Search

Insects visiting sporocarps of Elfvingia applanata, a wood-rotting bracket fungus, were examined in Kyoto, central Japan. Mycodrosophila flies (Drosophilidae: Diptera) were predominant and visited the spore-producing sporocarps exclusively. They were observed feeding on the spores, and a number of spores seemed to be alive even after having passed through insects’ digestive tracts. In addition, the insects attached a number of spores on their body surfaces. In a rearing experiment with insects caught from E. applanata sporocarps, Mycodrosophila flies excreted 7700–469 000 and dropped 10–000–329 000 of viable spores during 48 h after collection. They were supposed to migrate among the sporocarps of other bracket fungi growing on different logs or stumps, suggesting that Mycodrosophila flies may act as spore-dispersal agents for E. applanata.

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.

The composition and food habits of insects visiting fungi of two Dictyophora species, D. indusiata (Vent. & Pers.) and D. duplicata Fisch, were examined in Furano, northern Japan, and in Kyoto, central Japan. As well as field work being carried out, the quantity and the viability of spores in the recta of drosophilid and muscid flies were examined in vitro. Although the composition of insects varied locally and temporally, most of the insects were observed to feed on gleba, which contains spores. Among the insect assemblies, a few insects were specialized for mycophagy but most were secondarily or not at all mycophagous. Although Dictyophora-feeders rarely attached the spores on their body surfaces, they contained a quantity of spores in their gut, which was estimated to be about 35 000–240 000 for drosophilids and about 1.7 million for muscids. Those spores showed high germination rates, which were not significantly different from the intact spores. Thus, spores of Dictyophora are dispersed as excrement through the gut of Dictyophora-feeding insects but not as adherers on the insect body.

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.

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.

We compared aquatic invertebrate diversity in paddy fields under traditional and modern management practices. We also examined the general factors that may be related to diversity within each paddy field. The Kitadan area was farmed with traditional management practices, with much longer periods of irrigations compared with the Kahoku area, which was farmed with modern agricultural practices using intermittent irrigation. We measured physicochemical factors and collected aquatic invertebrates from the two areas. Collected animal specimens were taxonomically identified and classified based by desiccation tolerance ability. At Kitadan, the total biodiversity parameters increased over time, while, biodiversity fluctuated temporally at Kahoku. The mean Shannon-Wiener diversity index was higher at Kitadan than at Kahoku. However, the mean taxon richness was not significantly different between locations. Both paddy fields were dominated by highly desiccation-tolerant invertebrates at the beginning of the rice cultivation period. Over time, the ratio of desiccation-sensitive invertebrates increased more at Kitadan than at Kahoku. Our canonical correspondence analysis showed that the time since rice transplanting, water permanence, pH, water depth, and chlorophyll a were significant factors affecting faunal assemblage composition. Our results indicate that water management practices have important roles in the aquatic biodiversity of paddy-field ecosystems.

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 10 min 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 A. baimaii (4/25, 16.0%) and A. 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. © 2012 Elsevier B.V. All rights reserved.

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 (χ2 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 (Bi = 0.63) and An. minimus s.l. (Bi = 0.24) showed strong relative preferences (Bi) 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.

Although larvae feeding and food source are vital to the development, survival and population regulation of African malaria vectors, the prey organisms of Anopheles gambiae larvae in the natural environment have not been well studied. This study used a molecular barcoding approach to investigate the natural diets of Anopheles gambiae s.l. larvae in western Kenya. Gut contents from third- and fourth-instar larvae from natural habitats were dissected and DNA was extracted. The 18S ribosomal DNA gene was amplified, the resulting clones were screened using a restriction fragment length polymorphism method and nonmosquito clones were sequenced. Homology search and phylogenetic analyses were then conducted using the sequences of non-mosquito clones to identify the putative microorganisms ingested. The phylogenetic analyses clustered ingested microorganisms in four clades, including two clades of green algae (Chlorophyta, Chlorophyceae Class, Chlamydomonadales and Chlorococcales families), one fungal clade, and one unknown eukaryote clade. In parallel, using the same approach, an analysis of the biodiversity present in the larval habitats was carried out. This present study demonstrated the feasibility of the barcoding approach to infer the natural diets of Anopheles gambiae larvae. Our analysis suggests that despite the wide range of microorganisms available in natural habitats, mosquito larvae fed on specific groups of algae. The novel tools developed from this study can be used to improve our understanding of the larval ecology of African malaria vectors and to facilitate the development of new mosquito control tools.

金沢大学理工研究域 自然システム学系, キノコ類より発生した日本産フンコバエ科(改称)7種を記録した。日本においてフンコバエ類がキノコより発生した例は従来知られておらず, 今回が初めての記録である。フンコバエ類と発生したキノコ種は以下のとおりである。アシマダラオオフンコバエ, 新称Crumomyia annulus (Walker), キララタケ;ヤマトオオフンコバエ, 改称(マダラオオハヤトビバエ)C. nipponica (Richards), アミガサタケ;アシジロツヤホソフンコバエ, 新称Minilimosina (Svarciella) furculisterna (Deeming), キララタケ;モリフンコバエ, 新称Paralimosina japonica Hayashi, アミガサタケ;ヒメフンコバエ, 改称(ヒメハヤトビバエ)Spelobia luteilabris (Rondani), キララタケ・ヒトヨタケ・オオイチョウタケ・シカタケ;ホソカドマルフンコバエ, 改称(ホソカドマルハヤトビバエ)Terrilimosina longipexa Marshall, キララタケ;コガタカドマルフンコバエ, 改称(コガタカドマルハヤトビバエ)T. nana Hayashi, キララタケ。なお本科の科名には従来ハヤトビバエ科という和名が使われてきたが, 飛翔力が非常に弱い本科には実体に合わないので, 英名Lesser dung flyにちなみ, フンコバエ科という和名を新たに提唱した。 Seven species of the lesser dung flies emerged from fungi are recorded. Japanese records of fungi as food for sphaerocerid larvae are presented here for the first time. Two species, Minilimosina (Svarciella) furculisterna (Deeming, 1969) and Terrilimosina longipexa Marshall, 1987 are newly recorded from Hokkaido.

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.

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.

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.

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.

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.

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.

Experiments, using the capture-mark-release-recapture technique inside large nets, were carried out in Chiang Mai, northern Thailand, to examine heterogeneity in the host preference of Japanese encephalitis (JE) vectors. A significantly higher proportion of the vector species that were initially attracted to a cow fed when released into a net with a cow than when released into a net containing a pig. However, Culex vishnui individuals that had been attracted to a pig had a higher feeding rate in a net containing a pig rather than a cow. When mosquitoes were given a choice by being released into a net containing both animals, they exhibited a tendency to feed on the host to which they had originally been attracted. This feeding preference was, however, not shown by the offspring of pig-fed individuals. We have therefore shown evidence of physiological/behavioural conditioning in the host preference of JE vectors rather than genetic variability. Our results suggest that effective control of JE might be achieved by increasing the availability of cows (the dead-end hosts of JE virus) to deflect the vectors from pigs (the amplifying host). The behavioural imprinting which we have found would tend to re-inforce the initial tendency of the vectors to bite cows.

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.