Polarotaxis in egg-laying yellow fever mosquitoes Aedes (Stegomyia) aegypti is masked due to infochemicals

Aquatic and water-associated insects need to locate suitable bodies of water to lay their eggs in and allow their aquatic larvae to develop. More than 300 species are known to solve this task by positive polarotaxis, relying primarily on the horizontally polarized light reflected from the water surface. The yellow fever mosquito Aedes (Stegomyia) aegypti has been thought to be an exception, locating its breeding habitats by chemical cues like odour of conspecifics, their eggs, or water vapour. We now demonstrate through dual-choice experiments that horizontally polarized light can also attract ovipositing Ae. aegypti females when the latter are deprived of chemical cues: water-filled transparent egg-trays illuminated by horizontally polarized light from below gained a 94.2% higher total number of eggs than trays exposed to unpolarized light, but only when no chemical substances capable of functioning as cues were present. Ae. aegypti is the first known water-associated insect in which polarotaxis exists, but does not play a dominant role in locating water bodies and can be constrained in the presence of chemical cues.     

Properties of baked foams based on cassava starch, sugarcane bagasse fibers and montmorillonite

The objectives of this work were to develop biodegradable trays from cassava starch, sugarcane fibers and Na-montmorillonite (Na-MMT) using a baking process and to study the effects of these components on the microstructure and physicochemical and mechanical properties of the trays. All formulations resulted in well-shaped trays with densities between 0.1941 and 0.2966 g/cm³. The addition of fibers and Na-MMT resulted in less dense and less rigid trays. As observed in the water sorption isotherms, the increase in the equilibrium moisture content was more pronounced when the samples were stored at RH (relative humidity) above 75%. The foams had high water absorption capacities (>50%) when immersed in water (1 min). The studied processing conditions resulted in good nanoclay dispersion, leading to the formation of an exfoliated structure. The trays developed in this study represent an alternative for the packaging of foods with low water contents.     

四种昆虫饲养设备在昆虫学实验室的应用比较

本文比较了智能人工气候箱、智能型光照培养箱、全自动控制养虫室和简易型养虫室等4种常用昆虫饲养设备的优点和不足，分析了不同设备的适用情况。以西北农林科技大学应用昆虫学重点实验室正在应用的昆虫饲养设备为例，详细介绍了几种设备使用中的注意事项及维护方法。智能型人工气候箱和全自动控制养虫室可用于饲养对温度、湿度及光照要求较高的寄主植物及昆虫；智能型光照培养箱适用于对温度和光照有一定要求而对湿度要求不严格的试验；简易养虫室造价低，较容易建立，适用于饲养普通试验观察的昆虫种群。本文对4种设备的比较为农业科学研究中昆虫饲养设备的选择及管理维护提供了参考。     

Larval mortality of Culex tarsalis and Aedes aegypti when reared with different concentrations of Tetrahymena pyriformis

The paucity of information on infection and pathogenicity of mosquito larvae by ciliates under experimental conditions prompted the evaluation of the relationship between a clone of Tetrahymena pyriformis and two species of mosquitoes, Aedes aegypti and Culex tarsalis. A significant difference in mortality was observed between the two mosquito species when they were exposed to identical concentrations of ciliates. In rearing trays containing high concentrations of T. pyriformis, 76.3% of the C. tarsalis larvae died. Under similar conditions, death occurred in less than 3.0% of the A. aegypti larvae. Three figures illustrate daily results of these studies. Three criteria for facultative parasites are listed, and one, route of entry into the host, is discussed in detail.     

Effects of glyoxal cross-linking on baked starch foam

Starch trays and plates were prepared from native corn starch and corn starch cross-linked with glyoxal at different concentrations (0.126, 0.269, 0.271, 0.468 g/kg) using a foam baking process. The effect of cross-linking on baking parameters, including density, colour, water absorption, and tensile and flexural properties, was determined. Also, the morphologies of the trays were examined using a scanning electron microscope. Cross-linking considerably reduced the baking time, density and water absorption of the trays. Trays made from starch cross-linked with 0.126 and 0.269 g/kg glyoxal presented the best properties, with a homogenous microstructure and smooth surface quality. These trays had the lowest density (0.27 g/cm³) and had approximately 53% reduction in water absorption. Moreover, both the tensile and flexural strain of these foams was significantly higher than other foams.     

Performance of Five Food Regimes on Anopheles gambiae Senso Stricto Larval Rearing to Adult Emergence in Insectary

Background

Rearing of Anopheles gambiae s.s mosquitoes in insectary with quality cheap food sources is of paramount importance for better and healthy colony. This study evaluated larval survival and the development rate of aquatic stages of An.gambiae s.s under five food regimes; tetramin fish food (a standard insectary larval food), maize pollen, Cerelac, green filamentous algae and dry powdered filamentous algae.

Methods

Food materials were obtained from different sources, cerelac was made locally, fresh filamentous algae was taken from water bodies, dry filamentous algae was ground to powder after it was dried under shade, and maize pollen was collected from the flowering maize. Each food source type was used to feed three densities of mosquito larvae 20, 60, and 100 in six replicates each. Larval age structure was monitored daily until pupation and subsequently adult emergence. Tetramin was used and taken as a standard food source for An. gambiae s.s. larvae feeding in Insectary.

Results

Larval survivorship using maize pollen and Tetramin fish food was statistically insignificant (P = 0.564). However when compared to other food regime survivorship was significantly different with Tetramin fish food performing better than cerelac (P<0.001), dry algae (P<0.001) and fresh algae (P<0.001). The pupation rates and sex ratio of emerging adults had significant differences among the food regimes.

Conclusion

The findings of this study have shown that maize pollen had closely similar nutritional value for larval survivorship to tetramin fish food, a standard larvae food in insectary. Further studies are required to assess the effect of food sources on various life traits of the emerged adults.     

Combining GIS application and climatic factors for mosquito control in Eastern Province,Saudi Arabia

This study aims to determine the effect of climatic factors (temperature, relative humidity and rainfall) on mosquito abundance and to map mosquito larva breeding sites using GIS application in Eastern Province, Saudi Arabia. The data pertaining to larval and adult mosquito abundance/distribution and climatic factors were collected for the study period of 2014. Bi-variate and multivariate analyses were performed to determine the relationship between mosquito abundance and climatic factors (temperature, relative humidity and rainfall). The utilization of GIS with GPS facilitates to identify and map larva breeding sites in the study area. The result showed strong negative correlation between mosquito abundance and temperature while there appeared a strong positive correlation with relative humidity and moderate positive correlation with rainfall. Low mosquito abundance was observed at high temperatures whereas high and moderate mosquito abundance was observed at high humidity and during rainy months, respectively. In the adult mosquito, the regression model for three climatic factors (temperature, RH and rainfall) and other factors showed a variation of 84.5% of the variance accounted for the climatic factors while the remaining 15.5% were attributed to other factors. In larva, 64.3% of the variance accounted for climatic factors, and the remaining 35.7% attributed to other factors such as the presence of vegetation, waste materials and water reservoirs such as ditches. In comparison, the larva seems influenced by the presence of vegetation, waste material, water reservoirs and ditches and less influenced by climatic factors than the adult mosquito. Development of a risk map by considering the flying distance of the adult mosquito from the studied sites showed three major clusters where a recommendation for management control program was suggested.     

Laboratory testing of a lethal ovitrap for Aedes aegypti

Laboratory tests were conducted to determine the feasibility of making the mosquito ovitrap lethal to Aedes aegypti (L.) when they attempt to oviposit in the trap. Heavy-weight velour paper strips (2.54 x 11 cm) were used as an alternative to the wooden paddle normally provided as a substrate for mosquito oviposition. The paper strips were pretreated with insecticide solutions and allowed to dry before being used in oviposition cups of 473 ml capacity, filled with water initially to within 2.5 cm of the brim. Insecticides chosen for their quick knock-down efficacy were bendiocarb 76% WP (1.06 mg a.i./strip) and four pyrethroids: permethrin 25% WP (0.16 mg a.i./strip), deltamethin 4.75% SC (0.87 mg a.i./strip), cypermethrin 40% WP (2.81 mg a.i./strip), and cyfluthrin 20% WP (0.57 mg a.i./ strip). For experimental evaluation, two oviposition cups (one with an insecticide-treated strip and one with an untreated strip) were placed in cages (cubic 30 cm) with gravid female Ae. aegypti mosquitoes (aged 6-8 days) from a susceptible laboratory strain. Mortality-rates of female mosquitoes were 45% for bendiocarb, 47% for permethrin, 98% for deltamethrin, 100% for cypermethrin, and 100% for cyfluthrin. Young instar larvae added to the treated cups died within 2h. After water evaporation from the cups for 38 days, fresh mosquito females had access to previously submerged portions of the velour paper paddle, and mortality rates of 59% or more occurred. Cups that had water (360 ml) dripped into them, to simulate rain, produced female mosquito mortality rates of > 50% and all larvae died within 3 h of being added. These tests demonstrate that the ovitrap can be made lethal to both adults and larvae by insecticidal treatment of the ovistrip. Field efficacy trials are underway in Brazil to access the impact of this simple, low-cost, environmentally benign approach on populations of the dengue vector Ae. aegypti.     

三种性信息素诱捕器对烟田棉铃虫的诱捕效果比较

比较了笼罩、水盆、盘式粘胶诱捕器对烟田棉铃虫的诱捕效果。结果表明,3种诱捕器的诱蛾量变化趋势基本一致,其中笼罩诱捕器的诱蛾量最大,显著高于另外两种诱捕器,且诱捕效果比较稳定。水盆、盘式粘胶诱捕器诱蛾量差异不显著。笼罩诱捕器更适用于烟田棉铃虫成虫的防治及监测。     

Bioassays for comparative infectivity of mermithid nematodes (Romanomermis iyengari,Romanomermis culicivorax and Strelkovimermis spiculatus) for culicine mosquito larvae

Two improved bioassays were developed to establish infectivity baselines for selection experiments using mermithid nematode variants. Comparative infectivity of Romanomermis iyengari, Romanomermis culicivorax and Strelkovimermis spiculatus using larvae of three mosquito spp. Aedes sierrensis, Aedes aegypti and Culex pipiens were evaluated with “plate” and “tray” bioassays at selected intensity of infections. Using the “plate” bioassay, single mosquito larvae were immersed in 2 ml of water within individual depressions of 12-well, polystyrene tissue culture plates. One, three, or five preparasitic juveniles (J2) were added to each well. In the “tray” bioassay, polyethylene trays containing 500 ml water and 100 mosquito larvae were exposed to 500 (5:1, nematode:insect host) or 1000 (10:1) J2s. Percentage infection (PINF, infectivity) and intensity of infection (IINF, #nematodes per infected larvae) number were determined only after emergence of post-parasitic J3 juveniles. Under the bioassay conditions, all three species of nematodes resulted in infections in all mosquito hosts, but R. iyengari exhibited better effectiveness in the parasitism of mosquito larvae. The three species of mosquitoes presented high levels of susceptibility to each of the three species of nematodes, but in general Cx. pipiens and Ae. sierrensis were slightly more susceptible than Ae. aegypti. The “plate” bioassay was more efficient in measurement of infectivity of the mermithid species and in establishing baseline characteristics for these mosquito-parasitic nematodes. The “tray” bioassay was an effective bioassay for large cohorts of both infective juveniles and host larvae and, potential for field interactions.     

Effects of crowding on populations of Aedes albifasciatus larvae under laboratory conditions

Aedes (Ochlerotatus) albifasciatus(Macquart 1838) (Diptera: Culicidae) is a neotropical flood water mosquito, incriminated as the main vector of the western equine encephalitis virus, and which affects beef and milk production in central Argentina. The short time required to hatch and develop from egg to adult, usually in temporary pools, suggests a strategy which allows for exploitation of transient pools, thus evading predation and interspecific competition. Under these conditions intra specific competition could represent a major density-dependent source of larval mortality, but the relative importance of density-dependent regulation of mosquito populations has generated controversy. Therefore we examined the effects of larval density on basic population characteristics of Ae. albifasciatusin the laboratory. Larvae were obtained by synchronous hatching of eggs laid by field-trapped females. Emerging larvae (L1) were used to build cohorts of different initial densities, kept in plastic trays with 400 ml of distilled water, and food supplied daily during the first 10 days (0.1 g per larvae day^–1). Age-specific development time and specific and relative mortality were estimated, and their relation to initial larval density was assessed through linear and non-linear regressions and correlation analysis. First hatching was registered 3 h after flooding the eggs. Higher levels of pre-adult mortality were detected in groups with higher densities. Specific mortality and average time to enter a stage of L1 to L3 could directly be related to initial larval density, but no significant relations were found for L4 and pupae. Results suggest that crowding could be a factor capable of regulating the density of natural populations of Ae. albifasciatus.     

The influence of aquatic predators on mosquito abundance in animal drinking troughs in New Zealand

The occurrence and abundance of mosquito populations may be associated with the abundance of predators. We examined the relationship between aquatic predators and populations of mosquitoes in animal water troughs in Waikanae, New Zealand. We also investigated the effects of water volume and environmental factors (temperature, rainfall, wind speed, humidity, and pressure) in order to further understand factors influencing mosquito and predator populations. Logistic regression indicated that the presence or absence of mosquitoes was primarily affected by three factors: predator abundance, week of observation, and water volume. Pearson's correlation indicated that the presence of predators had a positive correlation with water volume (r²= 0.176, p< 0.05). Otherwise, the presence of mosquito larvae in water troughs was negatively correlated with water volume (r²=?0.159, p=0.022) and wind speed (r²=0.142, p=0.041). We established a translocation experiment in which predators or mosquitoes were moved between troughs in order to examine the prey survival rate after exposure to Anisops wakefieldi predators. The survival rate of mosquitoes was not significantly different, between 0–0.1%, irrespective of the number of predators translocated (1–9) or the initial mosquito density (20–70 larvae). Our results suggested that A. wakefieldi predators may have the potential to be a promising biological control tool for the control of mosquito populations by altering mosquito population dynamics.     

Oviposition diapause and other factors affecting the egg-laying of Phlebotomus papatasi in the laboratory

Stimuli which modulate oviposition of P. papatasi were investigated to improve insectary breeding efficiency. Oviposition and survival of gravid females were observed weekly during April-December 1987, in plastic cages at 28 +/- 1 degrees C with L:D 17:7. Oviposition of controls was subject to seasonal variation despite the relatively uniform insectary conditions. From April to mid-October (summer), mean weekly oviposition ranged from 11.6 to 18.6 eggs per fly, dropping to 1.4 eggs/fly in November (winter). Monthly yields of eggs were found to correlate with the seasonal cycle of ultraviolet (UV) radiation in sunlight. This was attributed to an endogenous rhythm since the flies were not normally exposed to UV under insectary conditions. Short exposure to UV sources of 254 nm and 312 nm, but not white light, raised the low rate of oviposition in October-November from 1.4 to 16.8-29.6 eggs/female/week, but female mortality also increased highly significantly. It is suggested that the seasonal oviposition cycle of P.papatasi is set by levels of UV irradiation. In the warm season oviposition was promoted, as compared to controls, by furrows in plaster of Paris lining the bottom of cages (29.6 v. 10.2 eggs/female) and by cow manure in the cages (39.7 v. 18.2 eggs/female), but the combination of both stimuli gave no greater fecundity (40.9 v. 20.9 eggs/female). Oviposition decreased when larvae were present (3.9 v. 15.0 eggs/female) and in half-volume cages (3.9 v. 12.5 eggs/female/week). Under standard insectary conditions, mean weekly mortality-rates of P.papatasi females were 18.3 +/- 4.8% in October-November and 36.5-59.1% during the warmer months. None of the experimental conditions yielded any significant improvement in survival-rates.     

Natural enemies of Bathycoelia thalassina (Herrich-Schaeffer) (Hemiptera: Pentatomidae), a pest of cocoa in Ghana

The natural enemies of Bathycoelia thalassina in Ghana are surveyed and their effect and suitability as natural controls of the pest in the field and in the insectary assessed. Mass rearing methods in the insectary for the most common parasites, Trissolcus spp. and Cylindromyia cribrata are described.     

驱蚊、灭蚊植物资源及其应用前景分析

蚊虫吸食人血、传播疾病,严重危害人类健康。长期以来,化学合成杀虫剂由于驱灭蚊虫的效果好、持续时间长,一直占据主要地位,但长期使用化学合成杀虫剂,不仅可使蚊虫产生抗药性,而且还会造成环境污染,因此环境友好型的蚊虫防治手段日益受到人们的关注。该论文基于蚊虫与水、植物等环境因素关系的分析,阐述了植物在防治蚊虫方面的潜力;概括了我国的驱蚊、灭蚊植物资源及开发利用现状;探讨了驱蚊、灭蚊植物在防治蚊虫产品开发、生态保健型园林绿地和健康湿地系统建设等方面应用情况并展望了驱蚊、灭蚊植物资源开发利用的广阔前景,以期为蚊虫的生态防治提供新思路。     

The biology of Bracon celer as a parasitoid of the olive fruit fly

A series of laboratory experiments was conducted on a colony of Bracon celer Szépligeti (Hymenoptera: Braconidae) reared on the olive fly, Bactrocera oleae (Rossi) (Diptera: Tephritidae). Female B. celer preferentially probe and oviposit into olives containing late third-instar fly larvae. The parasitoid develops as a solitary, ectoparasitic idiobiont. Mean development time (oviposition to adult eclosion) at 22 °C was, for females, 36±1 (SE) days, and for males, 34±1 days. The mean longevity of adult female wasps when provided honey and water was significantly greater than when they were provided water alone, or nothing. The females produced an average of 9.7±7.2 progeny during their lifetimes, but production levels in the insectary colony suggested that this level of fecundity was artificially low and could be improved. The discrepancy may be a consequence of constraints on oviposition behavior imposed by the experimental design. The results are discussed with respect to insectary production methods and the potential use of B. celer as a biological control agent for olive fly in California.     

A field study of potential ecological costs of resistance by ‘stem ducking’ in tall goldenrod,Solidago altissima

Culex quinquefasciatus Say (Diptera: Culicidae) is an abundant urban mosquito that is the vector of filariasis. Breeding in septic tanks, where there are very high levels of bacterial food, it is likely to have a different reaction to crowding compared with other mosquitoes. To test for the presence and type of crowding effects, four larval densities of C. quinquefasciatus varying from 0.4 to 3.2 larvae ml^?1 of water were reared in tubes. Mortality was found to greatly increase at densities above 0.8 larvae, whereas larval duration increased even above 0.4 larvae ml^?1. Changing the water in the tubes daily gave a small (but significant) response in reducing mortality and larval duration. However, when larvae kept at a low density shared the same water with larvae at high density, there was no chemical influence on their growth rate and mortality. The effect of crowding was primarily due to physical disturbances between larvae. When larvae were kept at a high density in the same volume of water, but in shallow trays with a large surface area and therefore much less contact between them, mortality was the same as for the lowest density. There was still, however, a significant increase in larval duration from 8.6 days at 0.4 larvae ml^?1 to 12.1 days at 3.2 larvae ml^?1. It is therefore concluded that the larvae respond to physical rather than chemical factors by prolonging larval development and having some increase in mortality.     

Experimental colonization of sand, gravel and stones by macroinvertebrates in the Acheron River, southeastern Australia

SUMMARY. 1. The contribution of drift to macroinvertebrate colonization was studied over 10 days using pairs of substratum-filled trays, one suspended above the streambed (and thus able to be colonized by drift only) and one buried flush with the streambed (and thus open to colonization from all directions). Trays were filled with sand, gravel or stones.
2. Colonization of sand-filled trays was rapid, being completed within 24h (i.e. no subsequent change in numbers of individuals per tray); colonization of gravel or stone-filled trays was not completed by the end of the experiment.
3. Drift contributed an average of 86% of the colonizing fauna of the sand-filled trays, 36% of the fauna of the gravel-filled trays and 25% of the fauna of the stone-filled trays. The low contribution of the drift to the gravel and stones is at odds with some studies which, using similar techniques, suggest that drift is the primary source of colonizing individuals.
4. Most individual species showed low contributions by drift to colonization, with the majority having contributions under 66%.
5. Distinct differences were noted between the fauna colonizing the sand-filled trays and those colonizing the gravel or stone-filled trays (which were similar).
6. Several species common in the drift were rare in the colonizing fauna and several species which were common colonizers were absent or rare in the drift.     

Heteropteran insects as mosquito predators in water jars in southern Vietnam

Residents of Vietnam living in areas with water shortages and/or poor tap water maintain water storage containers, such as jars, in and around their domiciles in order to store water used in daily life. Although these water jars are known to be important breeding sources of the Aedes mosquito, use of chemical larvicides in such containers is legally prohibited in Vietnam. In this study, we identified the dominant mosquito insect predators in water jars in and around residences located in Tan Chanh, Long An, southern Vietnam. Of 3,646 Heteroptera collected from such jars, Corixidae (Micronecta spp.) and Veliidae (Microvelia spp.) were revealed to be the dominant predators. Polymerase chain reaction (PCR) analysis revealed that 40% of Micronecta and 12% of Veliidae had Aedes aegypti‐positive reactions, indicating that these two dominant Heteroptera are important predators of Ae. aegypti. Our results suggest that aquatic Heteroptera may be an important mosquito control agent in addition to the currently used copepods.