Impact of irradiation on the reproductive traits of field and laboratory An. arabiensis mosquitoes

Comparison on the quality of sterile Aedes aegypti mosquitoes produced by either radiation-based sterile insect technique or Wolbachia-induced incompatible insect technique

Novel and alternative vector control approaches using a sterile male-based release to suppress Aedes aegypti mosquito vectors have recently been tested in the field in many countries. These approaches included the sterile insect technique (SIT), incompatible insect technique (IIT), and a combination of both techniques. In this study, we conducted a series of experiments to compare the quality between radiation-based and Wolbachia-induced sterile males in terms of flight ability, sterility, mating competitiveness, survival rate, and longevity. Aedes aegypti mosquitoes irradiated at 50 Gy (SIT) and those trans-infected with wAlbB Wolbachia (IIT) were used for quality comparison. Our results showed that irradiated and Wolbachia trans-infected males were not significantly different in flight ability (p > 0.05) and both could induce sterility in wild-type females. In addition, although irradiation at 50 Gy or Wolbachia trans-infection reduced male mating competitiveness, combined irradiation and Wolbachia wAlbB trans-infection increased male competitiveness at the one-to-one ratio. Increasing the number of sterile males released could compensate for reduced competitiveness but it does not make them more competitive. Irradiation did not affect the survival and longevity of irradiated males, but it showed significant negative impacts on females (p < 0.05); while the opposite was observed in the case of Wolbachia infection, i.e., with significant increase in the survival rate of Wolbachia trans-infected males (p < 0.05), but both survival and longevity were reduced in Wolbachia trans-infected females with no significant impacts (p > 0.05). In conclusion, neither irradiation nor Wolbachia trans-infection significantly affected the quality of sterile males except their mating competitiveness; but this could compensate by increasing the number of sterile males released. Sterility could be induced by either 50 Gy irradiation or wAlbB trans-infection. Mating competitiveness results showed that a higher number of sterile males produced by irradiation need to be released in comparison to those produced by Wolbachia trans-infection. Our results should be useful for planning SIT, IIT, or a combination for Ae. aegypti vector control.

Spatial and temporal characteristics of laboratory-induced Anopheles coluzzii swarms: Shape, structure, and flight kinematics

Malaria mosquitoes mate in swarms, but how these swarms are formed and maintained remains poorly understood. We characterized three-dimensional spatiotemporal flight kinematics of Anopheles coluzzii males swarming at sunset above a ground marker. The location, shape, and volume of swarms were highly stereotypic, consistent over the complete swarming duration. Swarms have an elliptical cone shape; mean flight kinematics varies spatially within the swarm, but remain rather consistent throughout swarming duration. Using a sensory system-informed model, we show that swarming mosquitoes use visual perception of both the ground marker and sunset horizon to display the swarming behavior. To control their height, swarming individuals maintain an optical angle of the marker ranging from 24° to 55°. Limiting the viewing angle deviation to 4.5% of the maximum value results in the observed elliptical cone swarm shape. We discuss the implications of these finding on malaria mosquito mating success, speciation and for vector control.

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 (90 kV/40 Gy) 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.

Infection of the malaria vector Anopheles coluzzii with the entomopathogenic bacteria Chromobacterium anophelis sp. nov. IRSSSOUMB001 reduces larval survival and adult reproductive potential

BACKGROUND

Vector control tools are urgently needed to control malaria transmission in Africa. A native strain of Chromobacterium sp. from Burkina Faso was recently isolated and preliminarily named Chromobacterium anophelis sp. nov. IRSSSOUMB001. In bioassays, this bacterium showed a promising virulence against adult mosquitoes and reduces their blood feeding propensity and fecundity. The current study assessed the entomopathogenic effects of C. anophelis IRSSSOUMB001 on larval stages of mosquitoes, as well as its impacts on infected mosquitoes reproductive capacity and trans-generational effects.

METHODS

Virulence on larvae and interference with insemination were assayed by co-incubation with C. anophelis IRSSSOUMB001 at a range of 10⁴ to 10⁸ cfu/ml. Trans-generational effects were determined by measuring body size differences of progeny from infected vs. uninfected parent mosquitoes using wing size as a proxy.

RESULTS

Chromobacterium anophelis IRSSSOUMB001 killed larvae of the pyrethroid-resistant Anopheles coluzzii with LT₈₀ of ~ 1.75 ± 0.14 days at 10⁸ cfu/ml in larval breeding trays. Reproductive success was reduced as a measure of insemination rate from 95 ± 1.99% to 21 ± 3.76% for the infected females. There was a difference in wing sizes between control and infected mosquito offsprings from 2.55 ± 0.17 mm to 2.1 ± 0.21 mm in infected females, and from 2.43 ± 0.13 mm to 1.99 ± 0.15 mm in infected males.

CONCLUSIONS

This study showed that C. anophelis IRSSSOUMB001 was highly virulent against larvae of insecticide-resistant Anopheles coluzzii, and reduced both mosquito reproduction capacity and offspring fitness. Additional laboratory, field, safety and social acceptance studies are needed to draw firm conclusions about the practical utility of this bacterial strain for malaria vector control.

Impact of paternal transmission of gamma radiation on reproduction, oogenesis, and spermatogenesis of the housefly, Musca domestica L. (Diptera: Muscidae)

PURPOSE

This study aimed to investigate the impact of gamma radiation of Musca domestica males (resulted from irradiated pupae) crossed with unirradiated females on fecundity, egg hatchability, adult emergence, sex ratio, sterility, in addition to reproductive development at the level of oogenesis and spermatogenesis compared to unirradiated group.

MATERIAL AND METHODS

The housefly, M. domestica pupae were exposed to three sublethal doses of 5, 10, and 15 Gy.

RESULTS

Fecundity was severely reduced particularly in F2 (11.33 ± 1.528; 7.33 ± 1.115 eggs/♀) and F3 (9.0 ± 1.00; 4.67 ± 1.115 eggs/♀) for doses of 10 and 15 Gy, respectively, compared with (52.0 ± 1.4 eggs/♀) for the control. Data revealed latent dose- and generation-dependent reduction in egg hatchability. Hatchability percentages reduced from 93.59 for the control to 10.07 (F1), 8.09 (F2), and 8.34 (F3) when the highest radiation dose 15 Gy was applied. Irradiation induced paternal deleterious substerility effects. Irradiation with 15 Gy induced substerility that reached about 97.0% in F2 and F3 generations. A significant (P < 0.05) reduction of the mean numbers of adult emergence was remarkably detected in the F1, F2, and F3 generations. Applied gamma doses did not affect the male to female ratio in the Parental or F1 generations. However, the F2 and F3 generations did show changes to the sex ratio with males occurring more frequently than females. This trend became more pronounced as dose increased. Ultrastructural examinations exhibited unusual damage and malformation either for males or female reproductive organs.

CONCLUSION

The obtained results clearly show that gamma radiation of M. domestica irradiated as pupae induced considerably visible impact on tested biological aspects and reproductive potential.

Effect of irradiation on the survival and susceptibility of female Anopheles arabiensis to natural isolates of Plasmodium falciparum

BACKGROUND

The sterile insect technique (SIT) is a vector control strategy relying on the mass release of sterile males into wild vector populations. Current sex separation techniques are not fully efficient and could lead to the release of a small proportion of females. It is therefore important to evaluate the effect of irradiation on the ability of released females to transmit pathogens. This study aimed to assess the effect of irradiation on the survival and competence of Anopheles arabiensis females for Plasmodium falciparum in laboratory conditions.

METHODS

Pupae were irradiated at 95 Gy of gamma-rays, and emerging females were challenged with one of 14 natural isolates of P. falciparum. Seven days post-blood meal (dpbm), irradiated and unirradiated-control females were dissected to assess the presence of oocysts, using 8 parasite isolates. On 14 dpbm, sporozoite dissemination in the head/thorax was also examined, using 10 parasites isolates including 4 in common with the 7 dpbm dissection (oocyst data). The survivorship of irradiated and unirradiated-control mosquitoes was monitored.

RESULTS

Overall, irradiation reduced the proportion of mosquitoes infected with the oocyst stages by 17% but this effect was highly inconsistent among parasite isolates. Secondly, there was no significant effect of irradiation on the number of developing oocysts. Thirdly, there was no significant difference in both the sporozoite infection rate and load between the irradiated and unirradiated-control mosquitoes. Fourthly, irradiation had varying effects on female survival with either a negative effect or no effect.

CONCLUSIONS

The effect of irradiation on mosquito competence strongly varied among parasite isolates. Because of such isolate variability and, the fact that different parasite isolates were used to collect oocyst and sporozoite data, the irradiation-mediated reduction of oocyst prevalence was not confirmed for the sporozoite stages. Our data indicate that irradiated female An. arabiensis could contribute to malaria transmission, and highlight the need for perfect sexing tools, which would prevent the release of females as part of SIT programmes.