Date of Award

Spring 5-10-2025

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Entomology

First Committee Advisor

Angela Mech

Second Committee Member

Andrei Alyokhin

Third Committee Member

William Livingston

Abstract

Browntail moth (BTM; Euproctis chrysorrhoea) is an invasive folivore that was introduced into North America in the late nineteenth century. It is a generalist of hardwoods and has been observed to feed most commonly on oaks and apples. BTM is also a threat to human health, as the larvae possess urticating hairs that detach easily and can cause skin irritation and respiratory distress. BTM is currently outbreaking in Maine, and like previous outbreaks, it is spreading rapidly northeast but has limited spread south of the outbreak location. This indicates there may be other factors influencing BTM dispersal, such as wind, which is predominantly north/northeast in Maine throughout the flight period of BTM.

This research assessed the flight capabilities and host selection of female BTM in order to aid in risk assessment of BTM’s spread and future outbreak locations. The flight capabilities of BTM were tested using a rotary flight mill, where the moths were tethered to one end of a mill arm of a known radius and as they flew each rotation interrupted an infrared sensor. This allowed for each rotation to be counted, and distance flown, speed, and time spent flying could be calculated. Results indicate that male moths are much stronger fliers than female moths. The average distance flown was more than twice as far for males than females. Male moths also spent more time flying. However, speed was not significantly different for male and female moths.

The host choice of female BTM was tested in the lab and the field. The lab trial utilized a Y-tube olfactometer. Females were placed at one end of the Y, and two choices were placed in each arm. Oak, apple, and maple leaves were offered in comparison to each other and to an empty arm. Unmated female BTM do not appear to be host seeking, as they often did not make a choice, and when a choice was made, it was just as often an empty arm over an arm with a leaf.

Oviposition preferences of female BTM were assessed in the field by placing trees from four different hosts – apple, maple, oak, and birch – in a mesh tent to allow for flight and air flow. Male and female moths were placed within the tent each night for the duration of the flight season, and the number of egg masses laid on each tree were counted. Female BTM did not seem to be choosing oviposition locations by host genus, however tree size may have played a role. Additionally, oviposition location seemed to be strongly influenced by direction, with a large majority of egg masses being found on the north side of the tent.

This research indicates that female BTM are likely poor fliers, and because dispersal during this outbreak closely matches wind direction, it may be a strong influence on the spread direction. Additionally, this research found that BTM females do not seem to be intentionally choosing hosts. The preference for oviposition on the north side of the tent also matches the predominant wind direction in the area. This indicates that BTM monitoring efforts in Maine may be best targeted towards regions north or northeast of current populations.

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