Avian defensive behavior and blood-feeding success of the West Nile vector mosquito, Culex pipiens

Avian defensive behavior against host-seeking arthropods influencestransmission of vector-borne pathogens by affecting mosquitobiting rate, either by preventing vector–host contactor by increasing the rate of multiple host feeding. We exposedhouse sparrows (Passer domesticus L.) and chickens (Gallus gallusdomesticus L.) to Culex pipiens pipiens L. overnight in a largeobservation cage and measured avian defensive behavior ratesand mosquito blood-feeding success. Both bird species exhibiteda range of defensive behaviors, 90% of which were foot stomps,head movements, and wing shakes. Total behavior rates increasedproportionately with mosquito density in both species, increasedafter the first hour of mosquito exposure, and decreased asindividual birds were exposed to mosquitoes multiple times.Mosquito blood-feeding success on house sparrows was high overall(82 ± 5%) and independent of behavior rates. Blood-feedingsuccess on chicks was lower (58 ± 5%) and negativelycorrelated with defensive behavior rate after the first hourof mosquito exposure. Results revealed a higher percentage ofpartial blood meals on chicks (18 ± 3% of all blood mealson chicks) than on house sparrows (4.9 ± 3%). Birds ofboth species ate an average of 9.4 ± 1.2% of mosquitoes,and this percentage was positively correlated with defensivebehavior. High mosquito feeding success on house sparrows supportsits role as a potential amplifying host of West Nile virus.     

Mosquito seasonality and arboviral disease incidence in Murray Valley, southeast Australia

Abstract. Adult female mosquito populations were monitored at weekly intervals during spring-autumn (November-March) for 4 years (1991-95) using dry-ice-baited light traps at forty sites in the Murray Valley of Victoria, Australia. Among twenty species of mosquitoes collected, Culex annulirostriswas the most abundant (66.6 ± 9.3%) followed by Cx australicus(15.3 ± 7.7%). From a total of 476, 682 mosquitoes collected, nearly all were females and only 1295 (0.27%) were males. Mosquito population densities were generally higher in 1992-93 and 1993-94 seasons than in 1991-92 and 1994-95 seasons. Greatest densities of Cx annulirostrisand Cx australicusoccurred in 1992-93, coinciding with outbreaks of Ross River (RR) and Barman Forest (BF) arboviruses causing human polyarthritis. In the majority of shires, Cx australicuswas the predominant species from spring to early summer (November and December), then was replaced by Cx annulirostrisfrom mid-summer to autumn (January-April). In three shires, Aedes bancroftianusand Ae.sagaxpredominated during the early part of the season. Densities of both Cx annulirostrisand Cx australicuswere related to temperature. Cx australicusadults were found to be trapped when the mean ambient temperature exceeded 6d?C, with peak population recorded at 20d?C. Cx annulirostrisadult density increased when the mean temperature rose above 12d?C, reaching a peak during February and March when temperature exceeded 25d?C. Cx annulirostrisdeclined rapidly from April onwards, with no adult activity evident from May to November. Population densities of Aedesspp. were generally less than reported from earlier studies, possibly due to lower rainfall in spring and summer as well as reduced flood irrigation practices. In each year, a significant correlation was detected between Cx annulirostrisdensity and RR virus incidence in humans. As Cx annulirostrisis the predominant local mosquito species and feeds on a wide spectrum of hosts including man, it seems likely that Cx annulirostrisis the major vector of RR in the inland Murray Valley region.     

Bait-fed adult Culex pipiens carry the larvicide Bacillus sphaericus to the larval habitat

Sugar meals of plant origin are a basic component of mosquito diet. We show that sugar baits have potential as vehicles for control agents. When Culex pipiens L. resting-sites were sprayed with sucrose solution, with or without incorporation of the larval toxicant Bacillus sphaericus Neide, 47% of female mosquitoes fed in situ. Dispersing B. sphaericus-carrier mosquitoes caused larval mortality in breeding-sites 60-100 m from the sprayed resting-sites. The effect was not seen where no adults rested in sparse vegetation above larval habitats. This approach may be useful for the application of biological control agents against mosquitoes in biotopes where the adults and larvae are juxtaposed.