Seasonal and Spatial Distribution Patterns of Ichthyoplankton Along the West Coast of Sri Lanka

Fundamental understanding of fish resources has become a crucial need in Sri Lanka for the sustainable management of fish stocks. Knowledge of ichthyoplankton essential in identifying the spawning dynamics of fish is scarce in this region of the Indian Ocean. A survey was conducted in 2018 covering different monsoon seasons to monitor the abundance, distribution, and diversity of ichthyoplankton along the west coast of Sri Lanka. Samples collected using vertical and horizontal WP2 hauls showed a total of 4095 fish eggs, with identification possible only to 3 families: Clupeidae, Engraulidae, and Cynoglossidae and 465 larval fish belonging to 23 families. The most dominant families recorded were the Siganidae, Blenniidae, Clupeidae, Gobiidae, and Engraulidae, which highlight the importance of pelagic and demersal fish along the west coast. A significant temporal pattern in egg abundance was observed with the highest abundance in March (535 10 m-3) in vertical WP2 net hauls. Furthermore, significant differences in spatial patterns of larval abundance were seen in vertical and horizontal samples. High larval fish abundances were recorded in March and during September - November, with northern regions generally having the highest abundances (~36 larvae 10 m-3). The spawning coincides with the productive southwest monsoon period (May to September). The high diversity and abundance of eggs and larvae recorded in this study indicate that the west coast is likely an important spawning and nursery ground for demersal and pelagic fish.

Influence of Weather Parameters on the Seasonal Abundance of Legume Pod Borer Maruca vitrata (Crambidae: Lepidoptera) on Dolichos Bean (Lablab purpureus var. typicus)

Background: Legume pod borer, Maruca vitrata (Fabricius), infests the Dolichos bean throughout the cropping season. However, there is no information on the seasonal abundance of M. vitrata over different seasons on Dolichos bean, which is an essential tool for forecasting and developing integrated pest management strategies. Methods: The seasonal abundance of M. vitrata on Dolichos bean were studied during three consecutive cropping seasons of 2019 Summer, Kharif and Rabi. The larval population in flowers and pods and the number of larval webbings and weather parameters were recorded and subjected to correlation and multiple linear regression analysis. Result: The overall larval abundance was observed to be higher in flowers than in pods. The highest larval abundance in flowers and pods was 14.60 and 13.40 during the 48th and 50th standard meteorological week (SMW) of Rabi 2019 respectively, which corresponds to 8 to 10 weeks after sowing (WAS) in flowers and 10 to 12 WAS in the case of pods. The number of larval webbings was higher, with 18.76 during the 49th SMW of Rabi 2019. The maximum temperature had a significant negative correlation with the larval abundance in flowers (r= -0.570), pods (r= -0.523) and the number of active webbings (r= -0.477). At the same time, the regression coefficient shows that rainfall had a significant negative influence on the larval abundance in pods (B= -1.26).

Entomological Risk Assessment for Dengue Virus Transmission during 2016–2020 in Kamphaeng Phet, Thailand

Individual houses with high risks of dengue virus (DENV) transmission might be a source of virus transmission within the neighborhood. We conducted an entomological risk assessment for DENV transmission at the household level, comprising family cohort members residing in the same location, to assess the risk for dengue virus transmitted by mosquito vectors. The studies were conducted in Kamphaeng Phet Province, Thailand, during 2016–2020. Entomological investigations were performed in 35 cohort families on day 1 and day 14 after receiving dengue case reports. DENV was found in 22 Aedes samples (4.9%) out of 451 tested samples. A significantly higher DENV infection rate was detected in vectors collected on day 1 (6.64%) compared to those collected on day 14 (1.82%). Annual vector surveillance was carried out in 732 houses, with 1002 traps catching 3653 Aedes females. The majority of the 13,228 water containers examined were made from plastic and clay, with used tires serving as a primary container, with 59.55% larval abundance. Larval indices, as indicators of dengue epidemics and to evaluate disease and vector control approaches, were calculated. As a result, high values of larval indices indicated the considerably high risk of dengue transmission in these communities.

Blepharipoda spinosa (H. Milne Edwards & Lucas, 1841) and Lepidopa chilensis Lenz, 1902 (Crustacea: Hippoidea) larvae on a north-central zone of Chile

The larvae of Blepharipoda spinosa and Lepidopa chilensis were collected from Chile's north-central coast (Paposo 25.0ºS and Oscuro Port 31.5ºS) in each February of 2013-2017. Larvae were separated by their development stage. Their abundance, occurrence, and distribution concerning its proximity to the coast were analyzed. Larval abundance and frequency of occurrence were low in both species. Zoea I dominated the highest concentrations detected in coastal stations and near the study area's longest sandy beaches. Interannual variation of larvae was seen in the abundance and composition by development stages. The highest abundance of B. spinosa larvae was found in February 2016, while L. chilensis larvae had the highest abundance in February 2014. Their presence and development stages in the wide sampling area provide information on both species' distribution and reproductive activity.

Mosquito Larval Abundance in Connected and Isolated Pools Beside a Stormwater Management Pond

ABSTRACT Twelve experimental pools (30 cm width × 30 cm depth) around a large stormwater management pond (SWMP) were used to test the hypothesis that small puddles of water similar to animal hoofprints or other irregularities support more abundant and diverse mosquito populations due to having fewer insect predators. Six of the 12 pools were connected to the SWMP by a deep channel (7 cm wide × 10 cm depth × 50 cm length). Mosquito larvae and potential predators were sampled weekly over 16 wk in the summer. More mosquito larvae were found in the isolated pools than in connected pools or in the pond itself (U = 5.5, z = 2.002, P = 0.045). The observed differences between isolated and connected pools are presented and results discussed in terms of SWMP design.

Seasonal Larval Abundance of the Blackfly, Simulium damnosum Complex and the Physico-chemical Properties of their Breeding Sites in Oji River System, Enugu State, Nigeria

Seasonal larval abundance of the blackfly, Simulium damnosum complex, and the physico-chemical properties of their breeding sites in Oji river system was carried out, with the aim of finding out the season that promotes the breeding of S. damnosum complex and the effect of the physico-chemical properties of the breeding sites of S. damnosum complex on larval abundance. Larvae of S. damnosum complex were collected monthly from forty-eight (48) breeding sites in four sampling units for three years, in dry and wet seasons. The physico-chemical properties of the breeding sites of S. damnosum complex studied were copper, dissolved oxygen, magnesium, nitrate, pH, phosphate, potassium, temperature, and water velocity. A total of six hundred and ninety one (691) larvae of S. damnosum complex were collected in the Oji river system in both seasons. Wet season catch was more and comprised 82% of the total catch, while dry season catch comprised 18% of the total catch. Dry and wet seasons catches in the sampling units were found to differ statistically. All the physico-chemical properties of the breeding sites of S. damnosum complex determined showed positive correlations with total larval abundance in both seasons, except copper which showed no correlation with total larval abundance in the dry season. Wet season promotes larval abundance of S. damnosum complex, and the physico-chemical properties of the breeding sites of S. damnosum complex play some roles (in varying degrees) in larval development.

The Effect of Breeding Habitat Characteristics on the Larval Abundance of Aedes Vector Mosquitoes (Diptera: Culicidae) in Three Localities, Galle District, Sri Lanka

Dengue has become a national burden in Sri Lanka, and the understanding of breeding ecology of vectors, Aedes aegypti Linnaeus and Aedes albopictus Skuse, is the most effective way to control the disease. The present study was undertaken to investigate the relative larval abundance of Ae. aegypti and Ae. albopictus in different types and characteristics of containers in three selected localities in Galle district, Sri Lanka. Totally, 550 containers were positive for both Ae. aegypti and Ae. albopictus larvae. Aedes albopictus showed the high larval abundance in all studied sites. The larval abundance of artificial containers (90.57%) was high than that of natural containers (9.43%) for both Aedes spp. ( P < 0.05 ). The breeding preference for A. aegypti was high in tires (rubber) (17.82%), while plastic cups (28.00%) were the most preferable container type for Ae. albopictus. Dark color containers than light color containers ( P < 0.05 ) and containers with leaf litter accumulated as detritus ( P < 0.05 ) showed high relative larval abundance for both Aedes species. Containers with 50–100 ml volume of water showed the highest relative abundance of both Ae. aegypti (29.28%) and Ae. albopictus (41.79%) ( P > 0.05 ). The high larval abundance of Aedes recorded in ground level containers (1–5 cm) and their abundance decreased significantly with the increasing of height where containers were found (1–20 cm) ( P < 0.05 ). The significantly high relative abundance was observed with the increase of the shady level for Ae. aegypti (57.34%) and Ae. albopictus (61.32%) ( P < 0.05 ). This knowledge will be helpfull to implement dengue surveillance programs in the area.

Climate drives long-term change in Antarctic Silverfish along the western Antarctic Peninsula

Over the last half of the 20th century, the western Antarctic Peninsula has been one of the most rapidly warming regions on Earth, leading to substantial reductions in regional sea ice coverage. These changes are modulated by atmospheric forcing, including the Amundsen Sea Low (ASL) pressure system. We utilized a novel 25-year (1993–2017) time series to model the effects of environmental variability on larvae of a keystone species, the Antarctic Silverfish (Pleuragramma antarctica). Antarctic Silverfish use sea ice as spawning habitat and are important prey for penguins and other predators. We show that warmer sea surface temperature and decreased sea ice negatively impact larval abundance. Modulating both sea surface temperature and sea ice is ASL variability, where a strong ASL is associated with reduced larvae. These findings support a narrow sea ice and temperature tolerance for adult and larval fish. Further regional warming predicted to occur during the 21st century could displace fish populations, altering this pelagic ecosystem.