Culex pipiens, Linnaeus, 1758

Ferguson, Laura V., Hillier, N. Kirk & Smith, Todd G., 2013, Influence of Hepatozoon parasites on host-seeking and host-choice behaviour of the mosquitoes Culex territans and Culex pipiens, International Journal for Parasitology: Parasites and Wildlife 2 (1), pp. 69-76 : 72-73

3.2. Host-seeking behaviour of infected and uninfected C. pipiens

C. pipiens did not respond to frogs at 15 days nor at 30 days PF ( Table 2). However, a proportion of C. pipiens , in both infected and control groups, was responsive to uninfected snakes at 15 days and 30 days PF ( Table 3). A significantly lower proportion of infected C. pipiens (31%) than uninfected mosquitoes (52%) obtained a second blood meal from snakes at 15 days PF (Chi-Square Test, / 2 1 = 3:83, P = 0.05). A very low proportion of both infected and uninfected mosquitoes obtained a blood meal at 30 days PF ( Table 3), and the difference in these proportions were not significant (P = 0.44). Infection of mosquitoes was confirmed at 30 days PF by presence of oocysts in the abdomen. Following blood meals, all C. pipiens included in analysis oviposited on moistened cotton pads.

3.3. Proportions of mosquitoes feeding on infected and uninfected frogs and snakes

Analysis of data from several trials of initial feeding (0 days PF) revealed that the proportion of mosquitoes that initially fed, versus did not feed, on frogs infected with H. clamatae (62%) and snakes infected with H. sipedon (69%), compared to the proportion of mosquitoes that initially fed on uninfected frogs (37%) or uninfected snakes (40%), respectively, was significantly higher ( Table 4; / 2 1 = 5:44, P = 0.02 for frogs and / 1 2 = 20, P <0.0001 for snakes).

3.4. Preference of mosquitoes for infected and uninfected green frogs: interrupted feeding, paired-choice trials

Higher numbers of mosquitoes chose to land on wild-caught frogs with high intensity infections of H. clamatae when paired with frogs with moderate intensity infections or without infection ( Fig. 1 ). However, similar numbers of mosquitoes chose to land on wild-caught frogs from the four other infection intensity combinations ( Fig. 1 ). Overall, infection level had a weakly significant effect on the number of mosquitoes choosing to land on a frog (Two-Way ANOVA, F 3 = 2.4, P = 0.09). Trials repeated with experimentally infected frogs revealed that infection level in a frog did not affect the number of mosquitoes that chose to land ( Fig. 2; F 2 = 0.17, P = 0.84).

3.5. Preference of mosquitoes for infected and uninfected green frogs: uninterrupted feeding, single-choice trials

Similar numbers of mosquitoes fed on both infected (n = 39) and uninfected (n = 35) frogs over six trials (Welch’s Two Sample T -test, t 74 = 0.5, P = 0.61). However, a significantly higher proportion of mosquitoes began to land on infected frogs later, or after approximately 20–30 min had elapsed in the trial, compared to the time to land on uninfected frogs ( Fig. 3 top; Wilcoxon Rank Sum, W = 542, P = 0.04). Fortuitously, the time to land was also recorded in interrupted host choice trials, which allowed comparison between interrupted and uninterrupted feeding trials. Statistically significant differences in the time for mosquitoes to land on infected and uninfected frogs were not found in interrupted host choice trials ( Fig. 3 bottom; W = 767, P = 0.36).

A significantly longer interval elapsed between the bite of one mosquito and the bite of the subsequent mosquito when between bites on infected frogs or uninfected frogs in either interrupted feeding trials (W = 445, P = 0.84) or uninterrupted trials (W = 529, P = 0.48) were not observed, and thus the total bites per trial, either with interrupted or uninterrupted feeding, were pooled for comparison.

mosquitoes were allowed to feed, as opposed to when they were removed from the frog after landing ( Fig. 4 ) (W = 992, P <0.0001). Statistically significant differences in the interval

Figures

Fig. 1. Number of mosquitoes that chose wild-caught frogs paired by different levels of infection. Each panel represents a pairing by infection level in green frogs. Each trial was repeated three times, and separate trials are shown by different shapes.Higher numbers of mosquitoes chose to land on wild-caught frogs with high infections of H. clamatae when paired with frogs with moderate infections or without infection. Infection level had a weakly significant effect on the number of mosquitoes that chose to land on a frog. UI = uninfected.

Fig. 2. Number of mosquitoes that chose laboratory-raised frogs that were uninfected or experimentally infected. Each panel represents a pairing of infected or uninfected green frogs. Each pairing was repeated four times and each trial is represented by a different shape. Infection level did not have a significant effect on the number of mosquitoes choosing to land on a frog.

Fig. 3. Time of mosquito biting activity on infected or uninfected frogs. Mosquitoes that fed on infected frogs are represented by the solid line, and those that fed on uninfected frogs are represented by the dashed line. The top figure represents the time for each mosquito to land in trials where mosquitoes were allowed to feed to repletion (i.e., uninterrupted trials). A significantly higher proportion of mosquitoes that fed on infected frogs began to land later in the trial, compared to mosquitoes feeding on uninfected frogs. The bottom figure represents the time for each mosquito to land in trials where mosquitoes were allow to land but were removed before feeding (i.e., interrupted trials). A significant difference in the time for mosquitoes to land on infected or uninfected frogs was not observed in interrupted trials.

Fig. 4. Time between mosquito bites on infected and uninfected frogs. Mosquitoes that were allowed to feed are represented by a solid line. Mosquitoes that were aspirated off the frog after landing are represented by the dashed line. A significantly longer amount of time passed between the bite of one mosquito and the bite of the following mosquito during trials in which mosquitoes were allowed to feed on a frog, compared to trials where mosquitoes were removed before feeding.