Effects of temperature and diet on development and interspecies competition in Aedes aegypti and Aedes albopictus

We asked whether climate change might affect the geographic distributions of Aedes aegypti (L.) and Aedes albopictus (Skuse) (Diptera: Culicidae). We tested the effects of temperature, diet and the presence of congeneric species on the performance of immature stages of these two aedine species in the laboratory. Mosquitoes in three different species-density combinations were reared at four constant temperatures (20 °C, 25 °C, 30 °C, 35 °C) on low- or high-level diets. Of the four temperatures tested, mortality increased only at 35 °C in both species. Mortality was higher on the high-level diet than on the low-level diet at 35 °C, but not at other temperatures. The presence of congeneric species had a significant positive effect on mortality in Ae. albopictus, but not in Ae. aegypti. Both species developed more quickly at higher temperatures within the range of 20-30 °C; development was not enhanced at 35 °C. Population growth of Ae. albopictus was more stable, regardless of diet and temperature; that of Ae. aegypti varied more according to these two factors. These species-specific attributes may help to explain the latitudinal distribution of the mosquitoes and degree of species dominance where they are sympatric. © 2011 The Authors. Medical and Veterinary Entomology © 2011 The Royal Entomological Society

Uranotaenia novobscura ryukyuana (Diptera: Culicidae) Population Dynamics Are Denso-Dependent and Autonomous From Weather Fluctuations

Larvae of the mosquito Uranotaenia novobscura ryukyuana Tanaka et al., have been reported in tree-holes, bamboo stumps, and artiTcial water containers. So far, no study has addressed the role that density dependence and weather suctuations could have played in the abundance of this nonvector mosquito. A year-long study was conducted on the population dynamics of this mosquito using oviposition traps in Okinawa, Japan. Time series analysis and the Ricker population model were used to analyze the association between mosquito density and population growth and suctuations in relative humidity, temperature, and rainfall. Our results suggest that Ur. novobscura ryukyuana has stable denso-dependent dynamics, which are autonomous from weather suctuations. Our results were opposite to patterns observedin other subtropical mosquito species, whose population dynamics might be partially driven by weather suctuations, thus highlighting the diversity of responses that mosquitoes can have to changing environments

Tempo-spatial variation in feeding activity and density of Aedes albopictus (Diptera: Culicidae) at peridomestic habitat in Nagasaki, Japan.

金沢大学理工研究域　自然システム学系1998年9月, 長崎大学熱帯医学研究所敷地内で家屋周辺の茂み及び裸地においてヒトスジシマカの24時間採集を行い, 周辺環境の異なる採集場所における吸血活動性と密度のちがいを調べた。ヒトスジシマカの密度は茂みで高く, 屋内や裸地で低かった。吸血活動は薄明薄暮に高まり, 夜も高かった。最も活動性が高い薄暮には, 統計的な有意差はみられないが, 昼間や夜間に比べて屋内や裸地で採集される雌個体の割合が高かった。以上の結果からヒトスジシマカの生態における夜間の吸血活動の重要性と薄明薄暮には茂み以外に裸地や屋内などでも吸血される機会が増加することが示唆された。 To clarify the tempo-spatial variation in feeding of Aedes albopictus, a field investigation was conducted in a field where the species heavily infested, in Nagasaki. Feeding activity was observed in the nighttime as well as at dawn and dusk. The density was high at sites with vegetation and low at sites without vegetation and indoors. At sites with vegetation, the proportion of females decreased at dawn and dusk, while it increased at sites without vegetation and indoors. Feeding activity in nighttime is possibly common in Ae. albopictus, and the place of feeding expands from sites with vegetation to sites without vegetation and indoors at dawn and dusk

Preliminary field experiments on exophagy of Aedes albopictus (Diptera: Culicidae) in peridomestic habitat.

金沢大学理工研究域　自然システム学系Preliminary field experiments were conducted to examine the exophagy of Aedes albopictus in peridomestic habitat by using three different types of experimental buildings in Nagasaki, Japan and Chiangmai, Thailand. The density of females collected by suction traps enhanced by CO2 was high inside net-walled buildings and at outdoor sites with vegetation. On the other hand, the densities inside a normal walled building and at outdoor sites without vegetation, the microclimate conditions of both of which were different from the outdoor sites with vegetation, were low. To evaluate the effect of blocking by walls for Ae. albopictus invading to feed, an additional experiment by using a bamboo hut with openings of different sizes in the walls was conducted in Thailand. As the opening in the walls was smaller, the difference in the number of females between inside and outside of the hut became significantly larger. Therefore, the effect of physical blocking by walls was suggested. We proposed the presence of vegetation, the difference in environmental conditions inside buildings from those in vegetation due to blocking, and physical blocking by walls for invasion as ecological factors influencing the exophagy of Ae. albopictus. (author abst.

琉球列島の西表島で蛙の鳴き声トラップに誘引された蚊類について

金沢大学留学生センター2004年6月12-18日に, 琉球列島の西表島の森林地帯の2ヵ所で, 蛙の声をCDプレイヤーで鳴らし, 直ぐ近くにCDCライトトラップを設置し蚊類を採集した.第一地点で合計777個体, 2地点で257個体のハエ目の昆虫が採集された.それらのうち, 次の4種の吸血性昆虫(雌)が両地点で目立って多く採集された.マックファレンチビカは第一地点で580個体(74.6%), 第二地点で193 (75.1), ヤエヤマカニアナチビカ19(2.4)と27 (10.5), ヤマトケヨソイカ106 (13.6)と20(7.8), また, ルソンコブハシカが第一地点のみで39個体(5.0%)が採集された.これらの蚊にケージ内でヌマガエルを暴露すると, 吸血行動が見られ, 多くの個体が吸血した.このことからこれらの蚊は自然界でカエルの鳴き声に誘引され, 吸血していると思われる. Mosquito collections were made at two foothill sites of Iriomote Island, the Ryukyu Archipelago, Japan, by modified CDC miniature light traps with a frog call CD player from June 12 to 18, 2004. A total of 777 and 257 female Diptera was collected at sites 1 and 2, respectively. Among them, 4 haematophagous species were predominant at sites 1 and 2-Uranotaenia macfarlanei with 580 (74.6%) and 193 (75.1%) individuals respectively, Ur. yaeyamana 19 (2.4%) and 27 (10.5%), and Corethrella nippon 106 (13.6%) and 20 (7.8%) which is a new record for Iriomote Island, and Mimomyia luzonensis with 39 (5.0%) individuals was predominant at site 1. The females of these species collected by the traps fed easily on a frog, Rana limnocharis exposed in the cage. The results demonstrated clearly that frog call is the primary stimulus in guiding these Culicine and Chaoborine flies in their search for host animals in nature

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

Host-feeding patterns of Culex tritaeniorhynchus and Anopheles sinensis (Diptera: Culicidae) in a ricefield agroecosystem.

金沢大学理工研究域　自然システム学系水田発生性蚊類成虫の吸血選択を調べるために, 佐賀県西有田町で1996及び1997年の5月から9月に成虫採集を行った。ドライアイス付加ライトトラップと吸虫管により合計31,804頭のコガタアカイエカとシナハマダラカ雌成虫を採集した。調査したすべての牛舎と豚舎ではライトトラップ採集により多数の成虫が捕獲されたが(牛舎7,933,豚6,441,鶏舎5,267), 鶏舎では吸血蚊がほとんど採集されなかった。コガタアカイエカとシナハマダラカの吸血率は, 牛舎と豚舎ではそれぞれ62%(N=7,113), 74%(N=7,261)であったが, 鶏舎では5%以下(N=5,267)であった。ELISAによる吸血源同定の結果, 両種とも鶏よりも牛と豚を選択していることが示された。また, 牛舎と隣接した鶏舎から採集された吸血蚊も90%以上(N=143)が牛を吸血していた。鶏よりも豚と牛から吸血する傾向は採集場所(棚田周辺か平野部), 採集方法(ライトトラップか吸虫管)を問わず観察された。 Adults of rice-field mosquitoes were collected between May and September of 1996 and 1997 in Nishi Arita, Saga Prefecture, Japan, to determine their feeding pattern in an area where animals were available in large numbers. In total, 31,804 female Culex tritaeniorhynchus and Anopheles sinensis were collected from animal sheds using dry ice-baited light traps and mouth aspiration. Light traps in all the animal sheds captured large numbers of mosquitoes (cowsheds 7,933,pigsties 6,441 and chicken sheds 5,267 mosquitoes), although few fed upon the chickens. Overall, 62% (N=7,113) of fed Cx. triaeniorhynchus and 74% (N=7,261) of An. sinensis were caught by light traps at the cowsheds and pigsties compared to less than 5% (N=5,267) at the chickens sheds. The type of animal in the shed was the most important factor determining the feeding rates. Blood-meal identification by direct ELISA indicated that both Cx. tritaeniorhynchus and An. sinensis preferred cows and pigs to chickens. Over 90% (N=143) of the fed mosquitoes collected from one chicken shed had fed upon cows in an adjoining cowshed. The tendency to feed upon cows and pigs more than on chickens was observed both in the hillside (terraced) and lowland ricefields. This trend is shown in the results obtained by both the aspirator and light trap collection methods

Environmental Forcing Shapes Regional House Mosquito Synchrony in a Warming Temperate Island

Seasonal changes in the abundance of exothermic organisms can be expected with climate change if warmer temperatures can induce changes in their phenology. Given the increased time for ectothermic organism development at lower temperatures, we asked whether population dynamics of the house mosquito, Culex pipiens s.l. (L.) (Diptera: Culicidae), in Jeju-do (South Korea), an island with a gradient of warming temperatures from north to south, showed differences in sensitivity to changes in temperature along the warming gradient. In addition, we asked whether synchrony, that is, the degree of concerted fluctuations in mosquito abundance across locations, was affected by the temperature gradient. We found the association of mosquito abundance with temperature to be delayed by 2 wk in the north when compared with the south. The abundance across all our sampling locations had a flat synchrony profile that could reflect impacts of rainfall and average temperature on the average of all our samples. Finally, our results showed that population synchrony across space can emerge even when abundance is differentially impacted by an exogenous factor across an environmental gradient

Nationwide Investigation of the Pyrethroid Susceptibility of Mosquito Larvae Collected from Used Tires in Vietnam

Pyrethroid resistance is envisioned to be a major problem for the vector control program since, at present, there are no suitable chemical substitutes for pyrethroids. Cross-resistance to knockdown agents, which are mainly used in mosquito coils and related products as spatial repellents, is the most serious concern. Since cross-resistance is a global phenomenon, we have started to monitor the distribution of mosquito resistance to pyrethroids. The first pilot study was carried out in Vietnam. We periodically drove along the national road from the north end to the Mekong Delta in Vietnam and collected mosquito larvae from used tires. Simplified susceptibility tests were performed using the fourth instar larvae of Aedes aegypti, Aedes albopictus, and Culex quinquefasciatus. Compared with the other species, Ae. aegypti demonstrated the most prominent reduction in susceptibility. For Ae. aegypti, significant increases in the susceptibility indices with a decrease in the latitude of collection points were observed, indicating that the susceptibility of Ae. aegypti against d-allethrin was lower in the southern part, including mountainous areas, as compared to that in the northern part of Vietnam. There was a significant correlation between the susceptibility indices in Ae. aegypti and the sum of annual pyrethroid use for malaria control (1998–2002). This might explain that the use of pyrethroids as residual treatment inside houses and pyrethroid-impregnated bed nets for malaria control is attributable to low pyrethroid susceptibility in Ae. aegypti. Such insecticide treatment appeared to have been intensively administered in the interior and along the periphery of human habitation areas where, incidentally, the breeding and resting sites of Ae. aegypti are located. This might account for the strong selection pressure toward Ae. aegypti and not Ae. albopictus

High potential risk of dengue transmission during the hot-dry season in Nha Trang City, Vietnam.

We visited houses and inspected water-holding containers to determine the potential risks of dengue transmission during different seasons. This survey was conducted in two neighbourhoods of Nha Trang City in July and December 2006, which correspond to the middle of the hot-dry season and the beginning of the cool-wet season, respectively. We inspected a total of 1438 wet containers in 196 premises during both survey periods; 20% of the containers were positive for Aedes aegypti larvae and 8% for A. aegypti pupae. Indoor water-holding containers, which were sparsely distributed, exhibited high pupal productivity and efficiency (pupal productivity of a type of container/prevalence of that type of container) in either the first survey conducted in July, or the second, conducted in December. Although rainfall may not influence the number and distribution of water-holding containers in the city, the high average temperature in the first survey period resulted in a higher potential risk of dengue transmission. Our analysis suggests that if intensive source reduction is conducted in summer and containers with high pupal productivity and efficiency are targeted, the risk of dengue transmission in the city could be effectively reduced