Color of Pan Trap Influences Sampling of Bees in Livestock Pasture Ecosystem

Abstract

The decline in insect pollinators has increased the importance of accurately monitoring pollinator diversity and abundance over time. Sampling techniques include the use of passive insect traps such as pan traps, yet there is still discussion over their utility and effectiveness in different ecosystems. The objective was to examine four different colors of pan traps (blue, green, yellow, and purple) for their utility in sampling bees in native forages rotationally grazed by sheep and to compare the relative abundance, richness, similarity, and community assemblage patterns among the four trap colors. Most bees were from the Halictidae family (89%). The most abundant species were Lasioglossum imitatum (42.2%), Augochlorella aurata (8.3%), L. subviridatum (6.8), Agapostemon texanus (6.4), and L. birkmani (4.1%). Blue color traps exhibited the highest rates of bee capture and species accumulation. Purple and yellow colored traps were moderately effective in capturing bees, while the green color pan traps were least effective. Similarly, observed and extrapolated species richness was highest in blue trap, followed by purple, yellow, and green. Notably, the blue trap captured the highest number of unique species, followed by purple, yellow and green traps. Considering the total number of insects collected (including bees and other insects), yellow and green traps captured a significantly higher number of insects than other colored traps. The light reflectance from blue, purple, green and yellow pan traps had peaks at ~450, 400, 550, and 600 nm, respectively. Since different insects respond to different light intensities, wavelengths, and reflectivity, these results could be used to guide future trapping protocols targeting certain insect groups in livestock pasture and similar ecosystems.

Keywords: bee vision; bees; pan traps; pasture ecosystem; pollinators; sampling method.

Figure 1

A colored pan trap platform used in the study. Picture by N. Joshi.

Figure 2

Differences in capture rate (±SE) of (A) total insects and (B) bees among four pan trap colors in livestock pastures. There were four trap color in each of the 4 plots. Samples were taken 4 times each week for 8 wk. Different lowercase letters indicate significant differences among trap colors (p < 0.05).

Figure 3

Rarefaction curve showing accumulation of the number of species in relation of the number of samples (A) and number of individuals (B). Dotted line in (B) indicates at what abundance value interpolated richness values were compared. Different superscript letters indicate significant differences among trap colors.

Figure 4

Ordination (CCA) biplot showing associations among wild bee species and different colored pan traps.

Figure 5

Light reflectance spectrum for four different colors of pan traps used for sampling pollinators and other insect communities.

Figure 6

Light reflectance spectrum of the white color base of pan trap platform used in this study. Light reflectance spectrum of new (New), one-year-old (1-Yr old), and two-year-old (2-Yr old) platforms is presented.