A new anthropophilic species of the genus Simulium (Simulium) Latreille is described from the endemic area of human onchocerciasis in Guatemala and also S. (S.) metallicum Bellardi is redescribed. The new species is very similar to S. (S.) metallicum, which is one of the vector of human onchocerciasis in tropical America, and separable by the features of genitalia at adult stage and by coloration at larval stage.

View full abstract

Prosimulium karibaense n. sp., taken from the several rivers and tributaries of the southern parts of Hokkaido, is described and compared with the closely related species, Prosimulium yezoense Shiraki, 1935,which is redescribed.

View full abstract

In order to estimate the age of the Norway rat, the lens weight was examined using two strains. The data on the mean weight of paired lenses of individual rats were obtained from the wild strain (males 72,females 65) and the Wistar albino strain (males 120,females 88) which were 1 to 24 months old. The relation between the age and the mean weight of paired lenses was given in Figs. 1 and 3. On the basis of the data, regression lines of the mean lens weight (y) to the age (x, log scale) were obtained as follows : Wild strain : male, y=17.68x+8.39 (correlation coefficient r=0.838,t value t_0=32.54,p<0.01), female, y=17.18x+8.36 (r=0.923,t_0=27.40,p<0.01). Wistar albino strain : male, y=18.01x+8.40 (r=0.97,t_0=62.73,p<0.01), female, y=17.29x+8.40 (r=0.975,t_0=57.41,p<0.01). From correlation coefficients and highly significant t value in both strains, it was concluded that the lens weight was closely related to age in the Norway rat and that the age could be estimated by lens weight with high reliability. However, when examining the relationship between the body weight or body length and lens weight at each age by correlation coefficient (r) and its significance, no correlation was observed, with few exceptions (Table 1). No difference was found in lens weight between offsprings born in winter and spring (Table 2). However, between the lens weights of litters kept at low and high densities, there was a significant difference (Table 3). From the results mentioned above, the lens weight method is recognized useful to estimate the age of Norway rats.

View full abstract

Few studies have been conducted on the biology of chironomid midges occurring in rice paddies, albeit their occurrence in significant number and biomass. This investigation was made for three years from 1977 to 1979 in four paddy plots at 50-km north of Tokyo, which were treated with three different fertilizers and with none. The organic fertilizer plot produced 1,765 midges per square meter per season, followed by the inorganic fertilizer plot producing 1,376. About half numbers were produced in the non-fertilizer and green manure plots. Fifteen species occurred from these paddies. Chironomus kiensis, Tanytarsus sp., Microtendipes sp. and Procladius crassinervis were most abundant in this order. Simpson's diversity index tended to be small at the beginning of the season but became large as it progressed. No spray of agricultural chemicals reduced the chironomid populations appreciably but mid-season drainage did. A significant correlation was obtained between chironomid population size and β-glucosidase activity in soil when 15 physical, chemical and biological characteristics were correlated. Rice leaf cover and phosphate ion concentration were also inversely correlated with the population size.

View full abstract

Intake of microfilariae of Onchocerca volvulus by Simulium ochraceum, the main vector of onchocerciasis in Guatemala, was studied. The initiation of intake of microfilariae was around 30sec after landing. Thereafter, the number of microfilariae taken by flies increased as the feeding time increased. After 3 to 4min of landing, 69% of flies finished their blood meal, and the intake of microfilariae reached the highest. Thereafter, increase of feeding time did not increase the intake. With the volunteers of moderate density of microfilariae (55-116 Mf per 10(mm)^2), the number of microfilariae taken by the flies was correlated with the density of microfilariae in human skin. With a volunteer of very low density (1.8 Mf per 10(mm)^2), however, an extraordinarily high intake of microfilariae was observed. This suggested the possibility of the flies attracting or stimulating the microfilariae in the skin of low density carriers.

View full abstract

Of the S. ochraceum in Guatemala, the shortest duration from emergence to blood-feeding, from blood-feeding to oviposition (both at 22℃) and from oviposition to next blood-feeding (under the field condition) were presumed to be 2 days, 5 days and 0 day, respectively. One gonotrophic cycle of this species was to be 5 days in the shortest case. The average parous rate observed in the blackflies collected at four locations from October to December, 1977 were 48.7% for S. ochraceum, 41.2% for S. metallicum, 46.9% for S. callidum and 38.9% for S. mexicanum. The parous rate showed diurnal change, those of which captured in the afternoon being somewhat higher. The survival rate of S. ochraceum for 9 days after blood-feeding when this species become infective, was estimated at 27.3%.

View full abstract

A description of a new species belonging to the subgenus Helodon Enderlein designated by Peterson is given with its illustrations. This is only a species of the subgenus Helodon found from Japan.

View full abstract