Forest Insect and Disease Newsletter


University Entomology and pardners doin' good work


Emerald ash borer (EAB) project receives funding

Mark Abrahamson (Minnesota Dept. of Agriculture), Dr. Brian Aukema (University of Minnesota Department of Entomology) and Dr. Rob Venette (USFS-Northern Research Station) submitted an EAB project to the Legislative-Citizen Commission on Minnesota Resources (LCCMR) entitled "Improving Emerald Ash Borer Detection Efficacy for Control." The three-year project was recommended for funding by the LCCMR and should begin in July 2013. The goal of the project is to relate EAB population density to our ability to detect EAB using different techniques, and to the density at which EAB causes tree decline. In other words, the goal is to determine thresholds for when to begin management and determine whether any detection techniques are sensitive enough to detect EAB before that threshold is reached. They also plan to evaluate some aspects of EAB biology that relate to its spread.

University of Minnesota - Forest Entomology is studying the current outbreak of eastern larch beetle

Older larch mortality aerial

Older larch mortality and new mortality (yellow crowns) in August. Photo by Fraser McKee.

Brian Aukema, Assistant Professor in the Entomology Department at the University of Minnesota, established his lab and working group in 2010. Fraser McKee, a PhD candidate, is working on eastern larch beetle. Recently, Fraser summarized his research intentions and work so far.

"We have been focusing on two areas of research: first, elucidating the biology of eastern larch beetle in Minnesota, and second, relating these life history characteristics to the sustained outbreak activity of eastern larch beetles in Minnesota."

"To increase understanding of eastern larch beetle biology, we have been recording seasonal flight patterns, periods of beetle attack on tamaracks, and developmental phenology of the parent and re-emergent parental broods established during the spring of the year. Recording the survivorship to adulthood of each brood and calculating the relative contributions of each brood to the spring-emergent reproductive adult cohort will provide insight into potential mechanisms of the sustained outbreak activity. Preliminary evidence indicates that bi-voltinism may have occurred in some of the stands, a new finding for this insect. Warmer climates may benefit larch beetles by allowing faster development times and increased brood numbers. Conversely, it is possible that less severe winters may be detrimental to beetle success if winter temperatures do not provide beetles with enough cold exposure necessary to break reproductive diapause. Hence we have also conducted laboratory studies to determine how much cold accumulation over-wintering adults of eastern larch beetles require before they can successfully break diapause and reproduce in the spring. We have also studied the effect of cold exposure on adult emergence synchronicity from over-wintering hosts. We hope to determine whether a warmer climate will benefit or harm eastern larch beetles and whether climate warming is at least partially responsible for the present beetle outbreak.

"We are also working to examine how tamarack quality affects the host selection behaviors of these insects as well as subsequent reproductive success and offspring fitness. Using weekly monitoring of colonized and un-colonized trees, exclusion and emergence cages, and host chemistry and growth analyses, we are examining 1) the effects of tamarack host quality on the host selection processes of female eastern larch beetles, 2) how host quality affects per capita brood production by colonizing female beetles, and 3) the effect of host quality on the fitness of subsequently emerging offspring. The goals of this research are to determine how eastern larch beetle outbreaks become established within a tamarack stand and then progress throughout the stand over time. Determining the relationship between available host quality, host selection, and offspring fitness will provide data on the factors that govern the rate of increase and success of eastern larch beetle populations in Minnesota.

"Finally, we are also attempting to characterize broad stand attributes that are associated with eastern larch beetle infestations. To do this, we are sampling infested and non-infested tamarack stands from across northern Minnesota and measuring characteristics such as stand density, species composition, mean tree age, recent growth rate, crown closure, and tree size. In collaboration with Dr. Tony D'Amato, we are analyzing trends in tree growth in relation to precipitation to determine if drought over the past decade has significantly reduced tree vigor across the landscape. Such widespread decline in tree health may be fostering outbreak propagation. Ultimately, we hope to create baseline data for a hazard risk assessment tool that could predict the probability of eastern larch beetle infestation in tamarack given a set of stand characteristics.