Predation on Eggs of Aedes aegypti (Diptera: Culicidae): Temporal Dynamics and Identification of Potential Predators During the Winter Season in a Temperate Region

In temperate regions, the populations of Aedes aegypti (L.) remain in the egg stage during the cold season. The ability of these eggs to survive until the next favorable season is affected by several mortality factors, including the action of predators. In the present study, we analyzed the temporal dynamics of the loss of eggs and identified predators of Ae. aegypti eggs along the unfavorable season in a temperate region of Argentina. To this end, eggs were exposed in field conditions in pitfall traps, where walking arthropod taxa were captured during 1-wk periods from early June to early September (Austral winter).The association of arthropod taxa with the loss of eggs was analyzed to identify potential predators. Based on the results obtained, two taxa were chosen to confirm their capacity to consume eggs in a laboratory study. The proportion of lost eggs and the abundance of predators were significantly higher in the winter–spring transition, although results were heterogeneous among traps in all exposure periods. Ants of the genus Strumigenys, isopods of the species Armadillidium vulgare (Isopoda: Armadilloidea), and dermapterans of the species Euborellia annulipes (Dermaptera: Anisolabidae) were positively associated with a high proportion of lost eggs. In laboratory conditions, A. vulgare and E. annulipes consumed the offered eggs, thus confirming their predator capacity.This study represents the first record of predation of Ae. aegypti eggs in temperate South America and the first evidence of dermapterans consuming mosquito eggs.Fil: Byttebier, Bárbara. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; ArgentinaFil: Fischer, Sylvia Cristina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentin

Hatching Response of Aedes aegypti (Diptera: Culicidae) Eggs at Low Temperatures: Effects of Hatching Media and Storage Conditions

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.Fil: Byttebier, Bárbara. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; ArgentinaFil: de Majo, María Sol. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; ArgentinaFil: Fischer, Sylvia Cristina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentin

Winter ecology of Aedes aegypti (Diptera: Culicidae) eggs in Buenos Aires city

Aedes aegypti es un mosquito de importancia epidemiológica por ser vector de varios virus que afectan a la salud humana. La ciudad de Buenos Aires se encuentra cerca del límite austral de la distribución de esta especie. La presencia endémica en esta región se relaciona con la capacidad de permanecer en el estado de huevos de resistencia durante la temporada invernal, y los procesos que reducen el número de huevos durante dicho período pueden afectar significativamente la persistencia interanual. En este trabajo se estudiaron los procesosrelacionados con la reducción del banco de huevos durante el período invernal, como lamortalidad, pérdida por predación y las eclosiones a destiempo. Se evaluaron además losfactores asociados a estos procesos como las condiciones climáticas, las característicasambientales del entorno, y el efecto de la predación sobre los huevos de Aedes aegypti. Losprincipales resultados indican que el banco de huevos es principalmente afectado por la pérdida de huevos, mientras que la mortalidad sería menos relevante. La ocurrencia de eclosiones en momentos en que las condiciones térmicas no son favorables para completar el desarrollo también generaría una reducción del banco de huevos. El comportamiento de la población local mostró características propias que la diferencian de las poblaciones de otras regiones.Aedes aegypti is an epidemiologically important mosquito because it is the vector of several viruses that affect human health. Buenos Aires city is located near the southern distribution limit of this species, and the endemic presence of Aedes aegypti in this region is related to its ability to remain in the egg stage during winter season. Thus, processes that reduce the number of eggs during this period may affect inter annual persistence. In thisthesis, processes related to the reduction of the eggs bank during the winter were studied,such as mortality, loss of eggs due to predation and hatching at unfavorable temperatures. Factors associated to these processes like climatic conditions, surrounding habitatcharacteristics, and effects of predation on Aedes aegypti eggs were also assessed. Mainresults indicate that eggs bank is most importantly affected by eggs loss, while mortality seemsless relevant. Occurrence of hatchings in periods when temperature conditions are not favorable to complete development might also reduce eggs bank. The dynamics of the local population exhibited particular characteristics, different from populations inhabiting other regions.Fil: Byttebier, Bárbara. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Dinámica estacional de larvas y adultos de dos especies de Enochrus Thomson (Coleoptera: Hydrophilidae) en cuerpos de agua temporarios y permanentes en un parque urbano de Buenos Aires

Se estudió la dinámica de Enochrus variegatus (Steinheil) y Enochrus vulgaris (Steinheil) en ambientes acuáticos temporarios y permanentes de un parque de Buenos Aires, Argentina. Las muestras fueron colectadas semanalmente a lo largo de un año en ambos tipos de ambiente, y se registraron variables como la superficie anegada y la cobertura vegetal. En los ambientes permanentes se capturaron ejemplares adultos de ambas especies a lo largo de todo el período de estudio, mientras que en temporarios su presencia varió de acuerdo con la disponibilidad de agua. Se observaron diferencias en la época reproductiva y sitios de cría de ambas especies. Enochrus vulgaris mostró una estrategia más oportunista, y sus larvas fueron detectadas en los dos tipos de ambiente asociadas principalmente con temperaturas de la primavera y el verano. En cambio las larvas de E. variegatus fueron registradas casi exclusivamente en cuerpos de agua temporarios durante el invierno y la primavera. En ambientes permanentes, ambas especies estuvieron asociadas con una mayor cobertura vegetal, lo cual podría estar relacionado con la disponibilidad de refugios de peces predadores. Para ambas especies el primer estadio larval fue colectado en mayor abundancia y frecuencia que los restantes. Las larvas de este estadio fueron registradas en semanas consecutivas y simultáneamente con larvas del tercer estadio, indicando que la oviposición o el desarrollo de los estadios inmaduros no estaban sincronizados dentro de cada una de las dos poblaciones estudiadas. En varias ocasiones se capturaron larvas del segundo estadio de ambas especies en charcos que estuvieron secos la fecha de muestreo anterior, sugiriendo que no eclosionaron de huevos recientemente puestos. Nuestros resultados muestran que los adultos de estas especies son capaces de dispersarse desde y hacia charcos temporarios para evitar la sequía, y que sus larvas podrían resistir la sequía en los ambientes temporarios enterrándose en el sustrato.The dynamics of Enochrus variegatus (Steinheil) and Enochrus vulgaris (Steinheil) in temporary pools and permanent ponds were studied in an urban park of Buenos Aires, Argentina. Samples were collected from both types of habitats weekly throughout one year, and variables like water surface and vegetation cover were recorded. In permanent ponds, adults of both species were found throughout the study period, while in temporary pools their presence depended on the availability of water. Differences in their reproductive seasons and breeding sites were observed. Enochrus vulgaris was characterized by an opportunistic strategy, and its larvae were detected in both types of habitats, associated mainly with spring and summer temperatures. Conversely, E. variegatus larvae were recorded almost exclusively in temporary pools, during the winter and spring seasons. In permanent ponds, both species were associated with vegetation cover, which could be related to the availability of refuges from fish predators. First instar larvae showed the highest abundance and were captured more frequently, in consecutive weeks and simultaneously with third instar larvae, suggesting that the two populations studied are not synchronized in oviposition time or development of immature stages. In several occasions, second instar larvae of both species were captured in a pool that had been dry during the previous sampling date, suggesting that they had not hatched from fresh laid eggs. Our findings show that adults of these species are capable of dispersal to and from temporary pools to avoid drought. In addition, their larval stages may also be able to resist drought in the pools by burrowing into the substrate.Fil: Byttebier, Bárbara. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ecología, Genética y Evolución; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Fischer, Sylvia Cristina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ecología, Genética y Evolución; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Torres, Patricia Laura Maria. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Biodiversidad y Biología Experimental; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Effects of scarcity and excess of larval food on life history traits of Aedes aegypti (Diptera: Culicidae)

Few studies have assessed the effects of food scarcity or excess on the life history traits of Aedes aegypti (L.) (Diptera: Culicidae) independently from larval density. We assessed immature survival, development time, and adult size in relation to food availability. We reared cohorts of 30 Ae. aegypti larvae from newly hatched to adult emergence with different food availability. Food conditions were kept constant by transferring larvae each day to a new food solution. Immature development was completed by some individuals in all treatments. The shortest development time, the largest adults, and the highest survival were observed at intermediate food levels. The most important effects of food scarcity were an extension in development time, a decrease in the size of adults, and a slight decrease in survival, while the most important effects of food excess were an important decrease in survival and a slight decrease in the size of adults. The variability in development time and adult size within sex and treatment increased at decreasing food availability. The results suggest that although the studied population has adapted to a wide range of food availabilities, both scarcity and excess of food have important negative impacts on fitness.Fil: Romeo Aznar, Victoria Teresa. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Alem, Iris Soledad. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: de Majo, María Sol. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Byttebier, Bárbara. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Solari, Hernan Gustavo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Fischer, Sylvia Cristina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentin