Effect of temperature, photoperiod, flooding, and drying on the hatching pattern of the eggs of Strelkovimermis spiculatus (Nematoda: Mermithidae).

We assessed the number of Strelkovimermis spiculatus preparasites obtained from a known initial number of nematode eggs and the effect of abiotic conditions (temperature, photoperiod, flooding-drying) on the number of emerged preparasites. Two egg groups were maintained: one continuously flooded, another with flooding-drying cycles (every 15, 30, 60 days). Each egg group was studied at 25°C and 14:10 (L:D) and 16°C and 12:12 (L:D). The flooded eggs contained a higher overall percentage of S. spiculatus preparasites compared to the wet-dry-cycle eggs. The conditions of continuous flooding at 16°C and 12:12 (L:D) produced the maximum percent of emerged J2s (30±15%). Preparasites were recorded by 7 (25°C) and 14 (16°C) days, suggesting this period as the minimum time for embryonic development. The preparasite-emergence time observed from the same flooded-egg batch (98 and 112 days at 25°C and 16°C, respectively) suggested a nonsynchronous hatching, possibly through nonuniform egg embryonation. The time of exposure to drought in the assays did not significantly affect the total average percentage of J2s obtained at 25°C and 14:10 (L:D), whereas at 16°C the number of emerged J2s diminished with a prolongation of the drying period. The oviposition period was also recorded only at 16°C and 12:12 (L:D): S. spiculatus eggs were detected at 12.6 days after postparasite emergence, and oviposition was complete at 51days under those conditions. We propose a flooding schedule to optimize the mass-rearing of S. spiculatus.

[Population dynamics of the immature stages of Aedes aegypti (Diptera: Culicidae), vector of dengue: a longitudinal study (1996-2000)]. / Dinámica poblacional de los estadios inmaduros del vector del dengue Aedes aegypti (Diptera: Culicidae): un estudio longitudinal (1996-2000).

A four year study was conducted on a natural population of immature stages of Aedes aegypti after the re-invasion of Argentina by this vector in 1987. Thirty six plastic containers with 700 ml of dechlorinated water were placed in the La Plata Zoological Garden, La Plata, Argentina. A strip of filter paper around each container was added to facilitate egg counting. Eggs, larvae and pupae were counted weekly in each container from September, 1996 to August, 2000. After egg counting, papers were submerged to facilitate egg hatching and a new paper was placed in each container. Presence of A. aegypti immature stages was recorded from December-January to June during each of the four years of this study. In 1997, 13,105 eggs, 7,978 larvae and 1,476 pupae were registered with 54.7 % positive containers; during 1998, 8,194 eggs, 668 larvae and 142 pupae were recorded with 28.3 % positive containers; 13,510 eggs, 3,690 larvae and 743 pupae were registered during 1999 with 56.7 % positive containers; and 16,327 eggs, 4,669 larvae and 715 pupae during 2000 with 59.3 % of containers with presence of A. aegypti. Egg number and hatching rate were drastically reduced in 1998 when temperatures from December to May were 1 to 2.5 degrees C lower than the other years of this study. These colder than usual temperatures in the summer of 1998 were a consequence of the El Niño event.

Efecto de la temperatura sobre la longevidad e infección con preparásitos del nematodo Strelkovimermis spiculatus (Nemata: Mermithidae), parásito de mosquitos culícidos / Effect of temperature on longevity and infection with the nematode Strelkovimermis spiculatus (Nemata: Mermithidae), a parasite of mosquitoes

Strelkovimermis spiculatus is a common parasite of culicid species in Argentina. Effect of temperature on longevity and infectivity of juvenile preparasites of S. spiculatus was determined at 4, 10, 20 and 27 degrees C. Three containers with 100 ml of dechlorinate water and 300 preparasites (12 hour-old), were placed for each day and temperature, during 40 days (total = 480 containers). Survived preparasites were counted on 12 containers per day (three for each temperature). When number of survived preparasites was determined, second instar larvae of Aedes aegypti were added to each container in a 10:1 ratio (preparasites:mosquito) to determine infectivity of daily survived preparasites. Longevity of preparasites decreased at higher temperatures. Maximum longevity of preparasites maintained at 4, 10, 20 and 27 degrees C were 35, 30, 25 and 27 days, respectively. Survivorship of preparasites, exposed to the same temperatures, varied from 57 to 100 at day two, from 21 to 77 at day five and from 9 to 33 at day ten. Infectivity of preparasites maintained at temperatures from 4 to 27 degrees C was always higher than 70. Extended longevity with maintenance of the infectivity capacity of preparasites, are important attributes to consider S. spiculatus an effective mean of controlling a large number of culicid species between 4 and 27 degrees C.

[Effect of temperature on longevity and infection with the nematode Strelkovimermis spiculatus (Nemata: Mermithidae), a parasite of mosquitoes]. / Efecto de la temperatura sobre la longevidad e infección con preparásitos del nematodo Strelkovimermis spiculatus (Nemata: Mermithidae), parásito de mosquitos culícidos.

Strelkovimermis spiculatus is a common parasite of culicid species in Argentina. Effect of temperature on longevity and infectivity of juvenile preparasites of S. spiculatus was determined at 4, 10, 20 and 27 degrees C. Three containers with 100 ml of dechlorinate water and 300 preparasites (12 hour-old), were placed for each day and temperature, during 40 days (total = 480 containers). Survived preparasites were counted on 12 containers per day (three for each temperature). When number of survived preparasites was determined, second instar larvae of Aedes aegypti were added to each container in a 10:1 ratio (preparasites:mosquito) to determine infectivity of daily survived preparasites. Longevity of preparasites decreased at higher temperatures. Maximum longevity of preparasites maintained at 4, 10, 20 and 27 degrees C were 35, 30, 25 and 27 days, respectively. Survivorship of preparasites, exposed to the same temperatures, varied from 57% to 100% at day two, from 21% to 77% at day five and from 9% to 33% at day ten. Infectivity of preparasites maintained at temperatures from 4 to 27 degrees C was always higher than 70%. Extended longevity with maintenance of the infectivity capacity of preparasites, are important attributes to consider S. spiculatus an effective mean of controlling a large number of culicid species between 4 and 27 degrees C.