Laura M. Blackburn

Slow the Spread: a national program to manage the gypsy moth

The gypsy moth is a destructive, nonindigenous pest of forest, shade, and fruit trees that was introduced into the United States in 1869, and is currently established throughout the Northeast and upper Midwest. The Slow the Spread Program is a regional integrated pest management strategy that aims to minimize the rate of gypsy moth spread into uninfested areas. The premise of the Slow the Spread Program is to deploy extensive grids of pheromone-baited traps (>100,000 traps per year) along the expanding population front to identify and subsequently eradicate newly establishing populations to prevent them from growing, coalescing, and contributing to the progression of the population front. This report provides a brief history of the gypsy moth in North America, describes the dynamics of gypsy moth spread, and then details the technological and operational aspects of implementing the Slow the Spread Program.

What Does “Local” Firewood Buy You? Managing the Risk of Invasive Species Introduction

ABSTRACT Firewood can serve as a vector in the transport of non-native species, including wood-boring insects that feed within the wood and thus can be transported accidentally. Governments have enacted limitations on the movement of firewood in an effort to limit the anthropogenic movement of non-native species through, for example, recreational camping. Although the movement of invasive species through firewood is a documented invasion pathway, it is not trivial for governments to determine a “safe” allowable distance for moving firewood. We were motivated by this challenge and developed a theoretical simulation to determine the campgrounds that could be potentially exposed to infested firewood based upon the hypothetical distribution of an invasive species and the allowable distance for moving firewood. We extend this concept to the known distributions of emerald ash borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae) and Asian longhorned beetle, Anoplophora glabripennis (Motschulsky) Coleoptera: Cerambycidae). We illustrate, based upon theoretical and empirical observations, that as the distribution of an invasive species increases, more rigid constraints on the movement of firewood would be required relative to those species that are distributed over a smaller scale. Also, on the level of management within a state, smaller states have far less margin for error than larger ones, as even extremely rigid restrictions on the movement of firewood could have little management effect unless the infested area is spatially limited. These results collectively suggest the potential for a dynamic management strategy that adjusts allowable distances for firewood movement based upon the distribution of the non-native species.

Persistent effects of aerial applications of disparlure on gypsy moth: trap catch and mating success

In forest plots treated aerially with a plastic laminated flake formulation (Disrupt® II) of the gypsy moth sex pheromone disparlure to disrupt gypsy moth, Lymantria dispar (L.) (Lepidoptera: Lymantriidae), mating was monitored the year of treatment and 1–2 years after treatment to determine the effects of the treatment on suppression of trap catch and mating success. In the year of treatment, there was a greater than 95% reduction in trap catch and a greater than 98% reduction in mating success compared to controls. One year after treatment at a dosage of 37.5 g active ingredient (a.i.) ha−1, trap catch was reduced by 46–56% and mating success was reduced by 60–79%. Both trap catch and mating success were significantly reduced compared to controls in plots treated 1 year previously at 15 g a.i. ha−1. Trap catch, but not mating success, was significantly reduced 2 years after treatment at 37.5 g a.i. ha−1. The efficacy of mating disruption (MD) treatments in the Slow‐the‐Spread of the Gypsy Moth program was significantly reduced 2 years compared to 1 year after treatment. No such reduction was observed in plots treated with aerial applications of Bacillus thuringiensis kurstaki. The higher apparent efficacy of MD treatments 1 year after application may result to some extent from the suppression of moth capture in pheromone traps from the persistent effects of the previous years treatment.

Predicting costs of alien species surveillance across varying transportation networks

Summary Efforts to detect and eradicate invading populations before they establish are a critical component of national biosecurity programmes. An essential element for maximizing the efficiency of these efforts is the balancing of expenditures on surveillance (e.g. trapping) versus treatment (e.g. eradication). Identifying the optimal allocation of resources towards surveillance requires an underlying model of how costs and the probability of detection fluctuate with survey intensity across various landscapes. Here, we develop a model, widely applicable across biological systems, for predicating costs associated with varying surveillance intensities across diverse road networks. We assumed that surveillance is conducted across a set of point locations. Resources needed to conduct surveillance include the fixed costs associated with surveying a point (e.g. cost of materials or labour time spent at the survey point) and variable costs that correspond to the expense of the time and distance travelled between points. We estimated travel time and distance between points as functions of surveillance intensity and road network characteristics using data from simulated least cost driving routes connecting points located on real-world road networks. Time and distance estimates were then combined with cost data from an actual gypsy moth Lymantria dispar surveillance programme in the state of Washington to predict per trap costs of surveillance across varying road network densities and surveillance intensities. Per point driving time, driving distance and total costs all decline with increasing survey point density and increasing road density. Surveillance intensity (planned point spacing) explains ˜94% of the average time driven per point and 97% of the distance driven per point – thus representing the primary explanatory variable. Incorporating road density and dead end road density explains relatively little additional variance in the model, although they improve goodness of fit. Synthesis and applications. This work predicts costs associated with surveillance of invasive species populations. We find that the cost per survey point diminishes with increasing survey point density and also depends on road network characteristics. When combined with maps for the relative risk of alien species establishment across landscapes and measures of surveillance efficacy dependent on effort, these cost predictions can increase efficiency of surveillance and eradication efforts for the gypsy moth and other invasive species.

The use of Bacillus thuringiensis kurstaki for managing gypsy moth populations under the Slow the Spread Program, 1996-2010, relative to the distributional range of threatened and endangered species

The Slow the Spread Program operates along the expanding population front of the gypsy moth, from Minnesota to North Carolina. The primary objective of the program is to eliminate newly-founded colonies that form ahead of the leading edge to reduce the gypsy moths rate of spread and delay the costs associated with infestation and outbreaks. Although the majority of areas under the STS Program are treated with control methods specific to the gypsy moth, commercial formulations of Bacillus thuringiensis var. kurstaki (Btk) are the second most used tactic. Bacillus thuringiensis kurstaki can directly affect other Lepidoptera, as well as indirectly affect species that depend on Lepidoptera for pollination services or as a food source. Because of these nontarget effects, proposed treatment areas are always reviewed by the U.S. Department of Interior - Fish and Wildlife Service as well as state agencies that are responsible for the conservation of threatened and endangered species to ensure that government programs to control gypsy moth are not likely to have an adverse effect. In this report, we used a variety of sources to compile a spatial database of the historical distributional ranges of 21 threatened and endangered species that occur within the STS management area. We then quantified the area of overlap between areas treated with Btk under the STS Program from 1996 to 2010 and the distributional ranges of these species to evaluate the use of Btk with regard to federal and state management guidelines.

Estimating spread rates of non-native species: the gypsy moth as a case study

Estimating rates of spread and generating projections of future range expansion for invasive alien species is a key process in the development of management guidelines and policy. Critical needs to estimate spread rates include the availability of surveys to characterize the spatial distribution of an invading species and the application of analytical methods to interpret survey data. In this chapter, we demonstrate the use of three methods, (i) square-root area regression, (ii) distance regression and (iii) boundary displacement, to estimate the rate of spread in the gypsy moth, Lymantria dispar, in the USA. The gypsy moth is a non-native species currently invading North America. An extensive amount of spatial and temporal distributional data exists for this invader. Consequently, it provides an ideal case study to demonstrate the use of methods to estimate spread rates.