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We examined the responses of a Spartina densiflora (Poaceae) marsh to an accidental summer fire taking place in the Otamendi Natural Reserve (Argentina). Green, standing dead, reproductive and litter fractions of S. densiflora, as well as forbs biomass were determined before and after burning using randomly selected quadrates. Fire reduced most of the aboveground biomass of the green, standing dead and litter fractions of S. densiflora. Green biomass attained higher values before the fire as compared to those from the first year after burning during the spring, while the second year spring attained intermediate values. The standing dead material represented the main fraction of S. densiflora biomass in the pre-fire period, and after burning, this fraction reappeared in autumn, 4 months after the fire. The litter showed zero values throughout the first 16 months after the fire, and reappeared at end of the second winter. The flower biomass was exclusively recorded on late summer and showed relatively low values. Seedling recruitment of S. densiflora was not observed throughout the study period. Forbs biomass showed large fluctuations both before and after fire and highest forbs biomass values were observed during the spring before fire, and at end of summer 1 year after the fire. Although the results of the present study showed a tendency towards the original structure, most of the biomass fractions did not reach values similar to those before the fire after 2 years of post-fire growing, suggesting that a longer recovering time is expected.

In temperate regions, the seasonal dynamics of Aedes aegypti (L.) (Diptera: Culicidae) is mainly influenced by temperature. It is assumed that, during the winter season, the population remains as eggs and that the development and population growth of surviving eggs begin during the following spring. The aim of the current study was to assess egg hatching of Ae. aegypti during the winter in Buenos Aires city (Argentina), and analyze the survival of immature stages. The experiments consisted of immersing eggs and studying the development of immature stages of cohorts from June and September under natural temperature conditions. The proportion of hatched eggs was compared between weeks of immersion and related to environmental variables. Survival was compared among cohorts and the development rate was related to the mean temperature during development. The results showed that, with few exceptions, egg hatching was over 45% during the winter period. The proportion of hatched eggs was positively associated with immersion temperature, pre-immersion temperature and photoperiod. The immature stages completed the development during the cold season, with a trend toward increased survival of late-hatching cohorts. Survival was 30% at 13.2 °C and above 90% at 20 °C, whereas the development time at low temperatures was 49.4 d at 13.2 °C and 17.7 d at 20 °C. The high hatching and survival compared with other studies suggest that the local population might be adapting to winter conditions. The anticipated emergence of adults would be adaptive if they are able to reproduce successfully in the early spring.

Notonectids are well-known predators in aquatic habitats, where mosquito larvae, chironomids, and cladocerans constitute their main diet. Our purpose was to assess the effect of structural complexity on the predatory ability of Buenoa fuscipennis, a common predator in aquatic habitats of Buenos Aires city (Argentina). Buenoa fuscipennis showed type 2 functional responses in both the presence and absence of prey refuge and no differences in attack rate or handling time between refuge treatments. Regarding mosquito size classes, B. fuscipennis exhibited a significantly higher preference for 2 nd instar larvae and no predation on pupae. In the presence of mosquito larvae and alternative prey, B. fuscipennis preferred mosquitoes over chironomid larvae and adult cladocerans over mosquito larvae. No switching behavior was detected in our experiments. Habitat structure only slightly affected the predator´s consumption rates on mosquito larvae. Overall, preference for prey did not vary with the presence of refuge, except for the preference for mosquitoes over chironomid larvae, which was significantly decreased in the presence of refuge as a consequence of reduced predation on mosquito larvae. The results suggest that B. fuscipennis could efficiently control mosquitoes in structurally simple habitats where chironomids are the most abundant alternative prey but not in temporary pools where cladocerans are abundant. Journal of Vector Ecology 38 (2): 215-223. 2013.

In temperate regions, populations of Aedes aegypti survive the cold season in the egg stage. In the present work, we studied the cold-season mortality of Ae. aegypti eggs and their subsequent hatching pattern in Buenos Aires city. Eggs were exposed during the winter season (three months) in three neighborhoods located along a gradient of distance toward the Río de la Plata River, coincident with a gradient of activity of Ae. aegypti. Results showed mortalities lower (30.6%) than those from tropical regions during the dry season. Significant differences were detected among the egg mortalities of each site with a maximum value at the site nearest the Río de la Plata River (50%), and a minimum value at the most continental site (9%). Post-experimental hatching response of eggs differed between sites, with the highest proportion of hatched eggs during the first immersion in the site nearest to the river and the lowest proportion in the most continental site. The hatching proportion also differed between age classes, with older (early-laid) eggs hatching later than new (late-laid) ones. Our results provide the first information of Ae. aegypti egg mortality in temperate South America and support the hypothesis that differences in egg mortality are associated with abundance patterns of Ae. aegypti in Buenos Aires city. Journal of Vector Ecology 36 (1): 94-99. 2011.

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In temperate regions, Aedes aegypti (L.) (Diptera: Culicidae) populations remain in the egg stage during the cold season. To ensure the start of a new breeding season, eggs should hatch at the beginning of a favorable period. The aim of the current study was to investigate the hatching response of two Ae. aegypti egg batches collected and stored for 3 mo under different conditions, to different low immersion temperatures. Two different hatching media (water and yeast solution) were used for the first batch and only one (water) for the second egg batch. Eggs were immersed for 8 d, during which the number of hatched eggs was recorded daily. The proportion of hatched eggs, delay of the hatching response, proportion of dead larvae, and proportion of remaining eggs within the first egg batch were compared between the two hatching media at each temperature. These parameters also were compared between the two batches immersed in water. Hatching rates were higher and faster in the yeast solution. The hatching response was lower at lower immersion temperatures and among eggs stored under field conditions at colder temperatures (second batch). Among the eggs stored in the laboratory (first batch), older eggs exhibited lower hatching response. The proportion of dead larvae was higher in the yeast solution and in the eggs stored in the laboratory. The conditions that triggered a lower hatching response led to higher proportions of remaining eggs, allowing the population to maintain an egg bank for future favorable opportunities.

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