Studies on the ovarian developments in Culex pipiens s. l. following artificial ingestion of blood components and other nutrients

Abstract

Under natural condition ovarial developments followed by oviposition of a mosquito is usually affected only sucking blood of host animals. In the present study, observations were made to see whether the blood, some of its components served to mosquitoes as liquids soaked in cotton layers might effect in producing the eggs, and such artificial breeding method might be used for maintaining laboratory colony of Culex pipiens form fatigans for which absence of autogeny had been checked for more than 20 generation. In a comparative observation on the efficiency of ingestion of the blood served by different methods, the mosquito was found to engorge either of the three routes, defibrinated bovine whole blood coated with chicken membrane, that soaked in cotton layer in a petri dish, or through biting on a laboratory mouse fixed in wire-screen cage, with the rates to the total mosquitoes of 94.0%, 85.7% and 72.3% respectively. However, the rates of reproduction as calculated by dividing the total numbers of eggs deposited by the number of females tested were 36.8, 37.9 and 98.8, and the above two artificial feeding methods were found to be less than half in the efficiency of reproduction than through natural bite on animals. Results of dissections of mosquitoes which ingested the blood soaked in cotton have shown that it is usually taken into dorsal or ventral diverticles of oesophagus but later transffered into the midgut, and that no peritrophic membrane is formed like after natural bite on animals. Many of the mosquitoes thus fed artificially were found to discharge the blood without fully utilizing it as the nutrient. However, developments of yolk in ovarian follicles as well as production of mature eggs were affected when the blood meal was served repeatedly for several days at least in a part of the mosquitoes tested. Further experiments were made to see which of the blood component was effective to induce maturation of the eggs when fed by the above method. Out of 25 mosquitoes tested for each lot oviposition was seen only in 8 females engorged with bonine whole blood with the average egg number of 80.8, and all of the others fed once by saline suspension of blood corpuscles, serum, purified hemoglobin or sugar solution failed to produce mature eggs. However, in another experiment in which hemoglobin was fed cotinuously for successive days, a part of females which ingested it for more than three times were found to produce small numbers of eggs. A similar experiment was made with hemolysed blood, the rates of the number of the oviposited mosquitoes to the number of the blood ingested mosquitoes were lower than the none hemolysed blood, but were no significant difference in the egg number. The whole blood obtained from chicken, cattle, horse, rabbit and mouse was all effective to induce egg production through the artificial ingestions, and no significant difference were seen in the rate of ingestions as well as the rate of reproductions by blood source. The course of blood digestions in the midgut and the development of ovaries after the artificial ingestion was carefully checked daily following Sella's classification proposed for Anopheles. However, the blood fed by the abnormal route was often discharged from the anus or often caused death of the mosquitoes probably due to an intoxication, thus cousing irregular results. The addition of 1, 000 unit percent of pencilline and 250mg percent of streptomycine to the blood were found to be effective to reduce the mortality and to increase the reproduction rates. In a similar experiment made with an autogenuous colony or molestus-form of Culex pipiens complex, the ingestion of blood or its components did not cause any significant increase in its first batch of autogenous egg production. The more oviposition was not seen in the groupes that did not engorge blood meal after the autogeny, and in this strain of the molestus-form

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