Seasonal variation in black fly (Diptera: Simuliidae) taxocenoses from the Brazilian Savannah (Tocantins, Brazil)

Community composition of black flies during and after the 2020 vesicular stomatitis virus outbreak in Southern New Mexico, USA

BACKGROUND

Vesicular stomatitis virus (VSV), a vector-borne pathogen of livestock, emerges periodically in the western US. In New Mexico (NM), US, most cases occur close to the Rio Grande River, implicating black flies (Simulium spp.) as a possible vector. In 2020, VS cases were reported in NM from April to May, although total black fly abundance remained high until September. We investigated the hypothesis that transience of local VSV transmission results from transient abundance of key, competent black fly species. Additionally, we investigated whether irrigation canals in southern NM support a different community of black flies than the main river. Lastly, to gain insight into the source of local black flies, in 2023 we collected black fly larvae prior to the release of water into the Rio Grande River channel.

METHODS

We randomly sub-sampled adult black flies collected along the Rio Grande during and after the 2020 VSV outbreak. We also collected black fly adults along the river in 2021 and 2022 and at southern NM farms and irrigation canals in 2022. Black fly larvae were collected from dams in the area in 2023. All collections were counted, and individual specimens were subjected to molecular barcoding for species identification.

RESULTS

DNA barcoding of adult black flies detected four species in 2020: Simulium meridionale (N = 158), S. mediovittatum (N = 83), S. robynae (N = 26) and S. griseum/notatum (N = 1). Simulium robynae was only detected during the VSV outbreak period, S. meridionale showed higher relative abundance, but lower absolute abundance, during the outbreak than post-outbreak period, and S. mediovittatum was rare during the outbreak period but predominated later in the summer. In 2022, relative abundance of black fly species did not differ significantly between the Rio Grande sites and farm and irrigation canals. Intriguingly, 63 larval black flies comprised 56% Simulium vittatum, 43% S. argus and 1% S. encisoi species that were either extremely rare or not detected in previous adult collections.

CONCLUSIONS

Our results suggest that S. robynae and S. meridionale could be shaping patterns of VSV transmission in southern NM. Thus, field studies of the source of these species as well as vector competence studies are warranted.

Population dynamics and seasonality of Euspilotus (Hesperosaprinus) azureus Sahlberg (Coleoptera: Histeridae: Saprininae)

ABSTRACT The effect of climatic conditions on the structure of populations has been perceived for different orders of insects and families of beetles. Here we described the population dynamics of Euspilotus azureus (Sahlberg, 1823) and determined its relationship with climatic variables. The specimens were collected monthly for one year in an area of Seasonal Semideciduous Forest, in Viçosa, Brazil. The seasonality of the population and of sexes was estimated through the absolute frequency of occurrence (AF) and the percentage frequency of occurrence (FO%) of the population and each sex, which were determined monthly. To test whether the changes in monthly AF of the population and of each sex are correlated with climatic variables, Spearman correlation tests were performed. To identify whether there are temporal fluctuations in the sex ratio, considering months and seasons, and within each season, we performed Chi-square tests. A total of 3,126 individuals (1,009 females and 2,117 males) were collected. The population had the highest abundance in spring and summer, and the lowest in autumn and winter. The highest AF and FO were found in December and January, and the lowest in June and July. The sex ratio of the population did not differ in the months of the year, but in the spring there was a marked predominance of males. For E. azureus, the temporal fluctuation in abundance of the population and in the sex ratio is related to the climatic variables of maximum temperature, humidity, and precipitation. Climatic variables, especially the temperature, provided a greater abundance of the population in the hottest and rainiest periods of the year for inducing reproductive activity and altering the population’s sex ratio.

Effects of Bacillus thuringiensis var. israelensis on the Black Fly Communities (Diptera, Simuliidae) in Tropical Streams

Bacillus thuringiensis var. israelensis (Bti) Berliner, 1911 is widely used in the biological control of black fly and mosquito populations. The objective of this study was to evaluate the effects of Bti on the black fly communities in streams in the Atlantic Forest domain. The study was carried out in eight streams of Serra do Mar, in the municipality of Ubatuba, São Paulo. Some parts of the streams in this locality have received applications of Bti fortnightly for more than 25 years by the sanitary agency of the region. In each stream, two sections were sampled, with and without application of Bti (June 2015 and 2016). Black flies were collected and identified to the species level in the laboratory with 1382 larvae being identified, distributed in six species. Of this total, 73% of the individuals were found in sections where Bti was not applied. There was a difference in the abundance of simulids between the sections with and without Bti application, being more abundant in the latter. We measured the head capsule of individuals of the most abundant species, Simulium pertinax Kollar 1832, using a stereoscopic microscope with millimeter lens. These measurements demonstrated that there was a difference between the sections regarding the age structure of Simuliidae populations. In the sections without Bti application, there was a higher proportion of larvae in the last instar, while in the Bti-treated sections, smaller instars were predominant, possibly due to constant recolonization processes.