: Tephritidae) that threaten fruit and vegetable production. Food-based attractants are an important component of these programs, as they are generalized baits that attract both sexes of all target species. However, food baits are considered weak attractants, and the development of improved food attractants would benefit surveillance efforts. Prior work on protein bait sprays demonstrated that the addition of ammonium acetate increased their attractiveness to tephritid fruit flies, and the present study was conducted to determine whether adding ammonium acetate to torula yeast borax solution (a commonly used food bait) similarly increased its attractiveness. Four field experiments were performed in Hawaii comparing captures of Ceratitis capitata (Wiedemann), Bactrocera dorsalis (Hendel), and Zeugodacus cucurbitae (Coquillett) in Multilure traps baited with standard torula yeast borax solution or with the standard solution plus 1% ammonium acetate. Captures of C. capitata and B. dorsalis were significantly higher for the ammonium acetate-supplemented solution, while results for Z. cucurbitae were inconsistent. In one experiment involving only C. capitata, an additional bait having 5% ammonium acetate was included, and captures for both 1% and 5% ammonium acetate exceeded the standard solution but did not differ from one another. Sex ratios of captured flies were similar between food baits for all three species. These results are compared with similar studies on Anastrepha spp., and implications for surveillance programs are discussed.

Insights into pupal development of Bactrocera dorsalis: factors influencing eclosion

In the life cycle of the oriental fruit fly where larvae reside within fruits and adults exhibit high activity, the pupal stage occurs in the soil, closely tied to agricultural soil management. This study investigates the impact of four variables (body orientation, burial depth, soil particle size, and pH) on Bactrocera dorsalis’ physiological preferences, eclosion rates, and pupal stage duration. Notably, body orientation, burial depth, soil texture (particle size), and pH affect eclosion rates. The fruit fly demonstrates a preference for a supine position during eclosion, with average eclosion rates of 97.33%, contrasting with decreases to 78.00% in a head-down position. Soil with mixed particle sizes is detrimental to pupal eclosion, reducing the eclosion rate to 56.67%. And at a pH of 9.98, eclosion rates decrease to 16.67%. These factors significantly influence eclosion rates However, these factors do not significantly alter the duration of the pupal stage, with mean changes not exceeding one day when experimental conditions are modified. These findings suggests that soil manipulations affecting these variables could reduce eclosion rates without compromising the uniformity of adult emergence. This study provides a foundation for environmentally friendly pest control practices and addresses gaps in the pupal stage research of the oriental fruit fly.

Pathobiont and symbiont contribute to microbiota homeostasis through Malpighian tubules-gut countercurrent flow in Bactrocera dorsalis.

Host-gut microbiota interactions are more complex than good or bad. Both gut symbiotic bacteria and pathobionts can provide essential functions to their host in one scenario and yet be detrimental to host health in another. So, these gut-dwelling bacteria must be tightly controlled to avoid harmful effects on the host. However, how pathobionts and other symbiotic bacteria coordinate to establish a host immune defense system remains unclear. Here, using a Tephritidae fruit fly Bactrocera dorsalis, we report that both pathobionts and other gut symbiotic bacteria release tyramine, which is recognized by the host insects. These tyramines induce the formation of insect-conserved Malpighian tubules-gut countercurrent flow upon bacterial infection, which requires tyramine receptors and aquaporins. At the same time, pathobionts but not gut symbiotic bacteria induce the generation of reactive oxygen species, which are preserved by the countercurrent flow, promoting bacteria elimination through increasing gut peristalsis. More importantly, our results show that the Malpighian tubules-gut countercurrent flow maintains proper microbiota composition. Our work suggests a model where pathobiont-induced reactive oxygen species are preserved by Malpighian tubules-gut countercurrent flow involving both pathobionts and symbiotic bacteria. Furthermore, our work provides a Malpighian tubules-gut interaction that ensures efficient maintenance of the gut microbiota.

Detoxification of Chlorfenapyr by a Parkin-GSTd2 Module in Bactrocera dorsalis (Diptera: Tephritidae).

The oriental fruit fly, Bactrocera dorsalis (Hendel), is a highly invasive and destructive pest. Chlorfenapyr is a widely used insecticide that disrupts mitochondrial activity. The Parkin protein plays conserved roles in maintaining mitochondrial homeostasis, but the role of Parkin in response to chlorfenapyr remains largely unknown. Here, we report that BdParkin is required for chlorfenapyr detoxification, and dsRNA targeting BdParkin improves the insecticidal efficacy of chlorfenapyr. Among the genes whose expression levels are affected by BdParkin RNAi, knock-down of the glutathione S-transferase gene BdGSTd2 increases the insecticidal efficacy of chlorfenapyr. Molecular docking reveals potential interactions between BdGSTd2 and tralopyril, an insecticidal metabolite of chlorfenapyr. These results suggest that BdParkin could impact the response of B. dorsalis to chlorfenapyr through metabolic processes regulated by BdGSTd2. Our findings could offer new insights into how insects detoxify chlorfenapyr and provide molecular targets for developing a sustainable management strategy for B. dorsalis.

Dynamic spatial network simulation accounting for multiple ecological factors provides practical recommendations for biosecurity early detection and rapid response (EDRR) strategies.

Globally the spread of invasive pests is being facilitated by increased human mobility and climate change. Simulation modelling can help assess biosecurity strategies for early detection and rapid response (EDRR), but has struggled to account for important factors in the invasion process, such as spatial and temporal variability in habitat suitability and connectivity; population dynamics; and multiple dispersal pathways. We developed a novel dynamic spatial network simulation approach based on spatial network theory that enables integration of a wider range of spatio-temporal factors than previous studies, calibrated it against extensive historical trapping data, and applied it to comprehensively analyse the EDRR strategy for Oriental fruit fly (Bactrocera dorsalis; OFF) in northern Australia. Simulations indicated that the chance of OFF reaching the mainland in the next 20 years could be up to 20% under the current EDRR strategy, depending on how optimistic or pessimistic model assumptions are, and highlighted possible improvements to the EDRR strategy for further consideration. Simulations under optimistic assumptions indicate that transport via wind is most important in OFF reaching the mainland, but under pessimistic assumptions transport via people carrying infected fruit becomes more important. Our new dynamic spatial network simulation approach can account for a wide range of spatio-temporal ecological factors to provide practical real-world recommendations. At a minimum, this approach only requires weather and population data, both of which are available globally from a variety of free and open sources, making it broadly applicable to assessing the EDRR strategies in place for different species in other locations. © 2024 Society of Chemical Industry.

Temperature-Dependent Pupation Depth in the Oriental Fruit Fly Bactrocera dorsalis and Its Implications for Biological Control.

The oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae), is a notable agricultural pest that undergoes pupation in the soil. Mortality risk from predation and parasitism decreases as the depth of the pupal location increases from the ground surface, with a one-centimetre increase in depth causing a significant change. Soil properties, such as moisture and hardness, influence pupation depth, but the effect of temperature has not been fully tested. This laboratory study examined whether a biologically important variation in pupation depth (e.g., one centimetre) is caused by naturally experienced temperature variations (20 to 35 °C) in B. dorsalis. The temperature-pupation depth relationship revealed a unimodal pattern, with the deepest pupation occurring at intermediate temperature levels and shallower pupation at the two extreme temperature ranges. Strong quantitative effects were observed, with the highest mean pupation depth of 40.8 mm at 27.5 °C and the lowest mean pupation depth of 15 mm at 35 °C. The observed quantitative effect suggests that temperature can strongly affect pupal mortality from predators and parasitoids by influencing pupation depth. Future studies that reveal the ability of biological control agents to forage underground for pupae at different temperatures are awaited, as this is key information for evaluating the effectiveness of these agents.

The miR-31b targets arylsulfatase B to regulate the ovarian development of Bactrocera dorsalis.

Reproduction is the basis of insect population growth and evolution, and encompasses ovarian development, reproductive behavior, and fecundity. Bactrocera dorsalis is a globally significant agricultural pest that is subject to quarantine, with mated females that can lay over 3000 eggs. The post-transcriptional regulation of ovarian development remains unclear. Here, miR-31b is shown to be involved in regulating Bactrocera dorsalis ovarian development. CRISPR/Cas9 was used to generate miR-31b loss-of-function mutations in Bactrocera dorsalis. The removal of miR-31b resulted in severely impaired ovarian development in adults, with phenotypes that included dramatically reduced egg production and hatching rates. The relationship between miR-31b and its target gene arylsulfatase B (ARSB) was subsequently identified using the methods of bioinformatics, transcriptomic sequencing, quantitative polymerase chain reaction (qPCR), RNA pull-down and dual-luciferase reporter assay. Finally, miR-31b was confirmed to bind the target gene arylsulfatase B to affect metabolism and thereby further hindered ovarian development of Bactrocera dorsalis. Overall, these results provide new insights into molecular mechanisms at the post-transcriptional level in regulating ovarian development and insect reproduction, consequently providing potential targets to control arthropod pests through the reproductive strategy. © 2024 Society of Chemical Industry.

Intestinal commensal bacteria promote Bactrocera dorsalis larval development through the vitamin B6 synthesis pathway

BackgroundThe gut microbiota can facilitate host growth under nutrient-constrained conditions. However, whether this effect is limited to certain bacterial species remains largely unclear, and the relevant underlying mechanisms remain to be thoroughly investigated.ResultsWe found that the microbiota was required for Bactrocera dorsalis larval growth under poor dietary conditions. Monoassociation experiments revealed that Enterobacteriaceae and some Lactobacilli promoted larval growth. Among the 27 bacterial strains tested, 14 significantly promoted larval development, and the Enterobacteriaceae cloacae isolate exhibited the most obvious promoting effect. A bacterial genome-wide association study (GWAS) revealed that the vitamin B6 synthesis pathway was critical for the promotion of E. cloacae growth. Deletion of pdxA, which is responsible for vitamin B6 biosynthesis, deprived the mutant strains of larval growth-promoting function, indicating that the 4-hydroxythreonine-4-phosphate dehydrogenase(pdxA) gene was crucial for promoting larval growth in E. cloacae. Importantly, supplementation of a poor diet with vitamin B6 successfully rescued the axenic larval growth phenotype of B. dorsalis.ConclusionOur results suggest that gut microbes promote insect larval growth by providing vitamin B6 under nutrient scarcity conditions in B. dorsalis.Dswoh3a91svsnnT3oBX6dHVideo

NompC regulates locomotion and touch sensation in Bactrocera dorsalis.

No mechanoreceptor potential C (NompC) is a major mechanotransduction channel with an important role in sensing of external mechanical stimuli by insects, which help these organisms to avoid injury and adapt to environmental changes. To explore the biological functions of NompC in Bactrocera dorsalis, a notorious agricultural pest, we successfully generated NompC knockout strains using clustered regularly interspaced small palindromic repeats (CRISPR) / CRISPR-associated nuclease 9 (Cas9) technology. BdorNompC knockout led to an adult lethal phenotype, with approximately 100% mortality at 3 d after eclosion. Morphological observation revealed that the legs and wings of BdorNompC knockout insects were deformed, while behavioral assays showed that the locomotion was impaired in both adults and larvae, relative to that of the wild-type strain. Moreover, BdorNompC knockout reduced gentle-touch response in larvae. These results suggest that BdorNompC is critical for B. dorsalis survival, and that this mechanosensation channel represents a potential new target for pest control agents. Our findings also represent novel evidence indicating that insect NompC is involved in modulating adult wing and leg morphology.

Effects of semiochemical pre-feeding, physiological state, and weather on the response of Bactrocera dorsalis to methyl eugenol baited traps

Plant-derived phenylpropanoids are semiochemicals that are often highly attractive to Bactrocera (Diptera: Tephritidae) males. One of these semiochemicals, methyl eugenol (ME), is used in the male annihilation technique (MAT) for the management of B. dorsalis (Hendel), a destructive horticultural pest. It is not normally viable to simultaneously implement MAT with the sterile insect technique (SIT), as released sterile males are attracted to MAT devices. However, prior semiochemical exposure can reduce the later response of Bactrocera males to the same or another semiochemical, which may allow the synchronous application of MAT and SIT. We determined how the interaction between semiochemical pre-feeding, weather, and fly physiology impacted the response of male B. dorsalis to ME baited traps. Response by a known number of males in field cages was determined in relation to temperature, relative humidity, semiochemical pre-feeding (ME, eugenol, or none), diet (protein supplemented and protein deprived) and age (4, 10 and 20 days old). Semiochemical pre-feeding of both ME and eugenol equally decreased the response of males that were 10 days old, or older, to ME baited traps. Adult diet had no effect on the response of males to ME baited traps. Response improved as temperature and relative humidity increased. These results highlight the feasibility of synchronous MAT-SIT programmes targeting B. dorsalis and the viability of continued protein supplementation of sterile males. We show that eugenol is an alternative to ME for suppression of male B. dorsalis response to MAT devices and that weather conditions significantly affect the variability and reliability of abundance estimates from trap captures.

Role of TRPV channels in texture discrimination during Bactrocera dorsalis egg-laying behaviour.

Deciding where to lay an egg is critical for the survival of insects' offspring. Compared with our understanding of the chemosensory assessment of egg-laying sites, the mechanisms of texture detection are largely unknown. Here, we show that Bactrocera dorsalis, a notoriously agricultural pest laying its eggs within ripening fruits, can discriminate substrate texture during the egg-laying process. Exposure to drugs targeting transient receptor potential vanilloid (TRPV) mechanosensory channels abolished their oviposition preference for hard textures. BdorNan and BdorIav are two members of the TRPV subfamily, and their transcripts were detected in the labellum, the foreleg tarsi and the ovipositor. Then, we successfully obtained knockout strains of each gene using the CRISPR/Cas9 technique. The results showed that BdorNan is required for the discrimination of stiffness difference. BdorIav knockout had no significant effect on the ability of B. dorsalis to choose harder substrates. Our study thus reveals that BdorNan plays a substantial role in the texture assessment of egg-laying behaviour in B. dorsalis.

Possibilities of competitive displacement of Bactrocera dorsalis (Hendel) by Bactrocera zonata (Saunders) (Tephritidae: Diptera) in guava Psidium guajava ecosystem in Sudan

Oriental fruit fly (OFF) Bactrocera dorsalis and peach fruit fly (PFF) Bactrocera zonata are the most notorious pests that invaded Sudan in 2005 and 2012, respectively, causing severe losses and hindering horticultural production and exports. Prior to 2012, OFF was the most abundant fly in guava orchards in Gezira State. Monitoring fruit flies to determine species composition, seasonality, and possibilities of competitive displacement was conducted in two guava (Psidium guajava) orchards in Gezira State; Fadasi and Gezirat Elfil, using food bait attractant and rearing flies from infested fruits..Longevity and survival percentages of developmental stages of the two species were also determined. Monitoring fly populations using Torula yeast and rearing of fruit flies from guava fruits revealed that OFF and PFF were the most prevalent species in guava ecosystem at both sites. At the Fadasi site, PFF was the predominant species representing (99.3%) of the guild of the trapped flies with an infestation level of 99.6%) flies/kg of guava fruits. At G. Elfil, OFF comprised 80.8% of the trapped flies with infestation level ca 53.6% while 19.2% of trapped flies were B. zonata with 46.4% infestation level. The high percentage of trapped OFF at G. Elfil might be attributed to multi-cropping system in the area. Developmental stages of PFF were shorter than that of OFF by 9.2 days, while its survival percentage was higher than that of OFF for all developmental stages. Competitive displacement of OFF by PFF in guava orchards at Fadasi site may have occurred as a result of the mono-cropping system, short developmental period, and high survival percentage of developmental stages of PFF on guava compared to that of OFF.

The effects of diet and semiochemical exposure on male Bactrocera dorsalis (Hendel) (Diptera: Tephritidae) metabolic rate at a range of temperatures

The oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae), is an invasive species that has rapidly spread across the African continent, endangering the security of agricultural industries. The sterile insect technique (SIT) is being investigated as a viable additional pest management tool to suppress B. dorsalis populations after its successful implementation in other parts of the world. There is evidence to suggest that pre-release nutritional and semiochemical treatments for sterilised males can enhance their competitive performance against wild type males in SIT programs. This study examined how sterilisation, a diet rich in protein (addition of yeast hydrolysate) or containing semiochemicals (methyl eugenol or eugenol) affected the resting metabolic (RMR) of male B. dorsalis at different temperatures (15 – 30 °C), measured using flow-through respirometry. Our results indicated that the negative effect of sterilisation on RMR decreased as temperature increased and that duration of exposure to semiochemicals for 1 to 4 days was not a significant influencing factor on male B. dorsalis RMR. Protein-rich diet increased average RMR, but the difference in RMR between dietary groups decreased as temperature increased. Semiochemical feeding reduced the average RMR in male B. dorsalis. The difference in RMR between males that consumed semiochemical and those that did not increased with as temperature increased.

Ionotropic Receptor 8a (Ir8a) Plays an Important Role in Acetic Acid Perception in the Oriental Fruit Fly, Bactrocera dorsalis.

Bactrocera dorsalis is one of the major invasive pests worldwide. The acetic acid-enriched sweet bait trapping is an important method for monitoring and controlling this fly. Several studies showed that acetic acid is perceived by ionotropic receptors (IRs). Thus, we annotated 65 IR genes in the B. dorsalis genome. We also investigated the IRs involved in acetic acid perception in this fly by behavioral, electrophysiological, and molecular methods. As the results indicated, the antennae are the main olfactory organs to sense acetic acid. Among the antennal IRs showed acetic acid-induced expression profiles, IR8a was proven to perceive acetic acid by CRISPR/Cas9-mediated mutagenesis. Additionally, calcium imaging showed that IR64a and IR75a are potential acetic acid receptors respectively co-expressed with IR76b and IR8a. This study represents the first comprehensive characterization of IRs in B. dorsalis at the whole-genome level, revealing the significant role of IRs in acetic acid perception.

The gustatory receptor BdorGr43a mediated sucrose preference in the feeding of Bactrocera dorsalis

The feeding behavior of animals is pivotal for their reproductive success and energy acquisition. In our study, we found that the Bactrocera dorsalis had a pronounced preference for sucrose among six plant-derived sugars during feeding. Then, we searched the entire genome of B. dorsalis for the gustatory receptors (Grs) responsible for sucrose sensation. Putative gustatory receptors involved in the detection of sweetness, bitterness, CO2 and other unknown functions. Together with phylogenetic analysis, expression profiling, calcium imaging, and CRISPR/Cas9 mediated mutagenesis, we found that BdorGr43a is the key receptor responding to sucrose. Our study elucidated the molecular mechanism underlying the sucrose preferences in the feeding of B. dorsalis. Meanwhile, our results will serve as a reference for the understanding of gustatory sensing in insect. Furthermore, BdorGr43a may serve as an important target for the development of food attractants against the oriental fruit fly.

Whole-Genome Sequencing of the Entomopathogenic Fungus Fusarium solani KMZW-1 and Its Efficacy Against Bactrocera dorsalis.

Fusarium solani KMZW-1 is recognized for its potential as a biocontrol agent against agricultural and forestry pests, particularly due to its compatibility with integrated pest management (IPM) strategies. This study aimed to investigate the complete genome of F. solani KMZW-1 and assess its pathogenicity against Bactrocera dorsalis. Whole-genome sequencing revealed a genome size of 47,239,278 bp, comprising 27 contigs, with a GC content of 51.16% and fungus identified as F. solani KMZW-1. The genome completeness was assessed as 97.93% using BUSCO analysis, the DFVF sequence identifier was Fusarium 0G092560.1, and AntiSMASH analysis identified 35 gene clusters associated with secondary metabolite biosynthesis, providing insights into the genetic basis of its pathogenic mechanisms and biocontrol potential. Comparative genomic analysis found 269 unique genes for F. solani KMZW-1, and collinearity analysis exhibited a high degree of synteny with Fusarium solani-melongenae. The pathogenicity of F. solani KMZW-1 was assessed using concentrations ranging from 1 × 104 to 1 × 1011 conidia/mL. Higher concentrations (1 × 1010 to 1 × 1011 conidia/mL) resulted in significantly increased cumulative mortality rates of B. dorsalis adults compared to the control group. Notably, the pathogenicity was higher in male adults than in females. Probit analysis yielded LC50 (50% lethal concentration) values of 5.662 for female and 4.486 for male B. dorsalis adults. In summary, F. solani, KMZW-1 exhibits strong insecticidal activity against B. dorsalis and shows potential as a biocontrol agent with IPM strategies. These findings provide robust genomic evidence supporting the use of F. solani KMZW-1 in managing against B. dorsalis populations.

Host Status of Persian Lime (Citrus latifolia Tan.) to Oriental Fruit Fly and Mediterranean Fruit Fly (Diptera: Tephritidae) in Hawai'i.

We investigated the host status of harvest-ready green Persian lime, Citrus x latifolia Tan. (Rutaceae), to Oriental fruit fly (Bactrocera dorsalis [Hendel]) and Mediterranean fruit fly (Ceratitis capitata [Wiedemann]) (Diptera: Tephritidae) using laboratory and field studies. In forced-infestation small cage exposures (using 25 × 25 × 25 cm screened cages with 50 gravid females) and large olfactometer cage tests (using 2.9 × 2.9 × 2.5 m walk-in screened cages with 100 gravid females), punctured limes were infested by Oriental fruit fly and Mediterranean fruit fly at low rates compared to papaya controls, whereas undamaged intact fruit was not infested. Field collection and packing of 45,958 commercial export-grade fruit and subsequent incubation to look for natural infestation resulted in no emergence of fruit flies. Forced infestation studies in the field using sleeve cages to enclose fruit with a high density of fruit flies (50 gravid females) on the tree also showed no infestation. Commercial export-grade Persian lime fruit should be considered a conditional nonhost for Oriental fruit fly and Mediterranean fruit fly.

Evaluating the Efficacy of the Male Annihilation Technique in Managing Oriental Fruit Fly (Diptera: Tephritidae) Populations through Microscopic Assessment of Female Spermathecae.

The male annihilation technique (MAT) plays a crucial role in the pest management program of the oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae). However, a suitable method for real-time and accurate assessment of MAT's control efficiency has not been established. Laboratory investigations found that motile sperms can be observed clearly under the microscope when the spermathecae dissected from mated females were torn, and no sperms were found in the spermathecae of virgin females. Furthermore, it was confirmed that sperms can be preserved in the spermathecae for more than 50 days once females have mated. Laboratory results also indicated that proportion of mated females decreased from 100% to 2% when the sex ratio (♀:♂) was increased from 1:1 to 100:1. Further observation revealed that there were no significant differences in the superficial area of the ovary or spermatheca between mated females and virgin females. Field investigations revealed that the proportion of mated females (PMF) could reach 81.2% in abandoned mango orchards, whereas the PMF was less than 36.4% in mango orchards where MAT was applied. This indicates that the PMF of the field population can be determined by examining the presence of sperms in the spermathecae. Therefore, we suggest that this method can be used to monitor the control efficiency when MAT is used in the field.

Electroantennographic and behavioral responses of Bactorcera dorsalis (Diptera: Tephritidae) adults to the volatiles of plum fruits.

Fruit volatiles play a crucial role in the host localization by the oriental fruit fly, Bactrocera dorsalis Hendel (Diptera: Tephritidae). This study focused on identifying the fruit volatiles from Sanyue plum and Sanhua plum (Prunus salicina Lindl.), which are 2 varieties of the same species, and examined their impact on the behavior of B. dorsalis by using a Y-olfactometer. A total of 35 and 54 volatiles from Sanyue plum and Sanhua plum were identified, respectively. Among these, 23 volatiles elicited electroantennographic (EAG) responses by B. dorsalis adults, showing concentration-dependent effects in males and females. Ethyl butyrate, butyl acetate, butyl hexanoate, ethyl caproate, ethyl hexanoate, and hexyl acetate significantly attracted B. dorsalis compared to liquid paraffin, while nonaldehyde was avoided. There was no significant difference in the behavioral responses of both sexes to sorbitol esters, hexyl isobutyrate, and 1-tetradecene compared with the control liquid paraffin group. Interestingly, (3Z)-C-3-hexenyl acetate significantly attracted females, but not males. The above findings suggest that plum fruit volatiles are likely to facilitate the localization of host fruit by B. dorsalis adults and may even aid in mate-finding. This study opens up new avenues for exploring novel plant-based attractants that might be of value for the integrated management of B. dorsalis.

The Sexual Dimorphism in Rectum and Protein Digestion Pathway Influence Sex Pheromone Synthesis in Male Bactrocera Dorsalis.

Sexual dimorphism is a crucial aspect of mating and reproduction in many animals, yet the molecular mechanisms remain unclear. In Bactrocera dorsalis, sex pheromones trimethylpyrazine (TMP) and tetramethylpyrazine (TTMP) are specifically synthesized by Bacillus strains in the male rectum. In the female rectum, Bacillus strains are found, but TMP and TTMP are not, indicating sexually dimorphic differences in sex pheromone synthesis. Our anatomical observations and precursor measurements revealed significant differences in rectal structure and ammonium levels between sexes. In vitro and in vivo experiments reveal that ammonium is vital for sex pheromone synthesis in rectal Bacillus strains. Comparative transcriptome analysis identified ammonium-producing genes (carboxypeptidase B and peptide transporter) in the protein digestion pathway that show much higher expression in the male rectum than in the female rectum. Knocking down the expression of either carboxypeptidase B (or inhibiting enzyme activity) or peptide transporter decreases rectal ammonium levels significantly, resulting in the failure of sex pheromone synthesis in the male rectum. This study provides insights into the presence of sexual dimorphism in internal organs and their functionalities in male-specific sex pheromone synthesis and has significant implications for understanding the molecular mechanisms underlying sex pheromone synthesis by symbionts in insects.