Assessing the Effects of Non-Native Flowering Plants and Anti-Herbivory
Plastic (Vexar®) Tubes on Insect Visitation to Native Plants
Authors: Sun Emily R. 
Published: January 2025

Bees (Hymenoptera: Apoidea) are among the most prominent pollinators of the
flowering plants and play an essential role in maintaining ecosystem function.
Disruption of plant-pollinator interactions is a growing global concern because
of the implications for biodiversity, ecosystem health, and agriculture. The
incursion of non-native plants globally is seen to adversely affect native
plants and alter plant-pollinator communities. In chapter one, I examined the
effects of a non-native weed, Sisymbrium altissimum (tall
tumblemustard), on bee visitation to nearby native Sphaeralcea
munroana (Munro’s globemallow), including genera-specific
differences among bees. The most common bee genera were Andrena,
Colletes, Diadasia, Halictus, and Lasioglossum. I
found that bees carried pollen from both tumblemustard and globemallow,
suggesting that bees were foraging at both plant species. I found little
evidence to support my hypothesis that non-native tumblemustard would positively
affect bee visitation by providing supplemental floral resources and attracting
bees to an area. Instead, in general, more bees visited the native globemallow
than tumblemustard and the number of bee visits was positively associated with
the number of globemallow blooms but not tumblemustard. Some generalist bees,
such as Andrena and Lasioglossum, increased
visitation in response to tumblemustard blooms, while Halictus
were only associated with globemallow blooms. Specialists, like
Colletes and Diadasia, increased
visitation with globemallow blooms and were only seen foraging at globemallow at
the plots. Although this study did not show strong effects of tumblemustard
abundance either positively or negatively affecting bee abundance to nearby
plants, at least some bees, notably generalists like Andrena
and Lasioglossum utilize these non-native plants and may
benefit from their presence.

In chapter two, I investigated whether Vexar®, an anti-herbivory plastic tube
used in restoration planting, prevents bees from visiting flowers. Planting
nursery-raised forb seedlings in restoration projects is increasing in sagebrush
steppe, especially following disturbances such as wildfire. Forbs provide
important resources for wildlife and pollinators. I wanted to understand whether
these commonly used anti-herbivory tubes have deterrent effects on bees, through
physical exclusion, visual deterrence, or both. To test these possibilities, I
altered the presence and color of Vexar protecting two native plant species,
Munro’s globemallow and shaggy fleabane (Erigeron pumilus), and
observed the visitation rates of bees to flowers in a controlled field setting.
I also examined the spectral signatures produced by Vexar painted in different
colors and related this information to the color spectrum detected by bees. I
found that Vexar did not create a physical barrier for bees (i.e., preventing
bees from visiting the flowers inside) as visitation was comparable across
treatments. My spectral analysis suggested that Vexar does not interfere with
the bees’ ability to detect the flowers, but asking manufacturers to use blue-
or yellow-dyed plastics may attract more bees. Future work regarding both of
these experiments should include measurements of native plant seed set to
elucidate whether tumblemustard or Vexar interfere with native plant pollination
success.