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Mating competitiveness trials have been conducted in large net-screened enclosures (8 by 5 by 2.8 m) built in a natural shaded environment, in the summers of 2006, 2007, 2008, and 2009 in northern Italy. Aedes albopictus (Skuse) males were radio-sterilized by applying gamma radiations at doses in the range 30-60 Gy. Gamma radiation was administered...
Contexts in source publication
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... albopictus Strains. Strains are described in Table 1 (Fig. 1). Lab colonies (R) from F5 to the F42 were used for the study. ...
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... 4 Ð 6 h from sexing, pupae were irradiated using the 137 Cs plan at the S. Anna Hospital, Department of Health Physic, Ferrara, Italy ( Balestrino et al. 2010). Different radiation doses were tested: 50 Ð 60 Gy in 2006, and 30 Ð 40 Gy in 2007Ð2009 (Table 1). ...
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... number of blood feeding females was registered to calculate the mean female fecundity over the total number of eggs laid in the ovitraps. All the eggs were collected at the end of the trial (see Table 1) and underwent a standard lab procedure for hatching ( Bellini et al. 2007) to calculate the fertility levels. ...
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... and Female Survival. In 2008 and 2009, trials ended with the collection of all the living adults after 5, 11, 13, 14, and 18 d from release (see Table 1). Data were used to estimate the average daily survival rate for control fertile males, males radiated at 30 and 40 Gy and for females. ...
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... 2006 trials, statistically signiÞcant differences were found in egg hatching percent between control enclosures (90.04 8.98%) and competitiveness enclosures (20.82 10.55%), but not between the two levels of radiation (F 35.26, df 6,8, P 0.0001). Different combinations of wild and reared, and fertile and sterile strains did not result in statistically signiÞcant differences (Table 1). The competitiveness index (CIS Index) showed an impres- sive variability, with sterile males always more com- petitive than fertile ones (CIS Index 1). ...
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... Combination Effect (2007). The mean fecundity, hatching rate, and CIS Index ob- tained for each single trial are reported in Table 1. On average, the mean fecundity in the competitiveness enclosures, was 44.74 19.25 eggs per female (min- imum 29.24, maximum 64.56) and in the control en- closures it was 44.99 24.88 eggs per female, without statistically signiÞcant differences (F 0.72 df 9, 20, and P 0.68). ...
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... of Males Radiated With 30 and 40 Gy. As showed in Table 1, both in 2008 and 2009 the mean hatching rate was signiÞcantly higher in the control enclosures than in those with males radiated at 30 and 40 Gy (2008: F 11.68, df 2,17, P 0.001;2009: F 8.52, df 2,17, P 0.01). Considering all the trials, in 2008, the CIS Index was higher for the 30 Gy radiated males (1.33 0.67) than for the 40 Gy radi- ated ones (0.83 0.38), but the difference was not statistically signiÞcant (F 3.03, df 1,13, P 0.11) because of the wide data variation between enclosures and trials. ...
Similar publications
The mosquito Aedes albopictus (Skuse, 1895) is a potent vector of several arboviral diseases, most notably chikungunya and dengue fever. In the context of the sterile insect technique (SIT), the sterilization of the male mosquitoes before their release can be achieved by gamma-ray irradiation. As gamma-ray irradiators are becoming increasingly prob...
Citations
... Females that mate with sterilized males do not produce progeny (Knipling 1955;Klassen 2005). Area-wide SIT based programs have considerable success in the control of agricultural pests and the expectations are high in the area of SIT-based vector control (Kittayapong et al. 2019;Bellini et al. 2013). ...
Mass-production of Aedes aegypti and Ae. albopictus for use in vector control programs involving the sterile insect technique (SIT) requires the standardization of rearing techniques, including the production of eggs. Following published protocols, egg quantification for both species was performed based on the weight and volume characteristics of batches of 1,000 to 27,000 eggs from insect colonies that originated from natural populations in Chiapas, Mexico. The findings were validated by direct measurement of egg dimensions. On average, Ae. aegypti eggs were ∼40% heavier and occupied ∼25% larger volume than those of Ae. albopictus (p < 0.001). Egg numbers were readily predicted by linear correlation with the weight and volume of eggs of both species (p < 0.001). Volumetric measures were significantly more consistent among replicates than the weight measurements (p < 0.02). Direct measurements revealed that the eggs of Ae. aegypti were ∼10% longer (p < 0.001), ∼13% wider (p < 0.001), and also more variable in size than those of Ae. albopictus. These species also differed significantly in egg length:width ratios (p < 0.001). We conclude that proxy indicators of egg numbers, such as weight and volume, should greatly assist in standardizing larval rearing procedures.
... Interestingly, a study by Madakacherry et al. showed that increasing the release ratio of sterile males could eliminate the effect of weakened male competitiveness [33]. In addition, Bellini et al. showed that in semi-field enclosure experiments, radiation caused premature maturation of sterile males, which led to the fact that sterile males could mate with females earlier than fertile males [34]. In this study, at the same proportion of sterile males to untreated males, there were no statistically significant differences in the highdose X-ray and low-dose γ-ray hatching rates, induced sterility, or male mating competitiveness index. ...
The mosquito Aedes albopictus can transmit various arboviral diseases, posing a severe threat to human health. As an environmentally friendly method, sterile insect technology (SIT) is considered an alternative to traditional methods such as chemical pesticides to control Ae. albopictus. In SIT, the sterility of male mosquitoes can be achieved by γ-ray or X-ray radiation. Compared with γ-rays, X-rays are easier to obtain, cheaper, and less harmful. However, there is a lack of comparative assessment of these two types of radiation for SIT under the same controlled conditions. Here, we compared the effects of X-ray and γ-ray radiation on the sterility of Ae. albopictus males under laboratory-controlled conditions. Neither type of radiation affected the number of eggs but significantly reduced the survival time and hatch rate. The same dose of γ-rays caused a higher sterility effect on males than X-rays but had a more significant impact on survival. However, X-rays could achieve the same sterility effect as γ-rays by increasing the radiation dose. For example, X-rays of 60 Gy induced 99% sterility, similar to γ-rays of 40 Gy. In the test of male mating competitiveness, the induced sterility and the male mating competitiveness index were also identical at the same release ratio (sterile males/fertile males). At a release ratio of 7:1, nearly 80% of eggs failed to hatch. Sterile males produced by X-ray and γ-ray radiation had similar male competitiveness in competition with field males. In conclusion, a higher dose of X-rays is required to achieve the same sterility effect, compared to γ-rays. When γ-rays are not readily available, high-dose X-rays can be used instead. This study provides data supporting the selection of more suitable radiation for the field release of sterile male mosquitoes.
... In order to integrate the SIT into operational area-wide mosquito management programs, it is essential to verify if mass production, sterilization, and release procedures adopted can negatively affect the quality of the males imposing critical costs. Irradiated sterile males were found to be equivalent to fertile wild competitor under laboratory and semi-field conditions (Bellini et al., 2013b;Madakacherry et al., 2014;Damiens et al., 2016), while the field estimation of the competitiveness index of radio-sterilized A. albopictus males under field conditions resulted in a range of 0.03-0.38 . One of the most used parameters to measure the effect of the sterile male releases on population suppression is the mating competitiveness value ) which directly depend on the sterile to male ratio obtained in the field . ...
... As previously showed Bellini et al., 2013b), the ovitrap monitoring system as employed in the three study localities can provide a good estimation of the A. albopictus wild population density. The authors of this study reported a highly positive correlation between the number of pupae per hectare (PHI) and the weekly mean number of eggs per ovitrap collected in similar field environment in northern Italy. ...
... Pilot trials have been conducted in Italy to reduce Ae. albopticus populations [64,65], and a field trial is ongoing in Reunion [66]. In addition to SIT, incompatible insect technique (IIT) is also considered. ...
Background
Dengue is the world’s most prevalent mosquito-borne viral disease. It is endemic in many tropical and subtropical countries and represents a significant global health burden. The first reports of dengue virus (DENV) circulation in the South West Indian Ocean (SWIO) islands date back to the early 1940s; however, an increase in DENV circulation has been reported in the SWIO in recent years. The aim of this review is to trace the history of DENV in the SWIO islands using available records from the Comoros, Madagascar, Mauritius, Mayotte, Seychelles, and Reunion. We focus in particular on the most extensive data from Reunion Island, highlighting factors that may explain the observed increasing incidence, and the potential shift from one-off outbreaks to endemic dengue transmission.
Methods
Following the PRISMA guidelines, the literature review focused queried different databases using the keywords “dengue” or “ Aedes albopictus ” combined with each of the following SWIO islands the Comoros, Madagascar, Mauritius, Mayotte, Seychelles, and Reunion. We also compiled case report data for dengue in Mayotte and Reunion in collaboration with the regional public health agencies in these French territories. References and data were discarded when original sources were not identified. We examined reports of climatic, anthropogenic, and mosquito-related factors that may influence the maintenance of dengue transmission independently of case importation linked to travel.
Findings and conclusions
The first report of dengue circulation in the SWIO was documented in 1943 in the Comoros. Then not until an outbreak in 1976 to 1977 that affected approximately 80% of the population of the Seychelles. DENV was also reported in 1977 to 1978 in Reunion with an estimate of nearly 30% of the population infected. In the following 40-year period, DENV circulation was qualified as interepidemic with sporadic cases. However, in recent years, the region has experienced uninterrupted DENV transmission at elevated incidence. Since 2017, Reunion witnessed the cocirculation of 3 serotypes (DENV-1, DENV-2 and DENV-3) and an increased number of cases with severe forms and deaths. Reinforced molecular and serological identification of DENV serotypes and genotypes circulating in the SWIO as well as vector control strategies is necessary to protect exposed human populations and limit the spread of dengue.
... In order to integrate the SIT into operational area-wide mosquito management programs, it is essential to verify if mass production, sterilization, and release procedures adopted can negatively affect the quality of the males imposing critical costs. Irradiated sterile males were found to be equivalent to fertile wild competitor under laboratory and semi-field conditions (Bellini et al., 2013b;Madakacherry et al., 2014;Damiens et al., 2016), while the field estimation of the competitiveness index of radio-sterilized A. albopictus males under field conditions resulted in a range of 0.03-0.38 (Bellini et al., 2021). ...
... As previously showed Bellini et al., 2013b), the ovitrap monitoring system as employed in the three study localities can provide a good estimation of the A. albopictus wild population density. The authors of this study reported a highly positive correlation between the number of pupae per hectare (PHI) and the weekly mean number of eggs per ovitrap collected in similar field environment in northern Italy. ...
Mark–release–recapture (MRR) trials have been conducted in Northern Italy to evaluate the capacity of radio-substerilized Aedes albopictus males to survive, disperse, and engage in mating in the field. Two MRR sessions with the human landing collection method (HLC) were conducted with the simultaneous release of irradiated males marked with four different pigment colors. The survival and dispersal rates seem to be influenced more by environmental factors such as barriers, shading, and vegetation rather than weather parameters. In this study, we confirmed a positive linear relationship between the sterile adult male’s daily survival rate and the relative humidity previously reported in similar experimental conditions and a different dispersal capacity of the released A. albopictus males in low- (NDVI index <0.4) and high (NDVI index >0.4)-vegetated areas. Consistent with previous studies, A. albopictus males have their maximal dispersion in the first days after release, while in the following days the males become more stationary. The similar field performances obtained with marked and unmarked radio-sterilized and untreated A. albopictus males on similar environments confirm the negligible effects of irradiation and marking procedures on the quality of the males released. The similar sterile to wild (S/W) male ratio measured in high- and low-vegetation areas in the release sites indicates a similar distribution pattern for the wild and the released sterile males. According to the MRR data collected, the Lincoln index estimated different A. albopictus mean population densities in the study areas equal to 7,000 and 3,000 male/ha, respectively.
... The insemination rate is typically used to assess male performance in mosquitoes (40)(41)(42), but the role of female choice and the degree to which it influences mating outcomes is not known (43,44). The interspecific mating frequencies in male choice groups observed in this study were significantly different and Ae. ...
Aedes albopictus is the most invasive mosquito in the world and often displaces Ae. aegypti in regions where their populations overlap. Interspecific mating has been proposed as a possible cause for this displacement but whether this applies across the range of their sympatry remains unclear. Aedes albopictus and Ae. aegypti collected from allopatric and sympatric areas in China were allowed to interact in cage experiments with different crosses and sex-choices. The results confirm that asymmetric interspecific mating occurs in these populations with matings between allopatric Ae. albopictus males and Ae. aegypti females being significantly higher (55.2%) than those between Ae. aegypti males and Ae. albopictus females (27.0%), and sympatric mosquitoes showed a similar but lower frequency bias, 25.7% versus 6.2%, respectively. The cross-mated females can mate second time (re-mate) with the respective conspecific males and the 66.7% remating success of female Ae. albopictus was significantly higher than the 9.3% of Ae. aegypti females. Furthermore, 17.8% of the matings of Ae. albopictus males exposed to mixed pools of Ae. albopictus and Ae. aegypti females and 9.3% of the matings of Ae. aegypti males with mixed Ae. aegypti and Ae. albopictus females were interspecific. The difference in the length of clasper between male Ae. albopictus (0.524mm) and Ae. aegypti (0.409mm) may be correlated with corresponding mates. We conclude that stronger Ae. albopictus male interspecific mating and more avid female intraspecific re-mating result in a satyr effect and contribute to competitive displacement of Ae. aegypti as allopatric Ae. albopictus invade during range expansion.
... Our trials indicate that sterile male mosquitoes have a reduced performance when compared with non-sterilized males, but they should be interpreted with caution, especially in assessing factors, such as mate propensity/competitiveness. Competitiveness tests that are carried out in large field enclosures may be more representative of real field condition [63]. For Ae. Albopictus, a previous study [60] determined that the mean CIS index (capacity to induce sterility index or competitiveness index) in the field strongly varied in space and time, ranging from 0.02 to 0.37, which indicates that the sterile males were 3 to 50 times less competitive than the wild males. ...
Genetic based mosquito control methods have been gaining ground in recent years for their potential to achieve effective suppression or replacement of vector populations without hampering environments or causing any public health risk. These methods require the mass rearing of the target species in large facilities sized to produce millions of sterile males, as already well established for a number of insects of agricultural importance. Assessing the performance of released males in Sterile Insect Technique (SIT) control programs is of the utmost importance for the success of the operation. Besides the negative effects of mass rearing and sterilization, the handling of sterilized insects and shipment to distant areas may also negatively impact the quality of sterilized males. The aim of the current study was to design and executive quality control (QC) tests for sterilized Aedes albopictus (Asian tiger mosquito) males delivered by air shipment from the mass production facility located in Italy to Greece and Montenegro field release sites. Mass reared mosquito strains were based on biological materials received from Italy, Greece and Montenegro. Tests conducted at the mass rearing facility before transportation revealed a rather high residual female contamination following mechanical sex separation (approximately 1.5% females, regardless of the mosquito strain). Irradiated males of all three mosquito strains induced high levels of sterility to females. Shipment lasting approximately 24 h resulted in approximately 15% mortality, while when shipment lasted nearly two days this increased to almost 40%. The flight ability of sterilized males following one day transportation time was satisfactory (over 60%). The response of sterile males to food and water starvation was comparable and slightly lower than that of wild non-transported males. Longevity of sterile males was shorter than that of wild counterparts and it seems it was not affected by mating to wild females. Both mating propensity and mating competitiveness for wild virgin females was higher for the wild, control males compared to the sterile, transported ones. Overall, the performance of sterile male Ae. albopictus delivered from the mass rearing facility of Italy to Greece in approximately 24 h was satisfactory. Transportation lasting two days or longer incurred detrimental effects on males, which called into question the outcome of the SIT release programs. In conclusion, our results demonstrate the need of quality control procedures, especially when sterile male production facilities are not near to the releasing point. Transportation could be a serious drawback for the implementation of Sterile Insect Releases and, consequently, it is important to establish an efficient and fast transportation of sterilized males in advance.
... albopictus in Catalonia, this control strategy would require regular monitoring for insecticide resistance [10]. The sterile insect technique (SIT) was tested on Ae. albopictus mosquitoes from Italy, but it did not significantly reduce their population due to detrimental effects on mating competitiveness among irradiated males [11]. Cyclopoid copepods were used successfully as biocontrol agents against mosquito larvae in the US [12], Australia [13], Vietnam [14], and Italy [15]. ...
Cyclopoid copepods have been applied successfully to limit populations of highly invasive Aedes albopictus mosquitoes that can transmit diseases of public health importance. However, there is concern that changes in certain mosquito traits, induced by exposure to copepod predation, might increase the risk of disease transmission. In this study, third instar Ae. albopictus larvae (focal individuals) were exposed to Megacyclops viridis predator cues associated with both the consumption of newly hatched mosquito larvae and attacks on focal individuals. The number of newly hatched larvae surrounding each focal larva was held constant to control for density effects on size, and the focal individual’s day of pupation and wing length were recorded for each replicate. Exposing late instar Ae. albopictus to predation decreased their chances of surviving to adulthood, and three focal larvae that died in the predator treatment showed signs of melanisation, indicative of wounding. Among surviving focal Ae. albopictus, no significant difference in either pupation day or wing length was observed due to copepod predation. The absence of significant sublethal impacts from M. viridis copepod predation on surviving later stage larvae in this analysis supports the use of M. viridis as a biocontrol agent against Ae. albopictus.
... By contrast, the effects of transportation and packing were more notable on transported pupal males; the exact mechanism cannot be adequately explained, but it might be attributable to mechanical shocks and vibrations absorbed by the pupae during transport that result in reduced flight ability, as documented in sterile male tsetse flies . It is also worth noting that sterile males were released threefold than the field males at a ratio of 3:1:1 (sterile males: fertile males: virgin females) to achieve comparable C indices, as reported in Ae. albopictus (Bellini et al., 2013b). An excessive number of sterile released males is required to compensate for physiological limitations in irradiated mosquitoes caused by a high radiation dose (70 Gy). ...
... The competitiveness of irradiated An. arabiensis male pupae were also compromised after gamma irradiation exposure at 120 Gy (Helinski and Knols, 2008). Nevertheless, some studies have indicated that gamma sterility doses do not substantially affect the male competitiveness of Ae. albopictus (Bellini et al., 2013b;Damiens et al., 2016). ...
Long-distance transportation from a radiation facility to a target site potentially affects the quantity and quality of sterile male mosquitoes. This study tested the effects of multi-hour land transportation on the survival, longevity, and mating performance of gamma-rays sterilized adult and pupal male mosquitoes at different densities in non-chilled condition. The results demonstrated that mortality rate, longevity, induced sterility (IS) level, and mating competitiveness (C index) were significantly affected by life stage, transportation treatment, and density. Transportation was detrimental to the survival and longevity of the adults, and transporting pupae was restricted by the overcrowding effect; particularly, those packing density of 200 pupae. The longevity of transported mosquitoes were 1-5 days shorter than that of non-transported mosquitoes regardless of packing density. The irradiated transported adult males exhibited an equal IS and C index to their non-transported counterparts. Although there was no evidence suggested an association between low mating competitiveness and packing density in the transported adults, the mating competitiveness of adult mosquitoes decreased with increased packing density. Additionally, the effects of transportation and packing density on the mating ability of transported pupal males were also notable. The results indicate the factors of packing density and life stages in transporting sterile males under non-chilled conditions should be taken into account in formulating the procedure in SIT operation.
... Several previous studies report on the irradiation dose's effect on survival, flight ability, level of sterility, and mating competitiveness of males from several mosquito species, including An. arabiensis (Helinski et al. 2006, Helinski andKnols 2008), An. coluzzii (Maïga et al. 2014), Ae. albopictus and Ae. aegypti (Bellini et al. 2013b, Shetty et al. 2016, Ernawan et al. 2018, Bond et al. 2019), but in the absence of a standard protocol for sterilization of mosquitoes using irradiation, procedures vary widely and make reliability and reproducibility difficult. Thus, the irradiation factors that influence the sensitivity of male mosquitoes to the procedure, including the type of irradiator, sterilization environmental factors (dose and ambient atmosphere [i.e., dissolved oxygen and temperature]), and biological parameters (developmental stage and age), have to be explored to develop a unified standard irradiation protocol (Bakri et al. 2005). ...
... The residual fertility was calculated as the percentage of the irradiated male's fertility compared to that of males in the control group (Yamada et al. 2014(Yamada et al. , 2020. The mating competitiveness index (C index) was calculated using the following equation (Fried 1971, Bellini et al. 2013b): C index = (Ha − E)/(E − Hs) * N/S. In which Ha represents the hatch rate of eggs from mating 50 unirradiated (fertile) males and 50 unmated females (1:1 ratio), Hs the hatch rate of eggs from mating 50 irradiated males and 50 unmated females (1:1 ratio), and E the hatch rate of eggs from the competitive mating of 150 irradiated males, 50 unirradiated males, and 50 unmated females. ...
... Thus, an appropriate irradiation dose is needed to produce good quality sterile male insects with a high level of sterility to maintain overall fitness and competitiveness in the field (Robinson 2005). Previous studies have investigated male mosquito response to the gamma irradiation dose for various species, including Ae. aegypti (Shetty et al. 2016, Ernawan et al. 2018, Ae. albopictus (Bellini et al. 2013b), An. arabiensis (Helinski et al. 2006, Helinski and Knols 2008, Munhenga et al. 2016, and An. coluzzii (Maïga et al. 2014). ...
The sterilization process using gamma irradiation is a crucial component in a program using sterile insect technique (SIT) to control Aedes aegypti. Unfortunately, there is no efficient standard protocol for sterilizing mosquitoes that can produce a high level of sterility while maintaining mating ability and longevity. Therefore, we conducted a study of the critical factors necessary to develop such a standard protocol. In this study, male Ae. aegypti pupae, as well as adults aged 1 d and 3 d, were irradiated using a Gamma-cell 220 irradiator doses of 0, 20, 40, 60, 70, 80, and 100 Gray (Gy). In addition, male Ae. aegypti in the pupal and adult stage aged 1 d were irradiated at a dose of 70 Gy at various temperatures. Changes in emergence rates, longevity, sterility, and mating competitiveness were recorded for each combination of parameters. Results showed that an increase of irradiation dose leads to a rise of induced sterility at all developmental stages, while simultaneously reducing emergence rate, survival, and mating competitiveness. Higher temperatures resulted in increased levels of sterility, reduced longevity, and did not affect the ability to mate. This study found that an irradiation dose of 70 Gy at a temperature between 20.00 and 22.30°C administered in the pupal stage induced a high level of sterility (around 98%), while maintaining mating competitiveness and longevity.
