Zhongming Wang

Identifying the Main Mosquito Species in China Based on DNA Barcoding

Mosquitoes are insects of the Diptera, Nematocera, and Culicidae families, some species of which are important disease vectors. Identifying mosquito species based on morphological characteristics is difficult, particularly the identification of specimens collected in the field as part of disease surveillance programs. Because of this difficulty, we constructed DNA barcodes of the cytochrome c oxidase subunit 1, the COI gene, for the more common mosquito species in China, including the major disease vectors. A total of 404 mosquito specimens were collected and assigned to 15 genera and 122 species and subspecies on the basis of morphological characteristics. Individuals of the same species grouped closely together in a Neighborhood-Joining tree based on COI sequence similarity, regardless of collection site. COI gene sequence divergence was approximately 30 times higher for species in the same genus than for members of the same species. Divergence in over 98% of congeneric species ranged from 2.3% to 21.8%, whereas divergence in conspecific individuals ranged from 0% to 1.67%. Cryptic species may be common and a few pseudogenes were detected.

First report on co-occurrence knockdown resistance mutations and susceptibility to beta-cypermethrin in Anopheles sinensis from Jiangsu Province, China.

The increasing prevalence of insecticide resistance in Anopheles sinensis, a major vector of malaria in Jiangsu province in eastern China, threatens to compromise the successful use of insecticides in malaria control strategies. It is therefore vital to understand the insecticide resistance status of An. sinensis in the region. This study examined the nucleotide diversity of the para-sodium channel and knockdown resistance (kdr) in five field populations of adult An. sinensis mosquitoes collected in Jiangsu province, identifying the L1014F and L1014C substitutions for the first time. Competitive polymerase chain reaction (PCR) amplification of specific allele (cPASA) and polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP) for resistance diagnosis were developed and validated. Comparing the results with direct sequencing revealed that the PCR-RFLP method was more sensitive and specific whereas the cPASA method was more convenient and suitable. The significant positive correlation between kdr allele frequency and bioassay-based resistance phenotype demonstrates that the frequency of L1014F and L1014C substitutions in the kdr gene provides a useful molecular marker for monitoring beta-cypermethrin resistance in natural populations of An. sinensis. Our results point to the L1014F substitution as the key mutation associated with beta-cypermethrin resistance. The high resistance and mutation frequency detected in the five populations also suggest cross-resistance with other pyrethroids may occur in An. sinensis, highlighting the need for further surveys to map insecticide resistance in China and the adoption of a rational management of insecticide application for resistance management and mosquito vector control.

Evaluation of lambda-cyhalothrin barrier spray on vegetation for control of Aedes albopictus in China.

Abstract Aedes albopictus is a primary nuisance pest and disease vector in China. Control of Ae. albopictus using current methods is difficult because of diverse larval breeding sites. In the present study, lambda-cyhalothrin was applied as a barrier spray to vegetation surrounding human dwellings for control of adult mosquito populations. Compared to the landing rate counts in the untreated control site, the barrier spray resulted in an 83–98% reduction of Ae. albopictus within 9 wk posttreatment. The study results indicate that lambda-cyhalothrin applied as a barrier spray to vegetation can reduce Ae. albopictus landing rates collections for more than 2 months.

Infection and Dissemination of West Nile Virus in China by the Potential Vector, Culex pipiens pallens

ABSTRACT: n The distribution of the West Nile virus (WNV) in the organs and tissues of the mosquito Culex pipiens pallens, a potential vector of WNV in China, was investigated up to 14 days after oral infection. The WNV antigen was detected in paraffin-embedded mosquitoes using immunocytochemistry and viral titers of post-infected mosquitoes determined by plaque assay. Viral titers sharply decreased 24 h post-infection, were undetectable for the first few days, then rose over the course of infection. The first midgut infection appeared after one day, and the overall infection rate (based on midgut infection) was 43.9%. Other tissues, including hindgut, foregut, ovarian follicles, Malpighian tubules, and ommatidia, showed weak WNV antigens as early as three days post-infection. Staining in the salivary glands first appeared after seven days, and the salivary gland infection rate on the 14th day was 37.5%. Specimens with no detectable WNV antigens in any tissues, and with positive results confined to the midgut, anterior midgut, and hindgut, were observed on the 14th day. The route of viral dissemination from the midgut, and the relative importance of amplifying tissues in mosquitoes susceptibility to infection, were evaluated. The results indicate that Cx. p. pallens has the ability to harbor WNV throughout its alimentary system and that midgut epithelial cells may be the initial site of the replication of this virus in this species.

Vector Competence of Five Common Mosquito Species in the People's Republic of China for Western Equine Encephalitis Virus

Two strains of the Western equine encephalitis virus (WEEV) were first detected and isolated in China in 2001. The maintenance and transmission cycles of WEEV in China are currently not well understood, and the mosquito vectors involved in these cycles are unknown. To understand the ability of the local mosquitoes in China to transmit WEEV, the vector competence of five mosquito species, namely, Culex pipiens pallens Coquillett, Cx. p. quinquefasciatus Say, Aedes (Stegomyia) albopictus Skuse, Ae. (Stegomyia) aegypti Linnaeus, and C. tritaeniorhynchus Giles, for WEEV were evaluated. Infection rates for Cx. p. pallens, Cx. p. quinquefasciatus, Cx. tritaeniorhynchus, Ae. Albopictus, and Ae. aegypti were 46%, 60%, 80%, 37%, and 25%, respectively. Dissemination rates for the same species were 60%, 61%, 75%, 55%, and 50%, respectively. Transmission rates were 41%, 53%, 57%, and 45% for Cx. p. pallens, Cx. p. quinquefasciatus, Ae. Albopictus, and Ae. Aegypti, respectively. Infection rates were significantly different between species, but the difference between dissemination and transmission rates were nonsignificant. These results suggest that several local mosquito species in China are competent laboratory vectors for WEEV.

Dissemination of western equine encephalomyelitis virus in the potential vector, Culex pipiens pallens.

ABSTRACT: Two western equine encephalomyelitis virus (WEEV) strains have been isolated in China. Our previous studies have verified that the mosquito Culex pipiens pallens Coquillett (Diptera: Culicidae) infected with WEEV was capable of transmitting this arbovirus, but it was not clear how the sequential multiplication and spread of virus occurred within the mosquito. In this study, we observed the distribution of WEEV antigen in orally-infected Cx. p. pallens by immunohistochemistry in order to better understand the initial infection, dissemination, and transmission of WEEV in the potential vector. Orally-infected WEEV dissemination varied within the different tissues of Cx. p. pallens, with virus antigen consistently observed in the salivary glands, foregut, midgut epithelial cells, Malpighian tubules, hindgut, and ovarian follicles of some individuals after various days of extrinsic incubation. We suggest that Cx. p. pallens, the potential vector of WEEV, has the ability to harbor the virus through the alimentary system, and the midgut epithelial cell may be the initial site of WEEV replication after ingestion of a viremic blood meal.

Biting activity and host attractancy of mosquitoes (Diptera: Culicidae) in Manzhouli, China.

ABSTRACT n The biting activity and host attractancy of vector mosquitoes are important in assessing the risk of arbovirus transmission, especially where migratory and nonmigrating bird species congregate, such as in Hulun Lake, Manzhouli. In 2009, the population distribution, species diversity, biting activity, and host attractancy of mosquitoes were investigated in Hulan Lake and its associated prairie area. The adult mosquitoes were captured either by human volunteers using aspirators in mosquito nets, by CO2-baited light traps, or by animal-baited traps. In total, 27,004 mosquitoes, representing three genera and 10 species, were collected from Manzhouli, China, in July 2009, of which Aedes dorsalis (Meigen) were most predominant species, followed by Ae. vexans (Meigen). Biting activity peaks by Ae. flavescens (Muller), Ae. dorsalis, and Culex modestus (Facalbi) on human subjects were investigated. Four mosquito species were captured from different animal sheds (sheep, cattle, and goose). Ae. flavescens was more abundant in the cattle shed than in the other two sheds. The Ae. dorsalis in the sheep shed was much higher than in the other animal sheds. The Ae. flavescens collected via chicken-baited traps were significantly higher than those collected via rabbit-baited and pigeon-baited traps. There were no significant differences in the number of Ae. dorsalis and Ae. vexans collected using the three different animal traps.