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 sublethal dose of diflubenzuron and azadirachtin on various life table attributes of Culex quinquefasciatus (Diptera: Culicidae).

The exposure of sublethal doses (25% emergence inhibition) of diflubenzuron (DFB) (0.0002 mg/liter) and azadirachtin (AZD; 0.0079 mg/liter) insect growth regulators was provided to late third- early fourth instars of Culex quinquefasciatus till emergence of adults to find out the effects on various biological and life table attributes of adults, and comparison was made with control (CTL) as well. Life expectancy of both males and females of DFB survivors was significantly less in comparison with AZD and CTL ones; however, it was nonsignificantly different between CTL and AZD. In all treatments, males were shorter lived than females of their respective treatments. DFB survivors showed significant reduction in number of blood-fed females, resulting in minimum of oviposition days, total number of egg rafts, total number of eggs, eggs per egg raft, eggs per female life span, and eggs per female per day than survivors of both AZD and CTL significantly, but these parameters did not differ significantly between CTL and AZD, except eggs per egg raft. The net reproductive rate, intrinsic rate of increase, and finite rate of increase were significantly less in DFB than rest of the survivors, whereas doubling time for generation was significantly high; however, difference in mean generation was not significant among them. This study reveals that DFB has the potency to affect severely the various life table attributes at sublethal dose, but AZD does not have such effectiveness at similar sublethal dose against Cx. quinquefasciatus.

Variation in morphology and morphometrics of eggs of Culex quinquefasciatus mosquitoes from different ecological regions of India.

Variation in egg surface morphology and morphometrics of Culex quinquefasciatus mosquitoes of the Jodhpur, Bikaner, Jamnagar, and Bathinda strains were correlated with geographical distribution in different ecological regions of India. We report the geographic variation in Cx. quinquefasciatus based on 44 attributes of micropylar and conical-shaped regions of eggs, including micropylar apparatus (corolla, disc, and mound), micropylar tubercles, and the exochorionic tubercle, pores, and network in anterior, middle, and posterior regions. No remarkable differences were observed in the surface morphology of eggs of these strains except the absence of small tubercles in the anterior and middle region of the JMN strain. However, a statistical analysis indicated significant morphometric variations in 66% of the attributes of the eggs. The cluster analysis of all egg attributes showed that the JD, BKN, and BTH strains are closer to each other than the JMN strain. The positive correlation (r = 0.95) also indicated an effect of geographical distribution on morphometry of various egg attributes of these strains. The present study suggests that ecological variation may have affected the morphometric attributes of the egg of four strains of Cx. quinquefasciatus from different geographical areas.

Scanning electron microscopic studies on egg surface morphology and morphometrics of Culex tritaeniorhynchus and Culex quinquefasciatus (Diptera: Culicidae).

Culex tritaeniorhynchus Giles, 1901 and Culex quinquefasciatus Say, 1823 is an important vector of Japanese encephalitis and Bancroftian filariasis, respectively in India and South East Asian countries. In this paper, we are describing the surface morphology and morphometrics of the egg of C. tritaeniorhynchus in comparison with C. quinquefasciatus for the first time. The results indicated that eggs of both the species appears to be similar to great extent in surface morphology, however, morphometrics provide 56.81% demarking attributes out of 44 attributes at various significant levels (p < 0.05-0.001), i.e., egg length, width and ratio of length/width, attributes of micropylar apparatus including corolla, disc, mound, tubercles size, and length of tubercular rows in micropylar region, size and density of tubercles, exochorionic pore in conical-shaped regions of eggs, and size of tubercular wheel units. Structurally, the additional presence of large tubercles strengthens the micropylar region to bear various collapsing forces in these species.