Publications by authors named "Nobuko Tuno"

24 Publications

  • Page 1 of 1

Fungal spore transport by omnivorous mycophagous slug in temperate forest.

Ecol Evol 2022 Feb 17;12(2):e8565. Epub 2022 Feb 17.

Laboratory of Ecology Graduate School of Natural Science and Technology Kanazawa University Kanazawa Japan.

Slugs are important consumers of fungal fruiting bodies and expected to carry their spores. In this study, we examined whether slugs () can act as effective dispersers of spores of basidiomycetes. The microscopic observation confirmed the presence of basidiospores in feces of field-collected slugs, and the DNA metabarcoding study revealed that Ascomycota and Basidiomycota were major fungal taxa found in the feces. In Basidiomycota, the dominant order was Agaricales followed by Trichosporonales and Hymenochaetales. The laboratory experiments using showed that slugs carried a large number of spores in their digestive tracts. It was also observed that , , and spores excreted by slugs had a higher germination capacity than control spores collected from spore prints. The field experiments showed that slugs traveled 10.3 m in 5 h at most by wandering on the ground, litter layers, wood debris, and tree trunks. These results suggest that slugs could carry spores of ectomycorrhizal, saprophytic, and wood-decaying fungi to appropriate sites for these fungi to establish colonies.
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http://dx.doi.org/10.1002/ece3.8565DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8855016PMC
February 2022

Ecological mechanism of climate-mediated selection in a rapidly evolving invasive species.

Ecol Lett 2021 Apr 7;24(4):698-707. Epub 2021 Feb 7.

Department of Biology, Georgetown University, 3700 O St NW, Washington, DC, 20057, USA.

Recurring seasonal changes can lead to the evolution of phenological cues. For example, many arthropods undergo photoperiodic diapause, a programmed developmental arrest induced by short autumnal day length. The selective mechanisms that determine the timing of autumnal diapause initiation have not been empirically identified. We quantified latitudinal clines in genetically determined diapause timing of an invasive mosquito, Aedes albopictus, on two continents. We show that variation in diapause timing within and between continents is explained by a novel application of a growing degree day (GDD) model that delineates a location-specific deadline after which it is not possible to complete an additional full life cycle. GDD models are widely used to predict spring phenology by modelling growth and development as physiological responses to ambient temperatures. Our results show that the energy accumulation dynamics represented by GDD models have also led to the evolution of an anticipatory life-history cue in autumn.
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http://dx.doi.org/10.1111/ele.13686DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8045958PMC
April 2021

Climate Change May Restrict the Predation Efficiency of Mesocyclops aspericornis (Copepoda: Cyclopidae) on Aedes aegypti (Diptera: Culicidae) Larvae.

Insects 2020 May 14;11(5). Epub 2020 May 14.

Institute of Tropical Medicine, Nagasaki University, Nagasaki 852-8523, Japan.

(1) Dengue is the most spread mosquito-borne viral disease in the world, and vector control is the only available means to suppress its prevalence, since no effective treatment or vaccine has been developed. A biological control program using copepods that feed on mosquito larvae has been practiced in Vietnam and some other countries, but the application of copepods was not always successful. (2) To understand why the utility of copepods varies, we evaluated the predation efficiency of a copepod species () on a vector species () by laboratory experiments under different temperatures, nutrition and prey-density conditions. (3) We found that copepod predation reduced intraspecific competition among larvae and then shortened the survivor's aquatic life and increased their pupal weight. In addition, the predatory efficiency of copepods was reduced at high temperatures. Furthermore, performance of copepod offspring fell when the density of mosquito larvae was high, probably because mosquito larvae had adverse effects on copepod growth through competition for food resources. (4) These results suggest that the increase in mosquitoes will not be suppressed solely by the application of copepods if the density of mosquito larvae is high or ambient temperature is high. We need to consider additional control methods in order to maintain the efficiency of copepods to suppress mosquito increase.
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http://dx.doi.org/10.3390/insects11050307DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7290431PMC
May 2020

Differences in Responses to Urbanization Between Invasive Mosquitoes, Aedes japonicus japonicus (Diptera: Culicidae) and Aedes albopictus, in Their Native Range, Japan.

J Med Entomol 2020 01;57(1):104-112

Laboratory of Ecology, Graduate School of Natural Science and Technology, Kanazawa University, Kanazawa, Japan.

The Asian mosquitoes, Aedes albopictus (Skuse) and Aedes japonicus japonicus (Theobald), have invaded North America, Europe, and other regions since the late 20th century. In invasive ranges, Ae. albopictus has well been recognized as urban, domestic species, whereas views about the macrohabitats of Ae. j. japonicus are inconsistent. Previous reports in Japan suggest the disappearance of Ae. j. japonicus from metropolises. However, container-mosquito larvae have not been inspected simultaneously for various macro and microhabitats in metropolises in Japan. The current study in Fukuoka City, a metropolis in southwest Japan, confirmed the absence of Ae. j. japonicus irrespective of macrohabitats (temples with graveyards, shrines, public graveyards, cultivated bamboo groves, and urban forests, all within the area densely inhabited by humans) and microhabitats (container types). In contrast, Ae. albopictus was dominant throughout the macro and microhabitats except forest tree holes rich with competitive species. Past records indicate the disappearance of Ae. j. japonicus from metropolitan Fukuoka within the last 70 yr. Based on careful examination of available evidence, we concluded that 1) both species benefit from human-made environments with artificial containers free from competitors, 2) Ae. j. japonicus disappeared due to hot, dry summer conditions facilitated by urban heat-island effects and a decrease in favored mammal hosts, and 3) Ae. albopictus has proliferated with higher tolerance to hot, dry climate and a wider blood-feeding host-range including humans. This difference is important for efficient control of each species as well as predicting and preventing the expansion into new distribution ranges.
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http://dx.doi.org/10.1093/jme/tjz145DOI Listing
January 2020

Reduction of Reproductive Capacity in Aedes albopictus (Diptera: Culicidae) in Hot, Dry Summer.

J Med Entomol 2019 10;56(6):1729-1733

Laboratory of Ecology, Graduate School of Natural Science and Technology, Kanazawa University, Kanazawa, Japan.

The summer of 2018 was very hot and dry with little rain nationwide in Japan. Particularly in July, temperature was 3°C higher in comparison with the normal year. We collected adults, pupae, third or fourth instar larvae of Aedes albopictus (Skuse) in Sendai city, Niigata city, and Kanazawa city in late July and early August 2018. Wild-collected adults were examined for reproductive capacity. On the other hand, wild-collected larvae and pupae were raised to adults in the laboratory and then examined for reproductive capacity. They did not lay eggs after single blood feeding. When they were supplied with bloodmeals twice or three times, they laid a small number of eggs, but these eggs did not hatch. When these adult individuals were maintained at 25°C for 3 wk and then fed with blood, they laid healthy eggs which developed to embryos. It is thought that extreme heat and/or extreme low humidity due to low precipitation reduced female reproductive capacity even if they could take bloodmeals.
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http://dx.doi.org/10.1093/jme/tjz092DOI Listing
October 2019

Simple Indices Provide Insight to Climate Attributes Delineating the Geographic Range of Aedes albopictus (Diptera: Culicidae) Prior to Worldwide Invasion.

J Med Entomol 2015 Jul 15;52(4):647-57. Epub 2015 Apr 15.

Consell Comarcal del Baix Llobregat, Parc Torreblanca, 08980 Sant Feliu de Llobregat, Spain.

Aedes albopictus (Skuse) has expanded its distribution worldwide during the past decades. Despite attempts to explain and predict its geographic occurrence, analyses of the distribution of Ae. albopictus in the context of broad climatic regions (biomes) has not been performed. We analyzed climate conditions at its distribution sites in the range before the worldwide invasions (from the easternmost Hawaii through westernmost Madagascar) by using thermal and aridity-humidity indices descriptive of major biomes. A significant advantage of this approach is that it uses simple indices clearly related to the population dynamics of Ae. albopictus. Although Ae. albopictus has been regarded as a forest species preferring humid climate, in areas with significant human habitation, the distribution sites extended from the perhumid, rain forest zone to the semiarid, steppe zone. This pattern was common from the tropics through the temperate zone. Across the distribution range, there was no seasonal discordance between temperature and precipitation; at sites where winter prevents Ae. albopictus reproduction (monthly means<10°C), precipitation was concentrated in warm months (>10°C) under the Asian summer monsoon. Absence of the species in northern and eastern coastal Australia and eastern coastal Africa was not attributable solely to climate conditions. However, Asia west of the summer monsoon range was climatically unsuitable because of low precipitation throughout the year or in warm months favorable to reproduction (concentration of precipitation in winter). We hypothesized that Ae. albopictus originated in continental Asia under the monsoon climate with distinct dry seasons and hot, wet summer, enabling rapid population growth.
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http://dx.doi.org/10.1093/jme/tjv038DOI Listing
July 2015

Seasonal abundance of Anopheles mosquitoes and their association with meteorological factors and malaria incidence in Bangladesh.

Parasit Vectors 2014 Sep 18;7:442. Epub 2014 Sep 18.

Laboratory of Entomology, Department of Zoology, Jahangirnagar University, Savar, Dhaka 1342, Bangladesh.

Background: The relationship between climatic factors and mosquito abundance is very important to determine parasite activity levels and, therefore, disease risk. Therefore, this study was conducted to investigate the seasonal abundance of anophelines and their association with meteorological variables and disease transmission in two malaria endemic areas of Bangladesh.

Methods: Monthly sampling was done from both indoors and outdoors in 12 selected houses using light traps (LTs) and pyrethrum spray (PS) during January, 2011 to January, 2012 in two malaria endemic areas of Bangladesh. Outdoor rainfall, temperature, and relative humidity data of the study areas were collected from the meteorological department of Bangladesh. Mosquitoes were killed with chloroform and identified morphologically under stereoscopic microscopes using taxonomic keys. Samples were tested for CSP of P. falciparum, P. vivax 210 and P. vivax 247 using ELISA. Pearson correlation and canonical correspondence analyses (CCA) were computed to investigate the associations with species abundance and rainfall, temperature, humidity and malaria cases.

Results: A total of 2,443 female anophelines, representing 22 species were captured. Every female Anopheles were tested for P. falciparum, P. vivax 210 and P. vivax 247 CSP, of which 10 species were found positive. The CSP positive species were An. annularis, An. baimaii, An. barbirostris, An. jeyporiensis, An. karwari, An. minimus s.l., An. philippinensis, An. umbrosus, An. vagus and An. wilmori. Anopheles vagus and An. philippinensis were the dominant species present almost throughout the year with highest peaks in March and smallest peaks in September but An. baimaii and An. willmori were found during monsoon (July -September) only. Lag rainfall and relative humidity were the most significant variables influencing An. baimaii, An. willmori, An. vagus, and An. subpictus density in Kumari area. Abundance of these four species positively related to malaria cases. The effects of temperature were not found as a significant variable on the abundance of anophelines mosquitoes in Bangladesh.

Conclusions: Our study demonstrates that the nature of relationship between malaria vector and climatic variables were multifaceted. Detailed studies of vector bionomics, continuous monitoring and malaria transmission dynamics is essential for predicting disease outbreaks and vector control in the region.
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http://dx.doi.org/10.1186/1756-3305-7-442DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4262261PMC
September 2014

Impact of climate change on the distribution of Aedes albopictus (Diptera: Culicidae) in northern Japan: retrospective analyses.

J Med Entomol 2014 May;51(3):572-9

The impact of climate change on the distribution of Aedes albopictus (Skuse) was analyzed in northern Japan, where chronological distribution records are incomplete. We analyzed local climate data using linear regression of the thermal suitability index (TSI) for the mosquito and mean annual temperature as functions of time. In northern Japan, thermal conditions since the early 20th century have become increasingly suitable for Ae. albopictus, more as a result of decreasing coldness in the overwintering season than increasing warmth in the reproductive season. Based on recent discovery records of Ae. albopictus in the northern border range, we determined thermal criteria for estimating when its persistent establishment became thermally possible. Retrospective analyses indicated that those criteria were reached in most coastal lowlands of northern Honshu before the accelerated temperature increase after the mid-1980s and the first records of this species after 1990; at some sites, temperature criteria were reached during or before the early 20th century. Expansion of the thermally suitable range after 1990 was supported only for inland areas and the northernmost Pacific coast. The estimated expansion rate was approximately 26 km per decade. Our analyses also demonstrated the importance of local climate heterogeneity (apart from north-south or altitudinal temperature gradients) in determining the expansion pattern.
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http://dx.doi.org/10.1603/me13178DOI Listing
May 2014

Multiple blood feeding and host-seeking behavior in Aedes aegypti and Aedes albopictus (Diptera: Culicidae).

J Med Entomol 2013 Jul;50(4):838-46

Laboratory of Ecology, Graduate School of Natural Science and Technology, Kanazawa University, Kanazawa 920-1192, Japan.

The body size of mosquitoes can influence a number of bionomic factors, such as their blood-feeding ability, host attack rate, and fecundity. All of these traits are important determinants of their potential to transmit diseases. Among abiotic and biotic factors, high temperature and low nutrition in the developing stages of mosquitoes generally result in small adults. We studied the relationship between body size and multiple feeding in a gonotrophic cycle and some fecundity attributes by using three strains of two competent vector species, Aedes aegypti (L.) and Aedes albopictus (Skuse). We raised small and large mosquitoes under low and high food conditions in the laboratory to measure parameters of fecundity and blood-feeding behavior. Fecundity was positively correlated with body size in both species, whereas the number of bloodmeals, the frequency of host-seeking behavior, and egg retention were negatively correlated with body size in the Ae. albopictus Nagasaki strain. We found that multiple feeding and host-seeking behavior were negatively correlated with body size, i.e., small mosquitoes tended to have more contact with hosts. We found that two mechanisms that inhibit engorged mosquitoes from seeking out hosts, distension-induced and oocyte-induced inhibition, were not strong enough to limit host-seeking behavior, and multiple feeding increased fecundity. Size-dependent multiple feeding and host-seeking behavior affect contact frequency with hosts and should be considered when predicting how changes in mosquito body size affect disease transmission.
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http://dx.doi.org/10.1603/me12146DOI Listing
July 2013

False positivity of circumsporozoite protein (CSP)-ELISA in zoophilic anophelines in Bangladesh.

Acta Trop 2013 Feb 19;125(2):220-5. Epub 2012 Oct 19.

Laboratory of Entomology, Department of Zoology, Jahangirnagar University, Savar, Dhaka, Bangladesh.

Circumsporozoite protein enzyme-linked immunosorbent assays (CSP-ELISAs) are widely used for malaria vector identification throughout the world. However, several studies have reported false-positive results when using this method. The present study was conducted to estimate the frequency of false positives among anopheline species in malaria endemic areas of Bangladesh. In total, 4724 Anopheles females belonging to 25 species were collected and tested for Plasmodium falciparum, Plasmodium vivax-210, and P. vivax-247 CSP. Initially, 144 samples tested positive using routine CSP-ELISA, but the number of positive results declined to 85 (59%) when the samples were tested after heating at 100°C for 10min to remove false-positive specimens. Ten species, Anopheles annularis, Anopheles baimaii, Anopheles barbirostris, Anopheles jeyporiensis, Anopheles karwari, Anopheles kochi, Anopheles minimus s.l., Anopheles peditaeniatus, Anopheles philippinensis, and Anopheles vagus were CSP-positive. The highest and lowest infection rates were found in An. baimaii (4/25, 16.0%) and An. jeyporiensis (1/139, 0.67%), respectively. A significant correlation was found (regression analysis, R(2)=0.49, F=8.25, P<0.05) between human blood index results and the true CSP-positive ratios in 15 Anopheles species. We confirmed that false-positive reactions occurred more frequently in zoophilic species. The relatively high proportion of false positives (40%) that was found in this study should warn malaria epidemiologists working in the field to be cautious when interpreting ELISA results.
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http://dx.doi.org/10.1016/j.actatropica.2012.10.004DOI Listing
February 2013

Blood-feeding patterns of Anopheles mosquitoes in a malaria-endemic area of Bangladesh.

Parasit Vectors 2012 Feb 15;5:39. Epub 2012 Feb 15.

Laboratory of Entomology, Department of Zoology, Jahangirnagar University, Savar, Dhaka, Bangladesh.

Background: Blood-feeding patterns of mosquitoes are crucial for incriminating malaria vectors. However, little information is available on the host preferences of Anopheles mosquitoes in Bangladesh. Therefore, the objective of the present study was to determine the hematophagic tendencies of the anophelines inhabiting a malaria-endemic area of Bangladesh.

Methods: Adult Anopheles mosquitoes were collected using light traps (LTs), pyrethrum spray (PS), and human bait (HB) from a malaria-endemic village (Kumari, Bandarban, Bangladesh) during the peak months of malaria transmission (August-September). Enzyme-linked immunosorbent assay (ELISA) and polymerase chain reaction (PCR) were performed to identify the host blood meals of Anopheles mosquitoes.

Results: In total, 2456 female anopheline mosquitoes representing 21 species were collected from the study area. Anopheles vagus Doenitz (35.71%) was the dominant species followed by An. philippinensis Ludlow (26.67%) and An. minimus s.l. Theobald (5.78%). All species were collected by LTs set indoors (n = 1094), 19 species were from outdoors (n = 784), whereas, six by PS (n = 549) and four species by HB (n = 29). Anopheline species composition significantly differed between every possible combination of the three collection methods (χ(2) test, P < 0.001). Host blood meals were successfully detected from 1318 (53.66%) Anopheles samples belonging to 17 species. Values of the human blood index (HBI) of anophelines collected from indoors and outdoors were 6.96% and 11.73%, respectively. The highest values of HBI were found in An. baimai Baimaii (80%), followed by An. minimus s.l. (43.64%) and An. annularis Van den Wulp (37.50%). Anopheles baimai (B(i) = 0.63) and An. minimus s.l. (B(i) = 0.24) showed strong relative preferences (B(i)) for humans among all hosts (human, bovine, goats/sheep, and others). Anopheles annularis, An. maculatus s.l. Theobald, and An. pallidus Theobald exhibited opportunistic blood-feeding behavior, in that they fed on either humans or animals, depending on whichever was accessible. The remaining 12 species preferred bovines as hosts.

Conclusions: The observed high anthropophilic nature of An. baimai, An. minimus s.l., and An. annularis revealed these species to be important malaria vectors in hilly areas of Bangladesh. Higher values of HBI in outdoor-resting mosquitoes indicated that indoor collection alone is not adequate for evaluating malaria transmission in the area.
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http://dx.doi.org/10.1186/1756-3305-5-39DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3305455PMC
February 2012

Blood-feeding behavior of Anopheles gambiae and Anopheles melas in Ghana, western Africa.

J Med Entomol 2010 Jan;47(1):28-31

Graduate School of Natural Science and Technology, Kanazawa University, Kakuma-machi, Kanazawa, I Ishikawa, 920-1192, Japan.

Anopheles gambiae is the predominant malaria vector species in Ghana, western Africa, with a strong local presence of Anopheles melas Theobald along the southern coast. We studied the biting behavior of these two species of the Anopheles gambiae complex inland and at the coast in Ghana, with special attention to the local peoples' preference for outdoor sleeping. We collected mosquitoes at two sites in 2007, representing the moist semideciduous forest zone and the strand and mangrove zone, and the sampling was repeated in the dry and rainy seasons. Sampled mosquitoes were examined for species, parity and size (wing length), and we identified the hosts of their bloodmeals. We interviewed 288 of the village people to determine where and when they slept outdoors. Our study confirmed that An. gambiae is the only species of the An. gambiae complex in the Ashanti region and revealed that An. melas is highly dominant on the western coast of Ghana. Both species showed high human blood rates in indoor resting mosquito samples. More people sleep outside on the coast than inland. An. melas demonstrated high exophily. An. gambiae bit people more frequently indoors and did so more often during the dry season than in the rainy season. We suggest that the degree of exophily in An. melas may be affected by humidity and the availability of human as well as by the mosquitoes' innate habits.
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http://dx.doi.org/10.1603/033.047.0104DOI Listing
January 2010

Comparative evaluation of fecundity and survivorship of six copepod (Copepoda: Cyclopidae) species, in relation to selection of candidate biological control agents against Aedes aegypti.

J Am Mosq Control Assoc 2008 Mar;24(1):61-9

Department of Vector Ecology and Environment, Institute of Tropical Medicine, Nagasaki University, Nagasaki 852-8523, Japan.

The fecundity and survival of 6 copepod species were assessed under laboratory conditions in order to choose the best candidates to control the aquatic stages of dengue mosquitoes in the field. Females of all the 6 species (Mesocyclops aspericornis, Mesocyclops pehpeiensis, Mesocyclops woutersi, Mesocyclops thermocyclopoides, Mesocyclops ogunnus, and Megacyclops viridis) mated more than once. Multiple mating resulted in increased egg production. The reproductive ability and longevity varied among the species, and M. aspericornis had the highest values. The lowest values were observed in M. thermocyclopoides. Multiple mating of males of M. aspericornis was also observed. The paternal fecundity decreased with each additional mating. There was no difference in the paternal fecundity between the males that mated at low and high female frequencies. The sperm stored in the M. aspericornis females remained viable for 30 days after storage under moist conditions at 25 degrees C or 15 degrees C. This feature in M. aspericornis represents an additional positive factor indicating that this species is a good biological agent for controlling mosquito larvae, especially in domestic water containers that may dry intermittently.
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http://dx.doi.org/10.2987/5672.1DOI Listing
March 2008

Influence of the distribution of host species on adult abundance of Japanese encephalitis vectors Culex vishnui subgroup and Culex gelidus in a rice-cultivating village in northern Vietnam.

Am J Trop Med Hyg 2008 Jan;78(1):159-68

Department of Vector Ecology and Environment, Institute of Tropical Medicine, Nagasaki University, Nagasaki, Japan; Entomology Laboratory, National Institute of Hygiene and Epidemiology, Hanoi, Vietnam.

A field study was conducted in a village in northern Vietnam to investigate how host distribution influences Japanese encephalitis (JE) vector abundance. Indoor and outdoor collections were conducted from 50 compounds. We collected three JE vector species--Culex tritaeniorhynchus and Culex vishnui that comprised the Culex vishnui group, and Culex gelidus. Spatial autocorrelation was not observed in the mosquito assemblies at any scale larger than the house compounds. Multivariate analyses revealed that the Cx. gelidus density correlated positively with both the host proximity to the breeding sites and cattle density; however, the Cx. vishnui subgroup density correlated positively only with cattle density. These results showed that the number of cattle in a compound influenced the JE vector abundance in that compound, and the abundance of Cx. gelidus, not of the Cx. vishnui subgroup, was affected by the host proximity to the breeding sites in the village.
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January 2008

Interspecific variation in diving activity among Anopheles gambiae Giles, An. arabiensis Patton, and An. funestus Giles (Diptera: Culicidae) larvae.

J Vector Ecol 2007 Jun;32(1):112-7

Department of Vector Ecology and Environment, Institute of Tropical Medicine, Nagasaki, University, Nagasaki 852-8523, Japan.

Anopheline larvae generally inhabit the near-surface of aquatic habitats, but they dive and remain at the bottom of these habitats for some time. This study examined forced and voluntary diving behavior and submergence tolerance in the three major African malaria vectors, Anopheles gambiae Giles, An. arabiensis Patton, and An. funestus Giles. The former two species occur sympatrically in temporal and shallow water bodies, while the latter occurs in permanent deeper water bodies. Anopheles funestus was the most tolerant of submergence, but the larvae tended to halt their descent before reaching the bottom by attaching onto a wall. The difference in diving behavior between An. funestus and the two species in the An. gambiae complex may be an adaptation to their contrasting breeding sites, because the former species must spend considerable energy to surface in its typical breeding sites. Both An. gambiae and An. arabiensis reached the bottom and crawled along the substrate, but An. gambiae voluntarily crawled more often than An. arabiensis. The possible importance of asymmetric bottom-feeding between these two sympatric species is discussed.
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http://dx.doi.org/10.3376/1081-1710(2007)32[112:ividaa]2.0.co;2DOI Listing
June 2007

Tolerance of Drosophila flies to ibotenic acid poisons in mushrooms.

J Chem Ecol 2007 Feb 29;33(2):311-7. Epub 2006 Dec 29.

Department of Vector Ecology and Environment, Institute of Tropical Medicine, Nagasaki University, Nagasaki, 852-8523, Japan.

The mushroom genus Amanita has a spectrum of chemical compounds affecting survival and performance of animals. Ibotenic acid is one of such compounds found in some Amanita mushrooms. We studied the effects of ibotenic acid and its derivative, muscimol, on egg-to-pupa survival, pupation time, and pupal size in five Drosophila species (Diptera: Drosophilidae), Drosophila bizonata, Drosophila angularis, Drosophila brachynephros, Drosophila immigrans, and Drosophila melanogaster. The first three species are mycophagous and use a wide range of mushrooms for breeding, whereas D. immigrans and D. melanogaster are frugivorous. We reared fly larvae on artificial medium with 500, 250, 125, and 62.5 microg/ml of ibotenic acid and/or musimol. The three mycophagous species were not susceptible to ibotenic acid, whereas the two frugivorous species were affected. In experiments with D. melanogaster, muscimol was less toxic than ibotenic acid.
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http://dx.doi.org/10.1007/s10886-006-9228-3DOI Listing
February 2007

Sensitivity of the larvivorous copepod species, Mesocyclops pehpeiensis and Megacyclops viridis, to the insect growth regulator, pyriproxyfen.

J Am Mosq Control Assoc 2005 Dec;21(4):483-8

Department of Vector Ecology and Environment, Institute of Tropical Medicine, Nagasaki University, Japan.

The effects of the insect growth regulator pyriproxyfen were evaluated on the mortality, fecundity, longevity, and predation capability of 2 species of copepods, Mesocyclops pehpeiensis Hu and Megacyclops viridis (Jurine), under laboratory conditions. Pyriproxyfen showed no significant effects on either the development or reproduction of M. pehpeiensis at 0.1 ppm, which is a 10-fold greater concentration than the reported effective dosage for controlling mosquito larvae (0.01 ppm). In contrast, the development of M. viridis was impaired by pyriproxyfen at 0.1 ppm. An 80% reduction in nauplius survivorship was observed in the experimental (treated) group compared with the control group. Although the application of pyriproxyfen caused high mortality in the nauplius stage of this species, the pyriproxyfen-treated group developed faster, killed more mosquito larvae, yielded more eggs per oviposition event, and survived longer than the control group. These results indicate that pyriproxyfen caused mortality in the earlier stages of this sensitive species but that the surviving individuals were those that were selected for significantly faster development, better predation ability, and greater longevity during their reproductive stage. Therefore, under natural conditions, pyriproxyfen would cause modifications in the characteristics of a copepod population rather than its complete loss. Our results suggest that the combined application of copepods and pyriproxyfen to control Aedes populations is feasible. However, repeated application of pyriproxyfen may cause changes in copepod populations and communities in the affected ecosystem.
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http://dx.doi.org/10.2987/8756-971X(2006)21[483:SOTLCS]2.0.CO;2DOI Listing
December 2005

Survivorship of Anopheles gambiae sensu stricto (Diptera: Culicidae) larvae in western Kenya highland forest.

J Med Entomol 2005 May;42(3):270-7

Department of Vector Ecology and Environment, Institute of Tropical Medicine, Nagasaki University, Nagasaki 852-8523, Japan.

The western Kenya highland has been experiencing dramatic landuse changes in the past three decades. Landuse change has been hypothesized to be one of the mechanisms for malaria epidemics in African highlands because it can alter the physical and chemical characteristics of mosquito breeding habitats. One important landuse change in western Kenya highland is deforestation. The current study examined the effects of forestation or deforestation on the survivorship of Anopheles gambiae larvae and colonization of other aquatic insects in larval habitats in Kakamega forest (elevation 1,500-1,700 m above sea level), western Kenya. We found that the survivorship of An. gambiae larvae was reduced from 55 to 57% in habitats fully exposed to sunlight (open habitats) to 1-2% in habitats with full forest canopy coverage (forest habitats) and partial canopy coverage (forest edge habitats) in two out of three trials. The average daily water temperature of the open habitats was approximately 3-3.4 degrees C higher than the forest habitats. Insect species in the orders of Diptera, Coleoptera, and Odonata colonized the larval habitats, but the three habitat types differed greatly in the animal assemblage. Canonical correspondence analysis found that water temperature and amount of leaf litter were the significant variables associated with animal assemblages. Redundancy analysis revealed that openness and the presence of predatory animals were significantly related to An. gambiae survivorship. This result suggests that deforestation facilitates the survival of the immature stage of An. gambiae in the highland.
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http://dx.doi.org/10.1093/jmedent/42.3.270DOI Listing
May 2005

Changes in malaria vector densities over a twenty-three year period in Mae Hong Son Province, northern Thailand.

Southeast Asian J Trop Med Public Health 2004 Jun;35(2):316-24

Office of Disease Prevention and Control No. 10, Department of Diseases Control, Ministry of Public Health, Chiang Mai, Thailand.

Mae Hong Son Province in northwestern Thailand has a long history of malaria. During the last two decades the province has had one of the highest malaria incidences of all provinces in Thailand. Data were analyzed to determine whether the vector populations were stable or increasing during the last two decades and to determine the seasonal prevalence of the main vectors, and whether or not they were related to the malaria transmission peak, in the wet season. We compiled and analyzed accumulated entomological records from 1977 to 1999. The aim was to investigate long-term changes in mean densities of malaria vectors between two periods (1977-1989 and 1990-1999), and the differences in vector densities between two seasons (wet and dry). A total of 141,144 adult anophelines of 29 species were collected on indoor and outdoor human baits and animal baits during the study period. Of the main malaria vectors, the densities of Anopheles minimus s.l. and Anopheles maculatus complex increased significantly. Anopheles dirus s.l., however, was stable between the two periods. These vector populations were associated with consistently high malaria incidence in the province during the last two decades. An. minimus s.l. density was not significantly different between seasons. However, in the second period, both An. dirus s.l. and An. maculatus complex showed a tendency for higher wet season densities. This can explain the high malaria incidence in the rainy season in Mae Hong Son. Environmental and climatic factors seem to have been favorable for supporting a consistently high vector population in the province, and consequently a high malaria transmission rate during the period of study.
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June 2004

Diving ability of Anopheles gambiae (Diptera: Culicidae) larvae.

J Med Entomol 2004 Jul;41(4):810-2

Department of Vector Ecology and Environment, Institute of Tropical Medicine, Nagasaki, University, Nagasaki, Japan.

Anopheles gambiae Giles larvae usually live near the surface of shallow and temporary aquatic habitats. How deep the larvae can dive and how long they can submerge may be related to feeding efficiency and predator avoidance. This study examined diving behavior of An. gambiae larvae in the laboratory. We recorded diving depths and larval mortality of second and fourth instars in clean water and muddy water by using deep water (32-cm) and shallow water (20-cm) columns. In deep water columns with clean water, we found that 2% of second instars and 6% of fourth instars died from diving, whereas 3% of second instars and 11% of fourth instars died in muddy water. The fourth instars dived deeper in muddy water than in clean water. The mortality rates of the fourth instars subjected to diving stimulations were significantly higher than those in the shallow water columns. Therefore, larval diving behavior may offer the benefits of predator avoidance and food acquisition but also incur energetic costs and increased mortality.
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http://dx.doi.org/10.1603/0022-2585-41.4.810DOI Listing
July 2004

Molecular variation and phylogeny of the Anopheles minimus complex (Diptera: Culicidae) inhabiting Southeast Asian countries, based on ribosomal DNA internal transcribed spacers, ITS1 and 2, and the 28S D3 sequences.

Southeast Asian J Trop Med Public Health 2003 Dec;34(4):771-80

Department of Parasitology and Tropical Public Health, University of Occupational and Environmental Health, Kitakyushu, Japan.

Anopheles minimus (Theobald) is one of the most important vectors of human malaria in Southeast Asia. Morphological studies now have revealed five sibling species as its complex, designated as species A to E. The present study investigated the genetic divergence among An. minimus populations from four countries (Japan, China, Thailand and Indonesia), based on the DNA sequences data of the D3 (the third domain of the 28S ribosomal gene) and ITS2 (the second internal transcribed spacer of the ribosomal gene) is reported. The D3 and ITS2 phylogenetic trees, and the electrophoretic profile of ITS1 (the first internal transcribed spacer of the ribosomal gene) indicated that our An. minimus populations are comprised of three groups: the Japanese population as group I, the population from Guangxi Province of China (GX population) as group II, and others, as group III. The results showed the morphological similarity of group III and GX with the species complex A and B, respectively. It is interesting that both two species A (YN population) and species B (GX) occur in China, and that both species, An. minimus species A (LB-95 population) and the closer population An. flavirostris (Ludlow) (LB-00 population) appeared to be present on the Lombok Island of Indonesia, although in far separated localities. Moreover, this molecular evidence confirms the previous suggestion that the population from the Ishigaki Island of Japan should be classified as a new genetic status species E.
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December 2003

Pre- and postprandial mosquito resting behavior around cattle hosts.

J Am Mosq Control Assoc 2003 Sep;19(3):211-9

Department of Vector Ecology and Environment, Institute of Tropical Medicine, Nagasaki University, Nagasaki 852-8523, Japan.

Spatial distribution of mosquitoes around a bovine host was studied in November 1997 in northern Thailand (17 degrees 38'N. 99 degrees 23'E). Forty bamboo stakes were arranged 1 m apart, in 4 rays of 10, around a cow tethered in an open field. All mosquitoes found resting on the stakes were collected by aspiration between 7:00 p.m. and 11:00 p.m., sexed, and identified to species; and feeding status was categorized as fed or unfed. Collections were repeated over 8 nights, with and without the host cow. A total of 1,566 mosquitoes from 25 species (5 genera) was collected. Anopheles aconitus was the most abundant species (643 individuals), followed by An. peditaeniatus. Culex vishnui, and Cx. pseudovishnui. We found that the number of mosquitoes collected from the stakes was related to the presence of the cow host: the number of mosquitoes collected was unrelated to the compass point location of the bamboo stakes, with the exception of Mansonia uniformis; unfed mosquitoes preferred bamboo-stake resting sites that were closer to the host; the daily fed to unfed ratio of the dominant species was negatively correlated with the daily total number of mosquitoes collected; and fed and unfed mosquitoes clustered in interspecific heterogeneous groups around the host cow. Cluster analysis separated the species into 2 groups. The 1st consisted of 5 species with higher proportions of fed mosquitoes, whereas the 2nd, represented by 7 species, aggregated around the host within a distance of 1-4 m with lower proportions of fed mosquitoes. The interspecific variation in the distribution of unfed females was presumed to be due to a lack or feeding success. We discuss the significance of prebiting resting. In cases in which large numbers of mosquitoes are present, prebiting resting can be adaptive to avoid host defensive behavior triggered by attacking mosquitoes.
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September 2003

Life history effects of prey choice by copepods: implications for biocontrol of vector mosquitoes.

J Am Mosq Control Assoc 2003 Mar;19(1):67-73

Department of Vector Ecology and Environment, Institute of Tropical Medicine, Sakamoto 1-12-4, Nagasaki 852-8523, Japan.

Macrocyclops distinctus, Megacyclops viridis, and Mesocyclops pehpeiensis, which are common in rice fields during the summer season in Nagasaki, Japan, showed variable potentialities as biological control agents of larval Aedes albopictus, Culex tritaeniorhynchus, and Anopheles minimus in the laboratory. Macrocyclops distinctus and M. viridis, the largest copepod species, had fewer eggs within an egg clutch in nature than the smallest species, M. pehpeiensis, which also had a lower developmental time for sexual maturation (based on the appearance of the 1st clutch). Longevity as well as fecundity were influenced by nutritional conditions and varied significantly between the species. All species had shorter life spans when starved, but resistance to starvation was more pronounced in the larger species. All the species had lower clutch production when starved. Also, although the frequency of clutch production was high in M. pehpeiensis (M. pehpeiensis produced a clutch every 2 days, whereas M. distinctus and M. viridis took on average almost 3 days), total clutch production was far higher in the larger species. The copepods fed readily on mosquito larvae, with M. distinctus and M. viridis killing fewer Ae. albopictus than M. pehpeiensis, which, however, killed fewer An. minimus. These copepods exhibited a similar and limited predation against Cx. tritaeniorhynchus. Results of our study support the contention that these copepods have the potential to be used as biological control agents of immature mosquitoes. Also, our results give useful information on colony maintenance and field introduction. In particular, releasing copepods with Paramecium as food could increase their survival in the habitat of the targeted pest.
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March 2003

Leaf litter decay process and the growth performance of Aedes albopictus larvae (Diptera: Culicidae).

J Vector Ecol 2002 Jun;27(1):31-8

Department of Medical Entomology, Institute of Tropical Medicine, Nagasaki, Japan.

Larvae of the mosquito Ae. albopictus typically develop in small aquatic sites such as tree holes and artificial containers. Organic detritus, in particular decaying leaves, is therefore their major carbon source. Here we demonstrate the importance of leaf characteristics, and in particular their rates of decay, in determining the development and survivorship of larvae. We compared the effects of a rapidly decaying leaf, the maple Acer buergerianum (Angiospermae: Aceraceae) and a slowly decaying leaf, the camphor Cinnamomum japonicum (Angiospermae: Lauraceae), on the larval development of Ae. albopictus at different larval densities in laboratory microcosms. Overall, the maple leaves provided a better substrate and the observed growth patterns could be explained on the basis of a difference in nutritive and chemical contents of the two leaf types. At the highest population density, the duration of the larval period was much shorter in maple litter microcosms. Larval mortality gradually increased with population density in the camphor treatment. In contrast in the rapidly decaying leaf litter microcosms, mortality remained low even as densities increased. Mean pupal size was greater in the individuals fed on the rapidly decaying leaf litter as well as at lower density. Size is likely to be correlated with fitness in the field. In general, rapidly decaying leaf litter will favor mosquito growth resulting in quicker development and higher population sizes. This work emphasizes the importance of the local environment on the development of vector mosquitoes and has important implications for control.
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June 2002
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