Protein hydrolysates and associated bacterial contaminants as oviposition attractants for the mosquito Culex quinquefasciatus

Abstract. Six protein or protein hydrolysate solutions were tested for activity as attractants for ovipositing Culex quinquefasciatus mosquitoes in the laboratory. Four of these solutions (egg albumin, lactalbumin hydrolysate, casein hydrolysate and yeast hydrolysate) were attractive to ovipositing females at varying concentrations, when compared to distilled water controls. Soy hydrolysate was repellent at 1%, but not significantly attractive or repellent at lower concentrations. 'Nulure', a tephritid fly bait containing protein hydrolysate, also had no significant effect on oviposition behaviour. Gravid females mostly oviposited within the first 4 h of the scotophase, regardless of the presence or absence of an oviposition attractant.
Lactalbumin hydrolysate 1% solution, with or without 0.1% neomycin antibiotic, was attractive to Cx quinquefasciatus . This effect was reduced by the presence of neomycin which, alone, had no effect on oviposition. Hence both lactalbumin hydrolysate and bacterial contaminants were shown to be attractive to gravid Cx quinquefasciatus .     

Swarming behaviour of the mosquito Culex pipiens quinquefasciatus: a quantitative analysis

ABSTRACT. Analysis of video recordings of Culex pipiens quinquefasciatus Say swarms showed that the overall swarming patterns of males and virgin females are similar, even though the short-term characteristics of their flight, such as speed and turning angle, differ. This suggests they have the same response to the visual cue of the swarm 'marker'. The swarming pattern of an individual consists of elliptical loops which, in the short-term, define an area smaller than the swarm as a whole. The foci of these ellipses drift gradually with respect to the marker; individuals do not seem to have preferred positions within the swarm, but drift at random. Male mosquitoes identify and locate females by the sound of their wing-beats. Diffuse sound at the wing-beat frequency of female C.p. quinquefasciatus (500–600 Hz) caused males within the swarm to slow down significantly. Their turning behaviour remained unchanged, so the ellipses decreased in size. The swarm as a whole collapsed into a smaller volume, centred over the marker. Apparently, the response of males to sound consists of at least two parts: initially they alter their flight speed, and then alter their turning behaviour once they have located the source of the sound.     

Odour-mediated upwind flight of Culex quinquefasciatus mosquitoes elicited by a synthetic attractant: a reappraisal

Abstract. Pile et al. (1991) report that the putative oviposition attractant ace-toxyhexadecanolide has four effects on gravid females of Culex quinquefasciatus Say: (1) it induces upwind anemotaxis, (2) near to an oviposition site it evokes an orthokinetic slowing of flight speed plus (3) a klinokinetic increase in turning rate, and (4) it causes females to stay longer at oviposition sites. This reappraisal shows that the first two of these conclusions are supported by the evidence provided but the second two are not.     

Odour-mediated upwind flight of Culex quinquefasciatus mosquitoes elicited by a synthetic attractant

Abstract A wind tunnel and video equipment are used to study the long-range and close-range responses of gravid females of Culex quinquefasciatus Say to a synthetic pheromone, eryrthro -6-acetoxy-5-hexadecanolide. In response to water and acetoxyhexadecanolide, together or independently, in the presence of wind, females follow meandering flight paths upwind. Females have a higher rate of turning and a lower flight-speed when landing at a site containing pheromone than at a comparable site without pheromone. Females stay longer at oviposition sites containing the attractant than at sites with no attractant.     

A behavioural and electrophysiological study of ovi position cues for Culex quinquefasciatus

Abstract. Both the synthetic oviposition pheromone, erythro-6-acetoxy-5-hexa-decanolide (0.01–80 μg) and a polluted water sample (0.01–80%) significantly increased oviposition by gravid female Culex quinquefasciatus Say (Diptera: Culicidae) in a laboratory assay against clean water. An additive effect resulted when 0.05 μg oviposition pheromone was combined with the polluted water dilution series. Undiluted, however, both the oviposition pheromone and the polluted water sample, alone and in combination, reduced the oviposition response to control levels. A previously reported oviposition site odour component, 3-methylindole, also significantly increased oviposition at 1 × 10^_8 to 1 × 10^-7g but at 1 × 10^_7g significantly less oviposition occurred than in control treatments. The biological activities of the compounds were additionally evaluated electrophysiologically by an EAG assay. Female mosquitoes were electrophysiologically sensitive to the oviposition cues, both pheromone and habitat-related; EAG responses of males were considerably lower than of females with 3-methylindole.     

An unsettling explanation for the failure of skatole‐baited ovitraps to capture Culex mosquitoes

Culex mosquitoes are primarily found in temperate and tropical regions worldwide where they play a crucial role as main vectors of filarial worms and arboviruses. In Recife, a northeast city in Brazil, high densities of Culex quinquefasciatus are often found in association with human populated areas. In marked contrast to another part of the city, field tests conducted in the neighborhood of Sitio dos Pintos showed that trapping of mosquitoes in skatole-baited ovitraps did not differ significantly from captures in control (water) traps. Thus, classical and molecular taxonomic approaches were used to analyze the Culex species circulating in Sitio dos Pintos. Results obtained from both approaches agreed on the cocirculation of Culex quinquefasciatus and Culex nigripalpus in three different areas of this neighborhood. What was initially considered as an unexpected failure of this lure turned out to be a more unsettling problem, that is, the first report in Recife of Culex nigripalpus, a vector of Venezuelan equine encephalitis virus and West Nile virus. Unplanned urbanization processes close to remnants of the Atlantic forest, such as observed in Sitio dos Pintos, may have contributed to the introduction of Cx. nigripalpus in urban areas.     

The effect of predatory fish exudates on the ovipostional behaviour of three mosquito species: Culex quinquefasciatus, Aedes aegypti and Culex tarsalis

Abstract.  Three mosquito species, Culex tarsalis Coquillett, Culex quinquefasciatus Say and Aedes aegypti L. (Diptera: Culicidae), were examined in laboratory binary choice experiments to investigate whether fish exudates from the mosquitofish, Gambusia affinis (Baird & Girard) (Cyprinodontiformes: Poecilliidae), deter oviposition and whether the responses of these mosquito species to fish exudates in oviposition sites are consistent with the risk of predation from fish experienced by each species in their respective natural breeding habitats. Culex tarsalis was deterred significantly from egg laying by the presence of fish exudates in oviposition cups, consistent with high levels of predation by fish in natural breeding sites. Egg laying by Cx quinquefasciatus was slightly reduced in water with fish exudates, but was not consistently deterred by water conditioned by mosquitofish, consistent with the species' relatively low risk of fish predation in natural habitats. Oviposition by container-breeding Ae. aegypti was not deterred by the presence of fish exudates in oviposition cups, consistent with a low risk of predation by fish in natural habitats.     

Cross-resistance between strains of Bacillus sphaericus but not B. thuringiensis israelensis in colonies of the mosquito Culex quinquefasciatus

Two colonies of Culex quinquefasciatus Say (Diptera: Culicidae) were selected with Bacillus sphaericus strains C3-41 and IAB59 in the laboratory for 13 and 18 generations; they attained 145,000- and 48.3-fold resistance, respectively, in comparison with a susceptible laboratory colony (SLCq) and showed very high levels of cross-resistance (8500- to 145,000-fold) to B. sphaericus strains C3-41, 1593, 2297 and 2362. They were relatively susceptible to B. sphaericus strains LP1-G and 47-6B (only 0.8- to 2.8-fold tolerance), with 24.8- to 48.3-fold cross-resistance to strain IAB59. B. sphaericus-resistant mosquito colonies remained highly susceptible to B. thuringiensis israelensis, suggesting that B.t.i. would be of value in the management of B. sphaericus-resistant Cx. quinquefasciatus colonies. The demonstration of low or no cross-resistance of two selected resistant Cx. quinquefasciatus colonies to IAB59, LP1-G and 47-6B strains of B. sphaericus and the finding of a major 49 kDa protein in these strains suggest that there is likely to be another mosquitocidal factor in the three strains.     

Evaluation of factors for rapid development of Culex quinquefasciatus in belowground stormwater treatment devices

Water samples from 11 belowground stormwater treatment Best Management Practices (BMPs) were evaluated for their capacity to support rapid development of the West Nile virus (WNV) mosquito vector, Culex quinquefasciatus. The observed minimum development time from egg to pupa ranged from six to over 30 days. Concentrations of potential food resources (total suspended solids and the particulate organic matter in water samples) were significantly correlated to development times. In addition, the rate of immature mosquito development was both site‐dependent and variable in time, suggesting that factors favorable to rapid development were strongly influenced by watershed characteristics and seasonal changes in temperature. Measured temperatures in belowground BMPs suggest that these structures may remain amenable to WNV virus activity longer each year than sites aboveground.     

Learning and memory in the mosquito Aedes aegypti shown by conditioning against oviposition deterrence

Oviposition site choice by female mosquitoes, Aedes aegypti (L) (Diptera: Culicidae), was affected by rearing them in water treated with 0.016% of the repellent Mozaway trade mark containing citronella and neem. Given a choice between a bowl of repellent-treated and a bowl of untreated water, Ae. aegypti reared in untreated water strongly preferred to oviposit on the clean water (93-98%) instead of repellent-treated water. This demonstrates effective deterrence of oviposition by dilute Mozaway trade mark. Those reared in repellent-treated water were less deterred: 38-46% of their eggs were laid on the repellent-treated water and 54-62% on the clean water. Evidently the female mosquitoes reared in repellent-treated water were conditioned against oviposition site deterrence, as shown when choice tests were conducted 6 days post-emergence from the treated water. This demonstrates learning and memory in the mosquito Ae. aegypti, with implications for dengue vector surveillance and control.     

Synergism between permethrin and propoxur against Culex quinquefasciatus mosquito larvae

To see if synergism occurs between carbamate and pyrethroid insecticides, we tested permethrin and propoxur as representatives of these two classes of compounds used for mosquito control. Larvicidal activity of both insecticides was assessed separately and together on a susceptible strain of the mosquito Culex quinquefasciatus (Diptera: Culicidae) by two methods. When mixed at a constant ratio (permethrin : propoxur 1 : 60 based on LC50) and tested at serial concentrations to plot dose/mortality regression, significant synergy occurred between them (co-toxicity coefficient = 2.2), not just an additive effect. For example, when the mixture gave 50% mortality, the same concentrations of permethrin and propoxur alone would have given merely 2 x 1% mortality. When a sublethal dose (LC0) of permethrin or propoxur was added to the other (range LC10-LC95), synergism occurred up to the LC80 level. Synergistic effects were attributed to the complementary modes of action by these two insecticide classes acting on different components of nerve impulse transmission. Apart from raising new possibilities for Culex control, it seems appropriate to consider using such mixtures or combinations for insecticide-treated mosquito nets in situations with insecticide-resistant Anopheles malaria vectors.     

Differential effects of Bacillus sphaericus strain 2362 on Culex quinquefasciatus and its competitor Culex cinereus in West Africa

The larval susceptibility to Bacillus sphaericus strain 2362 of the non-man-biting mosquito Culex cinereus and the urban filariasis vector Culex quinquefasciatus, two competitor mosquitoes in polluted habitats, was compared. In the laboratory, both species ingested a similar amount of B. sphaericus spores when fed c. 2 x 10(5) spores per ml for 30 min. However, in the same experiment, third-instar larvae of Cx quinquefasciatus were reduced by 98% at 24 h exposure while Cx cinereus larvae were only reduced by 6% at 72 h. In the field, preimaginal populations of Cx cinereus ingested, within a week, more than 99% of the applied spores, but showed no significant decrease through 14 days in cesspools treated at 10 g/m2 of a flowable concentrate of B. sphaericus 2362, containing 2 x 10(10) spores/g. It is proposed that specific biological control of Cx quinquefasciatus could result from appropriate treatment of breeding-sites with larvicidal B. sphaericus and competitive displacement by Cx cinereus or other mosquitoes with larvae that are more tolerant of B. sphaericus.     

Haemocyte population and ultrastructural changes during the immune response of the mosquito Culex quinquefasciatus to microfilariae of Wuchereria bancrofti

Abstract Haemocytes circulating in the haemolymph protect insects against pathogens that enter the haemocoel. Changes in haemocyte morphology and differences in haemocyte counts during the immune response of Culex quinquefasciatus Say (Diptera: Culicidae) to microfilariae of Wuchereria bancrofti (Cobbold) (Spirurida: Onchocercidae) were investigated in the present study. The mean number of total haemocytes was significantly elevated in infected mosquitoes (P < 0.001), reaching a peak on the third day post‐infection. Differential counts show that mean numbers of prohaemocytes, plasmatocytes, granular cells and oenocytoids increased significantly after infection with microfilariae granulocytes compared to the control and näive groups of Cx. quinquefasciatus (P < 0.05). Changes in proportional counts of haemocytes were also analysed in haemolymph perfusates of Cx. quinquefasciatus infected with W. bancrofti. On the first day post‐infection, infected mosquitoes showed an increase in the proportion of prohaemocytes (18.8% compared to 9.6% for the control) and of oenocytoids (7.1% compared to 4.7% control); however, they exhibited lower levels of plasmatocytes (36.6% compared to 42.1% control) and granular cells (36.1% compared to 41.4% control). On day 14 post‐infection, similar changes were observed for these haemocyte types, except that the proportion of granular cells was significantly greater than the control (41.2% compared to 31.3% control). Although an enhancement of prohaemocyte numbers was observed, this cellular type did not show any ultrastructural alteration. On the other hand, granular cells, plasmatocytes and oenocytoids presented morphological alterations indicative of innate immunological activation in mosquitoes infected with W. bancrofti.     

Screening of Brazilian Bacillus sphaericus strains for high toxicity against Culex quinquefasciatus and Aedes aegypti

Abstract:  In this work, 246 Bacillus sphaericus strains were evaluated against Aedes aegypti and Culex quinquefasciatus larvae to select the most effective ones to be used as the basis of a national product. All strains were isolated from different regions of Brazil and they are stored in a Bacillus spp. collection at Embrapa Genetic Resources and Biotechnology. The selected strains were characterized by biochemical and molecular methods. Based on selective bioassays, 87 strains were identified as toxic to one or both target species. All of these strains contain genes that encode the 42, 51 kDa proteins that constitute the binary toxin and the 100 kDa Mtx1 toxin. All toxic strains presented a very high LC₅₀ against A. aegypti , so, a product based on any of these B. sphaericus strains would not be recommended for use in programmes to control A. aegypti . S201 had highest activity against C. quinquefasciatus , presenting the lowest LC₅₀ and LC₉₀ in bioassays.     

Variations in life tables of geographically isolated strains of the mosquito Culex quinquefasciatus

Variations in the life tables and other biological attributes of four strains of Culex quinquefasciatus Say (Diptera: Culicidae) from geographically isolated regions of India that had been reared to the fifth generation in the laboratory were assessed under a standardized rearing regime under constant laboratory conditions. Two strains from arid habitats [Jodhpur (JD) and Bikaner (BKN)], one from a semi-arid inland habitat [Bathinda (BTH)], one from a semi-arid coastal habitat [Jamnagar (JMN)] and a standard laboratory strain (LAB) were compared. Horizontal life-table parameters were measured for each strain. Egg mortality ranged from 4.4% (JD and BTH) to 19.5% (BKN). The lowest rate of adult emergence and highest female : male ratio were found in BKN, and the highest rate of adult emergence and lowest female : male ratio were recorded in BTH. The egg-hatching period was longest in BTH and shortest in LAB. The duration from oviposition to adult emergence was longest in JD and shortest in LAB. Females lived longer than males in all strains. The net reproductive rates (R(0) ) of all field-derived strains (122.9-162.2) differed significantly between strains and were significantly greater than that of LAB (107.6). Similarly, both the intrinsic rate of increase (r(m) ) and finite rate of increase (λ) were found to be lower in LAB than in the field strains, but the mean generation time (T) and doubling time (DT) were longest in LAB. For several life-table attributes, JD and BTH clustered together and were more similar to JMN than to BKN and LAB. The results indicate that BTH, BKN and JD can be characterized as r-strategists, more so than JMN. Overall fecundity increased with age. Differences in annual temperature ranges and mean annual rainfall between locations were positively correlated (r = 0.46-0.97) with egg production, female life expectancy, R(0) , r(m) , λ and T. The results suggest that strains of Cx. quinquefasciatus from different geographical areas with contrasting habitats vary in their survival and reproductive strategies accordingly.     

Effect of fenthion treatment on larval densities of insecticide-resistant Culex quinquefasciatus in an urban area of Sri Lanka

Abstract. In Sri Lanka the national Anti-Filaria Campaign (AFC) has routinely employed fenthion since 1974 for larvicidal control of Culex quinquefasciatus , the vector of Bancroftian filariasis in urban areas, where this mosquito breeds prolifically in polluted waters. During 1994 the efficacy of AFC fenthion treatment against organophosphate-resistant Cx quinquefasciatus was investigated at Dehiwela, near Colombo.
The AFC target rate of fenthion application was 1 mg a.i./l, but the actual concentrations of fenthion in freshly treated pits ranged from 0.64 to 63.2 mg a.i./l. There was significant suppression of larval densities in treated soakage pits, the predominant breeding site of Cx quinquefasciatus , although the mosquito population was 6-fold resistant to fenthion at the LC_W level. Production of pupae was almost completely prevented in soakage pits which were sprayed weekly with fenthion, indicating that adult mosquito emergence from this source was minimal. The rapid decline in concentration of fenthion detected in the water of soakage pits indicated that a weekly treatment schedule is essential for effective control. With the rapid recolonization of treated sites, the weekly schedule must be strictly implemented in order to achieve control of resistant larvae. Fenthion activity levels detected in treated pits suggest that a 7–10 day schedule of retreatment would completely suppress susceptible Cx quinquefasciatus.     

Crossing type variability associated with cytoplasmic incompatibility in Australian populations of the mosquito Culex quinquefasciatus Say

An analysis of cytoplasmic crossing type variation in Australian populations of Culex quinquefasciatus, a member of the Culex pipiens complex of mosquitoes, revealed high levels of variability causing partial incompatibility between natural populations. Segregating crossing types were commonly found together within sampled sites. No correlation was evident between similarity of crossing type and environmental parameters of the sites, nor distance between sites. The nature of the observed variation did not support the hypothesis of paternally expressed nuclear 'restorer' genes. Such high levels of crossing type variation would be likely to impede attempts to control populations of the Culex pipiens complex using cytoplasmic incompatibility.