Vertically transmitted parasites (VTPs) such as Wolbachia are expected not only to minimize the damage they inflict on their hosts, but also to protect their hosts against the damaging effects of coinfecting parasites. By modifying the fitness costs of the infection, VTPs can therefore play an important role in the evolution and epidemiology of infectious diseases.

Using a natural system, we explore the effects of a Wolbachia–Plasmodium co-infection on mosquito fecundity. While Plasmodium is known to frequently express its virulence by partially castrating its mosquito vectors, the effects of Wolbachia infections on mosquito fecundity are, in contrast, highly variable. Here, we show that Plasmodium drastically decreases the fecundity of mosquitoes by ca. 20%, and we provide the first evidence that this decrease is independent of the parasite's burden. Wolbachia, on the other hand, increases fecundity by roughly 10%, but does not alter the tolerance (fecundity–burden relationship) of mosquitoes to Plasmodium infection.

Although Wolbachia-infected mosquitoes fare overall better than uninfected ones, Wolbachia does not confer a sufficiently high reproductive boost to mosquitoes to compensate for the reproductive losses inflicted by Plasmodium. We discuss the potential mechanisms and implications underlying the conflicting effects of these two parasites on mosquito reproduction.

The larvicidal activity of 13 essential oils, 14 major monoterpenoids and 9 N-methyl carbamates based on these monoterpenoids was tested according to the recommendations of the WHO against fourth instar larvae of Culex pipiens L. The results of the larvicidal assays after 24 hr revealed a high potential for the essential oils, such as cinnamon, chenopodium and eucalyptus. Of the monoterpenoids, chlorothymol was found to be the most effective followed by thymol, carvacrol and cinnamaldehyde. Conversion of the most active monoterpenoids into their N-methyl carbamate derivatives resulted in higher larvicidal activities than those of the corresponding monoterpenoids. The use of piperonyl butoxide (PBO) to improve the efficacy of the most active monoterpenoids resulted in higher larvicidal activity. Also, all N-methyl carbamate derivatives were synergized by PBO. Carvacrol derivative, which was strongly synergized by PBO, was comparable with the standard synthetic insecticide malathion.

Rapidly changing environments and an increase in human movement around the globe have contributed to a rise in new and emerging diseases, many of which are arthropod borne. The threat posed to the United Kingdom by such diseases is uncertain, and there is a real need to understand the distribution, seasonality and behaviour of potential vectors in the country. At present, there is no standard method for routine mosquito surveillance in the UK. Here we compared the catching efficiency of two carbon dioxide-baited traps, the CDC light trap and the MosquitoMagnet® Pro trap, for collecting British mosquitoes. Two of each type of trap were operated at four sites in central and southern England from June to September, 2003. To determine whether trap height affected collections, three light traps were operated at 1, 2.5 and 5 m above the ground in one site in 2004. Both types of trap were efficient at catching mosquitoes, collecting 5414 mosquitoes of 16 species. MosquitoMagnet® traps caught 2.7 times more mosquitoes than CDC light traps (P<0.001) and a wider range of species (16 species vs 11) than CDC light traps. Four to six times more female Culex pipiens s.l. were collected in light traps at 5 m (P<0.001) compared with traps at lower heights. MosquitoMagnet® traps ran continuously for up to 8 weeks, whilst the battery of a CDC light trap had to be replaced every 24 hrs. Although MosquitoMagnets® collected more specimens and a greater range of mosquito species, they were considerably more expensive, prone to breakdown and incurred higher running costs than the CDC light traps. MosquitoMagnets® are useful tools for collecting mosquitoes during longitudinal surveys during the summer months, whilst CDC light traps are to be preferred for rapid assessments of the presence or absence of mosquitoes, particularly the important species Culex pipiens.

The population genetic structures of Culex pipiens Linnaeus were evaluated in China over a 2000 km transect that encompasses the two subspecies, C. p. pallens and C. p. quinquefasciatus. Four polymorphic allozyme loci were investigated in 1376 mosquitoes sampled from 20 populations across four provinces. These loci were not statistically dependent with no apparent heterozygote deficit or excess. On a regional scale (intra-province), a low (Fst=0.007–0.016) and significant genetic differentiation was found, with no clear geographical pattern. On a wider scale (inter-province), the genetic differentiation was higher (Fst=0.059), and an isolation by distance emerged. The results are compared with previous population genetic surveys of this mosquito species in different geographic areas over the world. The overall pattern suggests that Culex pipiens requires considerable distance (500–1000 km) to show isolation by distance, irrespective of the subspecies (C. p. pipiens, C. p. quinquefasciatus and C. p. pallens) or the geographic location.

Dans ce travail, la lutte chimique anti-larvaire a été réalisée au laboratoire chez deux espèces culicidiennes Anopheles hispaniola,vecteur potentiel du paludisme (Guy 1963), et Culex pipiens. Dans ces essais, nous avons utilisé le téméphos, larvicide organophosphoré,sous forme liquide 500 EC (Concentration Emultionnable). Dans ces conditions, un litre de produit commercialcontient 500 g de produit actif (500 g.l-1).Cette étude a montré que la CL50 (30mn) pour le stade L2 est de 21 µg.l-1 chez A.hispaniola et de 10 µg.l-1 chez C. pipiens ;La CL50 (60mn) au stade L4 est respectivement de 23 µg.l-1 et 12 µg.l-1.Le taux de consommation des larves d'A.hispaniola (stade L4) par Gambusia affinis varie en fonction des milieux étudiés maisreste toujours plus élevé chez les femelles que chez les mâles.

Les conditions de sécheresse qui ont sévi au Maroc de 1981 à 1983 ont favorisé la sélection d'un nouvel habitat par Culex pipiens, espèce particulièrement plastique, le creux d'arbre en subéraie. La description morphologique de la larve du stade 4, de la nymphe et des imagos ♂ et ♀ montre que ces populations dendrolimniques s'apparentent à la forme Culex pipiens autogenicus.

The toxicity of dursban, reldan and abate were tested against the larvae of Culex pipiens L. and Aedes aegypti (L.), in addition to evaluating effect of two bacterial toxins (Bacillus thuringiensis H-14, and B. sphaericus 1593) against C. pipiens larvae.

The synergistic effects of bacterial toxin-insecticide combinations were calculated and the new LCp-lines were determined by using a sublethal toxin dose of B. thuringiensis and B. sphaericus in combination with the three tested insecticides against Culex pipiens larvae, which was the most tolerant mosquito species.

Bacterial toxins potentiated the three used insecticides at different levels of potentiation, depending on the chemical structure of the insecticide used.

The larvicidal activity of two entomopathogenic bacteria Bacillus thuringiensis H-14 and B. sphaericus 1593 against mosquito larvae of Culex pipiens has been evaluated. According to LC50 values obtained, B. thuringiensis (4.6 x 105 spores/ml) proved to be highly pathogenic to fourth instar larvae than fi. sphaericus (4.2 x 106 spores/ml).

Larval treatment with LC50 levels of both pathogens affected the reproductive potential of surviving adults during two successive gonotrophic cycles. These treatments caused insignificant changes in some basic morphometric characteristics of mosquito females that developed from surviving larvae.

Three polyvinyl chloride (PVC) formulations of malathion were prepared and tested as controlled-release formulations against mosquito larvae of Culex pipiens L. Non-expanded formulations gave effective control, with 100% larval mortalities, for 23–51 days, followed by expanded (16–33 days) and foamed (14–27 days) formulations. The results indicate that increasing the percentage of active ingredient in the present formulations increased their effective control against mosquito larvae for longer periods.

Larval treatments with these formulations of malathion led apart from lethal action to a decrease in the reproductive potential and in longevity of mosquito adults which survived from these treatments.

Nosema sp. naturally occurred in both Spodoptera littoralis (Boisd.) and S. exigua (Hübner) laboratory colonies in Alexandria, Egypt (since November 1984). It was responsible for the dramatic suppression of their laboratory populations. Both young (3-day-old) and old (9-day-old) larvae of S. littoralis were susceptible to Nosema sp. However, the pathogen was more effective against the young larvae, especially at high doses, than the old ones. The estimated LC50 was 4.0 × 107 spores'ml, for 3-day-old larvae. The slope value was low (1.2) as typical of protozoan insect pathogens. Heavily infected 9-day-old larvae tended to die as larvae; while less infected ones either pupate or produce larval-pupal intermediate forms (12–23%). The developmental period of both infected larvae and pupae was increased by 4–6 and 3–5 days, respectively. The number of infected insects that reached the adult stage was decreased as the concentration of Nosema sp. spores was increased. Furthermore, infection was shown to reduce adult longevity and fecundity, and viability of the eggs. Larval faecal pellets harboured large numbers of viable spores. Transovum transmission of infection occurred. Two dipterous species, Culex pipiens and Aedes aegypti, were not susceptible to Nosema sp.

Bacillus thuringiensis H-14 (Alex), originally isolated from moribund and dead larvae of the casuarina stem borer, Stromatium fulvum, was tested in the laboratory against the second and fourth-instar larvae of both mosquito species, Aedes aegypti and Culex pipiens. The pathogenicity of this bacillus was established when both insects were found to be susceptible to infection over the whole range of test concentrations (0.005–0.35 mg/1). However, A. aegypti showed a higher degree of susceptibility to B. thuringiensis H-14 (Alex) than C. pipiens. A mortality of 100% was achieved within 24 hr with concentrations of 0.09 and 0.25 mg/1 for second- and fourth-instar larvae of A. aegypti, respectively. Also, younger larvae of both test mosquito strains were more susceptible than mature ones.

The larvicidal activity of the pathogen Bacillus thuringiensis H-14 against mosquito larvae of Aedes aegypti (L.) and Culex pipiens L. has been evaluated.

The results showed that the susceptibility of culicine larvae to this pathogen was closely correlated with mosquito species tested and its larval instars. The toxicity curves indicated that the serotype H-14 had a higher pathogenicity against A. aegypti than C. pipiens. LC50 values showed that, for both mosquito species tested, the second instar larvae were more susceptible to the pathogen used than the fourth instar larvae.

Apart from lethal action, larval treatments with B. thuringiensis H-14 led to a decrease in the reproductive potential of female mosquitoes that emerged from these treatments.

The effect of six pyrethroids, NRDC 104 (resmethrin), NRDC 107 (bioresmethrin), NRDC 119 (cismethrin), NRDC 143 (permethrin), NRDC 156 and allethrin, against larvae and adults of the Egyptian mosquito Culex pipiens L. has been evaluated. Five strains were used, a field strain and DDT-susceptible, DDT-resistant, malathion-susceptible and malathion-resistant strains. Results obtained were also referred to a DDT highly susceptible strain of another mosquito Aedes aegypti (L.)

The toxicity curves showed that NRDC 156 proved to be the most effective compound tested, followed by NRDC 143, NRDC 119, NRDC 107 and NRDC 104, respectively, while allethrin was the least effective. Such a fact was highly pronounced either on the LC50 or on the LC95 basis.

As larvicides, data obtained proved that the DDT-susceptible strain was less susceptible to all the tested pyrethroids than the DDT-resistant strain by about 42.6-, 5.1-, 8.6-, 132-, 290.7- and 4.8-fold in the case of NRDC 104, 107, 199, 143, and 156 and allethrin, respectively. Tests also showed that there is no definite variation in susceptibility of both malathion-susceptible and malathion-resistant strains, except in the case of NRDC 143 and 156. Comparing tests against larvae of A. aegypti confirmed that the susceptibility to these pyrethroids was closely correlated with insect species and its strain, and cross-resistance might be developed among larvae of these species.

As adulticides, the pyrethroids used could be arranged in the following descending order according to their LC50 values: NRDC 156, NRDC 143, NRDC 104, allethrin, NRDC 107 and NRDC 119. The change in the trend of toxicity is possible due to the stage tested and the mode of action of these compounds on adult or larval stage.