Temporal dynamics of the egg bank of Aedes aegypti (Diptera: Culicidae) in the winter-spring transition in a temperate region.

In temperate regions, the populations of Aedes aegypti (L.) (Diptera: Culicidae) remain in the egg stage during the winter. In Buenos Aires, Argentina, a temperate region in the southern limit of Ae. aegypti distribution, the start of the next reproductive season and the rate of increase of the adult population depend on the egg bank that remains after the winter. This study aimed to analyze the mortality, field-hatching, and survival of eggs exposed to field conditions representative of those that occur in nature. In addition, the post-exposure hatching response of the eggs was assessed. Four egg batches were exposed to natural conditions starting in mid-winter and were recovered progressively after 3, 6, 9, and 12 weeks. One egg batch (initial control) was not exposed in the field and remained under laboratory conditions. After the exposure period, the recovered intact, collapsed, and hatched eggs were counted. Intact eggs were immersed three times in the laboratory to study their hatching response. Progressive increases in the proportion of lost (presumably by predation), dead, and hatched eggs in successive egg batches were recorded. Field-hatching was recorded from late winter onwards. The first hatchings occurred in conditions probably not favorable to complete development into reproductive adults. A progressive decrease in live eggs was observed, with 51% of the recovered eggs alive after 12 weeks of exposure. In the laboratory, the hatching response in the first immersion was low for the initial control and for the eggs exposed for 3 weeks, and increased for successive cohorts. The results confirm that the survival of Ae. aegypti eggs in the winter-spring transition ensures persistence throughout the next favorable season in Buenos Aires City. The observed inhibition to hatch of the first batches might relate to a photoperiod-induced diapause, as observed in previous studies.

Effect of Parental Photoperiod on Body Size and Developmental Time of Aedes aegypti (Diptera: Culicidae) in Buenos Aires City.

Many insects use photoperiod as a signal to anticipate upcoming unfavorable conditions. Photoperiod sensitivity may be a relevant factor in Aedes (Stegomyia) aegypti (L.) populations at the cool margins of the species' range, where winter conditions have a strong effect on population dynamics. In this study, we evaluated the effect of parental photoperiod on preimaginal survival and developmental time, and on wing length for the first generation of Ae. aegypti from a temperate region (Buenos Aires City, Argentina). Our experiment started with eggs from parents exposed to short-day (SD; 10:14 [L:D]) or long-day (LD; 14:10 [L:D]) photoperiods during their entire life span. Eggs were stored under the same photoperiod (SD or LD) as their parents for 91 d, until immersion. After hatching, larvae were reared until adult emergence in thermal baths at one of two constant temperatures (17 or 23°C), at a photoperiod of 12:12 (L:D) h and fed ad libitum. Survival from larva I to adult emergence was not affected either by parental photoperiod or rearing temperature. At a rearing temperature of 23°C, female offspring from the SD parental photoperiod developed faster and had shorter wings compared with those from the LD parental photoperiod. No effect of parental photoperiod was observed on female offspring reared at 17°C. In male offspring, parental photoperiod had no effect on developmental time and wing length, independently of the rearing temperature. Results indicate that the parental photoperiod may affect some offspring traits. This effect may be a characteristic of Ae. aegypti populations in temperate regions to deal with the winter conditions.

Adaptation to temperate climates: Evidence of photoperiod-induced embryonic dormancy in Aedes aegypti in South America.

Dormancy is a developmental arrest in arthropods, in response to unfavorable conditions in temporally varying environments. In Aedes aegypti, the supposed inability of eggs to inhibit hatching has been used to explain the restriction of this species to tropical and subtropical regions. However, the geographic range of Ae. aegypti is constantly expanding towards temperate regions. Thus, the aim of the present study was to assess the ability of Ae. aegypti individuals from a temperate region (Buenos Aires City, Argentina) to enter photoperiod induced dormancy. To this end, we exposed both the parental generation and the eggs to short-day (SD: 10L:14D) and long-day (LD: 14L:10D) photoperiods, and studied the temporal variation in egg hatching. The experiment consisted of 28 treatment combinations of three factors: parental photoperiod (SD or LD), egg storage photoperiod (SD or LD), and age of eggs (14, 28, 42, 56, 70, 91, and 112 days). The results showed a lower hatching response with the SD parental photoperiod, and a trend to higher hatching with longer egg storage time in all photoperiod treatment combinations. The egg storage photoperiod showed no effect on egg hatching. In both parental photoperiod treatments, egg replicates of most ages from different females showed a large variability, with some replicates with lowest hatching response and others with highest hatching response. Our results show the ability of Ae. aegypti to inhibit egg hatching in response to a short-day photoperiod, which could allow the further expansion of this species to regions with colder winters.

Seasonal and daily activity patterns of human-biting mosquitoes in a wetland system in Argentina.

Seasonal and daily activity patterns of human-biting mosquitoes were studied in the lower delta of the Paraná River from March 2003 to February 2004. Monthly captures at four daytime intervals using human volunteers collected 1,289 mosquitoes belonging to 14 species and six genera, with the most frequently captured being Ochlerotatus crinifer (49%), Psorophoraferox (36%), Ochlerotatus serratus (5%), and Isostomyia paranensis (3%). Oc. crinifer was collected during the four seasons and showed higher values in Summer and Autumn. Ps. ferox and Oc. serratus were not present in Winter and the highest values were recorded in Summer. Monthly captures of Ps. ferox and Oc. serratus were positively associated with temperature. With regard to daily activity patterns, Oc. crinifer, Oc. serratus, and Ps. ferox were captured during the four collection intervals with nocturnal captures concentrated during the warm months. The daily activity patterns of these species changed throughout the seasons.

Galls of Cecidoses eremita Curtis and Eucecidoses minutanus Brèthes (Lepidoptera: Cecidosidae) in Magdalena, Buenos Aires Province: preliminary study and associated fauna / Agallas de Cecidoses eremita Curtis y Eucecidoses minutanus Brèthes (Lepidoptera: Cecidosidae) en Magdalena, Prov. de Buenos Aires: muestreo preliminar y fauna asociada

In Argentina, five galling species of the family Cecidosidae (Lepidoptera), including Cecidoses eremita Curtis and Eucecidoses minutanus Brèthes, have been cited. This note reports a preliminary study of their galls in "molles" (Schinus longifolius (Lindl.) Speg.) of Magdalena (Buenos Aires, Argentina). In April 2013, galls of C. eremita and E. minutanus were censused in randomly selected "molles". In April and December 2013, randomly selected galls were then collected and transported to our laboratory in hermetic bags, and conserved at -18 ºC until examination. Maximum diameter and wall thickness of collected galls were measured. About 84% of the observed "molles" (103/123) had galls of C. eremita and/or E. minutanus. The median of galls per tree was 12 (Q1=6; Q3=22). Eucecidoses minutanus had galls with smaller diameter (U11;53= 583; P<0.05) and thinner wall (U10;52=506.5; P<0..05) than C. eremita. In open galls, we found Pseudoescorpionida, Araneae (Segestriidae and Salticidae), and larvae of Lepidoptera and Hymenoptera. Within closed galls, we found adults of Torymidae and Chalcidoidea, and larvae of Ichneumonoidea.

En Argentina se registran cinco especies cecidógenas de la familia Cecidosidae (Lepidoptera), entre ellas Cecidoses eremita Curtis y Eucecidoses minutanus Brèthes. Se reporta un estudio preliminar de agallas de estas dos especies en "molles" (Schinus longifolius (Lindl.) Speg.) de Magdalena (Buenos Aires). En abril de 2013 se censaron las agallas de C. eremita y E. minutanus en molles seleccionados al azar. En abril y diciembre de 2013, se colectaron mediante muestreo aleatorio agallas de ambas especies, se trasladaron en bolsas herméticas y se conservaron a -18 ºC hasta ser examinadas. Se midieron el diámetro máximo y el grosor de la pared. Un 84% de los molles observados (103/123) presentaron agallas de C. eremita y/o E. minutanus. La mediana de agallas cerradas por árbol fue 12 (Q1=6 y Q3=22). Las agallas de E. minutanus presentaron un diámetro menor (U11;53= 583; P<0,05) y una pared más delgada (U10;52=506,5; P<0,05) que las de C. eremita. Los organismos asociados a las agallas abiertas fueron Pseudoescorpionida, Araneae (Segestriidae y Salticidae), y larvas de Lepidoptera y de Hymenoptera. Dentro de las agallas cerradas se encontraron adultos de Torymidae y de Chalcidoidea, y larvas de Ichneumonoidea.

New record and larval habitats of Culex eduardoi (Diptera: Culicidae) in an irrigated area of Patagonia, Chubut Province, Argentina.

The object of the present work was to identify the larval habitats of Culex eduardoi and to determine the microenvironmental conditions related to their presence in different artificial freshwater environments (temporary, semi-permanent, irrigation ditches, and drainage ditches) in tillable areas of Chubut Province, Argentina. This report represents the first record of Cx. eduardoi from this Province and extends its range to latitude 45 degrees S. Immature stages of Cx. eduardoi were found in 8 out of 109 (7.3 %) freshwater habitats and were significantly more prevalent in semi-permanent water bodies. Positive sites had significantly larger surface areas and more vegetation cover than negative sites.

New record and larval habitats of Culex eduardoi (Diptera: Culicidae) in an irrigated area of Patagonia, Chubut Province, Argentina

The object of the present work was to identify the larval habitats of Culex eduardoi and to determine the microenvironmental conditions related to their presence in different artificial freshwater environments (temporary, semi-permanent, irrigation ditches, and drainage ditches) in tillable areas of Chubut Province, Argentina. This report represents the first record of Cx. eduardoi from this Province and extends its range to latitude 45°S. Immature stages of Cx. eduardoi were found in 8 out of 109 (7.3 percent) freshwater habitats and were significantly more prevalent in semi-permanent water bodies. Positive sites had significantly larger surface areas and more vegetation cover than negative sites.