She’s a femme fatale: low-density larval development produces good disease vectors

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.

Distribución vertical de haemagogus janthinomys (dyar) (diptera: culicidae) en bosques de la amazonía peruana / Vertical distribution of the mosquito Haemagogus jantinomys (Dyar) (Diptera: Culicidae) in forests of the Peruvian Amazon

Objetivos: Determinar si la abundancia del mosquito Haemagogus janthinomys está relacionada con la temperatura y lahumedad relativa, y si varía entre el dosel y el sotobosque en tres tipos de bosques de la selva Amazónica, medido porcebo humano. Materiales y métodos: Se colectó Hg. janthinomys al mismo tiempo en dos estratos de tres sitios en trestipos de bosques -bosque que se desarrolla sobre suelo arcilloso, sobre arena blanca (varillal), y bosques inundables(bajiales) cerca de Iquitos, Perú. Se midió la temperatura y la humedad relativa cada 15 minutos durante el tiempo decolecta. Resultados: No se encontró Hg. janthinomys en los bajiales mostrados. Su abundancia fue igual en el montealto que en los varillales (Z = 1, 48; p = 0,14), pero fue mayor en el dosel (2,9; ± 0,89) que en el sotobosque (0,4; ±0.23) (Z = 2,80; p = 0,005). No se encontró una relación entre la abundancia de Hg. janthinomys y la temperatura y lahumedad relativa (F1, 14 < 0,33; p > 0057; r2 < 0,03). Conclusiones: Estos resultados preliminares indican que alrededorde Iquitos, como en otras regiones, Hg. janthinomys es más abundante en el dosel. También, los resultados sugieren quela probabilidad de encontrar Hg. janthinomys puede depender del tipo de bosque en la selva amazónica peruana, perono depende en la variación de la temperatura ni la humedad relativa que es típica para los bosques tropicales.

Objectives: Our goals were to determine if the abundance of the mosquito Haemagogus janthinomys is correlated with environmental variables, and if it differs between the canopy and understory in three different Amazonian forest types. Materials and methods: Adult Hg. janthinomys mosquitoes were collected via human landings simultaneously in the canopy and understory of three replicate high forest, white sand forest, and seasonally flooded forest sites near Iquitos, Peru. Temperature and relative humidity were recorded every 15 min. during the collection periods. Results: No Hg. janthinomys were collected in seasonally flooded forest. Their abundance was similar between high forest and white sand forest (Z = 1, 48; p = 0,14), but more individuals were encountered in the canopy (2.9; ± 0.89) than in the understory (0,4; ± 0.23) (Z = 2.80; p = 0,005). Hg. janthinomys abundance was not correlated with temperature or humidity (F1, 14 < 0.33; p > 0057; r2 < 0.03). Conclusions: These preliminary results show that around Iquitos as in other regions, Hg. janthinomys are most abundant in the forest canopy. They also suggest that the probability of encountering Hg. janthinomys it can depends both on forest type and height of sampling within forests, but is not a function of temperature and humidity within the ranges commonly encountered in tropical forests.