The use of morphometric wing characters to discriminate female Culex pipiens and Culex torrentium

The reliability of the length of wing radial vein r_2/3 as a character for the morphological discrimination of the two potential arbovirus vectors Culex pipiens s.s. and Cx. torrentium from Germany was reassessed, after this character had been neglected for more than 40 years. Additionally, multivariate morphometric analyses were applied to evaluate wing shape variation between both species. Although high‐throughput molecular tools are now available to differentiate the two species, a simple, low‐cost routine alternative may be useful in the absence of a molecular laboratory, such as under semi‐field conditions. A thin‐plate splines transformation confirmed that primarily the shrinkage of vein r_2/3 is responsible for the wing differences between the two species. In the bivariate analysis, the r_2/3/r₃ indices of Cx. pipiens s.s. and Cx. torrentium were 0.185 and 0.289, respectively, resulting in a correct classification of more than 91% of all tested specimens. Using the absolute length of vein r_2/3 alone still allowed for more than 90% accurate discrimination. Furthermore, classification accuracy of linear discriminant analysis exceeded 97%.     

Oviposition bioassay responses of Culex tarsalis and Culex quinquefasciatus to neem products containing azadirachtin

Neem (Azadirachta indica A. Juss) products have been shown to exert pesticidal properties against a variety of insect species. In mosquito control programs, such products may have the potential to be used successfully as larvicides. In exploring other advantages of neem products, we studied the oviposition responses of Culex tarsalis Coquillett and Cx. quinquefasciatus Say to two experimental azadirachtin (AZ) formulations, wettable powder Azad ^– WP10 (WP) and emulsifiable concentrate Azad ^– EC4.5 (EC). Gravid Cx. tarsalis exhibited a distinct preference for the neem suspension of the WP, where significantly more egg rafts were collected from the treatment than from the control. The minimum effective AZ concentration for this activity was 0.5 ppm. The aged suspensions from 1–7 days at 0.5 and 1 ppm AZ were more active in eliciting oviposition responses in Cx. tarsalis than the fresh preparations. This activity of the aged suspensions lasted up to 14 and 21 days at 0.5 and 1 ppm AZ, respectively. Negative ovipositional responses were indicated in the tests of the EC vs. Cx. tarsalis, as well as both neem formulations vs. Cx. quinquefasciatus. In the tests of the EC formulation, significantly less gravid females were trapped by oviposition cups in the treatment than in the control, and in the tests of the WP significantly less egg rafts were collected from the treatment than from the control. The minimum effective concentrations for oviposition avoidance activity were 5 ppm AZ for Cx. tarsalis and 10 ppm AZ for Cx. quinquefasciatus, which lasted up to 1 and 4 days for these two species respectively. Neem products potentially used as mosquito larvicides may have many additional benefits in mosquito control programs, the oviposition modification noted in the current studies is one such example.     

The salivary gland chromosomes of Culex (Culex) vishnui (Culicidae: Diptera)

Culex vishnui is a member of the vishnui group comprising six closely resembling species. The salivary gland chromosomes are longer than those found in Anopheles, more fragile and spread with difficulty. The banding pattern is compared with that of Culex pipiens pipiens and Culex pipiens fatigans. Homologies are closest between vishnui and fatigans. The incidence of asynapsis between the homologues is very high.     

Persistent natural infection of a Culex tritaeniorhynchus cell line with a novel Culex tritaeniorhynchus rhabdovirus strain

Culex tritaeniorhynchus rhabdovirus (CTRV) is a mosquito virus that establishes persistent infection without any obvious cell death. Therefore, occult infection by CTRV can be present in mosquito cell lines. In this study, it is shown that NIID‐CTR cells, which were derived from Cx. tritaeniorhynchus, are persistently infected with a novel strain of CTRV. Complete genome sequencing of the infecting strain revealed that it is genetically similar but distinct from the previously isolated CTRV strain, excluding the possibility of contamination. These findings raise the importance of further CTRV studies, such as screening of CTRV in other mosquito cell lines.     

Ethanolamine kinase from Culex pipiens fatigans

Ethanolamine kinase was partially purified from the larvae of Culex pipiens fatigans and its properties were studied. The enzyme was separated from choline kinase by acetic acid precipitation at pH 5.0 of a 13,000g supernatant of the larval homogenate. Alkaline phosphatase activity was removed from the enzyme preparation by the acid treatment followed by ammonium sulfate fractionation. The enzyme was localized in the cytosolic fraction and had a requirement for Mg²⁺ as a cofactor. The K_m values for ethanolamine and ATP were 4 × 10^?4 and 1.54 × 10^?4m, respectively. The affinity of the enzyme for nucleotide triphosphates was in the order, ATP > ITP > GTP while UTP and CTP were poorly utilized. p-Chloromercuribenzoate and N-ethylmaleimide inhibited the enzyme activity and reduced glutathione protected the enzyme from their inhibition. Choline and serine had no effect on the enzyme activity. The enzyme had a molecular weight of 44, 000 daltons as determined by gel filtration chromatography. Eggs contained the highest specific activity of the enzyme while adult insects had the highest total enzyme activity.     

The arbovirus vector Culex torrentium is more prevalent than Culex pipiens in northern and central Europe

Two species of arbovirus vector, Culex torrentium and Culex pipiens (Diptera: Culicidae), occur in several European countries, but difficulties in their accurate identification and discrimination have hampered both detailed and large‐scale distribution and abundance studies. Using a molecular identification method, we identified to species 2559 larvae of Cx. pipiens/torrentium collected from 138 sites in 13 European countries ranging from Scandinavia to the Mediterranean coast. In addition, samples of 1712 males of Cx. pipiens/torrentium collected at several sites in the Czech Republic were identified to species based on the morphology of their hypopygia. We found that the two species occur together in large areas of Europe, and that Cx. torrentium dominates in northern Europe and Cx. pipiens dominates south of the Alps. The transition in dominance occurs in central Europe, where both species are roughly equally common. There was a strong correlation between the length of the growing season at different sites and occurrences of the two species. As the growing season increases, the proportion and detection of Cx. torrentium decrease, whereas those of Cx. pipiens increase. The present findings have important consequences for the interpretation of the results of studies on major enzootic and link‐vectors of mosquito‐borne bird‐associated viruses (i.e. Sindbis, West Nile and Usutu viruses), especially in central Europe and Scandinavia.