A comparison of girdled ash detection trees and baited artificial traps for Agrilus planipennis (Coleoptera: Buprestidae) detection.

Detection of newly established populations of Agrilus planipennis Fairmaire, the most destructive forest insect to invade the United States, remains challenging. Regulatory agencies currently rely on artificial traps, consisting of baited three-sided panels suspended in the canopy of ash (Fraxinus spp.) trees. Detection trees represent another survey option. Ash trees are girdled in spring to attract ovipositing A. planipennis females then debarked in fall to assess larval presence and density. From 2008-2010, systematic grids of detection trees and artificial traps were established across a 390-km(2) area for the SLow Ash Mortality pilot project. We compared probabilities of detection associated with detection trees and artificial traps along varying A. planipennis density proxies estimated as distance-weighted averages of larval counts (detection trees) or adult captures (traps) within 800 m of each detection tree or trap. Detection trees were consistently more likely to be positive, that is, detect A. planipennis, than traps in all three years, even when traps were placed in canopies of detection trees. Probability of detection with a single detection tree was >50% when density proxies for the area were <5 larvae per detection tree, while the probability of detection with an artificial trap placed in the same area was <35%, even when density proxies exceeded 25 larvae per detection tree. At very low densities of <5 larvae per detection tree, using three detection trees would increase detection probabilities to 90%, while five artificial traps would increase the detection probability only to 40%.

The influence of satellite populations of emerald ash borer on projected economic costs in U.S. communities, 2010-2020.

The invasion spread of the emerald ash borer (Agrilus planipennis Fairmaire) (Coleoptera: Buprestidae) is characterized by the formation of satellite populations that expand and coalesce with the continuously invading population front. As of January 2010, satellite infestations have been detected in 13 states and two Canadian provinces. Understanding how newly established satellite populations may affect economic costs can help program managers to justify and design prevention and control strategies. We estimate the economic costs caused by EAB for the 10-yr period from 2010 to 2020 for scenarios of fewer EAB satellite populations than those found from 2005 to 2010 and slower expansion of satellite populations found in 2009. We measure the projected discounted cost of treatment, removal, and replacement of ash trees (Fraxinus spp.) growing in managed landscapes in U.S. communities. Estimated costs for the base scenario with the full complement of satellites in 2005-2010 and no program to mitigate spread is $12.5 billion. Fewer EAB satellites from 2005 to 2010 delay economic costs of $1.0 to 7.4 billion. Slower expansion of 2009 satellite populations delays economic costs of $0.1 to 0.7 billion. Satellite populations that are both distant from the core EAB infestation and close to large urban areas caused more economic costs in our simulations than did other satellites. Our estimates of delayed economic costs suggest that spending on activities that prevent establishment of new satellite EAB populations or slow expansion of existing populations can be cost-effective and that continued research on the cost and effectiveness of prevention and control activities is warranted.

Allochronic isolation and incipient hybrid speciation in tiger swallowtail butterflies.

Hybridization leading to reproductively isolated, novel genotypes is poorly understood as a means of speciation and few empirical examples have been studied. In 1999, a previously non-existent delayed flight of what appeared to be the Canadian tiger swallowtail butterfly, Papilio canadensis, was observed in the Battenkill River Valley, USA. Allozyme frequencies and morphology suggest that this delayed flight was the product of hybridization between Papilio canadensis and its sibling species Papilio glaucus. The mitochondrial DNA (mtDNA) restriction fragment length polymorphisms presented here indicate that only P. canadensis-like mtDNA occurs in this population, suggesting that introgression likely occurred from hybrid males mating with P. canadensis females. Preliminary studies of this population indicated that delayed post-diapause pupal emergence in this hybrid genotype was the root cause behind the observed delayed flight, which suggests a potential empirical example of a mechanism leading to reproductive isolation. Here we provide further evidence of the role of adult pupal emergence as a reproductive barrier likely leading to reproductive isolation. In particular, we present results from pupal emergence studies using four different spring and two different winter temperature treatments. The results indicate a clear separation of adult emergences between the hybrid population and both parental species. However, our results indicate that exceptionally hot springs are likely to lead to greater potential for overlap between the local parental species, P. canadensis, and this delayed population with hybrid origins. Conversely, our results also show that warmer winters are likely to increase the temporal separation of the hybrid population and the parental species. Finally, we report recently collected evidence that this hybrid population remains morphologically distinct.