Effects of larval density and feeding rates on larval life history traits in Anopheles gambiae s.s. (Diptera: Culicidae)

Mosquito larval habitat determines the fitness, survivorship, fecundity, and vector capacity of emerging adults. We manipulated larval density and food provisioning in the laboratory to determine their effects on a number of life history parameters of Anopheles gambiae. Larval mortality was positively correlated with larval density. In addition, increased density skewed sex ratios that favored females.     

Effects of acorn abundance on density dependence in a Japanese wood mouse (Apodemus speciosus) population

We analysed the effects of Quercus crispula acorn abundance on the density dependence of the large Japanese wood mouse Apodemus speciosus using time series data (1992–2007). The data were obtained in a forest in northern Hokkaido, Japan, by live-trapping rodents and directly counting acorns on the ground. Acorn abundance in one year clearly influenced the abundance of wood mice in the following year in all models examined based on the Gompertz and Ricker model; in addition, the abundance of wood mice had effects on the population. Acorn abundance influenced the strength of density dependence (intraspecific competition) of the wood mouse population. When the abundance of acorns was high, density dependence was relaxed, and as a result the equilibrium density at which the population growth rate decreased to zero became higher. Those effects of acorn abundance were regarded as a nonlinear perturbation effect (sensu Royama 1992). The nonlinearity of density dependence was also detected; higher densities had stronger effects on population growth rates. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Transposon-mediated resistance to Bacillus sphaericus in a field-evolved population of Culex pipiens (Diptera: Culicidae)

The binary toxin is the major active component of Bacillus sphaericus, a microbial larvicide used for controlling some vector mosquito-borne diseases. B. sphaericus resistance has been reported in many part of the world, leading to a growing concern for the usefulness of this environmental friendly insecticide. Here we characterize a novel mechanism of resistance to the binary toxin in a natural population of the West Nile virus vector, Culex pipiens. We show that the insertion of a transposable element-like DNA into the coding sequence of the midgut toxin receptor induces a new mRNA splicing event, unmasking cryptic donor and acceptor sites located in the host gene. The creation of the new intron causes the expression of an altered membrane protein, which is incapable of interacting with the toxin, thus providing the host mosquito with an advantageous phenotype. As a large portion of insect genomes is composed of transposable elements or transposable elements-related sequences, this new mechanism may be of general importance to appreciate their significance as potent agents for insect resistance to the microbial insecticides.     

Estimating reaction norms for predictive population parameters,age specific mortality,and mean longevity in temperature‐dependent cohorts of Culex quinquefasciatus Say (Diptera: Culicidae)

Culex quinquefasciatus plays a major role in the transmission of important parasites and viruses throughout the world. Because temperature is an important limiting factor on growth and longevity of all mosquito species, estimating the reaction norms provides very important basic information for understanding both plasticity and individual variations of the population. In the present study, Cx. quinquefasciatus were maintained at five different constant temperatures (15°, 20°, 23°, 27°, and 30°C) for two subsequent generations. Reproductive population parameters in blood‐fed mated females and longevities of virgin and blood‐fed mated adults reared at different temperatures were compared for the two generations. Longevity increased as temperature decreased within a range of 15° to 30°C for the unmated adults, and 15° to 27°C for the mated and blood‐fed adults. Generation times were as long as 124.07 and 106.76 days for two subsequent generations reared at 15°C, and the highest intrinsic rate of increase (r_m) values were estimated at 0.22 and 0.18, respectively, from the cohorts reared at 27°C. For survival rates, reproductive rates (R₀), and r_m values, 30°C was found to be a critical temperature for this species. These cohorts produced the smallest amount of eggs (R₀= 5.06), r_m values decreasing across generations (from 0.11 to 0.06), and the survival rates from egg to adult were found to be insufficient (16.1 and 10.8%). Additionally, the rate of exponential increase with age and age specific mortalities (b) were calculated for the virgin cohorts. Age specific mortality rates increased as temperature decreased. The increase in mortality rates started to accelerate at 27°C and was more pronounced at 30°C, for both females and males. We estimated the coefficients of variation for the b values in which females have smaller coefficients than those of the males at all temperatures.     

Density-dependent regulation of Aedes cantans (Diptera: Culicidae) in natural and artificial populations

Abstract.

• 1 Mortality and size variation (siphon length) in Aedes cantans larvae were examined in natural populations in northern England in 1989 and 1990.
• 2 Under crowded conditions, density-dependent competition led to reduction in the size of both larvae and adults and increased larval mortality.
• 3 Larvae were also maintained in cages in the field at different densities. Results paralleled those for the natural populations in the ponds; larvae maintained at high densities showed increased mortality and reduced size.
• 4 Possible density-dependent factors leading to mortality and size reduction include cannibalism and contact inhibition leading to food shortages.
• 5 The main density-independent factor contributing to larval mortality was habitat desiccation.

     

The effect of temperature on the population growth potential of Culex annulirostris Skuse (Diptera: Culicidae)

The effect of temperature on the population growth potential of Culex annulirostris was determined by studying larval growth rate and survival at seven temperatures between 10 and 40°C, and adult survival and fecundity at 20, 25 and 30°C. All larvae died at Wand 40°C; survival was greatest at 25°C. The period for complete juvenile development ranged from 8.57 days (35°C) to 37 days (15°C). Development from egg to adult required 196 day-degrees above 9.7°C with incubation temperatures between 15 and 30°C. Population growth potential was positive at 20, 25 and 30°C, greatest at 25°C, but negative at 15°C. The minimum temperature for population growth was estimated as 17.5°C.     

Permethrin resistance variation and susceptible reference line isolation in a field population of the mosquito,Culex quinquefasciatus (Diptera: Culicidae)

This study examines the genetic variations and mechanisms involved in the development of permethrin resistance in individual mosquitoes from a field population of Culex quinquefasciatus, HAmCq^G0, and characterizes susceptible reference lines of mosquitoes with a similar genetic background to the field HAmCq^G0 strain. Six upregulated cytochrome P450 genes, CYP9M10, CYP9J34, CYP6P14, CYP9J40, CYP6AA7, and CYP4C52v1, previously identified as being upregulated in the larvae of resistant HAmCq^G8 mosquitoes were examined in the larvae of 3 strains (susceptible S‐Lab, parental HAmCq^G0 and permethrin‐selected highly resistant HAmCq^G8) and 8 HAmCq^G0 single‐egg raft colonies, covering a range of levels of susceptibility/resistance to permethrin and exhibiting different variations in the expression of A and/or T alleles at the L‐to‐F kdr locus of the sodium channel. The 2 lines with the lowest tolerance to permethrin and bearing solely the susceptible A allele at the L‐to‐F kdr locus of the sodium channels, from colonies Cx_SERC5 and Cx_SERC8, showed lower or similar levels of all 6 of the P450 genes tested compared with the S‐Lab strain, suggesting that these 2 lines could be used as the reference mosquitoes in future studies characterizing insecticide resistance in HAmCq mosquitoes. This study also provides a detailed investigation of the mechanisms involved in insecticide resistance in individuals within a population: individuals with elevated levels of resistance to permethrin all displayed one or more potential resistance mechanisms–either elevated levels of P450 gene expression, or L‐to‐F mutations in the sodium channel, or both.     

杭州石荠苎(Mosla hangchowensis)种群密度制约实验的统计分析

本文研究了我国特有、分布区极狭窄的一年生草本植物——杭州石荠苎(Mosla hangchowensis)种群的密度制约规律。结果表明：在生长季内,种群的死亡率与密度密切相关。种群的最适密度为200～1000株/m²左右。不同密度种群的平均株高、开花数等性状随时间的动态关系均符合“logistic”模型。高密度种群中60%左右的个体能完成生活史;低密度种群中80%以上的个体能完成生活史。种群密度较高制约杭州石荠苎的植株形态和繁殖投资。     

Effects of blood meal source on the reproduction of Culex pipiens quinquefasciatus (Diptera: Culicidae)

Culex pipiens quinquefasciatus were fed blood meals from a live chicken (LC), chicken blood in Alsever's (AC) solution, defibrinated bovine blood (DB), or bovine blood in citrate (CB) and incubated at 28° C. The effects of different blood meal sources were evaluated with respect to rates of blood feeding and reproduction (i.e., fecundity and fertility) over two gonotrophic cycles. Mosquitoes that fed on the first blood meal were subjected to a second blood meal as follows (first blood meal / second blood meal): LC/LC, LC/DB, DB/DB, CB/CB, AC/AC. Fecundity and fertility of Cx. p. quinquefasciatus were significantly (P < 0.05) greater in mosquitoes fed LC blood; however, fecundity and fertility in different treatment groups varied by gonotrophic cycle. These results contribute to our understanding of the impact of blood meal source on feeding and reproduction in Cx. p. quinquefasciatus. The potential impacts of blood meal source on virus transmission experiments are discussed.     

Larvicidal potency of selected xerophytic plant extracts on Culex pipiens (Diptera: Culicidae)

Chemical insecticides released into the environment may have adverse biological effects. Therefore, there is a need for ecofriendly insecticides for mosquito control. Xerophytic plant extracts that may provide more ecofriendly active component were evaluated against Culex pipiens 4th instars. Plant extracts prepared using different solvents with a Soxhlet apparatus and different concentrations were tested against Culex pipiens larvae. The effects were observed at 24 h and 72 h intervals and LD₅₀ and LD₉₀ values determined. Chloroform (CHCl₃) and ethyl acetate (EtOAc) extracts of Althaea ludwigii were the most effective against Cx. pipiens 4^th instars, but were highly dependent on extract concentrations and exposure time. Results suggest that A. ludwigii extracts contain bioactive compounds, such as phenols and saponins, that may provide effective Cx. pipiens larval control. However, the extract was found to be toxic to zebrafish larvae, and may be toxic to other aquatic fauna. Further studies to determine the active components and toxicity to other fauna are needed.     

Reduced productivity of Culex pipiens and Cx. restuans (Diptera: Culicidae) mosquitoes in parking area catch basins in the northeast Chicago metropolitan area

From June to September, 2016, 100 catch basins in eight parking areas were monitored weekly for the presence of mosquito pupae in the operational area of the North Shore Mosquito Abatement District (NSMAD) located just north of Chicago, IL, U.S.A. Weekly results from these basins were compared to weekly samples taken from residential street catch basins, the most common type of catch basin treated seasonally by the NSMAD with larvicides. Over the 17 study weeks, residential street basins had a mean rate of productivity (pupae per basin‐visit) 12 times that of parking area catch basins. The two parking area sites with the highest mean rate of productivity were associated with county forest preserves. Productivity in both street and parking area basins was positively associated with the presence of three or more deciduous trees within 20 m of basins and if they were located directly adjacent to curbs. Alternatively, productivity was negatively associated with the proportion of impervious surface within 10 m of basins and weekly rainfall. Findings suggest that reduced catch basin larvicide applications may be appropriate in many parking area sites.     

Patterns of natural mortality in stream‐living brown trout (Salmo trutta)

1. We tested the hypothesis that lifetime mortality patterns and their corresponding rates and causal factors differ among populations of stream‐living salmonids. To this end, we examined the lifetime mortality patterns of several successive cohorts of two stream‐living brown trout (Salmo trutta) populations in Spain and Denmark. 2. In the southern population, we observed a consistent two‐phase pattern, in which mortality was negligible during the first half of the lifetime and severe during the rest of the lifetime. In contrast, the northern population demonstrated a three‐phase pattern with an earlier phase varying from negligible to severe, followed by a second stage of weak mortality, and lastly by a third life stage of severe mortality. 3. Despite substantial differences in the mortality patterns between the two populations, the combined effect of recruitment (as a proxy of the density‐dependent processes occurring during the lifetime) and mean body mass (as a proxy of growth experienced by individuals in a given cohort) explained c. 89% of the total lifetime mortality rates across cohorts and populations. 4. A comparison with other published data on populations of stream‐living brown trout within its native range highlighted lifetime mortality patterns of one, two, three and four phases, but also suggested that common patterns may occur in populations that experience similar individual growth and population density.     

一个致倦库蚊杀虫剂敏感品系的筛选

化学防治是控制蚊虫传播疾病的主要方法, 抗性监测表明我国蚊虫已对有机磷、 有机氯、 氨基甲酸酯和拟除虫菊酯类杀虫剂产生了不同程度的抗性。蚊虫抗药性的分子机制主要包括靶标抗性和三大解毒酶家族带来的代谢抗性。筛选对杀虫剂敏感的品系是抗性监测和抗性机理研究必不可少的材料。本研究通过从一个致倦库蚊Culex pipiens quinquefasciatus野生种群筛选无乙酰胆碱酯酶G119S突变且具有低活性羧酸酯酶、 P450单加氧酶和谷胱甘肽-S-转移酶的单雌系, 建立了一个对杀虫剂敏感的致倦库蚊品系。该品系的羧酸酯酶活性是敏感品系S-lab的2.5倍, P450单加氧酶和谷胱甘肽-S-转移酶的活性与S-lab相当。生物测定表明, 与S-lab相比, 该品系对有机磷杀虫剂有低于2倍的抗性, 对氨基甲酸酯和拟除虫菊酯类杀虫剂没有抗性, 可以作为相对敏感品系用于抗性监测。     

Existence of Two Acetylcholinesterases in the Mosquito Culex pipiens (Diptera: Culicidae)

Abstract: Two acetylcholinesterases (AChEs), AChE1 and AChE2, differing in substrate specificity and in some aspects of inhibitor sensitivity, have been characterized in the mosquito Culex pipiens . The results of ultracentrifugation in sucrose gradients and nondenaturing gel electrophoresis of AChE activity peak fractions show that each AChE is present as two molecular forms: one amphiphilic dimer possessing a glycolipid anchor and one hydrophilic dimer that does not interact with nondenaturing detergents. Treatment by phosphatidylinositol-specific phospholipase C converts each type of amphiphilic dimer into the corresponding hydrophilic dimer. Molecular forms of AChE1 have a lower electrophoretic mobility than those of AChE2. However, amphiphilic dimers and hydrophilic dimers have similar sedimentation coefficients (5.5S and 6.5S, respectively). AChE1 and AChE2 dimers, amphiphilic or hydrophilic, resist dithiothreitol reduction under conditions that allow reduction of Drosophila AChE dimers. In the insecticide-susceptible strain S-LAB, AChE1 is inhibited by 5 × 10⁻⁴ M propoxur (a carbamate insecticide), whereas AChE2 is resistant. All animals are killed by this concentration of propoxur, indicating that only AChE1 fulfills the physiological function of neurotransmitter hydrolysis at synapses. In the insecticide-resistant strain, MSE, there is no mortality after exposure to 5 × 10⁻⁴ M propoxur: AChE2 sensitivity to propoxur is unchanged, whereas AChE1 is now resistant to 5 × 10⁻⁴ M propoxur. The possibility that AChE1 and AChE2 are products of tissue-specific posttranslational modifications of a single gene is discussed, but we suggest, based on recent results obtained at the molecular level in mosquitoes, that they are encoded by two different genes.     

Identification and classification of detoxification enzymes from Culex quinquefasciatus (Diptera: Culicidae)

Molecular characterization of the insecticide resistance has become a hot research topic ever since the first disease transmitting arthropod (Anopheles gambiae) genome sequence has unveiled in 2002. A recent publication of the Culex quinquefasciatus genome sequence has opened up new opportunities for molecular and comparative genomic analysis of multiple mosquito genomes to characterize the insecticide resistance. Here, we utilized a whole genome sequence of Cx. quinquefasciatus to identify putatively active members of the detoxification supergene families, namely cytochrome P450s (P450s), glutathione-S-transferases (GSTs), and choline/carboxylesterases (CCEs). The Culex genome analysis revealed 166 P450s, 40 GSTs, and 62 CCEs. Further, the comparative genomic analysis shows that these numbers are considerably higher than the other dipteran mosquitoes. These observed speciesspecific expansions of the detoxification super gene family members endorse the popular understanding of the involvement of these gene families in protecting the organism against multitudinous classes of toxic substances during its complex (aquatic and terrestrial) life cycle. Thus, the generated data set may provide an initial point to start with to characterize the insecticide resistance at a molecular level which could then lead the development of an easy to use molecular marker to monitor the incipient insecticide resistance in field environs.     

两品系蒙古裸腹溞种群补偿生长及适宜食物密度

研究了两品系蒙古裸腹溞(晋南品系和内蒙品系)继饥饿后的补偿生长及其生长发育的适宜食物密度。结果表明,两品系蒙古裸腹溞生长发育的最适食物——篕∏蛟迕芏染?50×104/mL。对两品系蒙古裸腹溞而言,饥饿0.5d的蒙古裸腹溞有全补偿生长,饥饿1~2d有部分补偿生长现象,饥饿超过3d已没有补偿生长。可以认为,蒙古裸腹溞仅在短时间饥饿时有补偿生长现象的发生。     

Laboratory evaluation of lactic acid on attraction of Culex spp. (Diptera: Culicidae)

The role of lactic acid was evaluated for attraction of Culex nigripalpus, Culex quinquefasciatus, Culex tarsalis, and Aedes aegypti in the laboratory using a dual‐port olfactometer. When lactic acid was combined with chicken odor, attraction was increased for Cx. quinquefasciatus compared to chicken odor alone but not for Cx. nigripalpus, Cx. tarsalis, and Ae. aegypti. Lactic acid combined with hand odor did not change attraction of Cx. tarsalis and Ae. aegypti but decreased attraction of Cx. nigripalpus and Cx. quinquefasciatus. The addition of lactic acid to CO₂ increased attraction of Ae. aegypti and Cx. quinquefasciatus but reduced attraction of Cx. nigripalpus and Cx. tarsalis. Use of commercial lactic acid baits with CO₂ resulted in a similar trend except for Cx. nigripalpus which showed no difference. A blend of lactic acid, acetone, and dimethyl disulfide was attractive to Ae. aegypti (63.4%) but elicited low responses by all Culex spp. (1.3–26.8%). Addition of the blend to CO₂ increased attraction of Ae. aegypti and Cx. quinquefasciatus but reduced attraction of Cx. nigripalpus and Cx. tarsalis. The mixture of compounds plus CO₂ was as attractive as a hand for Cx. quinquefasciatus, Cx. tarsalis, and Ae. aegypti.