Studies on the infectivity of gametocytes of Plasmodium berghei (NK 65) in Anopheles stephensi.

The infectivity of gametocytes of Plasmodium berghei (NK 65) has been studied in laboratory bred Anopheles stephensi. Mosquitoes were fed daily on infected male and female Mastomys natalensis and subsequent development of the oocysts was monitored in the midguts. Maximum number of oocysts were found in mosquitoes which were fed on infected female mastomys on D8 and in male mastomys on D7 post-inoculation. During the next peak of gametocytaemia, very few oocysts developed. These findings suggest that gametocytes are maximally infective only during the first peak, later on their infectivity declines although having sufficient number of gametocytes in the circulation.

Gametocytocidal and sporontocidal activity of some standard antimalarials on P. berghei (NK 65) infection M. natalensis.

Three standard antimalarials pyrimethamine, primaquine and quinine were tested against P. berghei (NK 65) for gametocytocidal and sporontocidal action. Pyrimethamine at 7.5, 3.25, 2.5 and 1.25 mg/kg., primaquine at 15, 10 and 7.5 mg/kg, quinine at 225, 168.5, 140.62 and 112.5 mg/kg were given orally to infected M. natalensis for 3 consecutive days i.e., day 6, 7 and 8 post inoculation of sporozoites. To assess sporontocidal action batches of mosquitoes (A. stephensi) were fed on infected-treated and control animals on day 8. Mosquitoes were dissected on day 10 post infective feed to compare the number of oocysts from control groups. Pyrimethamine at 2.5, primaquine at 10 and quinine at 140.62 mg/kg had total sporontocidal action. When mosquitoes were fed on animals treated with 2.5 mg/kg of pyrimethamine and 10 mg/kg of primaquine, very few oocysts were developed and sporozoites from these mosquitoes were not infective to Mastomys. When mosquitoes were fed on Mastomys treated with 140.62 mg/kg of quinine, no oocyst was observed.

Effect of variation in temperature on development of Plasmodium berghei (NK 65 strain) in Anopheles stephensi.

Effect of temperature on the sporogonic cycle of Plasmodium berghei (NK 65) has been studied in vector Anopheles stephensi. To determine the optimum temperature for development of parasite, fed mosquitoes were kept at 16 +/- 1 degree C, 19 +/- 1 degree C and 26 +/- 1 degree C temperature. The temperature 19 +/- 1 degree C was found to be optimum for normal development of parasite within the vector. Sporulated oocysts were observed on the 10th day post feed and salivary glands were loaded with thousands of sporozoites on day 14. Temperature 16 +/- 1 degree C, though did not exert any deleterious effect on the morphology of parasites it delayed the development of sporozoites in the oocysts by 5 days as compared to control group. In the case of long exposure to this temperature, the sporozoites obtained from salivary glands became non-infective. Temperature 26 +/- 1 degree C was responsible for deterioration of all the stages of sporogonic cycle and it also checked the formation of sporozoites in the oocysts.

Tobacco seedlings: damage by excessive nitrogen lessened by added phosphorus.

Concentrations of nitrogen (as ammonium nitrate) of 50 kilo-grams per hectare and greater are toxic to tobacco seedlings; symptoms are poor growth and white leaves. The leaves have markedly less chlorophylls (especially chlorophyll a) and more carotene and xanthophyll than seedlings grown in media low in nitrogen. These ill eflects are aggravated by short supply of phosphorus; they can be counteracted by more liberal supply of phosphorus.