Tsutomu Oda

Induction of Oogenesis in Mosquitoes (Diptera: Culicidae) by Infusion of the Hemocoel with Amino Acids

Abstract As done previously with adult females of Culex pipiens pallens Coquillett, a mixture of 17 amino acids was infused into the hemocoel of females of seven anautogenous and one autogenous mosquito species belonging to three genera. In Culex. p. quinquefasciatus Say, Cx. tritaeniorhynchus Giles, Cx. kyotoensis Yamaguti & LaCasse, Aedes albopictus (Skuse), Armigeres subalbatus (Coquillett), and Cx. p. molestus Forskal, which previously had laid autogenously matured first batch of eggs, ovarian development was stimulated and frequently continued to maturity. In most mosquitoes, the number of mature follicles nearly doubled when the period of infusion was extended from 24 to 48 h. Therefore, the two previously indicated roles of amino acids, one to initiate ovarian development and the other to regulate the number of maturing oocytes, were confirmed in these species. In Cx. halifaxii Theobald and Ae. japonicus (Theobald), however, the frequency of activation and maturation of ovaries was low compared with the other species, indicating that those species may require some factors other than an increase in amino acids for normal ovarian development after a blood meal.

Reproductive activity and survival of Culex pipiens pallens and Culex quinquefasciatus (Diptera: Culicidae) in Japan at high temperature.

Abstract The egg hatchability, insemination, and longevity of Japanese Culex pipiens pallens Coquillett and Japanese Culex quinquefasciatus Say were compared at 25 and 30°C. Egg hatchability was high in Cx. p. pallens at 25°C, but it was very low at 30°C because almost no females were inseminated at this temperature. In Cx. quinquefasciatus, the egg hatchability and insemination rates were very high, even at 30°C. The longevity of adult females and males was generally shorter in Cx. p. pallens than in Cx. quinquefasciatus at both temperatures. Because high temperatures may restrict the spread of Cx. p. pallens, we suggest that even if this species spreads to Okinawa, the possibility of it becoming established is very low.

Effects of Mating on Oogenesis Induced by Amino Acid Infusion, Amino Acid Feeding, or Blood Feeding in the Mosquito Anopheles stephensi (Diptera: Culicidae)

Abstract Hemocoel infusion of an amino acid mixture at a concentration of 7.5% and 10% (wt:vol) for 24 h rarely activated ovarian development in either mated or unmated females of Anopheles stephensi Liston. Infusion of either concentration mixture for 48 h into unmated females was also scarcely stimulatory, but the same 48 h infusion into mated females resulted in ovarian maturation in 25% (7.5% mixture) or in 78% (10% mixture) of the infused specimens. Similarly, feeding on an amino acid mixture (7.5%) containing sugar induced 44% ovarian maturation among mated females, while only 3% of unmated females showed matured oocytes. The increase of hemolymph amino acid concentration levels may be one of the essential factors for oogenesis of An. stephensi, and mating enhances ovarian development, especially in females ingesting poor meals. However, some additional factor(s) may be included for full development comparable to that induced by blood meals.

Ovarian development induced in decapitated female Culex pipiens pallens mosquitoes by infusion of physiological quantities of 20-hydroxyecdysone together with amino acids.

Infusion of 20-hydroxyecdysone into the hemocoel of unfed decapitated female Culex pipiens pallens mosquitoes, at a very low rate of 500-2000pg per day, often stimulated oögenesis of this species, when the hormone was infused together with amino acids. The hormone alone or amino acids alone showed no such stimulatory effect. Previous reports that using an abdomen ligated immediately after a blood meal for hormone injection reduced the quantity of 20-hydroxyecdysone needed to activate unfed female Aedes aegypti by a few thousand times, are therefore due mainly to a sufficient supply of amino acids from the midgut in the isolated abdomen.

Induction of protective immunity to Brugia pahangi in jirds by drug-abbreviated infection.

Protective immunity of homologous challenge infection was examined in jirds after drug-abbreviated infection with Brugia pahangi. Mebendazole (MBZ) treatment at the early prepatent (5-7 weeks of post infection) or the late prepatent (7-9 weeks of post infection) period was highly effective in causing almost complete eradication of the primary infection. After challenge infection, the worm burden was significantly reduced 19% (31.1 in average) and 77% (9.5) to that of the controls (38.8 and 41.7), respectively. The magnitude of eosinophil response paralleled the degree of protection. No or only a few microfilariae were seen after challenge infection in jirds treated during the prepatent periods. They were also resistant to intravenous challenge with the microfilariae of B. pahangi. MBZ treatment at the patent period was, on the contrary, incomplete against primarily infected adult worms, and was not able to induce either significant protection (30.1 vs 33.1 in control) or eosinophil response to the challenge infection.