Epidemiology of West Nile virus: a silent epiornitic in Northern Delaware in 2007 without associated human cases.

ABSTRACT. We performed a 2-year longitudinal study (2006-2007) of West Nile virus (WNV) infections in wild birds, mosquitoes, and sentinel chickens at 6 WNV-endemic sites in northern Delaware. We determined virus infection rates of Culex pipiens and other mosquito vectors as well as seroprevalence and antibody titers of amplifying hosts. Endemicity status varied widely among the 6 sites based on 3 criteria-mosquito infections, sentinel chicken seropositivity, and wild bird seropositivity. A highly endemic site would display at least 2 of the 3 criteria during each year of the study, while a site with just 1 positive criterion was considered to have low endemicity. Culex pipiens was the principal vector detected at 2 highly endemic sites in 2006 vs. 1 site in 2007. However, in 2006, we also found 2 other WNV-positive vector species as well as an unidentifiable Culex species at 1 highly endemic site, suggesting increased activity at the end of the 1st year of the study. Wild birds were early indicators of WNV at highly endemic sites in mid-July to early August of both 2006-2007. Mosquitoes were positive in mid- to late August, appearing concurrently with seroconverted sentinel chickens, with wild resident birds appearing approximately 4 wk prior to those indicators. Of birds tested with n > or = 9, Northern cardinals had the highest seropositivity rates (47%) followed by Carolina wrens (19%), house sparrows (13%), American robins (13%), tufted titmice (11%), and gray catbirds (9%). The overall seropositive rates in trapped birds increased from 5.0% in 2006 to 20.0% in 2007, while the geometric mean titers of all positive birds increased from 1:34 to 1:47 during the comparable periods. Based on these results, we suggest that an epiornitic in birds occurred in 2007, but that greatly reduced abundance of mosquito vectors caused by an extreme drought largely precluded human infection.

Copulatory courtship signals male genetic quality in cucumber beetles.

In the spotted cucumber beetle, Diabrotica undecimpunctata howardi (Coleoptera: Chrysomelidae), males court females during copulation by stroking them with their antennae. Stroking occurs exclusively during the first stages of copulation, after a male has penetrated a female's vaginal duct but before he is allowed access to her bursa copulatrix. Females accept the spermatophore of fast-stroking males and reject those of slow-stroking males by relaxing or constricting muscles distorting the vaginal duct. Here, we measure the repeatability of stroking behaviour within males, examine the effect of losing one antenna on male attractiveness and test whether such female control results in direct phenotypic benefits for the discriminating female or indirect genetic benefits that appear in her offspring. We also use a half-sibling design to quantify the variance and heritability of stroking speed and endurance. Female beetles were paired with a male that was known to stroke either quickly or slowly. No difference was found in the resulting fecundity or egg-hatching rate of the females, or in the survivorship, development rate, size, age at first reproduction or fecundity of their offspring indicating that no direct benefits are gained by discriminating among males on the basis of stroking speed. There were, however, good-genes benefits for the mates of fast-stroking males. Offspring of fast-stroking fathers were also fast strokers and were more likely to be accepted as mates than offspring of slow-stroking fathers. There was substantial variance among sires in stroking speed and endurance and the heritability of each trait was high. The antennal stroking rate was highly repeatable in successive mating attempts and males with only one antenna were not accepted as mates. The repeatability within males, variability between males and heritability between generations of copulatory stroking combine to provide females with a reliable and honest signal of the genetic quality of courting males.