Rapid response of midgut bacteria in Bactrocera tau (Walker) (Diptera: Tephritidae) to lambda-cyhalothrin- and spinosad-induced stress

In recent decades, the increasingly widespread application of chemical pesticides has exacerbated the emergence of insecticide resistance among insect pests. In this study, we examined the rapid response of bacteria in the midgut of the fruit fly Bactrocera tau (Walker) (Diptera: Tephritidae) to stress induced by the insecticides lambda-cyhalothrin and spinosad by analyzing the bacterial community structure and diversity in the midguts of 4-day-old B. tau. The results revealed that 4-day-old B. tau females were more resistant to lambda-cyhalothrin and spinosad than their 4-day-old male counterparts. Alpha- and beta-diversity analyses revealed no significant differences between male and female B. tau with respect to the diversity and richness of gut bacteria in response to the same treatments. In response to treatment with lambda-cyhalothrin and spinosad at lethal concentration 50 (LC50), we detected significant changes in the structure and diversity of the bacterial community in the midguts of both male and female B. tau. Particularly among the dominant bacterial genera, there were decreases in the relative abundances of Citrobacter, Enterobacter, Klebsiella, and Pectobacterium. Increases were observed in the relative abundances of Dysgonomonas, Erwinia, and Providencia. Our findings provide a theoretical basis for gaining a better understanding of the relationships between midgut bacteria and the insecticide resistance of B. tau.

Effects of four chemosterilants on Bactrocera tau

Bactrocera tau (Walker) is a fly pest species mainly distributed in Southeast Asia and the South Pacific; it causes substantial ecological and economic issues because of its destructiveness and rapid reproduction. Chemical sterilization technology can reduce the use of insecticides and is widely applied for insect pest control. In this study, the sterilization efficacy of varying concentrations of four chemosterilants, namely, hexamethylphosphoramide (HMPA), CSII Aqua, 5-fluorouracil (5-FU), and colchicine, on adult pumpkin flies was investigated. The results indicated that a solution of 0.03% HMPA had the highest sterilization efficacy. When the number of sterile males was equal to or exceeded 20 times that of untreated males, the hatching rate of offspring eggs was less than 10%. Chemosterilant treatment significantly altered the levels of acid phosphatase (ACP), alkaline phosphatase (AKP), and B. tau vitellogenin (BtVg); these substances have an important impact on reproductive development. The treatment also decreased the size of the reproductive organs (i.e., testes and ovaries). Our results suggest that 0.03% HMPA has unique sterilization properties and may represent a new chemical agent for the control of B. tau populations in agricultural settings.

Molecular identification of cultivable bacteria in the gut of adult Bactrocera tau (Walker) and their trapping effect

BACKGROUND

It has been shown that some bacteria can attract their hosts. Our research aimed to identify cultivable bacterial isolates in the guts of sexually mature adult female and male Bactrocera tau and to evaluate their utility in trapping of B. tau.

RESULTS

Forty-one strains of bacteria were isolated and identified from B. tau with morphological, physiological, biochemical and 16S rDNA analysis. The dominant bacterial genera shared by both females and males were Enterobacter, Providencia and Serratia. Thirteen bacterial isolates selected from female and male B. tau adults were cultured, and the attractiveness of bacterial fermented liquid and autoclaved supernatants from these strains to B. tau adults was tested. The laboratory test showed that both the autoclaved supernatants and fermented liquid could attract male and female B. tau, and the former was substantially more effective, with the autoclaved supernatants from all strains being significantly more attractive to adult B. tau. BF16, BF(12), BF23 and BF(32) were the most attractive bacteria to 8-day-old and sexually mature B. tau. Furthermore, the results of a subsequent field cage test showed that BF(12), BF23, and BF(32) were significantly more attractive to B. tau adults.

CONCLUSION

These results provide useful information for the development of bacterial biocontrol agents and their application as insecticides. © 2018 Society of Chemical Industry.

Behavioral, Morphological, and Gene Expression Changes Induced by 60Co-γ Ray Irradiation in Bactrocera tau (Walker)

The sterile insect technique (SIT) may reduce pest populations by allowing sufficient amount of irradiation-induced sterile males to mate with wild females whilst maintaining mating ability comparable to wild males. Although the SIT methods are well understood, the optimal sterilizing dose and processing development stage for application vary among species. To ensure effective pest control programs, effects of irradiation on physiology, behavior, and gene function in the target species should be defined, however, little is known about irradiation effects in Bactrocera tau. Here, the effects of irradiation on rates of fecundity, egg hatch, eclosion, mating competitiveness, flight capability, morphology of reproductive organs, and yolk protein (YP) gene expression were studied. The results showed that rates of female fecundity and egg hatch decreased significantly (51 ± 19 to 0.06 ± 0.06 and 98.90 ± 1.01 to 0, respectively) when pupae were treated with >150 Gy irradiation. Flight capability and mating competitiveness were not significantly influenced at doses <250 Gy. Ovaries and fallopian tubes became smaller after irradiation, but there was no change in testes size. Finally, we found that expression of the YP gene was up-regulated by irradiation at 30 and 45 days post-emergence, but the mechanisms were unclear. Our study provides information on the determination of the optimal irradiation sterilizing dose in B. tau, and the effects of irradiation on physiology, morphology and gene expression that will facilitate an understanding of sub-lethal impacts of the SIT and expand its use to the control of other species.

Evaluation of chromatic cues for trapping Bactrocera tau

BACKGROUND

Trapping technology based on chromatic cues is an important strategy in controlling Tephritidae (fruit flies). The objectives of this present study were to evaluate the preference of Bactrocera tau for different chromatic cues, and to explore an easy method to print and reproduce coloured paper.

RESULTS

Chromatic cues significantly affected the preference of adult B. tau. Wavelengths in the 515-604 nm range were the suitable wavelengths for trapping B. tau. Different-day-old B. tau had different colour preferences. Virtual wavelengths of 595 nm (yellow) and 568 nm (yellowish green) were the optimum wavelengths for trapping 5-7-day-old B. tau and 30-32-day-old B. tau respectively. The trap type and height significantly influenced B. tau attraction efficiency. The number of B. tau on coloured traps hung perpendicular to plant rows was not significantly higher than the number on traps hung parallel to plant rows.

CONCLUSION

The quantisation of colour on the basis of Bruton's wavelength to RGB function can serve as an alternative method for printing and reproducing coloured paper, but a corrected equation should be established between the theoretical wavelength and actual wavelength of coloured paper. Results show that a compound paper coloured yellow (595 nm) and yellowish green (568 nm) installed at 60 and 90 cm above the ground shows the maximum effect for trapping B. tau. © 2016 Society of Chemical Industry.

The complete mitochondrial genome of the pumpkin fruit fly, Bactrocera tau (Diptera: Tephritidae)

The pumpkin fruit fly, Bactrocera tau, is an important quarantine pest in many countries because of its mass destructiveness to a variety of vegetable and fruit plants. In this study, we report the complete mitochondrial genome (mitogenome) of B. tau. Its complete mitogenome sequence is 15,687 bp in length, which contains a non-coding control region and all of the 37 genes of bilaterian animals (13 protein-coding genes, 22 tRNA genes and 2 rRNA genes). A phylogenetic tree of the complete mitogenome of all available Tephritidae species was established to approve the accuracy. The base composition of mitogenome sequence and the gene arrangement including directions are rather conservative, compared to other published mitogenomes of Bactrocera species. This first complete mitogenome of B. tau will facilitate the development of new DNA markers for species diagnosis, therefore improving accurate detection of quarantine species.

Gamma Irradiation as a Phytosanitary Treatment of Bactrocera tau (Diptera: Tephritidae) in Pumpkin Fruits

The fruit fly Bactrocera tau (Walker) is an important quarantine pest that damages fruits and vegetables throughout Asian regions. Host commodities shipped from infested areas should undergo phytosanitary measures to reduce the risk of shipping viable flies. The dose-response tests with 1-d-old eggs and 3-, 5-, 7-, 8-d-old larvae were initiated to determine the most resistant stages in fruits, and the minimum dose for 99.9968% prevention of adult eclosion at 95% confidence level was validated in the confirmatory tests. The results showed that 1) the pupariation rate was not affected by gamma radiation except for eggs and first instars, while the percent of eclosion was reduced significantly in all instars at all radiation dose; 2) the tolerance to radiation increased with increasing age and developmental stage; 3) the estimated dose to 99.9968% preventing adult eclosion from late third instars was 70.9 Gy (95% CL: 65.6-78.2, probit model) and 71.8 Gy (95% CL: 63.0-87.3, logit model); and iv) in total, 107,135 late third instars cage infested in pumpkin fruits were irradiated at the target dose of 70 Gy (62.5-85.0, Gy measured), which resulted in no adult emergence in the two confirmatory tests. Therefore, a minimum dose of 85 and 72 Gy, which could prevent adult emergence at the efficacy of 99.9972 and 99.9938% at the 95% confidence level, respectively, can be recommended as a minimum dose for phytosanitary treatment of B. tau in any host fruits and vegetables under ambient atmospheres.