Predicting the Start of the Aedes albopictus (Diptera: Culicidae) Female Adult Biting Season Using the Spring Temperature in Japan

Aedes albopictus (Skuse) (Diptera: Culicidae) is distributed widely and is common in much of Japan. In Japan, female adults begin to bite in between April and June, except in the southern subtropics where the mosquito has no dormant period. It is difficult to estimate the first Ae. albopictus biting day because it varies annually depending on the location. Over several years, we surveyed the mosquitoes at different locations that covered a range of warmer to cooler areas of Japan. We found an association between the timing of first biting day by Ae. albopictus and spring temperature. In spring months, the strongest correlation was found with mean April temperatures, followed by March. Based on these data, it may, therefore, be possible to apply a simple formula to predict the timing of the first biting day at various geographical locations in Japan. Forecasting maps were created using a simple prediction formula. We found that the first biting day for Ae. albopictus changed depending on early spring temperatures for each year. There was an approximate 20-d difference in first biting day between years with warmer and cooler springs. This prediction model will provide useful insight for planning and practice of Ae. albopictus control programs, targeting larvae and adults, in temperate regions globally.ArticleJournal of Medical Entomology.54(6):1519-1524(2017)journal articl

Distribution of a Knockdown Resistance Mutation (L1014S) in Anopheles gambiae s.s. and Anopheles arabiensis in Western and Southern Kenya

In Kenya, insecticide-treated mosquito nets (ITNs) distributed to pregnant women and children under 5 years old through various programs have resulted in a significant reduction in malaria deaths. All of the World Health Organization-recommended insecticides for mosquito nets are pyrethroids, and vector mosquito resistance to these insecticides is one of the major obstacles to an effective malaria control program. Anopheles gambiae s.s. and Anopheles arabiensis are major malaria vectors that are widely distributed in Kenya. Two point mutations in the voltage-gated sodium channel (L1014F and L1014S) are associated with knockdown resistance (kdr) to DDT and pyrethroids in An. gambiae s.s. While the same point mutations have been reported to be rare in An. arabiensis, some evidence of metabolic resistance has been reported in this species. In order to determine the distribution of the point mutation L1014S in An. gambiae s.s. and An. arabiensis in southern and western Kenya, we collected larvae and screened for the mutation by DNA sequencing. We found high allelic and homozygous frequencies of the L1014S mutation in An. gambiae s.s. The L1014S mutation was also widely distributed in An. arabiensis, although the allelic frequency was lower than in An. gambiae s.s. The same intron sequence (length: 57 base) found in both species indicated that the mutation was introgressed by hybridization. The allelic frequency of L1014S was higher in both species in western regions, demonstrating the strong selection pressure imposed by long-lasting insecticide-treated nets (LLITN)/ITN on the An. gambiae s.s. and An. arabiensis populations in those areas. The present contribution of the L1014S mutation to pyrethroid resistance in An. arabiensis may be negligible. However, the homozygous frequency could increase with continuing selection pressure due to expanded LLITN coverage in the future

Multimodal pyrethroid resistance in malaria vectors, Anopheles gambiae s.s., Anopheles arabiensis, and Anopheles funestus s.s. in western Kenya.

Anopheles gambiae s.s., Anopheles arabiensis, and Anopheles funestus s.s. are the most important species for malaria transmission. Pyrethroid resistance of these vector mosquitoes is one of the main obstacles against effective vector control. The objective of the present study was to monitor the pyrethroid susceptibility in the 3 major malaria vectors in a highly malaria endemic area in western Kenya and to elucidate the mechanisms of pyrethroid resistance in these species. Gembe East and West, Mbita Division, and 4 main western islands in the Suba district of the Nyanza province in western Kenya were used as the study area. Larval and adult collection and bioassay were conducted, as well as the detection of point mutation in the voltage-gated sodium channel (1014L) by using direct DNA sequencing. A high level of pyrethroid resistance caused by the high frequency of point mutations (L1014S) was detected in An. gambiae s.s. In contrast, P450-related pyrethroid resistance seemed to be widespread in both An. arabiensis and An. funestus s.s. Not a single L1014S mutation was detected in these 2 species. A lack of cross-resistance between DDT and permethrin was also found in An. arabiensis and An. funestus s.s., while An. gambiae s.s. was resistant to both insecticides. It is noteworthy that the above species in the same area are found to be resistant to pyrethroids by their unique resistance mechanisms. Furthermore, it is interesting that 2 different resistance mechanisms have developed in the 2 sibling species in the same area individually. The cross resistance between permethrin and DDT in An. gambiae s.s. may be attributed to the high frequency of kdr mutation, which might be selected by the frequent exposure to ITNs. Similarly, the metabolic pyrethroid resistance in An. arabiensis and An. funestus s.s. is thought to develop without strong selection by DDT

Geospatial analysis of invasion of the Asian tiger mosquito Aedes albopictus: competition with Aedes japonicus japonicus in its northern limit area in Japan

The mosquito Aedes albopictus, indigenous to Southeast Asia and nearby islands, has spread almost worldwide during recent decades. We confirm the invasion of this mosquito, first reported in Yamagata city in northeast Honshu, Japan in 2000. Previously, only Ae. japonicus japonicus had been collected in this place, but 2 years later, the population of Ae. albopictus had increased, so more than 80% of the total number of larval colonies there consisted of this species. In contrast to Yamagata’s new residential area, now infested by Ae. albopictus, the original mosquito remains in the city but its habitats are generally closer to the surrounding mountains, where the normalized difference vegetation index is higher. The factors affecting the distribution of both species in Yamagata city were studied using geographical information systems (GIS) based on data derived from field surveys, aerial photographs, satellite images and digital maps. The range of Aedes mosquito habitats was estimated and visualised on polygon maps and no significant differences were noted when the polygon area was calculated by GIS software in comparison with the satellite images. Although Ae. j. japonicus was expected to be rapidly overrun by Ae. albopictus, this did not happen. Currently, both species coexist; not only in separate sites, but also simultaneously in various water bodies, where larvae from both species have frequently been seen. However, the competitive relationship between these two Aedes species within a warming environment is an issue that should be closely monitored

Geospatial analysis of invasion of the Asian tiger mosquito Aedes albopictus: competition with Aedes japonicus japonicus in its northern limit area in Japan

The mosquito Aedes albopictus, indigenous to Southeast Asia and nearby islands, has spread almost worldwide during recent decades. We confirm the invasion of this mosquito, first reported in Yamagata city in northeast Honshu, Japan in 2000. Previously, only Ae. japonicus japonicus had been collected in this place, but 2 years later, the population of Ae. albopictus had increased, so more than 80% of the total number of larval colonies there consisted of this species. In contrast to Yamagata’s new residential area, now infested by Ae. albopictus, the original mosquito remains in the city but its habitats are generally closer to the surrounding mountains, where the normalized difference vegetation index is higher. The factors affecting the distribution of both species in Yamagata city were studied using geographical information systems (GIS) based on data derived from field surveys, aerial photographs, satellite images and digital maps. The range of Aedes mosquito habitats was estimated and visualised on polygon maps and no significant differences were noted when the polygon area was calculated by GIS software in comparison with the satellite images. Although Ae. j. japonicus was expected to be rapidly overrun by Ae. albopictus, this did not happen. Currently, both species coexist; not only in separate sites, but also simultaneously in various water bodies, where larvae from both species have frequently been seen. However, the competitive relationship between these two Aedes species within a warming environment is an issue that should be closely monitored

Aedes albopictus: competition with Aedes japonicus japonicus

in its northern limit area in Japa

Genetic analysis of Aedes aegypti captured at two international airports serving to the Greater Tokyo Area during 2012-2015.

The introduction of exotic disease vectors into a new habitat can drastically change the local epidemiological situation. During 2012-2015, larvae and an adult of the yellow-fever mosquito, Aedes aegypti, were captured alive at two international airports serving the Greater Tokyo Area, Japan. Because this species does not naturally distribute in this country, those mosquitoes were considered to be introduced from overseas via air-transportation. To infer the places of origin of those mosquitoes, we genotyped the 12 microsatellite loci for which the most comprehensive population genetic reference is currently available. Although clustering by Bayesian and multivariate methods both suggested that all those mosquitoes captured at the airports in Japan belonged to the Asia/Pacific populations, they were not clustered into a single cluster. Moreover, there was variation in mitochondrial cytochrome oxidase I gene (CoxI) haplotypes among mosquitoes collected in different incidents of discovery which indicated the existence of multiple maternal origins. We conclude there is little evidence to support the overwintering of Ae. aegypti at the airports; nevertheless, special attention is still needed to prevent the invasion of this prominent arbovirus vector