SIGNIFICANCE OF PASSIVE MIGRATION IN EVOLUTION OF INSECTICIDE RESISTANCE IN THE MOSQUITO CULEX PIPIENS (DIPTERA: CULICIDAE)

In order to determine the combined effects of migration and gene flow on evolution of insecticide resistance in the mosquito Culex pipiens, four samples were collected in China, among which two were collected along the railway from Beijing to Guangzhou. Bioassay data showed that the resistance levels of the four populations to dichlorvos were high and to parathion moderate as compared with the susceptible strain and there was no significant difference among the four populations to the same organophosphate (OP) insecticide. Starch electrophoresis was done to identify the frequency of known overproduced esterases and to analyze genetic diversity among various populations by electrophoretic polymorphism of five presumably neutral loci. The results indicated that the gene flow between populations existed and the number of effective migrants (Nm) was related to collection geography (Nm from 1.67 to 40.07). In contrast with lower genetic differentiation between two nearby populations (between GZ and ZS, ZZ and SQ) and higher genetic differentiation between two distant populations (between GZ and ZZ), there was a significant and inconsistent difference in the distribution of resistance alleles, A2‐B2 when explained only with active migration. This divergent situation could be straightened out when considering passive migration (such as railway transport) which increased the spread of A2‐B2 along the railway, i.e., in GZ and ZZ. The resistance alleles, A2‐B2, dispersing to around areas by active migration suffered from the limitation of gene flow and the speed of invasion.     

被动迁移在抗性进化中的作用

为了明确迁移和基因交流在杀虫剂抗性基因进化中的作用,我们从四个不同的地区采集有机磷抗性的库蚊野生种群,利用淀粉电泳鉴定了各种群中存在的已知过量产生酯酶的分布频率,并通过5个假定的中性位点的电泳多态性分析了种群间的遗传多样性。结果表明种群间的基因交流是存在的,遗传分化与地理位置存在一定关系,而抗性等位基因A2一B2的分布却与种群间的遗传分化不一致。对这种差异的解释是：被动迁移(铁路运输等)加速了抗性基因的交流,而当抗性基因以自然迁飞的方式向周围地区扩散时,却是一个相对缓慢的过程。     

VOLATILE CONSTITUENTS OF CHAROPHYTES AS OVIPOSITION DETERRENTS OF CULEX PIPIENS PALLENS (DIPTERA: CULICIDAE)1

Four populations of charophytes (including three species), Chara inconnexa T. F. Allen (populations 1 and 2), C. vulgaris L., and Nitellopsis obtusa (Desv.) J. Groves, were studied for effective chemicals as oviposition deterrents of Culex pipiens pallens. The charophyte volatile organic compounds (VOCs) were retained in Tenax GR, subsequently desorbed using a thermal desorption cold trap injector (TCT), and analyzed by gas chromatography/mass spectrometry (GC/MS) to elucidate that charophytes have repellent properties. C. inconnexa (1) and C. inconnexa (2) exhibited strong repellent activities, and C. vulgaris showed some repellent activity against C. pipiens pallens with terpenes and benzothiazole playing major roles, while N. obtusa lacked those compounds and did not have an effect. These results suggest that charophytes have potential application as pesticides, but there are interspecific differences. In addition, benzene hydrocarbons were among the volatiles in Chara but not in N. obtusa, implying that some charophytes could be used to absorb these compounds.     

ESTERASE PHENOTYPES IN NATURAL POPULATIONS OF CULEX PIPIENS PALLENS (DIPTERA: CULICIDAE) AND THEIR VARIATIONS UNDER INSECTICIDE SELECTION*

Abstract Three populations of Culex pipiens pallens Coquillett, from Hangzhou, Linhai and Jinhua, were determined for their probability of resistant esterase phenotypes. Further, each population was selected with dipterex, chlorpyrifos, temephos and malathion at a given dose of 60%‐70% mortality and was determined for the variation of resistant esterase phenotypes in its offspring. The results indicated that esterase B₁ phenotype was dominant in three populations although different natural populations have a different probability distribution of esterase B phenotypes. Insecticide selection showed that various esterase loci seemed to have different selective advantages under different insecticide pressures. The esterase B₁ phenotype was selected under temephos, and the esterase B₂ phenotype was selected under dipterex and chlorpyrifos. Except for the esterase B₁ phenotype, the heterozygote of B₁/B₂ phenotypes was detected under malathion pressure. These results are discussed in relation to the selective advantages of esterase genes to OP pressure and mosquito control strategies.     

THE EFFECT OF TEMPERATURE ON EGGS AND IMMATURE STAGES OF CULEX ANNULIROSTRIS SKUSE (DIPTERA: CULICIDAE)

Abstract
No immature stages of Culex annulirostris were found during field sampling in 1979–1980 when the average water temperature was < 17 °C; they reappeared when the average water temperature was 19 °C and reached the peak density (mean 107 immatures/cylinder) at 26.5 °C.
The effect of 6 temperatures (15–40°C) on egg hatching, development and survival of the immature stages of Cx annulirostris in the laboratory showed that at 15 and 40°C, eggs failed to hatch and larvae died in the first instars. The optimum temperatures for egg hatching and the survival of immature stages were 25 and 30°C. At these temperatures, 85 and 82% respectively of egg rafts hatched, the mean number of larvae per raft was 258 ± 9.8 and 260 ± 11.4 with immature survival of 83.5 and 79.0% respectively. Mean time to hatch at 20–35°C ranged from 1.2 d (35°C) to 2.9 d (20 °C). Developmental times from first instar to adult ranged from 7.1 d (35 °C) to 25.2 d (20 °C). The threshold for development of the immatures was 15.6 ± 2.5°C and the thermal constant was 142.9 ± 26.5 day—degrees (incubation temperatures 20–35°C). At less suitable temperatures of 20 and 35 °C, hatching (57.5 and 45%), number larvae per raft (mean 139.8 ± 9.8 and 102.6 ± 14.2) and survival were low.     

POPULATION STRUCTURE AND DYNAMICS OF SELECTED GENES IN THE MOSQUITO CULEX PIPIENS

To determine the outcome of the combined effects of gene flow, genetic drift, and selection on the evolution of insecticide-resistance genes in the mosquito Culex pipiens, samples were collected along three transects crossing treated and nontreated areas in northern Spain and southern France. Electrophoretic polymorphisms of five presumably neutral genes disclosed that differentiation among samples was low, and that both Wright F-statistics and Slatkin private-alleles methods provided a high estimate for Nm. In contrast, there was a strong differentiation in the distribution of resistance genes closely associated with insecticide treatments. These divergent situations are explained in relation to both the very recent origin of some resistance genes that are still localized geographically (A2-B2 and C1), and the high fitness cost of the older and ubiquitous ones in nontreated areas (A1, A4-B4, and Ace^R).     

淡色库蚊 (Culex pipiens pallens Coquillett)的抗性酯酶表现型及其在杀虫剂压力下的变化趋势(英文)

对来自杭州、临海和金华三个城市的淡色库蚊种群进行了抗性酯酶表现型频率分布的测定和分析 ,同时对三个种群进行双硫磷、敌百虫、毒死蜱和马拉硫磷等四种有机磷杀虫剂的抗性品系筛选 ,逐代测定和分析各种群在不同杀虫剂压力下 ,其抗性酯酶表现型频率分布的变化。结果表明 ,三个自然种群中都存在酯酶B1 、B2 纯合表现型及酯酶B1 /B2 杂合表现型 ,其中酯酶B1 纯合表现型占优势。各自然种群中的抗性酯酶表现型频率分布有差异。经过杀虫剂的逐代筛选 ,各种群相对于某一杀虫剂的压力 ,表现出选择较为单一的抗性酯酶表现型的趋势 :双硫磷有利于酯酶B1 纯合表现型的选择 ,敌百虫和毒死蜱有利于酯酶B2 纯合表现型的选择 ,马拉硫磷则似乎有利于酯酶B1 纯合表现型和酯酶B1 /B2 杂合表现型的选择 ,但酯酶B1 纯合表现型相对于B1 /B2 杂合表现型来说 ,对马拉硫磷抗性更强一些。根据研究结果 ,就蚊虫的抗性酯酶基因对不同杀虫剂的选择优势及相应的蚊媒控制策略进行了讨论。     

中国库蚊属库状蚊亚属一新种：双翅目：蚊科

本文记述库蚊属库状蚊亚属一新种——刺端库蚊,新种Culez(Culiciomyia) spiculostylussp.nov.。本新种阳茎侧板背角短粗而端钝,密布小齿并形成明显的齿簇为其独具特征。模式标本系1985年8月11日采自云南省西双版纳勐腊县新公社一积水坑,存放于贵阳医学院生物学教研室。     

库蚊属一新种记述：双翅目：蚊科

本文记述发现于云南省的库蚊属一新种,巨叶库蚊Culex(Eumelanomyia)megafolius sp.nov.并对其亲缘种巨端库蚊 Cx.(Eum.)macrastylus和山栖库蚊 Cx.(Eum.)oresbius进行分类讨论。