This is a review of Japanese studies on the vector mosquitoes of dengue fever. The article consists of four parts. The first describes the process of vector incrimination with a focus on Aedes albopictus. The next, vector studies during the epidemic occurred in Japan, 1942-43. The third part summarizes recent advances in biological and epidemiological studies on Aedes albopictus, particularly after the second world war. Finally, I discuss the cause of the sharp increase in dengue fever during 1942 and 1943. A list of papers on dengue vector mosquitoes in Japan is presented.

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The susceptibility of mosquito larvae against pyriproxyfen was examined in the laboratory for 9 colonies of the following six species; Aedes aegypti (Linnaeus), Ae. albopictus (Skuse), Anopheles dirus Peyton and Harrison, An. minimus Theobald, Culex pipiens pallens Coquillett, Cx. tritaeniorhynchus Giles. The late fourth instar larvae were exposed to different concentrations of pyriproxyfen for 24 hours, then the number of dead or emerging pupae collected within 2 days after exposure were counted by sex. A higher susceptibility of males than females to pyriproxyfen was observed for all colonies. The comparison of IC_<50> among the three Ae. aegypti colonies showed that susceptibility of the Ae. aegypti RR colony, which is resistant to DDT and permethrin, was lower than that of other colonies.

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The algogenic effects of venom gland extract (VGE) from the red back widow spiders (Latrodectus hasseltii) and its component α-latrotoxin were investigated in mice. Mice were given an intraplantar injection of VGE or α-latrotoxin into the hind paw, and licking of the injected site was assessed as a pain-associated response. The VGE increased dose dependently the licking behavior at doses of 1/300th to 1/30th venom gland. The licking behavior elicited by an injection of VGE at a dose of 1/100th venom gland was significantly suppressed by subcutaneous pretreatment with the opioid analgesic morphine hydrochloride (3 and 10 mg/kg) but not the aspirin-like drugs, such as ketoprofen (10 and 30 mg/kg) and diclofenac sodium (10 and 30 mg/kg). An intraplantar injection of heat-treated VGE did not elicit licking behavior. An injection of α-latrotoxin (30 and 300 ng) markedly increased licking behavior. These findings suggest that an injection of VGE causes severe pain through non-inflammatory mechanisms. It is possible that the algogenic action of VGE is at least partly mediated by α-latrotoxin.

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In the course of epidemiological studies on mosquito-borne diseases in Lao PDR in 2000, an undescribed species of genus Armigeres was collected from bamboo internodes with a bamboo hole in Khammouane Province. This species has special morphological characteristics in the male genitalia with an expanded gonostylus having 20 strong teeth, of which the anterior half was longer than the rest. Careful comparisons with related species show that the newly collected material belongs to a new species. It is named as Armigeres (Armigeres) laoensis sp. nov. after the country Lao PDR.

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Hayesomyia tripunctata (Goetghebuer, 1922) (Chironomidae, Tanypodinae) is recorded for the first time in Japan. The adult male of Hayesomyia is similar to that of Rheopelopia, while the former differs from the latter in retention of small ScuL (scutal lamella), but this difference is often unclear. It seems the most distinctive characteristic of the former is the structure of gonostylus which narrows abruptly before the apex. Rheopelopia seiryuuvea (Sasa, Suzuki et Sakai, 1998) is sunk as a synonym of H. tripunctata, based on type-examination.

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Since the redback spider, Latrodectus hasseltii Thorell, was first confirmed in November 1995 in the Osaka Bay area in Japan and became established in high density in areas adjacent to the Kansai International Airport, its distribution range continues to expand. Based on the outcome of the redback spider surveys, we implemented address matching and tabulated the survey year, the address of confirmed infested sites and number of webs by year using GIS computer software and digital maps. We furthermore mapped the expanded areas of the spider infestation by year and address and produced density distribution maps for each year from 1995 to 2001 and a map for the period of the surveillance. In addition, since biting cases have been reported, we examined the relationship between the spider density and the number of biting cases. From our GIS analysis it became clear that the distribution range of the redback spider clearly continues to expand in Osaka Prefecture and the expansion of the spider occurred gradually in some coastal areas and dispersed from the densely distributed areas to the more inner areas in Osaka Prefecture. These analyses also show that the number of biting cases by the redback spider will increase in Osaka and surrounding prefectures infested with redback spiders.

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Effects of the predator Mesocylops pehperiensis (Hu) (Copepoda: Cyclopoida) on the survivorship and the development of a cohort of Aedes albopictus (Skuse) (Diptera: Culicidae) to pupation were examined in large (diameter = 8.5 cm and depth = 5.5 cm) and small (diameter = 3.5 cm and depth = 5.5 cm) containers with leaves from the maple Acer buergerianum (Miq.) (Angiospermae: Aceraceae) as larval food. In the absence of the predator, survival was higher and developmental time shorter in the large container. M. pehpeiensis reduced the survivorship of Ae. albopictus from 93% to 12% in the large container and from 34% to 0% in the small container. Ae. albopictus larvae developed to larger size in shorter time in the large container with the predator than in those without the predator. These results indicate that the predator has both direct (reducing the number of mosquitoes) and indirect (enhancement of the fitness of survived individuals fitness) effects on mosquito populations, which may cause difficulty in mosquito control under some conditions. So, vector control operations including the use of copepods can be counterproductive with regard to potentially crucial interactions between the absence of competition, body size and its epidemiological importance in container-breeding mosquito such Ae. albopictus.

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The feeding activity of Amblyomma testudinarium Koch nymphs that were placed outdoors from engorged larvae was observed under laboratory conditions (24℃, 10L-14D photoperiod) from October to December 2001. The rates of engorgement of the nymphs ranged from 48.3 to 55.0% in October to December. The rate of engorgement was not reduced even in December. These results suggest that A. testudinarium nymphs do not enter behavioral diapause on exposure to the short days of autumn. Since the vertical activity of the nymphs in the plastic cyliders becomes lower as the temperatures of autumn drop, their low activity in late autumn appears to be a simple quiescence due to the temperature.

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