Sterile Insect Technique Programs Research Articles

Radioactivity and GMO-Free Sterile Insect Technology for the Sustainable Control of the Invasive Pest Drosophila suzukii.

Drosophila suzukii (D. suzukii), commonly known as the spotted wing drosophila, is a highly invasive crop pest that is difficult to control using chemical insecticides. To address the urgent need for alternative and more sustainable control strategies, the sterile insect technique (SIT) is improved, which involves the release of sterilized male insects to mate with fertile conspecifics, thereby reducing the size of the pest population in the subsequent generation. The three critical aspects that influence the success of SIT programs in D. suzukii are addressed. First, an accurate and nondestructive method is established to determine the sex of individual insects based on the differential weight of male and female pupae. Second, conditions for X-ray sterilization are systematically tested and an optimal dose (90kV/40Gy) is identified that ensures the efficient production of sterile D. suzukii for release. Finally, the inherent thermosensitivity of D. suzukii males is exploited to develop a temperature-based sterilization technique, offering an alternative or additional SIT method for this pest. These advances will contribute to the development of a comprehensive and effective strategy for the management of D. suzukii populations, reducing their impact on agriculture and helping to safeguard crop yields.

Screening the optimal dose of gamma radiation for Tuta absoluta sterility: paving the way for sterile insect technique programs

Screening the optimal dose of gamma radiation for Tuta absoluta sterility: paving the way for sterile insect technique programs

Suitability of false codling moth eggs from different sterile to fertile moth ratios in the sterile insect technique programme, to parasitism by Trichogrammatoidea cryptophlebiae

The sterile insect technique (SIT) and augmentative releases of egg parasitoids, Trichogrammatoidea cryptophlebiae have been employed to manage false codling moth (FCM), Thaumatotibia leucotreta in South Africa. To enhance FCM control, simultaneous releases of sterile moths and egg parasitoids are conducted. It is, therefore, necessary to determine the compatibility and combined values of these approaches. A laboratory study was conducted to explore the susceptibility of FCM eggs resulting from various pairings of sterile and fertile moths to parasitism by egg parasitoids. The ratios of sterile to fertile FCM used in the study were 0:1, 10:1, 20:1, 40:1, and 60:1. The fitness of the egg parasitoids emerging from these ratios was assessed using a flight chamber test. Sterile male and female FCM treated with 150 Gy of gamma irradiation were crossbred with fertile counterparts. The resulting eggs were then exposed to egg parasitoids for parasitism. The study evaluated the parasitism rates of newly laid (24 h), 48 h and 72 h old eggs. Overall, eggs from all ratios were suitable for egg parasitoid development and acceptable for oviposition. Significantly higher proportions of parasitised eggs were recorded between the control (0:1) and ratios 40:1 and 60:1 with 48 h old eggs. Additionally, a higher number of egg parasitoids emerged across the ratios, with a higher proportion of female-to-male parasitoids recorded. These findings indicate that egg parasitoids can successfully accept and hatch from FCM eggs from different sterile to fertile moth ratios. This suggests the potential for achieving a synergistic suppressive effect by combining SIT and augmentative releases of egg parasitoids for improved FCM control. Nevertheless, further studies are necessary to investigate the combined releases of sterile moths and parasitoids under field conditions.

Assessment of radiation-induced sterility, longevity, and reproductive characteristics of the Aedes aegypti (Diptera: Culicidae) strain of Swat: A step towards the implementation of SIT in Pakistan.

Biological approaches for vector mosquito control such as sterile insect technique (SIT) requires sterilization of male mosquitoes through specific radiation doses for sterility induction in males. Under the SIT program, the males used must be compatible with the wild males in vigor, flight and selection of mate. Much of this potential is determined by the diet provided in the larval stages and optimizing the irradiation doses that cause complete sterility but have very minimal effect on the lives of irradiated males. The current study is designed to evaluate gamma radiation doses for inducing sterility in male Aedes aegypti mosquitoes with a genomic background from Pakistan (Swat district) and to assess the effects of radiation exposure on the competency of irradiated males and other life traits of irradiated mosquitoes. Sterilization of 17-hour-old male pupae (groups of 50 pupa/cup in three replicates) of the Ae. aegypti Swat strain was conducted using radiation doses of 30, 60, 70, 90, and 105 gray (Gy) from (Co60) at the Nuclear Institute for Food and Agriculture (NIFA) in Peshawar, Pakistan. Post-irradiated pupae were released in adult cages. Virgin females of the same cohort were released (1:1) to mate with the irradiated males. Mortality, longevity, mating competitiveness of males, and female fecundity were recorded. An average of 71 eggs per female was recorded in control with 86% hatch rate. Individual females mated with a 60 Gy treated males produced 60 ± 0.6 eggs per female with 17% hatch rate, and those mated with 70 Gy males produced 42 ± 0.01 eggs with a nil hatch rate, whereas females mated with males treated with ≥70 Gy doses did not reproduce to next generation. Females in groups of 50 mated with 60, 70 Gy treated males (equal pairs), produced 369±1.3 and 98±0.01 eggs with 15% and zero hatch rate. Significant dose dependent reduction in longevity was observed for >30 Gy doses. The matting competence of irradiated males was about half that of un-irradiated males. Aedes aegypti with a Pakistani genomic background treated with a ≥70 Gy dose of gamma radiation induced complete sterility in males and provided the first- step foundation for SIT application in Pakistan. Further extensive studies are required to optimize the SIT techniques so that fully sterile males with very minor quality changes can be produced on large scales for field trials.

On the impact of re-mating and residual fertility on the Sterile Insect Technique efficacy: Case study with the medfly, Ceratitis capitata.

The sterile insect technique (SIT) can be an efficient solution for reducing or eliminating certain insect pest populations. It is widely used in agriculture against fruit flies, including the Mediterranean fruit fly (medfly), Ceratitis capitata. The re-mating tendency of medfly females and the fact that the released sterile males may have some residual fertility could be a challenge for the successful implementation of the SIT. Obtaining the right balance between sterility level and sterile male quality (competitiveness, longevity, etc) is the key to a cost-efficient program. Since field experimental approaches can be impacted by many environmental variables, it is difficult to get a clear understanding on how specific parameters, alone or in combination, may affect the SIT efficiency. The use of models not only helps to gather knowledge, but it allows the simulation of a wide range of scenarios and can be easily adapted to local populations and sterile male production. In this study, we consider single- and double-mated females. We first show that SIT can be successful only if the residual fertility is less than a threshold value that depends on the basic offspring number of the targeted pest population, the re-mating rates, and the parameters of double-mated females. Then, we show how the sterile male release rate is affected by the parameters of double-mated females and the male residual fertility. Different scenarios are explored with continuous and periodic sterile male releases, with and without ginger aromatherapy, which is known to enhance sterile male competitiveness, and also taking into account some biological parameters related to females that have been mated twice, either first by a wild (sterile) male and then a sterile (wild) male, or by two wild males only. Parameter values were chosen for peach as host fruit to reflect what could be expected in the Corsican context, where SIT against the medfly is under consideration. Our results suggest that ginger aromatherapy can be a decisive factor determining the success of SIT against medfly. We also emphasize the importance of estimating the duration of the refractory period between matings depending on whether a wild female has mated with a wild or sterile male. Further, we show the importance of parameters, like the (hatched) eggs deposit rate and the death-rate related to all fertile double-mated females. In general, re-mating is considered to be detrimental to SIT programs. However, our results show that, depending on the parameter values of double-mated females, re-mating may also be beneficial for SIT. Our model can be easily adapted to different contexts and species, for a broader understanding of release strategies and management options.

Assessment of optimal blood exposure time at 37 °C during in vitro tsetse flies feeding for quality production in mass-rearing colonies.

Control of African animal trypanosomosis is implemented through an integrated control strategy, with the sterile insect technique (SIT) as one of its components. The SIT requires mass rearing of tsetse fly colonies using an in vitro feeding system. The exposure of blood at 37 °C on heating plates over time can have an impact on the quality of fly productivity. In this study, we investigated the survival and fecundity of adult tsetse flies fed at 37 °C on 8 blood exposure times ranging from 30min to 4h with increments of 30min (treatment 1, flies were fed 30min after exposure to blood at 37 °C; treatment 2, 1h and so on until treatment 8 [4h after]) in order to determine the optimal exposure time. In addition, bacterial growth in blood from each treatment was assessed by agar culture at 37 °C for 72h. The results showed that the adult female survival rates were similar regardless of the treatment. For males, only those of treatment 1 (30min) showed a marginal lower survival than those of treatments 7 and 8 fed after 3h 30min and 4h of blood exposure, respectively. Over the 4-h interval of blood exposure at 37 °C, the results showed that the number of pupae produced per initial female and pupal weight tended to increase with exposure time, but the differences were not significant. We discuss the implications of these results on tsetse mass rearing for the SIT program.

Mass irradiation of adult Aedes mosquitoes using a coolable 3D printed canister

In the last decade, the use of the sterile insect technique (SIT) to suppress mosquito vectors have rapidly expanded in many countries facing the complexities of scaling up production and procedures to sustain large-scale operational programs. While many solutions have been proposed to improve mass production, sex separation and field release procedures, relatively little attention has been devoted to effective mass sterilization of mosquitoes. Since irradiation of pupae en masse has proven difficult to standardise with several variables affecting dose response uniformity, the manipulation of adult mosquitoes appears to be the most promising method to achieve effective and reliable sterilization of large quantities of mosquitoes. A 3D-printed phase change material based coolable canister was developed which can compact, immobilize and hold around 100,000 adult mosquitoes during mass radio sterilization procedures. The mass irradiation and compaction treatments affected the survival and the flight ability of Aedes albopictus and Aedes aegypti adult males but the use of the proposed irradiation canister under chilled conditions (6.7–11.3 °C) significantly improved their quality and performance. The use of this cooled canister will facilitate adult mass irradiation procedures in self-contained irradiators in operational mosquito SIT programmes.

The effect of permanent protective netting on insect pest prevalence in citrus orchards in South Africa

The use of protective netting is becoming an increasingly popular practice in the citrus industry in South Africa. However, data on its effects on biotic factors, particularly insect pests, are limited. This study focused on the effect nets have on key citrus pests in the Eastern Cape province. Orchards under nets and open orchards, of similar cultivars, ages and management practices, were monitored at several sites over two seasons for pest infestation and damage. Weekly monitoring was conducted for Thaumatotibia leucotreta infestation. Other pests were monitored either monthly or once a season. During the first season, T. leucotreta infestation was higher in orchards under nets, probably because, unlike the open orchards, the nets provided protection for the existing high levels of T. leucotreta. No T. leucotreta infestation was recorded in both orchard types in 2019. This was due to generally lower than usual pest abundance and dramatically improved area-wide management of T. leucotreta. Pheromone traps were used to monitor T. leucotreta males, including sterile moths used in a sterile insect technique programme. Although higher catches of wild T. leucotreta moths were recorded in orchards under nets, so too were there higher numbers of sterile moths and a higher ratio of sterile to wild moths, indicating the potential for better pest suppression for orchards under nets. Various other key pests were monitored during this time, with variable results for each species. Pests that were elevated under nets include Planococcus citri and Aonidiella aurantii. Pests that seemed to be lower under nets were Ceratitis capitata and Scirtothrips aurantii. Nets had no effect on Empoasca distinguenda, Penthimiola bella and Eriophyes sheldoni. These differences in pest levels in netted and open orchards trigger an important debate on whether nets are beneficial for or detrimental to the successful implementation of an integrated pest management programme.

Deep orange gene editing triggers temperature-sensitive lethal phenotypes in Ceratitis capitata

BackgroundThe Mediterranean fruit fly, Ceratitis capitata, is a significant agricultural pest managed through area-wide integrated pest management (AW-IPM) including a sterile insect technique (SIT) component. Male-only releases increase the efficiency and cost-effectiveness of SIT programs, which can be achieved through the development of genetic sexing strains (GSS). The most successful GSS developed to date is the C. capitata VIENNA 8 GSS, constructed using classical genetic approaches and an irradiation-induced translocation with two selectable markers: the white pupae (wp) and temperature-sensitive lethal (tsl) genes. However, currently used methods for selecting suitable markers and inducing translocations are stochastic and non-specific, resulting in a laborious and time-consuming process. Recent efforts have focused on identifying the gene(s) and the causal mutation(s) for suitable phenotypes, such as wp and tsl, which could be used as selectable markers for developing a generic approach for constructing GSS. The wp gene was recently identified, and efforts have been initiated to identify the tsl gene. This study investigates Ceratitis capitata deep orange (Ccdor) as a tsl candidate gene and its potential to induce tsl phenotypes.ResultsAn integrated approach based on cytogenetics, genomics, bioinformatics, and gene editing was used to characterize the Ccdor. Its location was confirmed on the right arm of chromosome 5 in the putative tsl genomic region. Knock-out of Ccdor using CRISPR/Cas9-NHEJ and targeting the fourth exon resulted in lethality at mid- and late-pupal stage, while the successful application of CRISPR HDR introducing a point mutation on the sixth exon resulted in the establishment of the desired strain and two additional strains (dor 12del and dor 51dup), all of them expressing tsl phenotypes and presenting no (or minimal) fitness cost when reared at 25 °C. One of the strains exhibited complete lethality when embryos were exposed at 36 °C.ConclusionsGene editing of the deep orange gene in Ceratitis capitata resulted in the establishment of temperature-sensitive lethal mutant strains. The induced mutations did not significantly affect the rearing efficiency of the strains. As deep orange is a highly conserved gene, these data suggest that it can be considered a target for the development of tsl mutations which could potentially be used to develop novel genetic sexing strains in insect pests and disease vectors.

Sterile Insect Technique (SIT) field trial targeting the suppression of Aedes albopictus in Greece.

The sterile insect technique (SIT) involves releasing large numbers of sterile males to outcompete wild males in mating with females, leading to a decline in pest populations. In the current study, we conducted a suppression trial in Greece against the invasive dengue vector mosquito Aedes albopictus (Skuse) through the weekly release of sterile males for 22 weeks from June to September 2019. Our approach included the long-distance transport of sterile mosquitoes, and their release at a density of 2,547±159 sterile males per hectare per week as part of an area-wide integrated pest management strategy (AW-IPM). The repeated releases of sterile males resulted in a gradual reduction in egg density, reaching 78% from mid-June to early September. This reduction remained between 70% and 78% for four weeks after the end of the releases. Additionally, in the SIT intervention area, the ovitrap index, representing the percentage of traps containing eggs, remained lower throughout the trial than in the control area. This trial represents a significant advance in the field of mosquito control, as it explores the viability and efficacy of producing and transporting sterile males from a distant facility to the release area. Our results provide valuable insights for future SIT programmes targeting Ae. Albopictus, and the methodology we employed can serve as a starting point for developing more refined and effective release protocols, including the transportation of sterile males over long distances from production units to intervention areas.

A classic screening marker does not affect antennal electrophysiology but strongly regulates reproductive behaviours in Bactrocera dorsalis.

The key phenotype white eye (white) has been used for decades to selectively remove females before release in sterile insect technique programs and as an effective screening marker in genetic engineering. Bactrocera dorsalis is a representative tephritid pest causing damage to more than 150 fruit crops. Yet, the function of white in important biological processes remains unclear in B. dorsalis. In this study, the impacts of the white gene on electrophysiology and reproductive behaviour in B. dorsalis were tested. The results indicated that knocking out Bdwhite disrupted eye pigmentation in adults, consistent with previous reports. Bdwhite did not affect the antennal electrophysiology response to 63 chemical components with various structures. However, reproductive behaviours in both males and females were significantly reduced in Bdwhite-/- . Both pre-copulatory and copulation behaviours were significantly reduced in Bdwhite-/- , and the effect was male-specific. Mutant females significantly delayed their oviposition towards γ-octalactone, and the peak of oviposition behaviour towards orange juice was lost. These results show that Bdwhite might not be an ideal screening marker in functional gene research aiming to identify molecular targets for behaviour-modifying chemicals. Instead, owing to its strong effect on B. dorsalis sexual behaviours, the downstream genes regulated by Bdwhite or the genes from white-linked areas could be alternate molecular targets that promote the development of better behavioural modifying chemical-based pest management techniques.

X-rays are as effective as gamma-rays for the sterilization of Glossina palpalis gambiensis Vanderplank, 1911 (Diptera: Glossinidae) for use in the sterile insect technique

An area-wide integrated pest management strategy with a sterile insect technique (SIT) component requires a radiation source for the sterilisation of male insects. Self-contained gamma irradiators, which were exclusively used in past SIT programmes, are now facing increasing constraints and challenges due to stringent regulations. As a potential alternative, new generation high output X-ray irradiators have been proposed. The feasibility of using X-ray irradiators was assessed by comparing the effects of both gamma- and X-ray irradiators on biological parameters of Glossina palpalis gambiensis (Vanderplank, 1911), that are important for SIT applications. The gamma irradiator Foss Model 812 and two X-ray irradiators, the Rad Source 2400 and the blood irradiator Raycell Mk2 were used. Glossina palpalis gambiensis males were exposed to radiation as pupae. A radiation dose of 110 Gy or above induced more than 97% sterility in females that mated with the irradiated males for all the irradiators. Adult emergence rate, flight propensity, survival and mating performance did not differ between gamma- and X-rays irradiators. These results suggest that irradiating pupae with a dose of 110 Gy is optimal for both gamma-and X-ray irradiators used in this study, to achieve a sterility of approximately 99%. Similar research on other tsetse species could gradually phase out the use of gamma-ray irradiators in favour of X-rays irradiators, especially for smaller SIT programmes.

Development of a novel genetic sexing strain of Ceratitis capitata based on an X-autosome translocation

Genetic sexing strains (GSS), such as the Ceratitiscapitata (medfly) VIENNA 8 strain, facilitate male-only releases and improve the efficiency and cost-effectiveness of sterile insect technique (SIT) applications. Laboratory domestication may reduce their genetic diversity and mating behaviour and hence, refreshment with wild genetic material is frequently needed. As wild males do not carry the T(Y;A) translocation, and wild females do not easily conform to artificial oviposition, the genetic refreshment of this GSS is a challenging and time-consuming process. In the present study, we report the development of a novel medfly GSS, which is based on a viable homozygous T(XX;AA) translocation using the same selectable markers, the whitepupae and temperature-sensitivelethal genes. This allows the enmasse cross of T(XX;AA) females with wild males, and the backcrossing of F1 males with the T(XX;AA) females thus facilitating the re-establishment of the GSS as well as its genetic refreshment. The rearing efficiency and mating competitiveness of the novel GSS are similar to those of the T(Y;A)-based VIENNA 8 GSS. However, its advantage to easily allow the genetic refreshment is of great importance as it can ensure the mass production of high-quality males and enhanced efficacy of operational SIT programs.

Effects of different diets on Aedes aegypti adults: improving rearing techniques for sterile insect technique.

The aim was to evaluate the effect of different energy diets available in adulthood on the longevity, dispersal capacity and sexual performance of Aedes aegypti produced under a mass-rearing system. To evaluate the effects of diets in relation to the survival of the adult male insects of Ae. aegypti, six treatments were used: sucrose at a concentration of 10%, as a positive control (sack10); starvation, as a negative control (starvation); sucrose at a concentration of 20% associated with 1 g/l of ascorbic acid (sac20vitC); wild honey in a concentration of 10% (honey10); demerara sugar in a 10% concentration (demerara10); and sucrose at a concentration of 20% associated with 1 g/l of ascorbic acid and 0.5 g/l of amino acid proline (sac20vitCPr). Each treatment had 16 cages containing 50 adult males. For the tests of flight ability and propensity to copulation, five treatments were used (saca10; sac20vitC; mel10; demerara10; and sac20vitCPr), with males each for flight ability and females copulated by a single male for copulation propensity. The diet composed of sucrose at a concentration of 20% associated with ascorbic acid, as an antioxidant, improved the survival, flight ability and propensity to copulate in Ae. aegypti males under mass-rearing conditions, and may be useful to enhance the performance of sterile males, thus improving the success of sterile insect technique programmes.

Male exposure to guava volatiles affects female remating behavior in Anastrepha fraterculus

AbstractPlant‐derived volatiles can have positive or negative effects on insects. Exposure to volatiles of guava (Psidium guajava L.) (Myrtaceae) enhances male mating success in the South American fruit fly, Anastrepha fraterculus (Wiedemann) (Diptera: Tephritidae), an important pest of various fruits. These volatiles can therefore be used as a post‐teneral, pre‐release supplement in sterile insect technique (SIT) programs. In SIT, mass‐reared sterile males compete for and mate with wild females, in order to reduce populations of insect pests. However, the success of SIT will be diminished if males are not able to inhibit females from remating with other (potentially wild) males. Here, we investigated the remating propensity of A. fraterculus females mated with males exposed to guava volatiles or non‐exposed (control) in choice and no‐choice tests. In addition, we tested whether exposure to guava volatiles affected male reproductive organ size (testes, accessory glands, and seminal vesicles) and cuticular hydrocarbon (CHC) profile. Females mated with guava‐exposed males were more likely to remate than females mated with control males, but there was no difference in the length of the refractory period (i.e., the time between the first and second mating event). Reproductive organ size did not differ between exposed and non‐exposed males, but exposed males had a higher quantity of waxes than non‐exposed males, and CHC profiles differed. The results are discussed in the context of SIT programs for the control of this insect pest.

Effects of radiation on the fitness, sterility and arbovirus susceptibility of a Wolbachia-free Aedes albopictus strain for use in the Sterile Insect Technique.

The sterile insect technique (SIT) is a green and species-specific insect pest control technique that suppresses target populations by releasing factory-reared, radio-sterilized males into the wild. Once released, it is important to be able to distinguish the released males from the wild males for monitoring purposes. Several methods to mark the sterile males exist. However, most have limitations due to monetary, process efficiency, or insect quality. Aedes albopictus is naturally infected with Wolbachia at a high prevalence. Therefore, the elimination of Wolbachia can serve as a biomarker to distinguish the factory-reared male mosquitoes from wild conspecifics. In this study, a Wolbachia-free Ae. albopictus GT strain was developed and its fitness evaluated, which was found to be comparable to the wild GUA strain. In addition, GT male mosquitoes were irradiated at the adult stage and a dose of 20 Gy or more induced over 99% sterility. Moreover, a dose of 30 Gy (almost completely sterilizing male and female mosquitoes) had limited effects on the mating competitiveness of GT males and vector competence of GT females, respectively. However, radiation reduced mosquito longevity, regardless of its sex. Our results indicated that the Ae. albopictus GT strain can be distinguished from the wild mosquitoes based on Wolbachia status and shows similar fitness, radio-sensitivity and arbovirus susceptibility to the GUA strain, indicating that it is feasible to use the GT strain to suppress Ae. albopictus populations for SIT programmes. This article is protected by copyright. All rights reserved.

Developing methods for chilling, compacting, and sterilizing adult Aedes aegypti (Diptera: Culicidae) and comparing mating competitiveness between males sterilized as adults versus pupae for sterile male release.

The yellow fever mosquito, Aedes aegypti L., can transmit several pathogens responsible for human diseases. With insecticide resistance development becoming a concern, alternative control strategies are needed for Ae. aegypti. Sterile insect technique (SIT) is an increasingly popular option being explored. However, logistical issues in mass production and sterilization make it difficult to maintain a SIT program. Male mosquitoes are typically irradiated as pupae because this is the earliest developmental point at which females can be separated from males, but asynchrony in pupation and high variability in pupal responses to irradiation based on pupal age make it difficult to sterilize mass quantities of pupae on a regular schedule in a rearing facility. Young adult mosquitoes have wider windows for irradiation sterilization than pupae, which can allow facilities to have fixed schedules for irradiation. We produced a workflow for adult Ae. aegypti irradiation in a mosquito control district with an operational SIT program that currently irradiates pupae. The impacts of chilling, compaction, and radiation dose on survival were all assessed before combining them into a complete adult irradiation protocol. Males chilled up to 16 h prior to compaction and compacted to 100 males/cm3 during radiation resulted in low mortality. Males irradiated as adults had increased longevity and similar sterility compared to males irradiated as pupae. Additionally, males sterilized as adults were more sexually competitive than males sterilized as pupae. Thus, we have shown that irradiating adult males can be a viable option to increase the efficiency of this operational mosquito SIT program.

Effects of Irradiation on Biology and Mating Behaviour of Wild Males of Brown Marmorated Stink Bug Using a 6 MV Medical Linear Accelerator

The brown marmorated stink bug, Halyomorpha halys, is a pentatomid bug of Eastern Asian origin that became an economically relevant pest in the Eurasian and American continents. Management of this species is limited to use of chemical insecticides: an inefficient method due to the strong adaptability of the target pest. The sterile insect technique (SIT) is potentially a valid tactic in the search for nontoxic alternatives. In this work, we investigated the suitability of mass-trapped overwintering males, collected during the aggregation phase before the winter diapause, for their release as competitive sterile males in an SIT programme. Differently from previous studies, irradiation was applied with a linear accelerator device that produced high-energy photons. Following a similar scientific protocol with newly emerged irradiated males, the effects of X-ray irradiation on physiological parameters (longevity, fecundity and fertility) were assessed. In addition, behavioural bioassays were carried out in no-choice conditions to evaluate if irradiation interferes with mating processes. The results are very encouraging; the effects of the irradiation at 32 Gy did not differ from the controls in the longevity or fecundity of the exposed overwintering adults. The hatching rate of the eggs laid by the fertile females that had mated with the irradiated males was less than 5%. The results of behavioural bioassays showed that the irradiation did not cause a significant impact on the quality of the sterile males. More research is warranted to evaluate the mating competitiveness of sterile males in semi-field and field conditions.

Effect of chilling on pupal developmental arrest and subsequent impact on quality control parameters of adult blowfly, Lucilia cuprina (Diptera: Calliphoridae)

The chilling process will surely be a very cost-effective measure for repeated mass rearing and be an effective source for the requirements of a huge number of pupae collected and supplied for the sterile insect technique (SIT) program. In Bangladesh, blowfly (Lucilia cuprina) is a main cause of damage of marine fish during sun drying in coastal areas. The chilling for a certain duration at a certain temperature may store pupae for a specific time by reducing their metabolism. In this study, the effect of chilling temperature and exposure period on pupal developmental arrest was assessed and the subsequent impact on quality control parameters of the adult blowfly, L. cuprina was also observed. We considered the effects of three temperature (4, 7, and 10 °C) regimes and three exposure periods (10, 20, and 30 days) on 3-day-old pupae. Results showed that all the parameters were affected significantly by all the chilling temperatures and durations. Adult emergence, flight ability, pupal weight, adult longevity, fecundity, and fertility decreased with the increase of exposure duration, but partial emergence and pupal duration increased with exposure durations. Storages at 4 °C for 20 and 30 days had no adult emergence. Emergence occurred before the chilling duration at 10 °C for 20 and 30 days which clearly indicated the unsuitable condition for storage parameters. Though the emergence, flight ability, pupal weight, and longevity at 10 °C for 10 days had no significant difference with control, the fecundity and fertility did have a significant difference. In addition, treatment at 7 °C for 10days, the adult emergence, flight ability, pupal weight, longevity, fecundity, fertility, pre-oviposition, and oviposition period had no significant difference with control. Considering all the parameters, it can be concluded that the pupae of L. cuprina can be stored at 7 °C of chilling temperature for 10 days long without any deterioration towards the quality of adult flies.

Suitability of Raycell MK2 Blood X-ray Irradiator for the Use in the Sterile Insect Technique: Dose Response in Fruit Flies, Tsetse Flies and Mosquitoes.

The sterile insect technique (SIT) is based on the inundatory field release of a target pest following their reproductive sterilization via exposure to radiation. Until recently, gamma irradiation from isotopic sources has been the most widely used in SIT programs. As isotopic sources are becoming increasingly expensive, especially for small programs, and regulations surrounding their procurement and shipment increasingly strict, irradiation capacity is one of the limiting factors in smaller or newly developing SIT projects. For this reason, the possibility of using X-ray irradiators has been evaluated in the recent decade. The availability of "off-the-shelf" blood X-ray irradiators that meet the technical requirements for insect irradiation can provide irradiation capacity for those SIT projects in which the acquisition of gamma ray irradiators is not feasible. Following the recent technical characterization of a Raycell MK2 X-ray blood irradiator, it was found in this study, that MK2 instruments were suitable for the sterilization of fruit flies, tsetse flies and mosquitoes, inducing comparable, even slightly higher, sterility levels compared to those achieved by gamma ray irradiation. This, together with its estimated processing efficiency, shows that MK2 irradiators are suitable for small- to mid-sized SIT programs.