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.
Infertility , Animals , Humans , Insecta , Mammals , Pupa/radiation effects , Radiation Dosage
The Sterile Insect Technique (SIT) is a successful autocidal control method that uses ionizing radiation to sterilize insects. However, irradiation in normal atmospheric conditions can be damaging for males, because irradiation generates substantial biological oxidative stress that, combined with domestication and mass-rearing conditions, may reduce sterile male sexual competitiveness and quality. In this study, biological oxidative stress and antioxidant capacity were experimentally manipulated in Anastrepha suspensa using a combination of low-oxygen conditions and transgenic overexpression of mitochondrial superoxide dismutase (SOD2) to evaluate their role in the sexual behavior and quality of irradiated males. Our results showed that SOD2 overexpression enhances irradiated insect quality and improves male competitiveness in leks. However, the improvements in mating performance were modest, as normoxia-irradiated SOD2 males exhibited only a 22% improvement in mating success compared to normoxia-irradiated wild type males. Additionally, SOD2 overexpression did not synergistically improve the mating success of males irradiated in either hypoxia or severe hypoxia. Short-term hypoxic and severe-hypoxic conditioning hormesis, per se, increased antioxidant capacity and enhanced sexual competitiveness of irradiated males relative to non-irradiated males in leks. Our study provides valuable new information that antioxidant enzymes, particularly SOD2, have potential to improve the quality and lekking performance of sterile males used in SIT programs.
Infertility, Male/etiology , Insect Control/methods , Oxygen/metabolism , Superoxide Dismutase/genetics , Tephritidae/physiology , Animals , Animals, Genetically Modified , Hormesis , Insect Proteins/genetics , Insect Proteins/metabolism , Male , Mutation , Oxidative Stress , Sexual Behavior, Animal/physiology , Sexual Behavior, Animal/radiation effects , Superoxide Dismutase/metabolism , Tephritidae/enzymology , Tephritidae/radiation effects
Phytosanitary irradiation (PI) has been successfully used to disinfest fresh commodities and facilitate international agricultural trade. Critical aspects that may reduce PI efficacy must be considered to ensure the consistency and effectiveness of approved treatment schedules. One factor that can potentially reduce PI efficacy is irradiation under low oxygen conditions. This factor is particularly important because storage and packaging of horticultural commodities under low oxygen levels constitute practices widely used to preserve their quality and extend their shelf life. Hence, international organizations and regulatory agencies have considered the uncertainties regarding the efficacy of PI doses for insects infesting fresh commodities stored under low oxygen levels as a rationale for restricting PI application under modified atmosphere. Our research examines the extent to which low oxygen treatments can reduce the efficacy of phytosanitary irradiation for tephritids naturally infesting fruits. The effects of normoxia (21% O2), hypoxia (~5% O2), and severe hypoxia (< 0.5% O2) on radiation sensitivity of third instars of Anastrepha fraterculus (sensu lato), A. ludens (Loew), Bactrocera dorsalis (Hendel), and Ceratitis capitata (Wiedemann) were evaluated and compared at several gamma radiation doses. Our findings suggest that, compared to normoxia, hypoxic and severe-hypoxic conditioning before and during irradiation can increase adult emergence and contribute to advancement of larval development of tephritid fruit flies only at low radiation doses that are not used as phytosanitary treatments. With phytosanitary irradiation doses approved internationally for several tephritids, low oxygen treatments applied before and during irradiation did not increase the emergence rates of any fruit fly species evaluated, and all treated insects died as coarctate larvae. Thus, the findings of our research support a re-evaluation of restrictions related to phytosanitary irradiation application under modified atmospheres targeting tephritid fruit flies.
The Anastrepha fraterculus (Wiedemann) complex is currently comprised of at least eight morphotypes, including several that are likely to be described as new species. It is critical to evaluate whether the morphotypes differ in tolerance to phytosanitary treatments. Temperatures from 0 to 3°C are used as a phytosanitary treatment for some commodities exported from the region and at risk of infestation by the A. fraterculus complex. Description of A. fraterculus morphotypes as new species could result in the annulation of phytosanitary treatment schedules for the new species. This study compared the relative cold tolerance of five populations from three morphotypes of the A. fraterculus complex: Andean, Peruvian, and Brazilian-1. Both a laboratory and wild strain of the Brazilian-1 morphotype were studied. Differences in mortality of third instars of the five A. fraterculus populations reared on nectarines were observed only with short treatment durations at temperatures ranging from 1.38 ± 0.04°C to 1.51 ± 0.08°C (mean ± SEM). Estimated times to achieve the LT99.99682 (probit 9) showed that Brazilian-1 wild, Brazilian-1 laboratory, and Cusco population were the most cold tolerant, followed by Andean and Peruvian, the least cold tolerant morphotype (i.e., Brazilian-1 wild = Brazilian-1 laboratory = Cusco population > Andean > Peruvian). These findings suggest that the current cold treatment schedules of 15 d at ≤ 1.11°C and 17 d at ≤ 1.67°C can be applied as cold treatments to any potential new species that may arise from the A. fraterculus complex.
Tephritidae , Animals , Brazil , Cold Temperature , Fruit
In many species, courtship displays are reliable signals of male quality, and current hypotheses suggest that these displays allow females to choose males with high cellular function. Environmental stressors generate excess reactive oxygen species (ROS) that impair cellular function, and thus antioxidant pathways that remove ROS are probably critical for preserving complex sexual behaviours. Here, we test the hypothesis that enhanced antioxidant activity in mitochondria preserves mating performance following oxidative stress. Using a transgenic approach, we directly manipulated mitochondrial antioxidant activity in the Caribbean fruit fly, Anastrepha suspensa, a lek-mating species with elaborate sexual displays and intense sexual selection that is also a model for sterile insect technique programmes. We generated seven transgenic lines that overexpress mitochondrial superoxide dismutase (MnSOD). Radiation is a severe oxidative stressor used to induce sterility for sterile insect programmes. After radiation treatment, two lines with intermediate MnSOD overexpression showed enhanced mating performance relative to wild-type males. These improvements in mating corresponded with reduced oxidative damage to lipids, demonstrating that MnSOD overexpression protects flies from oxidative stress at the cellular level. For lines with improved mating performance, overexpression also preserved locomotor activity, as indicated by a laboratory climbing assay. Our results show a clear link between oxidative stress, antioxidant capacity and male performance. Our work has implications for fundamentally understanding the role of antioxidants in sexual selection, and shows promise for using transgenic approaches to enhance the field performance of insects released for area-wide pest management strategies and improving performance of biological control agents in general.
Antioxidants/metabolism , Reactive Oxygen Species/metabolism , Sexual Behavior, Animal , Superoxide Dismutase/metabolism , Tephritidae/physiology , Animals , Animals, Genetically Modified/metabolism , Animals, Genetically Modified/physiology , Female , Male , Mating Preference, Animal , Oxidative Stress , Superoxide Dismutase/genetics , Tephritidae/genetics , Tephritidae/metabolism
The importance of the protein ingestion during the adult stage on the mating success of males of Ceratitis capitata Wiedemann was evaluated in experiments of laboratory and field cage. In laboratory, the effects of protein ingestion during the first four or 12 days of the male adult life was assessed by the following parameters: mating success (capacity of being chosen by the female) and the number of males that give out pheromonal signals. Some experiments of mating success had been carried through with males in different ratios. In these tests, the number of males which had ingested protein (an unique male) was remained constant and the number of males fed without protein was gradually increased from 1:1 to 1:5. In the field cages, the mating success experiments were done using a 1:1 ratio. The results showed that the protein ingestion in the first four days of life did not influence any of the analyzed parameters. When the period of ingestion of protein was extended to 12 days, protein-fed males fed produced more pheromonal signals and had a higher mating success when at a 1:1 ratio in laboratory and field cage assays. In laboratory, females randomly chose males in any other tested ratio (1:2, 1:3, 1:4 and 1:5), indicating that the female may lose the perception to identify the male who ingested protein in the first 12 days.
Ceratitis capitata , Dietary Proteins , Sexual Behavior, Animal/physiology , Animals , Male
The importance of the protein ingestion during the adult stage on the mating success of males of Ceratitis capitata Wiedemann was evaluated in experiments of laboratory and field cage. In laboratory, the effects of protein ingestion during the first four or 12 days of the male adult life was assessed by the following parameters: mating success (capacity of being chosen by the female) and the number of males that give out pheromonal signals. Some experiments of mating success had been carried through with males in different ratios. In these tests, the number of males which had ingested protein (an unique male) was remained constant and the number of males fed without protein was gradually increased from 1:1 to 1:5. In the field cages, the mating success experiments were done using a 1:1 ratio. The results showed that the protein ingestion in the first four days of life did not influence any of the analyzed parameters. When the period of ingestion of protein was extended to 12 days, protein-fed males fed produced more pheromonal signals and had a higher mating success when at a 1:1 ratio in laboratory and field cage assays. In laboratory, females randomly chose males in any other tested ratio (1:2, 1:3, 1:4 and 1:5), indicating that the female may lose the perception to identify the male who ingested protein in the first 12 days.
Animals , Male , Ceratitis capitata , Dietary Proteins , Sexual Behavior, Animal/physiology
The objective of this study was to evaluate the effect of male ageing on male pheromone release and mating success of Ceratitis capitata (Wiedemann). The effects of male ageing on mating were evaluated on five and 21 d-old males by assessing their mating success (males chosen by a female for copulation) and the amount of males releasing the sex pheromone. The mating success was evaluated by using several ratios of young to older males by increasing the number of older males:young males from 1:1 to 5:1. The mating success of the 1:1 ratio was also evaluated in field cages. The evaluation of the mating success (in the 1:1 ratio) showed a clear preference of the females for young males. Sex pheromone emission was much more common on young than older males. Even in cases were older males were more abundant (ratios 2:1 and 3:1), females still chose the young males. However, females could not distinguish young from older males in ratios of 4:1 or 5:1. Our data indicate that the ageing of C. capitata males has a considerable negative effect on their reproductive success, especially if they are found in a proportion any lower than 3:1.
Aging , Ceratitis capitata/physiology , Mating Preference, Animal , Animals , Male
O objetivo deste estudo foi avaliar o efeito da senescência no sucesso de cópula e na secreção de feromônio sexual por machos de Ceratitis capitata (Wiedemann). O efeito do envelhecimento do macho sobre o acasalamento foi analisado utilizando-se machos com cinco e 21 dias de idade, através do seu sucesso de copula (escolha dos machos pela fêmea para cópula) e pela quantidade de machos que emitiram feromônio sexual. O sucesso de cópula foi avaliado através de várias proporções de machos jovens em relação a machos velhos pelo aumento do número de machos velhos:machos jovens de 1:1 até 5:1. O sucesso de cópula na proporção de 1:1 também foi avaliado em gaiola de campo. A avaliação do sucesso de cópula (na proporção 1:1) demonstrou clara preferência das fêmeas pelos machos jovens. A emissão de feromônio sexual foi mais comum em machos jovens do que em machos velhos. Mesmo em casos onde os machos velhos foram mais abundantes (proporções 2:1 e 3:1), as fêmeas continuaram escolhendo os machos jovens. Entretanto, as fêmeas não distinguiram mais os machos jovens em relação aos machos velhos nas proporções 4:1 ou 5:1. Os resultados indicam que o envelhecimento dos machos de C. capitata tem considerável efeito negativo sobre seu sucesso reprodutivo, especialmente se eles são encontrados em proporção menor do que 3:1.
The objective of this study was to evaluate the effect of male ageing on male pheromone release and mating success of Ceratitis capitata (Wiedemann). The effects of male ageing on mating were evaluated on five and 21 d-old males by assessing their mating success (males chosen by a female for copulation) and the amount of males releasing the sex pheromone. The mating success was evaluated by using several ratios of young to older males by increasing the number of older males:young males from 1:1 to 5:1. The mating success of the 1:1 ratio was also evaluated in field cages. The evaluation of the mating success (in the 1:1 ratio) showed a clear preference of the females for young males. Sex pheromone emission was much more common on young than older males. Even in cases were older males were more abundant (ratios 2:1 and 3:1), females still chose the young males. However, females could not distinguish young from older males in ratios of 4:1 or 5:1. Our data indicate that the ageing of C. capitata males has a considerable negative effect on their reproductive success, especially if they are found in a proportion any lower than 3:1.
Animals , Male , Aging , Ceratitis capitata/physiology , Mating Preference, Animal
