Mamoru Watanabe

Ecological and Genetic Analyses of the Complete Genomes of Culex Flavivirus Strains Isolated From Culex tritaeniorhynchus and Culex pipiens (Diptera: Culicidae) Group Mosquitoes

ABSTRACT Culex flavivirus (CxFV) is an insect-specific flavivirus that was first reported in 2007 in Japan. CxFV strains were isolated from Culex tritaeniorhynchus Giles and Culex pipiens L. group mosquitoes and genetically characterized in Toyama Prefecture, Japan, from 2004 to 2009, to reveal host specificity, mode of transmission, and seasonal and geographical distribution. The minimum infection rate (MIR) of CxFV within Cx. tritaeniorhynchus populations was 0.3 and much lower than that within Cx. pipiens group (17.9). The complete genome sequences of 11 CxFV isolates (four from Cx. tritaeniorhynchus and seven from Cx. pipiens group) consisted of 10,835–10,837 nucleotides. When these 11 isolates and five reference strains (NIID-21-2 and Tokyo strains from Japan, Iowa07 and HOU24518 strains from the United States, H0901 strain from China) were compared, there were 95.2–99.2% nucleotide and 98.1–99.8% amino acid identities. Phylogenetic analysis showed that the 11 isolates were divided into four clusters. One cluster consisted of five isolates from Cx. pipiens group and Cx. tritaeniorhynchus from one site and their nucleotide sequences almost completely matched. One cluster consisted of an isolate with a unique sequence from a Cx. pipiens group mosquito captured in an aircraft from Taiwan, suggesting that it was introduced from abroad. CxFV strains were divided into several groups according to countries when nucleotide sequences of CxFV available in GenBank and 11 Toyama isolates were compared. These results suggest that CxFV is maintained in nature among Culex mosquitoes in a mosquito habitat-specific but not a species-specific manner.

A quantitative analysis of dispersal in a horse-fly,Tabanus iyoensis Shiraki and its application to estimate the population size

A horse-fly, Tabanus iyoensis SHIRAKI, often occurs in large numbers at various places in Japan, and annoys seriously the inhabitants and their cattles because of its blood-sucking habit. This paper forms the second report of our research on the biology and population dynamics of this insect and is mainly concerned with the analysis of dispersal pattern of adult flies and the application of the results to the estimation of population size. The research on dispersal of animals and plants has been approached from two ways. One is inductive approach adopted by WOLFENBARGER (1946), KETTLE (1952) and others, and the other is deductive one exemplified by SKELLEM (1951)and WATANABE et al.(1952). Several empirical equations to describe the dispersal have been obtained through the former approach, but they cannot explain the biological process involved. On the other hand, the simplified assumptions underlying theoretical models of the latter make it difficult to apply them to the dispersal of organisms under field conditions. The approach in the present study is essentially inductive, but is not purely descriptive, in that we have tried to describe the dispersal pattern with aid of some analytical methods derived from theoretical considerations. These methods may be of some value for the dispersal studies in other organisms as well. The estimation of population size is done by using the mark-and-recapture data obtained in the dispersal study. In this process some problems which arise when we use the data obtained by trapping are discussed.

Risk analysis of the re-emergence of Plasmodium vivax malaria in Japan using a stochastic transmission model.

ObjectivesThis study analyzed the risk of infection with Plasmodium vivax in local residents through a stochastic simulation in which an infected tourist, local resident, or immigrants from an endemic area would visit Himi-shi, Toyama prefecture, which is a formerly endemic area in Japan.MethodsIn Toyama, the habitats of Anopheles sinensis, which can transmit P. vivax, have been examined previously. We constructed a stochastic model of P. vivax transmission that can handle small numbers of infected persons and infected mosquitoes. The seasonal fluctuation in the numbers of captured An. sinensis was taken into account in the model.ResultsTen thousand trial simulations were carried out stochastically with a range of human blood indexes (HBI) of 1–10% for a range of months (June–September). The simulation results for a realistic assumption of a 1% HBI showed that the risk of infection for local residents was low (below 1%) except for the immigrants scenario.ConclusionsThe risk of infection among local residents (second cycle) was estimated to be very low for all situations. Therefore, there is little possibility for P. vivax infection to become established in this area of Japan.

Egg Load and Multiple Matings of a Cabbage Butterfly, Pieris canidia indica(Evans), in the Wild.

The mating frequency of wild females of Pieris canidia indica was examined by dissection of the bursa copulatrix. Most females of age class 0 had at least one spermatophore, suggesting that they mated soon after eclosion. Aged females were observed to have two or more spermatophores. The volume of the bursa copulatrix increased when the female mated. Virgin females carry about 300 immature eggs. Older females have about 100 immature eggs, so at least 200 mature eggs are thought to be deposited throughout the female life span.