Session 1 – Vector-borne Disease Research and Implications on Integrated Pest Management Strategies in Maine

PowerPoint slide presentations are available for talks in this session. Links are provided with each abstract.

Morning Session: 8:30AM-10:30AM

Howard Room (First Floor, North Wing)

Session Chairs:
Andres Urcuqui-Bustamante, School of Forest Resources, University of Maine, Orono, ME
Hillary Peterson, Maine Department of Agriculture, Conservation and Forestry, Augusta, ME

Traditional management strategies for disease vectors such as mosquitos and ticks often involve monthly scheduled inputs of pesticides. Research points to integrated strategies that can involve cultural control methods to reduce these inputs. This session brings together current leading specialists in vector-borne disease (VBD) studies and their implications for both human health and the environment. The state of Maine has seen an increase of VBD cases over the last 20 years that evidences a strong relationship between environmental and social factors, such as the effects of climate change on patterns of precipitation, snowfall and temperature, the variability in wildlife-host populations, invasive plant species which harbor habitats for vectors, and changes in land uses and forest management practices. Up-to-date research is key to understanding and communicating the challenges researchers and regulators face to minimize human exposure to VBD.

Session Presentations:

Presenters are indicated in bold font.

8:30AM-8:55AM
Impacts of native and invasive plants on mosquito ecology and management

Allison Gardner
School of Biology and Ecology, University of Maine

A PowerPoint slide presentation is available for this talk.

Mosquitoes, including vectors of human and wildlife pathogens, interact with terrestrial plants throughout their life cycles. Inputs of leaf detritus into the aquatic habitat provide an energy base for developing larvae, and plants mediate the distribution of adult mosquitoes by influencing microclimate conditions, supplying sugar sources, and altering communities of wildlife blood-meal hosts. This research examines direct and indirect effects of understory shrubs, including both native and invasive species, on the ecology of an important North American vector for West Nile virus (Culex pipiens). We demonstrate that leaf detritus species in the aquatic environment alters two components of mosquito production (i.e., oviposition site selection and adult emergence) via the microbial community that forms as leaves decompose. In particular, we found an invasive plant (Amur honeysuckle, Lonicera maackii) yielded high oviposition and emergence rates; in contrast, we identified a native plant (common blackberry, Rubus allegheniensis) that functions as an ecological trap for Cx. pipiens, attracting gravid females to oviposit yet deleterious to larvae yielding low emergence rates. We then explored two vector management applications of these findings. First, a field experiment demonstrated the viability of exploitation of a naturally-occurring ecological trap (blackberry leaves) and an artificial ecological trap (honeysuckle leaves mixed with Bacillus thuringiensis var. israelensis larvicide) for attract-and-kill mosquito control in storm water environments. A second field experiment showed that eradication of Amur honeysuckle decreases abundance of Culex spp. mosquitoes in forest fragments embedded within a residential neighborhood, most likely via effects on microclimate conditions and the bird host community.

9:00AM – 9:25AM
Use of Cervid Serosurveys to Monitor Eastern Equine Encephalitis Virus Activity in Northern New England, United States, 2009-2017

John-Paul Mutebi1, Abigail A. Mathewson2, Susan P. Elias3, Sara Robinson4, Alan C. Graham5, Patti Casey5, Charles B. Lubelczyk 3

1. Centers for Disease Control and Prevention (CDC), Fort Collins, CO
2. New Hampshire Department of Health and Human Services, Concord, NH
3. Vector-borne Disease Laboratory, Maine Medical Center Research Institute, Scarborough, ME
4. Maine Center for Disease Control and Prevention, Augusta, ME
5. Vermont Agency of Agriculture, Food & Markets, Montpelier, VT

A PowerPoint slide presentation is available for this talk.

Vertebrate surveillance for eastern equine encephalitis virus (EEEV) activity usually focuses on three types of vertebrates: horses, passerine birds, and sentinel chicken flocks. However, there is a variety of wild vertebrates that are exposed to EEEV infections and can be used to track EEEV activity. In 2009 we initiated a pilot study in northern New England, United States, to evaluate the effectiveness of using wild cervids (free-ranging white-tailed deer and moose) as spatial sentinels for EEEV activity. In Maine, New Hampshire, and Vermont during 2009 – 2017, we collected blood samples from hunter-harvested cervids at tagging stations and obtained harvest location information from hunters. U.S. Centers for Disease Control and Prevention processed the samples for EEEV antibodies using plaque reduction neutralization tests (PRNTs). We detected EEEV antibodies in 6% to 17% of cervid samples in the different states and mapped cervid EEEV seropositivity in northern New England. EEEV antibody-positive cervids were the first detections of EEEV activity in the state of Vermont, in northern Maine, and in northern New Hampshire. Our key result was the detection of the antibodies in areas far outside the extent of documented wild bird, mosquito, human case, or veterinary case reports of EEEV activity in Maine, New Hampshire, and Vermont. These findings showed that cervid (deer and moose) serosurveys can be used to characterize the geographic extent of EEEV activity, especially in areas with low EEEV activity or with little or no EEEV surveillance. Cervid EEEV serosurveys can be a useful tool for mapping EEEV activity in areas of North America in addition to northern New England.

9:30AM-9:55AM
The effects of timber harvesting on tick densities and small mammal foraging behavior and abundance

Stephanie Hurd (student)1, Jessica Leahy1, Laura Kenefic2, Allison Gardner1
1. University of Maine
2. U.S. Forest Service

A PowerPoint slide presentation is available for this talk.

Timber harvesting is a property-scale forest management practice that involves the cutting and removal of trees. Our previous work has shown that forest structural characteristics that result from timber harvesting can reduce densities of nymphal blacklegged ticks, Ixodes scapularis, the vector of the Lyme disease bacterium, Borrelia burgdorferi. One potential mechanism driving this relationship may depend on the small mammals (e.g., white-footed mouse, Peromyscus leucopus; eastern chipmunk, Tamias striatus, etc.) that serve as hosts for the blacklegged tick and B. burgdorferi. Timber harvesting modifies wildlife habitat through changes in overstory cover and understory vegetation. This change potentially alters the abundance or behavior of these small mammals directly, or indirectly by changing predator activity and the resulting threat, or perceived threat, of predation. Altered small mammal foraging and/or abundance could affect tick-host encounter rates, thereby affecting small mammals’ tick burdens and, consequently, tick densities in the environment. No study has examined the mechanistic links among forest stand attributes that result from timber harvesting histories, small mammal behavior and population sizes, and blacklegged tick densities. This study uses a combination of techniques (i.e., live trapping, track plates, and foraging trays) that capture different aspects of small mammal population dynamics and behavior to (1) assess small mammal foraging and population sizes in forest stands with varied structural attributes; and (2) to compare the efficacy and correlation between these different sampling techniques to determine their ability to predict tick burdens.

10:00AM – 10:25AM
Blacklegged Ticks, Climate, and White-Tailed Deer in Maine

Susan P. Elias1, Allison M. Gardner2, Kirk A. Maasch3,4, Sean D. Birkel3,4, Norman T. Anderson5, Peter W. Rand1, Charles B. Lubelczyk1, Robert P. Smith, Jr1

1 Maine Medical Center Research Institute, Vector-borne Disease Research Laboratory, Scarborough, ME
2 School of Biology and Ecology, University of Maine, Orono, ME
3 School of Earth and Climate Sciences, University of Maine, Orono, ME
4 Climate Change Institute, University of Maine, Orono, ME
5 Anderson Environmental Health, Winslow, ME

A PowerPoint slide presentation is available for this talk.

The pathogens causing Lyme and other diseases in Maine can be transmitted through the bites of infected blacklegged ticks (Ixodes scapularis). Maine is a high Lyme disease incidence state, and has been experiencing warmer and shorter winter seasons. Because we expect both white-tailed deer and climate to influence blacklegged tick densities, we investigated the interacting impacts of deer and seasonal climatology on the statewide distribution of blacklegged ticks. We modeled nymph abundance as additive linear/nonlinear functions of deer abundance, temperature, and humidity. We used tick surveillance data to index nymph abundance, 1990–2013. We used the Maine Department of Inland Fisheries and Wildlife’s big game wildlife management districts (WMDs) as the spatial unit. Nymphs were correlated with increasing deer densities up to 13 deer/mi2 (5 deer/km2), but beyond this threshold nymphs did not vary with deer density. This corroborated the idea of a saturating relationship between I. scapularis and deer density, meaning that local overabundant deer populations should be lowered to WMD goals. Nymphs also were correlated with warmer winters but only where deer density exceeded ~2 deer/km2 (~6/mi2). Thus, climate change may aid range expansion of ticks as long as there are enough deer blood meals to maintain a tick population. Anticipated increases in I. scapularis in the northern tier could be partially mitigated through deer herd management. We touch on the history of deer herd management for tick control, and Maine’s need for vector control districts as a way to organize around tick control.