Background: Radiation induced sterility is the basis of the Sterile Insect Technique, by which a target insect pest population is suppressed by releasing artificially reared sterile males of the pest species in overflooding numbers over a target site. In order for the sterile males to be of high biological quality, effective standard irradiation protocols are required. Following studies investigating the effects of mosquito pupae irradiation in water versus in air, there is a need to investigate the oxy-regulatory behavior of mosquito pupae in water to better understand the consequences of irradiation in hypoxic versus normoxic conditions. Methods: Pupae of Aedes aegypti, Ae. albopictus, and Anopheles arabiensis were submerged in water inside airtight 2 ml glass vials at a density of 100 pupae/ml and the dissolved oxygen (DO) levels in the water were measured and plotted over time. In addition, male pupae of Ae. aegypti (aged 40-44 h), Ae. albopictus (aged 40-44 h) and An. arabiensis (aged 20-24 h) were irradiated in a gammacell220 at increasing doses in either hypoxic (water with < 0.5% O 2 content) or normoxic (in air) conditions. The males were then mated to virgin females and resulting eggs were checked for induced sterility. Results: All three species depleted the water of DO to levels under 0.5% within 30 minutes, with An. arabiensis consuming oxygen the fastest at under 10 minutes. Following irradiation, the protective effect of hypoxia was observed across species and doses (P < 0.0001), increasing at higher doses. This effect was most pronounced in An. arabiensis. Conclusions: The consumption of dissolved oxygen by pupae submerged in water was significantly different between species, indicating that their oxy-regulatory capacity seems to have possibly evolved according to their preferred breeding site characteristics. This needs to be considered when sterilizing male mosquitoes at pupal stage in water. Depending on species, their DO consumption rates and their density, irradiation doses needed to achieve full sterility may vary significantly. Further assessments are required to ascertain optimal conditions in terms of ambient atmosphere during pupal irradiation to produce competitive sterile males, and temperature and density dependent effects are expected.
The success of the sterile insect technique (SIT) relies on the achievement of high levels of sterility and mating success of the factory-reared sterile males and thus their biological quality, which can be enhanced by the reduction of stress factors encountered during rearing, handling, and irradiation procedures. The achievement of consistent sterility levels requires reliable and standard irradiation protocols. Additionally, mosquito adults require immobilization prior to, and during irradiation to increase processing efficiency and to avoid physical damage caused by movement in restricted space. Common methods for immobilization include chilling and anesthetics such as nitrogen. Here we assessed the effects of chilling and exposure to nitrogen on the irradiation dose-response of Aedes mosquitoes, and their downstream effects on some male quality parameters including longevity and flight ability. We found that chilling does not incur damage in the insects in terms of longevity and flight ability when chilling duration and temperature are carefully controlled, and a recovery phase is provided. Irradiation in nitrogen shows high radioprotective effects during irradiation, resulting in reduced induction of sterility. Overall, longevity of males can be improved by irradiating in anoxia, however the exposure to nitrogen itself comes with negative impacts on flight ability. The results reported here will assist in the standardization and optimization of irradiation protocols for the SIT to control mosquito populations of medical relevance.
Reproductive sterility is the basis of the sterile insect technique (SIT) and essential for its success in the field. Numerous factors that influence dose–response in insects have been identified. However, historically the radiation dose administered has been considered a constant. Efforts aiming to standardize protocols for mosquito irradiation found that, despite carefully controlling many variable factors, there was still an unknown element responsible for differences in expected sterility levels of insects irradiated with the same dose and handling protocols. Thus, together with previous inconclusive investigations, the question arose whether dose really equals dose in terms of biological response, no matter the rate at which the dose is administered. Interestingly, the dose rate effects studied in human nuclear medicine indicated that dose rate could alter dose–response in mammalian cells. Here, we conducted experiments to better understand the interaction of dose and dose rate to assess the effects in irradiated mosquitoes. Our findings suggest that not only does dose rate alter irradiation-induced effects, but that the interaction is not linear and may change with dose. We speculate that the recombination of reactive oxygen species (ROS) in treatments with moderate to high dose rates might minimize indirect radiation-induced effects in mosquitoes and decrease sterility levels, unless dose along with its direct effects is increased. Together with further studies to identify an optimum match of dose and dose rate, these results could assist in the development of improved methods for the production of high-quality sterile mosquitoes to enhance the efficiency of SIT programs.
Background Mosquitoes are the deadliest animals in the world. Their ability to carry and spread diseases to humans causes millions of deaths every year. Due to the lack of efficient vaccines, the control of mosquito-borne diseases primarily relies on the management of the vector. Traditional control methods are insufficient to control mosquito populations. The sterile insect technique (SIT) is an additional control method that can be combined with other control tactics to suppress specific mosquito populations. The SIT requires the mass-rearing and release of sterile males with the aim to induce sterility in the wild female population. Samples collected from the environment for laboratory colonization, as well as the released males, should be free from mosquito-borne viruses (MBV). Therefore, efficient detection methods with defined detection limits for MBV are required. Although a one-step reverse transcriptase quantitative polymerase chain reaction (RT-qPCR) method was developed to detect arboviruses in human and mosquito samples, its detection limit in mosquito samples has yet to be defined. Methods We evaluated the detection sensitivity of one step RT-qPCR for targeted arboviruses in large mosquito pools, using pools of non-infected mosquitoes of various sizes (165, 320 and 1600 mosquitoes) containing one infected mosquito body with defined virus titers of chikungunya virus (CHIKV), usutu virus (USUV), West Nile virus (WNV) and Zika virus (ZIKV). Results CHIK, USUV, ZIKV, and WNV virus were detected in all tested pools using the RT-qPCR assay. Moreover, in the largest mosquito pools (1600 mosquitoes), RT-qPCR was able to detect the targeted viruses using different total RNA quantities (10, 1 and 0.1 ng per reaction) as a template. Correlating the virus titer with the total RNA quantity allowed the prediction of the maximum number of mosquitoes per pool in which the RT-qPCR can theoretically detect the virus infection. Conclusions Mosquito-borne viruses can be reliably detected by RT-qPCR assay in pools of mosquitoes exceeding 1000 specimens. This will represent an important step to expand pathogen-free colonies for mass-rearing sterile males for programmes that have a SIT component by reducing the time and the manpower needed to conduct this quality control process.
For the sterile insect technique, and other related biological control methods where large numbers of the target mosquito are reared artificially, production efficiency is key for the economic viability of the technique. Rearing success begins with high quality eggs. Excess eggs are often stockpiled and stored for longer periods of time. Any pests that prey on these eggs are detrimental to stockpiles and need to be avoided. Psocids of the genus Liposcelis (Psocoptera, Liposcelididae) are common scavengers consuming various types of organic material that are distributed globally and thrive in warm damp environments, making insectaries ideal habitats. In this short report, we investigated the species that has been found scavenging stored mosquito eggs in our insectary and identified it to be Liposcelis bostrychophila Badonnel, 1931. Additional observations were made to determine whether these predators indeed feed on mosquito eggs, and to suggest simple, effective ways of avoiding infestation.
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