She's a femme fatale: low-density larval development produces good disease vectors.
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In the laboratory, longevity increases with size, then decreases at the largest sizes.Thus, our data indicate that uncrowded, low competition conditions for larvae produce the females that are most likely to be important vectors of dengue.More generally, ecological conditions, particularly crowding and intraspecific competition among larvae, are likely to affect vector-borne pathogen transmission in nature, in this case via effects on longevity of resulting adults.
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PubMed Central - PubMed
Affiliation: School of Biological Sciences, Illinois State University, Normal, IL, USA.
ABSTRACT
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Two hypotheses for how conditions for larval mosquitoes affect vectorial capacity make opposite predictions about the relationship of adult size and frequency of infection with vector-borne pathogens. Competition among larvae produces small adult females. The competition-susceptibility hypothesis postulates that small females are more susceptible to infection and predicts frequency of infection should decrease with size. The competition-longevity hypothesis postulates that small females have lower longevity and lower probability of becoming competent to transmit the pathogen and thus predicts frequency of infection should increase with size. We tested these hypotheses for Aedes aegypti in Rio de Janeiro, Brazil, during a dengue outbreak. In the laboratory, longevity increases with size, then decreases at the largest sizes. For field-collected females, generalised linear mixed model comparisons showed that a model with a linear increase of frequency of dengue with size produced the best Akaike's information criterion with a correction for small sample sizes (AICc). Consensus prediction of three competing models indicated that frequency of infection increases monotonically with female size, consistent with the competition-longevity hypothesis. Site frequency of infection was not significantly related to site mean size of females. Thus, our data indicate that uncrowded, low competition conditions for larvae produce the females that are most likely to be important vectors of dengue. More generally, ecological conditions, particularly crowding and intraspecific competition among larvae, are likely to affect vector-borne pathogen transmission in nature, in this case via effects on longevity of resulting adults. Heterogeneity among individual vectors in likelihood of infection is a generally important outcome of ecological conditions impacting vectors as larvae. Related in: MedlinePlus |
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Mentions: Frequency of dengue infection was best predicted by a model with wing length as a lineareffect (Table I) and this linear effect waspositive (slope ± SE = 1.24 ± 0.56, t476 = 2.20, p = 0.0285). wi indicated that the model with linear +quadratic effects of wing length also had some support, given this data set, based onAICc [and, indeed, any of the other information theoretic indices reported by SAS Institute (2011)]. For the quadratic model, thelinear effect of wing length was again positive (linear coefficient ± SE = 9.33 ± 7.33,t475 = 1.27, p = 0.2034), whereas the quadratic effect was negative (quadraticcoefficient ± SE = -1.46 ± 1.32, t475 = 1.11, p = 0.2688). The model omitting wing length entirely wassubstantially less likely as a model generating these data (Table I). Predicted frequencies of dengue infection for these twomost likely models, holding the random site effect constant at the value for theValqueire collection (Supplementary data, Fig. 2A,B, TableII) show that in both cases predicted frequency of dengue infection increasesfrom wing lengths of 2.0 mm to about 3.5 mm. At wing lengths from 3.5-4.0 mm thequadratic model predicts frequency of dengue infection declines, though never to the lowlevels observed for the smallest females (Fig.2B). We expected frequency of dengue infection to be related to day of collectionand the relationship proved to be quadratic, with frequency first increasing to a peakin the middle of the epidemic, then declining (Fig.2A, B). |
View Article: PubMed Central - PubMed
Affiliation: School of Biological Sciences, Illinois State University, Normal, IL, USA.