Performance of a Genetically Modified Strain of the Mediterranean Fruit Fly (Diptera: Tephritidae) for Area-Wide Integrated Pest Management With the Sterile Insect Technique

Perspectives on Odor-Based Control of Tsetse Flies in Africa

Tsetse-transmitted trypanosomiases are among the most neglected tropical diseases in sub-Sahara Africa. Although all tsetse species are susceptible to trypanosome infections, their differential attraction/feeding preferences for different wildlife, domestic animals, and/or humans constitute critical determinants of trypanosomes species they predominantly transmit. Artificial bait technologies, based on long-range tsetse olfactory responses to natural cues emitted by preferred hosts and blends of synthetic versions that mimic these cues, have successfully been applied in attractant-odor-based (“pull” tactic) reduction of field populations of some tsetse species. Olfactory attribute associated with active avoidance of tsetse-refractory non-hosts has similarly been exploited in design of repellent-odor-based (“push” tactic) protection of livestock. These tactics have opened possibility of spatially strategic deployment of the two sets of odor baits in “push-pull” tactics. Possibility of developing blends with enhanced attraction and repellence compared with those associated with savannah tsetse fly hosts and non-hosts, respectively, have been explored, where structure activity and blends of different components generated two novel blends. The studies evaluated structure activity and blends of different components. One based on attractive constituents associated with buffalo (Syncerus caffer) comprised of ε-nonalactone, nonanoic acid, 2-nonanone (in 1:3:2 proportion) delivered together with acetone, which showed significantly better attractancy on savannah tsetse fly than the standard blend comprised of 3-propylphenol, octenol, p-cresol, and acetone (POCA). The other blend comprised of δ-nonalactone, heptanoic acid, 4-methylguaiacol and geranylacetone (in 6:4:2:1 proportion) was significantly more repellent than previously characterized blend based on tsetse fly refractory waterbuck (Kobus defassa) constituents (δ-octalactone, pentanoic acid, guaiacol and geranylacetone). So far, no effective attractants or repellents of riverine tsetse fly species have been characterized. Optimized attractant and repellent blends for savannah tsetse flies lay down useful groundwork for future development of the “push-pull” deployment tactic for area-wide control of tsetse flies. Better understanding of the physiological, cellular, and molecular basis of response in the tsetse fly to odors can potentially augment the current tsetse fly-control interventions.

Introgression of the Aedes aegypti Red-Eye Genetic Sexing Strains Into Different Genomic Backgrounds for Sterile Insect Technique Applications

Aedes aegypti is an invasive mosquito species and major vector of human arboviruses. A wide variety of control methods have been employed to combat mosquito populations. One of them is the sterile insect technique (SIT) that has recently attracted considerable research efforts due to its proven record of success and the absence of harmful environmental footprints. The efficiency and cost-effectiveness of SIT is significantly enhanced by male-only releases. For mosquito SIT, male-only releases are ideally needed since females bite, blood-feed and transmit the pathogens. Ae. aegypti genetic sexing strains (GSS) have recently become available and are based on eye colour mutations that were chosen as selectable markers. These genetic sexing strains were developed through classical genetics and it was shown to be subjected to genetic recombination, a phenomenon that is not suppressed in males as is the case in many Diptera. The genetic stability of these GSS was strengthened by the induction and isolation of radiation-induced inversions. In this study, we used the red eye mutation and the inversion Inv35 line of the Ae. aegypti red-eye GSS s and introgressed them in six different genomic backgrounds to develop GSS with the respective local genomic backgrounds. Our goal was to assess whether the recombination frequencies in the strains with and without the inversion are affected by the different genomic backgrounds. In all cases the recombination events were suppressed in all Inv35 GSS strains, thus indicating that the genomic background does not negatively affect the inversion result. Absence of any effect that could be ascribed to genetic differences, enables the introgression of the key elements of the GSS into the local genomic background prior to release to the target areas. Maintaining the local background increases the chances for successful matings between released males and wild females and addresses potential regulatory concerns regarding biosafety and biosecurity.

Probiotic based-diet effect on the immune response and induced stress in irradiated mass reared Ceratitis capitata males (Diptera: Tephritidae) destined for the release in the sterile insect technique programs

Ceratitis capitata (medfly) is one of the most devastating crop pests worldwide. The Sterile Insect Technique (SIT) is a control method that is based on the mass rearing of males, their sterilization, and release in the field. However, the effectiveness of the technique depends on the quality of the released males and their fitness. We previously isolated and selected a probiotic bacteria (Enterobacter sp.), from wild-caught medflies, according to criteria that improved biological quality traits of reared medfly males.We firstly evaluated the impact of the irradiation on the expression of different immune and stress genes in the medfly sterile males. Expression was measured at differents time points ranging from 0 to 168 h after irradiation to capture the response of genes with distinct temporal expression patterns. Then, we supplemented the larval diet with previously isolated Enterobacter sp.strain, live and autoclaved at various concentrations to see whether the probiotic treatments affect, through their protective role, the gene expression level, and quality traits. The irradiation had significant effect on the genes attacin, cecropin, PGPR-LC, hsp23, and hsp70 level expression. The expression of attacin and PGPR-LC was up-regulated while that of cecropin was down-regulated. Hsp genes showed decreased levels between 0 and 18 h to peak at 72 h. However, the supplementation of the probiotic strain, either live or autoclaved, was statistically significant only for attacingene. However, significant interaction time x probiotic was noticed for attacin, cecropin, hsp23 and hsp70. The probiotic treatments also improved the quality control parameters like pupal weight. From this work we can conclude that a consortium of parabiotics (autoclaved probiotics) treatment will be recommended in insectaries considering both the beneficial effects on mass reared insects and its general safety for insectary workers and for environment.

Comparison of classical and transgenic genetic sexing strains of Mediterranean fruit fly (Diptera: Tephritidae) for application of the sterile insect technique

The development of genetic sexing strains (GSSs) based on classical genetic approaches has revolutionized the application of the sterile insect technique (SIT) against the Mediterranean fruit fly Ceratitis capitata (Wiedemann) (Diptera: Tephritidae). The global use of Mediterranean fruit fly GSS for SIT applications as part of area-wide integrated pest management (AW-IPM) programmes is testimony to their effectiveness. During recent years, transgenic sexing strains (TSSs) have been developed through genetic engineering techniques offering the possibility to produce male-only progeny by introducing female embryonic lethal genes and to increase the efficacy to identify released sterile males by means of the expression of fluorescent transgene markers. Here, we present a comparative analysis of two Mediterranean fruit fly strains: the classical GSS VIENNA 8^D53-/Toliman and the transgenic FSEL#32. The strains were compared for production efficiency and quality control indices under semi mass-rearing conditions, response to sterilizing irradiation doses, male mating performance in walk-in field cages, and production cost of male-only pupae. The results showed that, the FSEL #32 TSS had a similar fecundity but a higher production of male-only pupae than the VIENNA 8^D53-/Toliman GSS. For some of the quality control parameters tested, such as pupal weight and survival under starvation conditions, the FSEL #32 TSS was inferior to the VIENNA 8^D53-/Toliman GSS. Both the transgenic and the classical genetic sexing strains have shown acceptable and similar mating competitiveness when compared with wild males for mating with wild females. The cost production for both strains is similar but the FSEL#32 TSS may potentially be more cost effective at higher production levels. The results are discussed in the context of incorporating the transgenic strain for SIT application.

Evaluation of horizontal gene transfer risk between the Mediterranean fruit fly Ceratitis capitata (Tephritidae) and its parasitoid Fopius ceratitivorus (Braconidae)

The transgenic strain of the Mediterranean fruit fly (medfly), Ceratitis capitata (Wied.) VIENNA 8 1260, developed from the classical genetic sexing strain VIENNA 8, has two molecular markers that exhibit red fluorescence in the body and green fluorescence in testicles and sperm. These traits offer a precise tool to discriminate between mass-reared sterile males and wild fertile males, and they could potentially increase the effectiveness of control programs for this pest. To assess the risk of horizontal transfer of the fluorescence transgenes in natural ecosystems, we used the VIENNA 8 1260 strain and the medfly parasitoid Fopius ceratitivorus. The fluorescence signal and the inheritance of the fluorescence gene markers were monitored for over 16 generations (about two years) in both species using fluorescence microscopy and a PCR-based assay. The PCR analysis was performed in four independent laboratories. Both fluorescence microscopy and PCR analysis indicated that no horizontal gene transfer of the DsRed transgene occurred during 16 generations of medfly parasitoid rearing under experimental conditions.

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.