Dispersal of the Old World screw-worm fly Chrysomya bezziana

Abstract. Dispersal of the Old World screw-worm fly, Chrysomya bezziana Villeneuve, was studied in Papua New Guinea by releasing radio-isotope labelled, laboratory-reared flies and collecting their labelled egg masses from sentinel cattle. A log-linear model was developed to describe recapture rate. Distance was found to dominate the model and was represented by a bilinear ('broken-stick') term as log-distance. Further terms in the model such as attractiveness of the site (estimated from the number of non-labelled egg masses), the season of the year and a time trend were statistically significant but of minor importance. From the model, the median distance females dispersed before depositing an egg mass was 10.8 km. The maximum distance from the release site that egg masses were recovered was 100 km.
The dispersal ability of C. bezziana is discussed in terms of its impact on the prospects of eradicating this species using SIRM if an outbreak occurred in Australia.     

Dispersal of mass‐reared sterile,laboratory‐domesticated and wild male Queensland fruit flies

Queensland fruit flies, Bactrocera tryoni (Froggatt) (Diptera: Tephritidae) (‘Q‐flies’) were released as sexually immature adults from a point within an orchard. Marked male Q‐flies were recaptured in the trap furthest from the release point (1087 m) by 2 weeks after release, although 98.25 ± 1.04% of recaptured males were trapped <500 m from the release point. Comparison of gamma‐irradiated (sterile), laboratory‐adapted and wild male Q‐flies indicated that dispersal distance was not significantly affected by fly type. There was no significant correlation between temperature and mean dispersal distance, but total recaptures were significantly negatively correlated with increasing daily maximum, minimum and average temperature.     

Understanding Bactrocera dorsalis trapping to calibrate area-wide management

Knowing the dispersal of released insects and estimating the size of field populations are keys to the successful implementation of area-wide management (AWM) programmes based on the sterile insect technique (SIT), as they determine the release strategy of sterile males. Mark–release–recapture (MRR) is a common method used to estimate field populations and spatiotemporal dynamics. However, the extent to which the pest is attracted to lures is often difficult to identify, thereby biasing extrapolation to movement patterns and population size. We performed MRR experiments on the Oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae), in a fruit-growing area in Senegal. Methyl eugenol and protein baits were used to trap males and females, respectively. After studying the suitability of marking B. dorsalis with fluorescent pigments at the laboratory, two releases of marked sterile flies were organized in the centre of an organic mango orchard, first in the late mango fruiting stage and second in the fruit setting stage. Traps were placed symmetrically along a 250 and 500 m radius from the release point. A very small fraction of the released individuals was recaptured: 0.45% in the first release and 3.08% in the second. Trapping of both sterile and wild flies was completely anisotropic. Sterile flies were mostly trapped at a relatively short distance (250 m) from the release point, in the first two days. Male trapping using methyl eugenol was highly effective, whereas the response of females to food bait traps was low. The direction of the wind was the main driver of recapture, with flies heading upwind. The results underline the importance of taking the odour plume around the traps into account when estimating populations, and the heterogeneous spread of the wild population in the landscape for the set-up of the release strategy of sterile insects for SIT-based AWM.     

Eradication of the melon fly,Dacus cucurbitae,from Kume is., Okinawa with the sterile insect release method

The sterile insect release method was applied to eradicate the melon fly, Dacus cucurbitae, from the 58.5 km² island of Kume, in the Okinawa Islands group. Weekly releases of 1 to 1.5 million flies irradiated as pupae with 6–7 kR from a cobalt-60 source did not decrease the wild melon fly population. Releases of 1.5–2 million pupae per week made from September, 1975 to January, 1976 decreased the percent egg-hatch of females caught on Kume Is., but did not decrease the percent infestation significantly. The number of pupae released was increased from February, 1976 to accelerate the eradication process. When the number of pupae released exceeded 3.5 million per week, a rapid increase in the ratio of marked (sterile) to unmarked (wild) flies, a remarkable decrease in percent egg-hatch, and a decrease in percent infestation of fruits were observed. There has been no sign of melon fly infestation in wild cucurbit fruits from October, 1976 to the present time (April, 1977), despite the fact that more than 70,000 fruits were carefully examined. The eradication of the melon fly from Kume Is. was thus achieved by April, 1977, after the release of 264 million sterile fly pupae.     

Capture of mass‐reared vs. wild‐like males of Ceratitis capitata (Dipt., Tephritidae) in trimedlure‐baited traps

The sterile insect technique (SIT) is widely used to suppress or eradicate infestations of the Mediterranean fruit fly, Ceratitis capitata (Wied.), an insect whose broad polyphagy poses a serious threat to fruit and vegetable crops. The SIT involves the production, sterilization and release of sterile insects to obtain sterile male by wild female matings, thus yielding infertile eggs. Mass‐rearing over many generations is known to produce dramatic changes in the behaviour and life history of C. capitata. This study investigated the possibility that mass‐rearing also alters male response to trimedlure, a sex‐specific attractant widely used in detection and monitoring programmes. We compared captures of released males from a mass‐reared strain and a recently established colony of wild flies in trimedlure‐baited Jackson traps at three spatial scales – open field, large field enclosures (75 m²) and small field cages (7 m²) – in two separate years. In the first year, males were used independently of flight ability, while in the second year only males with demonstrated flight capability were used. Trap capture was scored 2 days after release for the open field and the large field enclosures but either 1 h or 1 day after release in the small field cages. The findings were consistent across these different experiments: wild‐like males were captured in significantly greater numbers than mass‐reared males in both years of study, except in the trials lasting 1 day in the small field cages where significantly more wild than mass‐reared males were captured in 1 year but not the other. These results are compared with other studies, and their implications for SIT are discussed.     

Sterile males of Ceratitis capitata (Diptera: Tephritidae) as disseminators of Beauveria bassiana conidia for IPM strategies

Sterile Mediterranean fruit fly, Ceratitis capitata (Wied.), males were evaluated as vectors to spread Beauveria bassiana (Bals) conidia to wild C. capitata populations under field conditions. The inoculated sterile males were released by air, using the chilled adult technique over 7000 ha of coffee growing in Chimaltenango, Guatemala, Central America. The impact of releases was determined using dry traps baited with a food attractant. The effects of these releases on Apis mellifera, Linnaeus (honey bee), Hypothenemus hampei, Ferrari (coffee berry borer) and the parasitic mite Varroa destructor (Oudeman) were also evaluated. Inoculated sterile males were able to transmit fungal spores to 44% of the wild C. capitata flies captured in traps, which likely were infected through intra- and intersexual interactions during leks, mating or mating attempts. There was no transmission of the fungal spores to non-target insect species such as coffee berry borer, honey bees or varroa. We conclude that sterile males of Mediterranean fruit fly inoculated with B. bassiana can act as effective vectors of conidia to wild populations, constituting a safe, environmentally friendly and selective alternative for suppressing the medfly under a Sterile Insect Technique-based IPM approach.     

Assay of old-world screw-worm fly, Chrysomya bezziana, labelled with 32P

Techniques for ³²P labelling of larvae and adults of the screw-worm fly, Chrysomya bezziana, are described. Egg masses of labelled flies were readily identified. At the doses used for field releases, oviposition activity, fecundity, fertility and longevity of female flies were not adversely affected. Radioactive egg masses were recovered from sentinel animals following field release of labelled flies.

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Résumé Cet article décrit les techniques utilisées pour marquer avec le ³²p les larves et adultes de Chrysomya bezziana. Les pontes des mouches marquées ont été aisément identifiées. Aux doses utilisées pour le relâchement des insectes dans la nature, ni l'activité de ponte, ni la fécondité, fertilité et longévité des femelles n'ont été défavorablement modifiées. Les pontes radioactives ont été recueillies sur des animaux-pièges mis en place après le lâcher des mouches marquées.

     

Spatial patterns of sterile Mediterranean fruit fly dispersal

The success of the sterile insect technique (SIT) for the control of the Mediterranean fruit fly or medfly, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), depends largely on the ability of sterile flies to spread in the target area and compete with the wild males for wild females. Our objectives in the present study were three‐fold: (1) to evaluate the dispersal ability of sterile male medflies and compare their spatial dispersion patterns with that of wild males, (2) to evaluate how different release methods affect subsequent spatial dispersal, and (3) to determine whether manipulating the pre‐release diet of sterile males affects their dispersal. To achieve these objectives, we conducted three experiments in the field where we quantified and analyzed the spatial and temporal dispersal patterns of sterile medflies and the dispersion of resident wild males. Overall, ca. 5% of the released sterile flies were recaptured 100 m from the release point, and ca. 2% were recaptured 200 m from the release point. The released flies rarely survived longer than 5–7 days. We repeatedly found that the spatial dispersion patterns of sterile males significantly correlated with those of wild males. Release methods strongly affected subsequent fly dispersal in the field as significantly more flies were recaptured following a scattered release vs. a central one. Finally, we show that enriching sterile fly pre‐release diet with protein did not affect subsequent dispersal in the field. We conclude that sterile males are able to match the dispersion patterns of wild males, an outcome that is highly important for SIT success. Large releases from central points distant from each other may leave many areas uncovered. Accordingly, scattered releases, repeated twice a week, will provide better coverage of all available aggregations sites. The spatial performance of protein‐fed males suggests that pre‐release diet amendments may be used without detriment as a sexual stimulant in SIT programs.     

Bacterially enriched diet improves sexual performance of sterile male Mediterranean fruit flies

The Mediterranean fruit fly, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), (medfly) is a polyphagous and cosmopolitan agricultural pest, targeted in many areas for control by the Sterile Insect Technique (SIT). Our objective in the present study was to test the hypothesis that a bacterially enriched diet provided to sterile males will improve their sexual performance in competitive settings that emulate natural conditions. Specifically we determined how feeding on diets enriched with Klebsiella oxytoca affected the ability of sterile males to compete for wild females against wild males, their ability to inhibit female receptivity, and their survival. We found that enriching the sterile male diet with K.oxytoca significantly improved mating competitiveness in the laboratory and in field cages. In addition, bacterially enriched sterile males inhibited female receptivity more efficiently than sugar fed males and survived longer duration of starvation. We conclude that inoculating mass reared sterile flies with bacteria prior to their release is a valid approach to improve the efficacy of SIT.     

Sterile insect technique and Mediterranean fruit fly (Diptera: Tephritidae): assessing the utility of aromatherapy in a Hawaiian coffee field

The sterile insect technique (SIT) is widely used in integrated programs against tephritid fruit fly pests, particularly the Mediterranean fruit fly, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae). Unfortunately, the mass-rearing procedures inherent to the SIT often lead to a reduction in the mating ability of the released males. One potential solution involves the prerelease exposure of males to particular attractants. In particular, exposure of male Mediterranean fruit flies to ginger, Zingiber officinale Roscoe, root oil (GRO) has been shown to increase mating success in laboratory and field cage trials. Here, we describe a field experiment that compares the level of egg sterility observed in two Hawaiian coffee, Coffea arabica L., plots, with GRO-exposed, sterile males released in one (treated) plot and nonexposed, sterile males released in the other (control) plot. Once per week in both plots over a 13-wk period, sterile males were released, trap captures were scored to estimate relative abundance of sterile and wild males, and coffee berries were collected and dissected in the laboratory to estimate the incidence of unhatched (sterile) eggs. Data on wild fly abundance and the natural rate of egg hatch also were collected in a remote area that received no sterile males. Despite that sterile:wild male ratios were significantly lower in the treated plot than in the control plot, the incidence of sterile eggs was significantly higher in the treated plot than in the control plot. Correspondingly, significantly higher values of Fried's competitiveness index (C) were found, on average, for treated than control sterile males. This study is the first to identify an association between the GRO "status" of sterile males and the incidence of egg sterility in the field and suggests that prerelease, GRO exposure may represent a simple and inexpensive means to increase the effectiveness of Mediterranean fruit fly SIT programs.     

Empirical evidence of the mediterranean fruit fly movement between orchard types

Understanding species movement in the agroecological system is an important theme in ecology. A mark–release–capture experiment was conducted to study the dispersion behaviour of the Mediterranean fruit fly, Ceratitis capitata (Wied.; Diptera: Tephritidae; Medfly) in northern Israel. Four pairs of pear and citrus orchards were selected for the field experiments. Sterile flies dyed with different colours were released in three seasons during 2015 and 2016, based on the phenological stages of the hosts. The total number of captured marked sterile flies per trap (FT) was approx 300 in both April and August. In November, FT values decreased by about 35% to approximately 200. The wild Medfly that were also captured showed an opposite trend, from an FT of 1.8 and 6.4 in April and August, respectively, to an FT of about 330 in November. Marked sterile flies were captured in both the release and the neighbouring orchard sites. We found that the Medfly migrates from pear to citrus orchards during spring and from citrus to pear during summer, when there are no fruit-bearing trees in the orchards. However, during November, when the wild Medfly population prevails in the area, a clear pattern of migration is hard to identify, perhaps because of a possible interaction with the wild fly's population.     

Pre-release feeding on yeast hydrolysate enhances sexual competitiveness of sterile male Queensland fruit flies in field cages

Recent laboratory studies of mass‐reared flies in small cages have found that periods of just 24‐ or 48‐h access to yeast hydrolysate can substantially enhance mating performance of mass‐reared male Queensland fruit flies, Bactrocera tryoni (Froggatt) (Diptera: Tephritidae) (‘Q‐flies’). Using field cage tests that provide a better approximation of nature, we here investigated whether access to yeast hydrolysate for 48 h after adult emergence improves the ability of male and female mass‐reared, sterile Q‐flies to compete sexually with wild‐type flies that had been provided continuous access to yeast hydrolysate. Mating probability of sterile males was significantly increased by 48‐h access to yeast hydrolysate; sterile males provided 48‐h access to yeast hydrolysate had mating probability similar to that of wild males provided continuous access to yeast hydrolysate, whereas sterile males deprived of access to yeast hydrolysate had much lower mating probability. Unlike males, access to yeast hydrolysate for 48 h did not increase mating probability of sterile female Q‐flies. We instead found that wild females provided continuous access to yeast hydrolysate had higher mating probability than sterile females that did or did not have 48‐h access to yeast hydrolysate. This result raises the possibility that a bisexual Q‐fly strain might operate essentially as a male‐only release when the flies are given access to yeast hydrolysate during a 48‐h pre‐release holding period. Sterile males given access to yeast hydrolysate for 48 h mated significantly earlier in the evening than wild males and, as in other recent studies, this tendency was associated with an increased tendency to mate on the trees rather than the cage walls. There was no evidence of sexual isolation in this study, as wild and sterile mass‐reared flies showed no evidence of preferential mating with their own kind. Further studies are now needed to assess the potential for pre‐release access to yeast hydrolysate to improve sexual performance and longevity of sterile, mass‐reared, Q‐flies in the field.     

Recapture of sterile Mediterranean fruit flies (Diptera: Tephritidae) in California's Preventative Release Program

In southern California, the sterile insect technique has been used since 1994 to prevent establishment of the Mediterranean fruit fly, Ceratitis capitata (Wiedemann). This method involves the continual mass release of sterile flies, which suppress or eliminate any introduced wild fly populations. In addition, Jackson traps baited with trimedlure are deployed throughout the preventative release region for the dual purpose of detecting wild flies and monitoring released sterile flies. Sterile fly recapture data for a 3-yr period was compared with climate and to host plant (in which traps were placed). Precipitation was negatively correlated; and temperature and relative humidity were positively correlated with fly recapture levels. The highest numbers of flies were recaptured during trapping periods associated with intermediate relative humidity and temperature, and low precipitation. Flies were recaptured throughout the entire year, in traps that had been frequently relocated to host plants with fruit. This finding suggests that these flies were capable of locating acceptable fruit in a variety of abiotic conditions. However, these data do not necessarily suggest that measurements unimportant in explaining sterile fly recapture are not of value in determining other outcomes important to the goals of sterile release programs, such as reducing the likelihood of establishment of an introduced wild Mediterranean fruit fly population. Future research might build on these results in developing more precise models useful in predicting recapture of sterile flies.     

The New World screwworm fly in Libya: a review of its introduction and eradication

The New World screwworm fly, Cochliomyia hominivorax (Coquerel) (Diptera: Calliphoridae), became established in the Old World for the first time during 1988, in the Socialist People's Libyan Arab Jamahiriya. An obligate parasite of mammals in its larval stages, causing wound myiasis, it is one of the most serious insect pests of livestock in the Americas. To avert a major disaster for the livestock industry and wildlife of Africa and southern Europe, the Libyan Government and the Food and Agriculture Organization of the United Nations launched a massive screwworm eradication programme, based on the sterile insect technique, SIT. An initial containment operation involved veterinary teams working in the infested area (25,000 km2 around Tripoli), regularly inspecting livestock and, if necessary, treating them with insecticide. Quarantine stations were also set up, to prevent the movement of infested livestock out of the area. Sterile flies from the Mexican-American Commission for Eradication of Screwworms were first released in December 1990 at the rate of 3.5 million per week. This built up to 40 million per week by May 1991. The release of sterile flies was terminated on 17 October 1991, 6 months after the last detected case of screwworm myiasis in Libya. Intensive surveillance and quarantine activities will, however, continue through 1992. During 1992 the Libyan Government should be able to officially declare the New World screwworm eradicated from Libya, making it one of the most important success stories of pest control.     

Age-dependent variation in mating success of sterile male Mediterranean fruit flies (Diptera: Tephritidae): implications for sterile insect technique

The sterile insect technique (SIT) is widely used in integrated programs against the Mediterranean fruit fly, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae). Unfortunately, the mass-rearing procedures inherent to the SIT often lead to a reduction in the mating ability of the released males. To counter this deficiency, SIT programs rely upon the production and release of large numbers of sterile males to achieve high overflooding (sterile:wild male) ratios. To ensure a high release volume, emergence facilities release adult males at a young age (2 d old in some cases). The primary objective of this study was to describe age-dependent variation in the mating propensity and competitiveness of sterile males of C. capitata. Males that were 2 or 3 d old had lower mating propensity than males that were > or =4 d old, and 3-d-old males had lower mating competitiveness than males that were > or =4 d old. Given these results, we measured the effect of a longer holding period on male mortality in storage boxes. With delayed food placement, males held in storage boxes for 4 d after emergence showed no higher mortality than males held for only 2 d (the standard interval). Using large field enclosures, we compared the levels of egg sterility attained via releases of 2- versus 4-d-old sterile males at two overflooding ratios (5:1 and 100:1). At the lower ratio, the proportion of unhatched eggs observed for trials involving 2-d-old sterile males was not, on average, significantly higher than that observed for matings between wild flies (33 versus 25%, respectively), whereas the level of egg sterility observed for releases of 4 d old sterile males was 62%. At the 100:1 overflooding ratio, the proportion of unhatched eggs associated with the 2-d-old sterile males was 58%, a level not significantly different from that induced by 4-d-old sterile males at the 5:1 ratio and significantly lower than the level (79%) observed for 4-d-old sterile males at 100:1 overflooding ratio. The implications of these results for SIT are discussed.     

Factors affecting the dispersal of large‐scale releases of the Queensland fruit fly,Bactrocera tryoni

This study investigated two factors potentially affecting the spatial distribution of Queensland fruit fly Bactrocera tryoni (Froggatt) after release from a single point. First, the effect of age at release was investigated using a single cohort of 205 000 males from a mass‐rearing strain used for sterile insect releases. Approximately half were released as immature males and the remainder as sexually mature males (1 week later). Males were collected over 3 weeks from a grid of 135 traps, each containing a pheromone/insecticide bait, positioned between 4 and 500 m from the release point. Variation in the distribution of fly density around the release point was assessed by regressing trapped fly counts against distance. Unexpectedly, no significant differences were found in the spatial distribution of the flies. Second, the effect of inbreeding on spatial distribution was investigated using replicated simultaneous releases of two strains of B. tryoni. One strain was the existing (inbred) mass‐rearing strain that has been selected for high productivity in a mass‐rearing facility. The second strain was deliberately outbred but also selected for high productivity. Almost 100 000 males of each strain were released over the two experiments. Regression of trappings against distance differed significantly between strains in only one of five releases, but in all cases the outbred strain had a greater dispersal distance. As our trapping grid was not regular but contained gaps of up to 100 m, a small preliminary experiment investigated whether flies move faster along tree rows or across open fields. At distances up to 100 m, we found no detectable difference in fly distributions. These results are primarily relevant to the large‐scale point releases carried out as part of an existing B. tryoni sterile insect programme and are discussed in that context.     

Effect of diet on survival,in the laboratory and the field,of sterile male Mediterranean fruit flies

To improve the effectiveness of the sterile insect technique against the Mediterranean fruit fly, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), our objectives in this study were two‐fold. First, to evaluate the ability of sterile males of the Vienna‐8 strain to survive starvation, we compared them to wild males under laboratory conditions. The second objective was to determine the effect of protein‐rich nutrition on sterile male fly survival, under starvation conditions in the laboratory, under semi‐natural conditions in a field enclosure, and under natural conditions in the open field. Therefore, we released marked sterile flies of the two diet regimes, protein‐fed or protein‐deprived, and monitored their survival by recapturing them after 4, 6, and 7 days. In the laboratory, wild males endured starvation significantly better than sterile ones and protein addition to sterile fly diet resulted in even greater reduced capability to endure starvation. On the other hand, the addition of protein to sterile‐male diet did not affect their ability to survive in a field enclosure or in the open field. We conclude that under natural conditions, where food is available, sterile male fly survival is unaffected by protein‐rich pre‐release diet.     

Factors affecting abundance and oviposition rates of a field population of the Old World screw-worm fly, Chrysomya bezziana (Diptera: Calliphoridae)

Sentinel cattle and a grid of swormlure-baited sticky traps were used to monitor a Malaysian population of the Old World screw-worm fly, Chrysomya bezziana Villeneuve. Observations were carried out on an isolated cattle station at monthly intervals during the period August 1996 to June 2000. The number of flies caught was unaffected by weather conditions at the time of trapping, but was positively correlated with the total rainfall and the average daily air temperature prevailing 15-28 days earlier, when trapped flies were still juveniles. Trap catches were biased in favour of females, but daily catch rates of both sexes increased significantly the longer traps were open, suggesting that efficacy was related to the differential volatility of the chemicals comprising swormlure. Oviposition on sentinel cattle occurred mostly in late afternoon or early evening but increased significantly as the wound aged. Oviposition rates were positively correlated with female catch rates, but the relationship was curvilinear, suggesting that fly populations may be subject to some form of density-dependent constraint. Consistent differences in oviposition rates on sentinel cattle at different localities on the cattle station suggested the existence of highly clumped, quasi-stationary populations. Differences in trap catches between traps located in pastoral areas and those sited in nearby oil palm or rubber plantations supported this interpretation of the data. These findings are discussed in relation to the use of the sterile insect technique for the control of screw-worm fly infestations.     

Establishment and dispersal of the fire ant decapitating fly Pseudacteon tricuspis in North Florida

The decapitating fly Pseudacteon tricuspis Borgmeier was released at eight sites in North Florida between the summer of 1997 and the fall of 1999 as a self-sustaining biocontrol agent of the red imported fire ant, Solenopsis invicta Buren. Several releases used parasitized fire ant workers while most involved adult flies released over disturbed ant mounds. Establishment and dispersal of fly populations were monitored by disturbing about 10 fire ant mounds at each site and then inspecting them closely for hovering flies over a period of about 30 min. Overwintering populations of flies were successfully established at 6 of 8 release sites. Over several years, fly populations at these sites increased to levels as high or higher than those normally seen in their South American homeland. By the fall of 1999, flies had expanded out 1–6 km from five release sites and occupied about 125 km². By the fall of 2000 the five initial release sites plus one new site had fused into one large area about 70 km in diameter. The flies had expanded out an additional 16–29 km and occupied about 3300 km². By the fall of 2001 the flies had expanded out an additional 10–30 km and occupied approximately 8100 km². Fly dispersal was not related to wind patterns in the Gainesville area. Based on the above rates of dispersal and an establishment rate of 66%, we estimate that a state the size of Florida would require 5–10 releases spaced over a 3-year period to cover the state in 6–9 years.     

Combining paratransgenesis with SIT: impact of ionizing radiation on the DNA copy number of Sodalis glossinidius in tsetse flies

Background

Tsetse flies (Diptera: Glossinidae) are the cyclical vectors of the causative agents of African Trypanosomosis, which has been identified as a neglected tropical disease in both humans and animals in many regions of sub-Saharan Africa. The sterile insect technique (SIT) has shown to be a powerful method to manage tsetse fly populations when used in the frame of an area-wide integrated pest management (AW-IPM) program. To date, the release of sterile males to manage tsetse fly populations has only been implemented in areas to reduce transmission of animal African Trypanosomosis (AAT). The implementation of the SIT in areas with Human African Trypanosomosis (HAT) would require additional measures to eliminate the potential risk associated with the release of sterile males that require blood meals to survive and hence, might contribute to disease transmission. Paratransgenesis offers the potential to develop tsetse flies that are refractory to trypanosome infection by modifying their associated bacteria (Sodalis glossinidius) here after referred to as Sodalis. Here we assessed the feasibility of combining the paratransgenesis approach with SIT by analyzing the impact of ionizing radiation on the copy number of Sodalis and the vectorial capacity of sterilized tsetse males.

Results

Adult Glossina morsitans morsitans that emerged from puparia irradiated on day 22 post larviposition did not show a significant decline in Sodalis copy number as compared with non-irradiated flies. Conversely, the Sodalis copy number was significantly reduced in adults that emerged from puparia irradiated on day 29 post larviposition and in adults irradiated on day 7 post emergence. Moreover, irradiating 22-day old puparia reduced the copy number of Wolbachia and Wigglesworthia in emerged adults as compared with non-irradiated controls, but the radiation treatment had no significant impact on the vectorial competence of the flies.

Conclusion

Although the radiation treatment significantly reduced the copy number of some tsetse fly symbionts, the copy number of Sodalis recovered with time in flies irradiated as 22-day old puparia. This recovery offers the opportunity to combine a paratransgenesis approach – using modified Sodalis to produce males refractory to trypanosome infection – with the release of sterile males to minimize the risk of disease transmission, especially in HAT endemic areas. Moreover, irradiation did not increase the vector competence of the flies for trypanosomes.