Floral Visitors to Helianthus verticillatus, a Rare Sunflower Species in the Southern United States

Helianthus verticillatus Small (whorled sunflower) is a federally endangered plant species found only in the southeastern United States that has potential horticultural value. Evidence suggests that H. verticillatus is self-incompatible and reliant on insect pollination for seed production. However, the identity of probable pollinators is unknown. Floral visitors were collected and identified during Sept. 2017 and Sept. 2018. Thirty-six species of visitors, including 25 hymenopterans, 7 dipterans, 2 lepidopterans, and 2 other insect species, were captured during 7 collection days at a site in Georgia (1 day) and 2 locations in Tennessee (6 days). Within a collection day (0745–1815 hr), there were either five or six discrete half-hour collection periods when insects were captured. Insect visitor activity peaked during the 1145–1215 and 1345–1415 hr periods, and activity was least during the 0745–0845 and 0945–1015 hr periods at all three locations. Visitors were identified by genus and/or species with morphological keys and sequences of the cox-1 mitochondrial gene. The most frequent visitors at all sites were Bombus spp. (bumblebees); Ceratina calcarata (a small carpenter bee species) and members of the halictid bee tribe Augochlorini were the second and third most common visitors at the two Tennessee locations. Helianthus pollen on visitors was identified by microscopic observations and via direct polymerase chain reaction of DNA using Helianthus-specific microsatellites primers. Pollen grains were collected from the most frequent visitors and Apis mellifera (honeybee) and counted using a hemocytometer. Based on the frequency of the insects collected across the three sites and on the mean number of pollen grains carried on the body of the insects, Bombus spp., Halictus ligatus (sweat bee), Agapostemon spp., and Lasioglossum/Dialictus spp., collectively, are the most probable primary pollinators of H. verticillatus.

An updated genetic marker for detection of Lake Sinai Virus and metagenetic applications

Background Lake Sinai Viruses (LSV) are common RNA viruses of honey bees (Apis mellifera) that frequently reach high abundance but are not linked to overt disease. LSVs are genetically heterogeneous and collectively widespread, but despite frequent detection in surveys, the ecological and geographic factors structuring their distribution in A. mellifera are not understood. Even less is known about their distribution in other species. Better understanding of LSV prevalence and ecology have been hampered by high sequence diversity within the LSV clade. Methods Here we report a new polymerase chain reaction (PCR) assay that is compatible with currently known lineages with minimal primer degeneracy, producing an expected 365 bp amplicon suitable for end-point PCR and metagenetic sequencing. Using the Illumina MiSeq platform, we performed pilot metagenetic assessments of three sample sets, each representing a distinct variable that might structure LSV diversity (geography, tissue, and species). Results The first sample set in our pilot assessment compared cDNA pools from managed A. mellifera hives in California (n = 8) and Maryland (n = 6) that had previously been evaluated for LSV2, confirming that the primers co-amplify divergent lineages in real-world samples. The second sample set included cDNA pools derived from different tissues (thorax vs. abdomen, n = 24 paired samples), collected from managed A. mellifera hives in North Dakota. End-point detection of LSV frequently differed between the two tissue types; LSV metagenetic composition was similar in one pair of sequenced samples but divergent in a second pair. Overall, LSV1 and intermediate lineages were common in these samples whereas variants clustering with LSV2 were rare. The third sample set included cDNA from individual pollinator specimens collected from diverse landscapes in the vicinity of Lincoln, Nebraska. We detected LSV in the bee Halictus ligatus (four of 63 specimens tested, 6.3%) at a similar rate as A. mellifera (nine of 115 specimens, 7.8%), but only one H. ligatus sequencing library yielded sufficient data for compositional analysis. Sequenced samples often contained multiple divergent LSV lineages, including individual specimens. While these studies were exploratory rather than statistically powerful tests of hypotheses, they illustrate the utility of high-throughput sequencing for understanding LSV transmission within and among species.

Cross-infectivity of honey and bumble bee-associated parasites across three bee families

Recent declines of wild pollinators and infections in honey, bumble and other bee species have raised concerns about pathogen spillover from managed honey and bumble bees to other pollinators. Parasites of honey and bumble bees include trypanosomatids and microsporidia that often exhibit low host specificity, suggesting potential for spillover to co-occurring bees via shared floral resources. However, experimental tests of trypanosomatid and microsporidial cross-infectivity outside of managed honey and bumble bees are scarce. To characterize potential cross-infectivity of honey and bumble bee-associated parasites, we inoculated three trypanosomatids and one microsporidian into five potential hosts – including four managed species – from the apid, halictid and megachilid bee families. We found evidence of cross-infection by the trypanosomatids Crithidia bombi and C. mellificae, with evidence for replication in 3/5 and 3/4 host species, respectively. These include the first reports of experimental C. bombi infection in Megachile rotundata and Osmia lignaria, and C. mellificae infection in O. lignaria and Halictus ligatus. Although inability to control amounts inoculated in O. lignaria and H. ligatus hindered estimates of parasite replication, our findings suggest a broad host range in these trypanosomatids, and underscore the need to quantify disease-mediated threats of managed social bees to sympatric pollinators.

Bee and Flowering Plant Communities in a Riparian Corridor of the Lower Rio Grande River (Texas, USA)

The Rio Grande in Texas serves as the geo-political boundary between the United States and Mexico. It is considered one of the world’s most at-risk rivers and has been the subject of intensified management by the inhabitants of both countries lining its banks. Additionally, invasion by non-native Arundo donax (Linnaeus) (Cyperales: Poaceae), giant reed, has been extensive in the riparian corridor, with potential impacts to native wildlife. Locally, there remains a significant lack of ecological community data of riparian and upland habitats parallel to the river. We sampled bee and flowering plant communities monthly over two years, along a 3.22 km stretch of the lower Rio Grande in Webb County, TX. Data show that bee and plant richness and abundance was highest during March-April and September among both habitat types. Analysis of bee communities showed low spatial and temporal variation at the habitat level. Although common bee taxa (Halictidae and Apidae) were numerically dominant, NMS and ISA found key bee species driving community patterns. This included higher abundances of two species in the riparian habitat Anthophora occidentalis (Cresson) (Hymenoptera: Apidae) and Lasioglossum sp.L (Curtis) (Hymenoptera: Apidae) and one showing affinity for the upland habitat Halictus ligatus (Say) (Hymenoptera: Halictidae). Additionally, ISA analysis of plant data revealed that three species were significant indicator taxa in riparian habitats. Further analysis showed a positive correlation between bee generic richness and abundance with various climate attributes. Management of the riparian corridor and associated watershed could include significant areas for ecological restoration to assist pollinators.

Influence of Plant Taxa on Pollinator, Butterfly, and Beneficial Insect Visitation

Insects provide ecosystem services, such as pollination and biological control. Additionally, flowering ornamental plant species have the potential to support beneficial insect communities, such as pollinating bees, wasps, and predatory plant bugs. We conducted visual observations and sampled via sweep nets to assess the potential of flowering ornamentals to act as a conservation resource for pollinators. Hoverflies (family: Syrphidae), small bees [Lasioglossum (dialictus) imitatum Smith and Halictus ligatus Say], skippers (family: Hesperiidae), predatory plant bugs (family Miridae), and parasitic wasps were frequent visitors to the specially designed Butterfly and Conservation Gardens. Agastache (Pursh) Kuntze ‘Black Adder’ and Celosia spicata L. were the most frequently visited by pollinators among 74 plant taxa. The results obtained will be useful in formulating recommendations on planting the best species for the purpose of attracting pollinators as well as for conservation purposes.

Acrostichus megaloptae n. sp. (Nematoda: Diplogastridae), a phoretic associate of Megalopta spp. (Hymenoptera: Halictidae) in Central America

Adults of the dusk-flying and rotting wood-nesting bees Megalopta genalis and/or M. ecuadoria were collected at Barro Colorado Island, The Smithsonian Tropical Research Institute (BCI, STRI), Panama and La Selva, Costa Rica, and examined for nematodes. Nematodes were recovered as dauer juveniles from the Dufour's gland of female bees and aedeagus of male bees. Adult nematodes isolated from M. genalis (BCI and La Selva) and M. ecuadoria (BCI) were successfully cultured and kept in the laboratory. All three populations were used for morphological observations and molecular analyses and were identified as a new species that is described herein as Acrostichus megaloptae n. sp. It is characterised by its stomatal morphology, possession of six triangular cuticle flaps covering stomatal opening, duplicated cheilo- and gymnostomatal walls, large dorsal tooth and sclerotised ventral stegostomatal ridges, female with vulval flap, male spicule and gubernaculum morphology, i.e., relatively straight spicule with oval-shaped manubrium, rounded flap-like rostrum and separated and strongly ventrally curved spicule with bifurcate tip, gubernaculum L-shaped in lateral view and anchor-shaped in ventral view, and filiform tail of both sexes. Sequences from the three A. megaloptae n. sp. geographical/host isolates were not significantly different and molecular phylogenetic analysis and biological and morphological comparisons place the new species close to A. halicti from Halictus ligatus and A. puri from Augochlora pura from North America, although the new species is distinguished from A. halicti and A. puri based upon its stomatal morphology of males and females, male spicule and gubernaculum morphology and female vulval structure.