Browsing by Author "Vreysen, Marc JB"

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    Eliminating female Anopheles arabiensis by spiking blood meals with toxicants as a sex separation method in the context of the sterile insect technique
    (2013-07-03) Yamada, Hanano; Soliban, Sharon M; Vreysen, Marc JB; Chadee, Dave D; Gilles, Jeremie RL
    Abstract Background Ivermectin has longevity reducing effects in several insect species, including disease transmitting mosquitoes after feeding on hosts that have received ivermectin treatment. This has important implications in mosquito population control and thus the reduction of disease transmission. In addition, ivermectin could play an enormous role in mosquito control operations by its use in the female elimination process during mass-rearing, enabling the release of only sterile males in the context of the sterile insect technique (SIT). Methods Blood meals were spiked with various toxicants and were then offered to adult Anopheles arabiensis and killing effects were observed. Varying concentrations of the most effective substance were then tested in subsequent trials to obtain an optimal dose for quick and total female elimination. The remaining males were mated with untreated virgin females to assess whether their mating efficiency had been compromised. The most promising substance at the optimal concentration was further tested on a larger number of adults, after they had been irradiated and partially sterilised as pupae with 70and#160;Gy to evaluate the feasibility of the method in a mass-rearing, and SIT context. The males resulting from the latter trial were also checked for mating efficiency post treatments. Results Ivermectin (Virbamecand#174;) at a concentration of 7.5and#160;ppm was chosen from the toxicants tested as sufficiently effective in eliminating all female An. arabiensis in 4and#160;days, the shortest time required for female elimination of all chemicals tested. Mating efficiency of the non-blood feeding male mosquitoes was not compromised significantly compared to controls even when they were kept for a total of 4and#160;days (from emergence) before theoretical release. The irradiation treatment did not affect overall female feeding behaviour in this setting, nor were the sterile males less competitive for mating with virgin females after the treatments than virgin sterile males that had not been in the ivermectin treatment environment. Conclusions Spiking bloodmeals with ivermectin has shown potential as a viable treatment to eliminate female An. arabiensis from laboratory colonies although its practical use in a mass-rearing facility still needs to be tested.
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    The effects of genetic manipulation, dieldrin treatment and irradiation on the mating competitiveness of male Anopheles arabiensis in field cages
    (2014-08-13) Yamada, Hanano; Vreysen, Marc JB; Gilles, Jeremie RL; Munhenga, Givemore; Damiens, David D
    Abstract Background To enable the release of only sterile male Anopheles arabiensis mosquitoes for the sterile insect technique, the genetic background of a wild-type strain was modified to create a genetic sexing strain ANO IPCL1 that was based on a dieldrin resistance mutation. Secondly, the eggs of ANO IPCL1 require treatment with dieldrin to allow complete elimination of female L1 larvae from the production line. Finally, male mosquito pupae need to be treated with an irradiation dose of 75and#160;Gy for sterilization. The effects of these treatments on the competitiveness of male An. arabiensis were studied. Methods The competitiveness of ANO IPCL1 males that were treated either with irradiation or both dieldrin and irradiation, was compared with that of the wild-type strain (An. arabiensis Dongola) at a 1:1 ratio in 5.36and#160;m3 semi-field cages located in a climate-controlled greenhouse. In addition, three irradiated: untreated male ratios were tested in semi-field cages (1:1, 5:1 and 10:1) and their competition for virgin wild-type females was assessed. Results The ANO IPCL1 males were equally competitive as the wild-type males in this semi-field setting. The ANO IPCL1 males irradiated at 75and#160;Gy were approximately half as competitive as the unirradiated wild-type males. ANO IPCL1 males that had been treated with dieldrin as eggs, and irradiated with 75and#160;Gy as pupae were slightly more competitive than males that were only irradiated. Ratios of 1:1, 5:1 and 10:1 irradiated ANO IPCL1 males: untreated wild-type males resulted in 31, 66 and 81% induced sterility in the female cage population, respectively. Conclusions An irradiation dose of 75and#160;Gy reduced the competitiveness of male ANO IPCL1 significantly and will need to be compensated by releasing higher numbers of sterile males in the field. However, the dieldrin treatment used to eliminate females appears to have an unexpected radioprotectant effect, however the mechanism is not understood. A sterile to wild-type ratio of 10:1 effectively reduced the populationand#8217;s fertility under the experimental field cage conditions, but further studies in the field will be needed to confirm the efficiency of sterile ANO IPCL1 males when competing against wild males for wild females.