Orchid Bee Survey Continues in the Amazon

2024 FIELD REPORT: ORCHID BEE DIVERSITY SURVEY (pdf)
5E Lesson Plan – Coming Soon!

Date: July 14 – 17, 2024
Location: Explorama’s Napo-Sucusari Biological Reserve, Loreto Peru
Study Site: The Amazon Conservatory for Tropical Studies (ACTS) Canopy Walkway
Lead Researcher: Dr. Robert Naczi
Team Members: Kathy Richardson*, Andrea Camilo, Tammy Harris, Roldan Hidalgo, Mike McAloon, Cinda Murray, Matthew Naczi, Ben Olsen, Garly Aliaga Pashanaste, Deborah Prestridge, Piero Marcello Mazzei Ugaz, Jordan Wolf, and Alli Yen ( *= author of this report)

Abstract
This study aims to establish a long-term inventory of orchid bee diversity at the Amazon Conservatory for Tropical Studies (ACTS), focusing on the distribution and species richness of these bees on the forest floor and in canopy. Over four days of surveys at the Napo-Sucusari Biological Reserve in Loreto, Peru, we used scented cotton balls as baits to attract orchid bees and collected 101 specimens, to be deposited in the Museo de Historia Natural de la Universidad Nacional Mayor de San Marcos, Lima. Results from this year suggest that there is a significant difference in orchid bee visitation to baits between the forest floor and canopy, with Euglossa as the most common genus observed. Environmental factors such as temperature and wind may have influenced specimen collection, highlighting the need for further investigation into these abiotic variables.

Lay/Marketing Summary
Orchid bee research at the Amazon Conservatory for Tropical Studies explored the diversity and habitat preferences of these vibrant insects. Our findings indicate that this important group is more abundant on the forest floor than in the canopy. This study provides insight that can help improve our understanding of orchid bee natural history and improve strategies for protecting biodiversity in the Amazon.

Introduction
The Amazon hosts an immense level of biodiversity, yet many species remain unidentified and unmonitored in changes in their diversity patterns over time and space. Scientists often use indicator species to learn about the diversity of other species and track ecological shifts. In this project, we are building a long-term inventory of orchid bee diversity of Amazon Conservatory for Tropical Studies (ACTS). We will test hypotheses about the distribution and species richness of orchid bees on the forest floor and in the canopy. By monitoring orchid bee biodiversity and abundance over time, this long-term study will enable us to identify environmental trends.

Materials and Methods
Orchid bee surveys were conducted at the Napo-Sucusari Biological Reserve, Loreto, Peru, both on the forest floor and on the ACTS Canopy Walkway (3.25105°S, 72.90759°W). To attract orchid bees, we used cotton balls tied on a string, each saturated with a concentrated and unique scent (benzyl acetate, eucalyptol, eugenol, methyl salicylate, and vanillin). Each set of scented cotton balls was arranged in alphabetical order according to their scent and placed either ca. 1.5 meters above the forest floor or on ACTS Canopy Walkway (Platform 2, lower platform elevation 22.2 m, upper platform elevation 25.6 m above the forest floor).

The two stations (forest floor and canopy) were monitored daily by team members over four mornings from ca. 9:00–11:40 AM. Each day, we saturated and hung a new set of cotton balls. On the second day, an additional set of cotton balls were added to each bait site, leaving the first day cotton balls suspended nearby, in case the first ball maintained attractiveness. The procedure continued: on the third day, we removed the first day’s set of cotton balls and left the second day’s set suspended, and on the fourth day, we removed the second day’s set, leaving the most recent 2 sets of cotton balls suspended.

We captured orchid bees by hand in resealable bags, which were immediately marked with the date, scent, location, and time of capture. Start and stop times for each station were synchronized.

Captured orchid bees were frozen in the late morning for pinning and drying in the afternoon. They were then placed in a Schmitt box for preservation and transportation.

Results
We documented three genera of orchid bees during the 2024 sampling period: Euglossa, Eulaema, and Exaerete. Euglossa was the dominant genus in our collection, though Eulaema was also commonly collected. Exaerete was recorded only once on July 15, 2024 and was not observed on any subsequent collection days. We did not collect any specimens of Eufriesea or Aglae.

Overall, we collected a total of 101 orchid bee specimens across four sampling days (Supplemental Table 1). Of these, we collected 9 orchid bee specimens in the canopy and 91 specimens on the forest floor. The Euglossa specimen was collected on the forest floor, but because scented cotton balls were not indicated, this record was excluded from the data table and graphs. Using a chi-square test, we rejected the null hypothesis of no difference in bee frequency between the sites (χ2 = 65.62, P < 0.0001; Figure 6), suggesting that orchid bees are significantly more likely to be found closer to the forest floor. Using another chi-square test, we rejected the null hypothesis of no difference in orchid bee visitation rates to each of the scented cotton ball baits (χ2 = 70.80, P < 0.0001; Figure 7); most bees were found near the eucalyptol and eugenol baits.

Figure 6: Elevation Preferences of Orchid Bees.

Figure 7: Frequency of Bees Collected at Each Bait (BA = benzyl acetate, EUC = eucalyptol, EUG = eugenol, MS = methyl salicylate, V = vanillin).

Discussion
In 2023, we collected 158 orchid bee specimens, whereas in 2024, we collected 100 specimens. Despite spending the same amount of time collecting orchid bees, we noticed a difference in the number of specimens between the two years. Several factors may have contributed to this discrepancy, particularly at the canopy collection location. Conditions in 2024 included overall lower temperatures, increased cloud cover, and slightly higher wind speeds compared to 2023. Unfortunately, abiotic factors were not recorded as rigorously as in 2023, so this comparison relies on the authors’ observations from both years.

Recommendations
To improve future collections, we suggest reevaluating the placement of the canopy baits. The canopy platform was heavily trafficked, leading to quite a bit of movement (some baits more than others), which could have influenced orchid bee attraction to baits. Although we attempted to mitigate this, some movement persisted, and its impact on orchid bee attraction is unclear. Additionally, the placement of baits very close to the anchoring tree on the lower platform may have affected orchid bee behavior, as bees did not have 360° access.

We also recommend incorporating more consistent abiotic data collection, as variability in wind, light, precipitation, and temperature could impact our results. Starting collection times earlier may also be beneficial, as we observed numerous bees on the cotton balls before the official collection times but did not capture them later.

Next Steps
Future work should focus on identifying orchid bee species by morphology under microscopes and DNA analysis, particularly for the remaining Euglossa species. Collected specimens will be deposited in the Museo de Historia Natural de la Universidad Nacional Mayor de San Marcos, Lima.

Previous Field Reports

2023 Field Report

For additional information or questions about this field report, please contact Dr. Lindsey Swierk (lindseyns@gmail.com), Director of Scientific Research for The Morpho Institute and Associate Director of Research for the Amazon Conservatory for Tropical Studies.  

Learn more about the Amazon Research Initiative for Educators (ARIE)

Download Syllabus 

Supplemental Table 1. Numbers of specimens collected by genus at each scented bait at the two sampling locations.