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.     

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.     

Irradiation of Anastrepha ludens (Diptera: Tephritidae) revisited: optimizing sterility induction

Irradiation doses currently applied to sterilize Mexican fruit flies, Anastrepha ludens (Loew) (Diptera: Tephritidae), for release under the sterile insect technique eradication campaign in Mexico, were reviewed in an effort to increase sterile male performance in the field. A dose maximizing sterility induction into wild populations was sought by balancing somatic fitness with genetic sterility. Doses of 40, 60, and 80 Gy induced 95% or more sterility in all males, which in turn induced similar degrees of sterility into a cohort of wild flies in the laboratory. However, a low dose of 40 Gy was sufficient to completely suppress egg production in females. Similarly, a mild carryover of genetic damage might have been transferred to the F1 progeny of males irradiated at 40 Gy crossed with fertile wild females. Our results suggest that the 80-Gy dose currently applied in Mexico can be lowered substantially without jeopardizing program goals. This view could be strengthened by comparing performance of males irradiated at different doses under more natural settings. In general, we discuss the value of determining irradiation doses for pest species where females are more radiosensitive than males, by selecting the dose that causes 100% sterility in females.     

The sterile insect technique and the Mediterranean fruit fly: assessing the utility of aromatherapy in large field enclosures

The sterile insect technique (SIT) is widely used in integrated programs against tephritid fruit flies, 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 male mating competitiveness. One potential solution involves the prerelease exposure of males to particular attractants. In particular, male exposure to ginger root oil [Zingiber officinale Roscoe (Zingiberaceae); hereafter GRO], has been shown to increase mating success dramatically in field cage trials. To evaluate more rigorously the effectiveness of GRO exposure, we here describe two projects that compared levels of egg sterility or pupal yield, respectively, following the release of wild flies and either GRO‐exposed (treated) sterile males or GRO‐deprived (control) sterile males in large field enclosures. In both projects, sterile males from a genetic sexing strain were exposed as adults to GRO for 24 h while held in large storage boxes. In Hawaii, we dissected eggs from fruits to determine the percentage of egg hatch at four overflooding ratios, ranging from 5 : 1 to 60 : 1 (sterile : wild males), and found that, at all four ratios, the proportion of unhatched (sterile) eggs was significantly greater in enclosures containing GRO‐exposed males than control males. In Guatemala, we allowed larvae to develop in fruits and counted the number of pupae produced. At the only overflooding ratio tested (25 : 1), pupal yield was approximately 25% lower for enclosures containing GRO‐exposed males than control males, although this difference was not statistically significant. An explanation for the differing outcomes is proposed, and the implications of these findings for the SIT are discussed.     

Do sterile females affect the sexual performance of sterile males of Anastrepha ludens (Diptera: Tephritidae)?

The release of sterile males to suppress the Mexican fruit fly Anastrepha ludens (Loew) population was simulated in field cages to compare the sexual performance of sterile males with wild females in the presence and absence of sterile females. Using different release ratios of sterile and wild individuals, this study showed that the presence of sterile females negatively affected the sexual performance of sterile males in mating with wild females. We found that the sterility induced was proportional to the magnitude of the sterile/fertile ratio. These results indicate that the release of sterile males without sterile females can significantly improve the efficiency of the sterile insect technique for the control of A. ludens.     

Radiation biology of mosquitoes

There is currently renewed interest in assessing the feasibility of the sterile insect technique (SIT) to control African malaria vectors in designated areas. The SIT relies on the sterilization of males before mass release, with sterilization currently being achieved through the use of ionizing radiation. This paper reviews previous work on radiation sterilization of Anopheles mosquitoes. In general, the pupal stage was irradiated due to ease of handling compared to the adult stage. The dose-response curve between the induced sterility and log (dose) was shown to be sigmoid, and there was a marked species difference in radiation sensitivity. Mating competitiveness studies have generally been performed under laboratory conditions. The competitiveness of males irradiated at high doses was relatively poor, but with increasing ratios of sterile males, egg hatch could be lowered effectively. Males irradiated as pupae had a lower competitiveness compared to males irradiated as adults, but the use of partially-sterilizing doses has not been studied extensively. Methods to reduce somatic damage during the irradiation process as well as the use of other agents or techniques to induce sterility are discussed. It is concluded that the optimal radiation dose chosen for insects that are to be released during an SIT programme should ensure a balance between induced sterility of males and their field competitiveness, with competitiveness being determined under (semi-) field conditions. Self-contained ⁶⁰Co research irradiators remain the most practical irradiators but these are likely to be replaced in the future by a new generation of high output X ray irradiators.     

Comparative rearing parameters for bisexual and genetic sexing strains of Zeugodacus cucurbitae and Bactrocera dorsalis (Diptera: Tephritidae) on an artificial diet

The Sterile Insect Technique (SIT) is an important component of area wide programs to control invading or established populations of pestiferous tephritids. The SIT involves the production, sterilization, and release of large numbers of the target species, with the goal of obtaining sterile male x wild female matings, which yield infertile eggs. A major advance in SIT involved sex-linked, genetic manipulations that allowed the production and release of male-only strains (also termed genetic sexing strains, GSS). The use of GSS avoids matings between sterile males and females, which may divert males from seeking and mating with wild females, and studies show that male-only releases result in greater suppression of wild populations than standard bisexual releases (i.e., those including both males and females). GSS based on sex-linked pupal color exist for Zeugodacus cucurbitae (Coquillett) and Bactrocera dorsalis (Hendel), two important agricultural pest species, but their rearing characteristics have not been documented in detail. The goal of the present study was to compare the pupal color sexing and bisexual strains for each of these species with respect to important rearing parameters, including egg production and eclosion of larvae from eggs (egg hatch), pupal recovery, and weight, emergence rate, and flight ability. In both species, most of these parameters were significantly greater for the bisexual strain than the GSS, and, for a given number of eggs, the production of flight-capable adults was approximately 2 times greater in the bisexual strains of both species. The potential usefulness of GSS in SIT against Z. cucurbitae and B. dorsalis is assessed based on these findings.     

Mass rearing history negatively affects mating success of male Anastrepha ludens (Diptera: Tephritidae) reared for sterile insect technique programs

Mating competitiveness and sterility induction into cohorts of wild Anastrepha ludens (Loew) (Diptera: Tephritidae) was compared among wild and laboratory flies reared for use in the sterile insect technique Mexican program. Laboratory flies stemming from an 11-yr-old bisexual strain were either not irradiated, irradiated at 3 krad (low dose), or irradiated at 8 krad. In 30 by 30 by 30-cm Plexiglas cages, where a cohort of laboratory flies (male and female) irradiated at different doses (0, 3, and 8 krad) was introduced with a cohort of wild flies, males and females of each type mated randomly among themselves. Compared with nonirradiated laboratory and wild males, irradiated males, irrespective of dose (3 or 8 krad), induced shorter refractory periods and greater mating frequency in wild females. Nevertheless, laboratory flies irradiated at a low dose induced greater sterility into cohorts of wild flies than laboratory flies irradiated at a high dose. In a 3 by 3 by 3-m walk-in cage, wild males gained significantly more matings with wild females than nonirradiated and irradiated laboratory males a finding that revealed a strong effect of strain on mating performance. Mating incompatibility of the laboratory strain might have obscured the effect of reduced irradiation doses on male mating performance in the walk-in cage. Our results highlight an urgent need to replace the A. ludens strain currently used by the Mexican fruit fly eradication campaign and at least suggest that reducing irradiation doses result in an increase in sterility induction in wild populations.     

A new method for the production of sterile colonies of Lucilia sericata

Maggot debridement therapy (MDT) refers to the use of blowfly larvae to clean or debride an infected wound. Most commonly, larvae of Lucilia sericata (Meigen) (Diptera: Calliphoridae) are used, and are sterilized prior to use to ensure no further bacterial infections are introduced during treatment. Current methods sterilize eggs from laboratory‐reared blowfly colonies, after which sterile early second instar maggots can be provided to hospitals for use in treatment. Maggots not required for treatment are used for colony regeneration, in which sterility is not maintained. The ability to maintain sterility beyond this would allow further research into fly–bacteria interactions and the effects of different bacteria on the blowfly lifecycle. This study aimed to produce a colony of sterile adults, using current egg sterilization practice, but maintaining sterility through to pupation and emergence. The production of a sterile colony allows further research into the impact of bacteria on fly development and survival. Eggs were placed on a sterile food source within autoclaved plant tissue culture containers to allow growth under sterile conditions. Nutrient agar plating of sterilized and non‐sterilized eggs, larvae and adults (post‐emergence), as well as the pupation medium and feed source in nutrient broth confirmed the aerobic sterility of all samples involved. The lifecycle of L. sericata was successfully completed through pupation to emergence with no effects on lifespan or oviposition by the newly emerged, sterile adult colony.     

Prerelease exposure to methyl eugenol increases the mating competitiveness of sterile males of the oriental fruit fly (Diptera: Tephritidae) in a Hawaiian orchard

Males of the oriental fruit fly, Bactrocera dorsalis (Hendel), are strongly attracted to methyl eugenol (ME), and recent work demonstrated that ingestion of this chemical enhances male mating success, apparently owing its role as a precursor in the synthesis of the male sex pheromone. The current study expanded upon earlier laboratory and field-cage experiments by assessing whether prerelease exposure to ME increased the mating competitiveness of mass-reared, sterile males in Hawaiian orchards. Releases of sterile males from a pupal color-based sexing strain were made weekly in two fruit orchards over 8 mo, with the sterile males at one site given ME for 24 h before release (treated) and the sterile males at the other site given no ME before release (control). Fruits were collected periodically during the study period, and eggs were dissected and incubated to score hatch rate. At both sites, releases of sterile males increased the proportion of unhatched eggs well above prerelease levels, but the incidence of egg sterility was consistently, and statistically, greater in the orchard receiving ME-exposed males. Computed over the entire release period, the average value of Fried's competitive index (that characterizes the mating success of sterile males relative to their wild counterparts) for ME-treated males was 3.5 times greater than that for control males, although this difference was not statistically significant. However, when computed over the period during which egg sterility values were elevated and stable, presumably when females inseminated before the releases were rare or absent, the competitive indices were significantly higher for ME-treated sterile males. The implications of these results for implementing the Sterile Insect Technique against this species are discussed.     

Prolongation of the effective copulation period by fractionated‐dose irradiation in the sweet potato weevil,Cylas formicarius

The sterile insect technique (SIT), based on the principles of population and behavioral ecology, is widely used to suppress or eradicate target pest insect populations. The effectiveness of SIT depends on the ability of released sterile males to mate with and inseminate wild females; however, the use of gamma radiation to induce sterility negatively affects both somatic cells as well as reproductive cells. Consequently, sterilization by irradiation drastically diminishes mating performance over time. It is well known that fractionated‐dose irradiation, in which a sterilizing dose is delivered via a series of smaller irradiations, reduces radiation damage. In the present study, we evaluated the effect of fractionated‐dose irradiation on fertility, longevity, and mating propensity in Cylas formicarius (Summers) (Coleoptera: Brentidae) for 16 days after irradiation. Fractionated‐dose irradiation with 200 Gy induced full sterility regardless of the number of radiation doses. Although the mating propensity of males sterilized by a single 200 Gy dose (the current standard of the Okinawa Prefecture SIT program) was equal to that of non‐irradiated weevils for the first 6 days, the mating propensity of males sterilized by a series of three doses was maintained for at least the first 12 days. These results demonstrated that fractionated‐dose irradiation can be highly advantageous in C. formicarius eradication programs.     

Improving male mating competitiveness and survival in the field for medfly,Ceratitis capitata (Diptera: Tephritidae) SIT programs

The success of the sterile insect technique (SIT) depends critically upon mating between released sterilized males and wild females. In Hawaii, improvements in the efficiency of sterile males were attempted on two separate fronts – mating enhancement and survival improvement. In the former, two methods have been investigated – selective breeding and aromatherapy. In the latter, flies which survived in field cages for several days were selected and bred to produce progeny with enhanced survival ability compared to control flies. Regarding mating selection, standard laboratory-reared males that successfully mated with wild females in field cages were allowed to breed. F1 offspring were inbred, then the selection procedure was repeated for four additional cycles. In the aromatherapy procedure, laboratory-reared males were exposed to ginger root oil for several hours 1 day prior to testing in field cages. Compared to controls, the selected flies improved the mating competitiveness of male flies ca. 3-fold, irradiation reduced this increase to ca. 2.5-fold. Exposing the selected, hybrid strain raised the fitness of the lab males to ca. 9-fold that of wild males. In the ongoing survival selection study, we have obtained lines in which the selected males survived ca. 2-fold better than laboratory control males over several days in an outdoor field cage, with food and water provided. The goal is to combine the traits of higher survival and mating ability into a single strain for SIT release.     

Trichogramma releases in North Carolina cotton: why releases fail to suppress heliothine pests

Field studies were conducted in 1996 and 1997 to determine the fate of naturally oviposited F3 heliothine eggs in cotton plots treated with augmentative releases of Trichogramma exiguum Pinto & Platner and nontreated plots. Four cohorts of newly oviposited eggs (< 24 h old) were followed in 1996 and two cohorts in 1997. In 1996, mean +/- SD percent parasitism, estimated by in-field studies following the fate of naturally oviposited eggs, ranged from 7 +/- 7 to 61 +/- 8% in T. exiguum release plots and 0 +/- 0 to 35 +/- 13% in control plots. The mean +/- SD percent of eggs hatched in T. exiguum release plots ranged from 1 +/- 2 to 11 +/- 4% and 7 +/- 4 to 28 +/- 10% in control plots. In 1997, mean +/- SD percent egg parasitism ranged from 27 +/- 4 to 40 +/- 3% in T. exiguum release plots and 15 +/- 18 to 25 +/- 8% in control plots. The mean +/- SD percent of eggs hatched in T. exiguum release plots ranged from 7 +/- 3 to 12 +/- 2% and 18 +/- 6 to 28 +/- 8% in control plots. Despite increased parasitism and reduced egg hatch in T. exiguum release plots, overall, there was no significant difference in larval density (all instars combined) between T. exiguum release and control plots. Combined analysis of the heliothine larval populations and egg fate data revealed that the additional egg mortality produced by released T. exiguum was offset by lower larval mortality in release plots. Because of the occurrence of compensatory mortality, the egg stage of heliothines is not an appropriate target for biological control using Trichogramma wasp releases.     

A field cage study of the optimal age for release of radio-sterilized Aedes albopictus mosquitoes in a sterile insect technique program

The use of the sterile insect technique (SIT) is being considered as an additional tool for the control of Aedes albopictus (Skuse) (Diptera: Culicidae), the vector of Chikungunya and Dengue viruses in Mauritius. The aim of this study was to assess the competitiveness value of sterile males of different age and under various release conditions. Three release ratios were tested with sterile males of either 1, 3, or 5 days old at release. The competition of sterile males against same age or a mixed age population of fertile males (which is more representative of the field situation) was also investigated. The participation in mating (observed through single female oviposition), the average-induced sterility, and the male competitiveness index indicated that 3-day-old sterile males have the best balance between survival and mating capacity, and should therefore be the favored age of release in the field. Reduction in the cage fertility was obtained at 5-to-1 release ratio; however, it is speculated that at least a 10-fold ratio of sterile-to-fertile males should be chosen to induce substantial sterility in the wild Ae. albopictus population in the SIT pilot release site in Mauritius. Interestingly, this study showed for the first time that the age of the fertile male population against which the sterile males compete is a very important parameter that can significantly affect the sexual performance of sterile males, leading to overestimation of their competitiveness values.     

Sterility and Sexual Competitiveness of Tapachula-7 Anastrepha ludens Males Irradiated at Different Doses

A genetic sexing strain of Anastrepha ludens (Loew), Tapachula-7, was developed by the Mexican Program Against Fruit Flies to produce and release only males in programs where the sterile insect technique (SIT) is applied. Currently, breeding are found at a massive scale, and it is necessary to determine the optimum irradiation dose that releases sterile males with minimum damage to their sexual competitiveness. Under laboratory and field conditions, we evaluated the effects of gamma irradiation at doses of 0, 20, 40, 60 and 80 Gy on the sexual competitiveness of males, the induction of sterility in wild females and offspring survivorship. The results of the study indicate that irradiation doses have a significant effect on the sexual behavior of males. A reduction of mating capacity was inversely proportional to the irradiation dose of males. It is estimated that a dose of 60 Gy can induce more than 99% sterility in wild females. In all treatments, the degree of offspring fertility was correlated with the irradiation dose of the parents. In conclusion, the results of the study indicate that a dose of 60 Gy can be applied in sterile insect technique release programs. The application of this dose in the new genetic sexing strain of A. ludens is discussed.     

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.     

Conceptual framework and rationale

The sterile insect technique (SIT) has been shown to be an effective and sustainable genetic approach to control populations of selected major pest insects, when part of area-wide integrated pest management (AW-IPM) programmes. The technique introduces genetic sterility in females of the target population in the field following their mating with released sterile males. This process results in population reduction or elimination via embryo lethality caused by dominant lethal mutations induced in sperm of the released males. In the past, several field trials have been carried out for mosquitoes with varying degrees of success. New technology and experience gained with other species of insect pests has encouraged a reassessment of the use of the sterility principle as part of integrated control of malaria vectors. Significant technical and logistic hurdles will need to be overcome to develop the technology and make it effective to suppress selected vector populations, and its application will probably be limited to specific ecological situations. Using sterile males to control mosquito vector populations can only be effective as part of an AW-IPM programme. The area-wide concept entails the targeting of the total mosquito population within a defined area. It requires, therefore, a thorough understanding of the target pest population biology especially as regards mating behaviour, population dynamics, dispersal and level of reproductive isolation. The key challenges for success are: 1) devising methods to monitor vector populations and measuring competitiveness of sterile males in the field, 2) designing mass rearing, sterilization and release strategies that maintain competitiveness of the sterile male mosquitoes, 3) developing methods to separate sexes in order to release only male mosquitoes and 4) adapting suppression measures and release rates to take into account the high reproductive rate of mosquitoes. Finally, success in area-wide implementation in the field can only be achieved if close attention is paid to political, socio-economic and environmental sensitivities and an efficient management organization is established taking into account the interests of all potential stakeholders of an AW-IPM programme.     

Chemosterilization of the cabbage root fly under field conditions

Removing hedgerow feeding sites from within 40, 80 or 160 m of cauliflower plots, failed to reduce populations of the cabbage root fly (Erioischia brassicae (Bouché)). Oviposition on the plots was unchanged but the efficiency of yellow water-traps was improved. Traps along-side cleared hedgerows caught more gravid than non-gravid females. In cages, 94% of the eggs laid were sterile when both sterilant baits containing tepa [tris-(i-aziridinyl) phosphine oxide] and hedgerow flowers were present. In the field, maximum egg-sterility rarely exceeded 30% when sterilant was present when natural sterility averaged 8%. Chemosterilization was an inadequate control since sufficient eggs and larvae survived to produce root-damage indices of 49 % in contrast to 2 % on insecticide-treated plants. Most eggs were sterile when chemosterilant baits were placed 0.75 m apart and bait was most effective when placed around the crop during the pre-oviposition period and through the crop at the time of maximum oviposition. Increasing the concentration of tepa failed to increase the effectiveness of the bait but a higher proportion of the eggs laid were sterile on large than on small plots. When chemosterilant treatments were stopped, egg-fertility gradually reverted to the natural level. Protracted immigration, an innate tendency for females to disperse, reductions in the competitiveness of sterile males, and the failure of males to re-disperse once sterilized, appeared to be the main factors limiting the levels of sterility in root-fly populations exposed to tepa-baited lures in the field.     

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.     

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.