<p>Urban areas are warmer than
surrounding rural areas. During the cold of winter, warming increases
surrounding host temperature and may improve the overwintering survival of marginally
hardy insects like evergreen bagworms. Similarly, during the summer, it has the
potential to increase the fecundity and abundance of sap feeding insect pests
such as scale insects in ways that change the capacity of their natural enemies
to regulate their populations. </p>
<p>Although in parts of Indiana
winters can be cold enough to kill bagworm eggs, they thrive in cities. I
conducted field experiments to determine the extent to which impervious surface
near an infestation could keep temperatures warm enough to affect bagworm survival
during cold of winter. My results suggest that the percentage of live eggs
inside overwintering pupae decreased as ambient temperature drops. This
response was moderated by the presence of impervious surface around an infested
plant. Eggs found in bagworms collected from host trees surrounded by more
impervious surface had a higher chance of survival than those collected from
trees with low levels of hardscape. However, impervious surface has its limit
such that egg mortality was not buffered by impervious surfaces at temperatures
at or below -21.67°C. Similarly, I also conducted field experiments with sap
feeding insects on honeylocust trees, a commonly planted tree in cities. Hot
sites had a mean daily temperature more than 1.5 °C warmer than cool sites and
scale insects were more abundant and fecund on trees in the hottest part of
Indianapolis compared to cooler areas. No differences were observed in rates of
parasitism on the scale insect. However, I found strong density dependence
relation between parasitoids and scales abundance at scale density at or below
the levels present in cool sites. The top-down regulation was prevalent at or
below a critical density of scale hosts. Conversely, bottom-up regulation was
prevalent above this host density as pests benefit from bottom-up factors. This
suggests that urban habitats helped the scales to escape biological control by
resident natural enemies above critical density of scale hosts. </p>
<p>My findings can be useful to
landscape designers to design landscapes that are less prone to insect pests. My
finding adds to a growing body of evidence that suggests that planting urban
trees with lesser amount of impervious surface can help reducing the urban
warming effect and increase the regulation from natural enemies. </p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/19333421 |
| Date | 18 April 2022 |
| Creators | Sujan Dawadi (12218648) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/thesis/EFFECTS_OF_IMPERVIOUS_SURFACES_ON_OVERWINTERING_SURVIVAL_OF_EVERGREEN_BAGWORM_AND_ABUNDANCE_OF_SCALE_INSECT_PESTS_IN_THE_URBAN_ENVIRONMENT/19333421 |
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