Swarming of mosquitoes

Experiments have been made on the swarming of a number of mosquitoes, especially Culex fatigans, under laboratory conditions and the influence of light intensity, temperature, different color swarm markers; and time factors, both in regard to duration of the change of light and the time lapse between experiments, have been studied.

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Résumé Des expériences sur l'essaimage des moustiques mâles (surtout Culex fatigans) ont été faites au laboratoire. La cage dans laquelle se formaient les essaims était placée dans une chambre dont l'éclairage, la température et l'humidité pouvaient être réglés.Les essaims qui comprenaient le plus grand nombre d'individus et qui duraient le plus longtemps, étaient obtenus quand le changement d'éclairement (crépuscule artificiel) durait plus de 20 minutes et quand la température était de 24–25° après une durée de plus de cinq heures depuis le dernier changement.Dans ces conditions artificielles les moustiques faisaient des essaims tous les matins et tous les soirs. Le commencement de l'essaimage le soir, et sa fin le matin avaient lieu à un même éclairement (1,6 log lux). Si l'éclairement était tenu inférieur à 1,6 log lux, les essaims duraient toute la nuit jusqu'à ce que la lumière soit relevée.Quelques observations sur Culex nigripalpus et Anopheles quadrimaculatus indiquent que les déliminations de l'éclairement permettent l'essaimage. Chez. C. nigripalpus ils étaient presque les mêmes que celles de Culex fatigans. Psorophora howardii et Aëdes taeniorhynchus ne font pas d'essaimage dans la petite cage mais la dernière espèce fait un essaim dans une cage plus grande après un éclairement subit.

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Contribution No. 113, Florida State Board of Health, Entomological Research Center, Vero Beach, Florida. This investigation was supported by Public Health Research Grant E-1492, from the National Institute of Allergy and Infectious Diseases, Public Health Service.     

Radiation biology of mosquitoes

There is currently renewed interest in assessing the feasibility of the sterile insect technique (SIT) to control African malaria vectors in designated areas. The SIT relies on the sterilization of males before mass release, with sterilization currently being achieved through the use of ionizing radiation. This paper reviews previous work on radiation sterilization of Anopheles mosquitoes. In general, the pupal stage was irradiated due to ease of handling compared to the adult stage. The dose-response curve between the induced sterility and log (dose) was shown to be sigmoid, and there was a marked species difference in radiation sensitivity. Mating competitiveness studies have generally been performed under laboratory conditions. The competitiveness of males irradiated at high doses was relatively poor, but with increasing ratios of sterile males, egg hatch could be lowered effectively. Males irradiated as pupae had a lower competitiveness compared to males irradiated as adults, but the use of partially-sterilizing doses has not been studied extensively. Methods to reduce somatic damage during the irradiation process as well as the use of other agents or techniques to induce sterility are discussed. It is concluded that the optimal radiation dose chosen for insects that are to be released during an SIT programme should ensure a balance between induced sterility of males and their field competitiveness, with competitiveness being determined under (semi-) field conditions. Self-contained ⁶⁰Co research irradiators remain the most practical irradiators but these are likely to be replaced in the future by a new generation of high output X ray irradiators.     

Pathology of malaria-infected mosquitoes

Concepts of the basic case reproduction rate of malaria, or the vectorial capacity of malaria vectors, tend to assume that the behaviour of infected and non-infected mosquitoes will be similar. However, recent years have seen a series of studies demonstrating that mosquitoes infected with malaria or other parasites show many pathological features with important effects on their behaviour and on the transmission dynamics of the parasite. Parasitology Today will be featuring a series of reports discussing these effects and attempting to unravel the expected effects on parasite transmission dynamics; this article sets the scene.