|Groot, P. de|
Submitted to: The Canadian Entomologist
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/14/2009
Publication Date: 1/20/2010
Citation: Turgeon, J.J., Groot, P., Smith, M.T., Jones, C., Orr, M., Gasman, B. 2010. Density and location of simulated signs of injury affect efficacy of ground surveys for Asian longhorned beetle. The Canadian Entomologist. 142(1):80-90. Interpretive Summary: Visual examination of trees looking for the signs of attack, including oviposition pits (pits chewed by female beetles into which an egg is then laid) and exit holes (holes in the bark through which the beetles then emergence), is currently used to determine if trees are infested by the Asian Longhorned Beetle. This approach is essential for establishing the outer boundaries of an infestation and thereby delineating the areas where beetles are controlled. Efficiency of visual examination for signs of attack is affected by their density, position within tree (bole or branches), height above ground and presence or absence of leaves. Understanding how these factors affect the efficacy of inspectors in finding these signs of attack is critical to designing visual examination protocols, and to eradication and management programs to eliminate or slow the spread of this invasive species. The study reported here was conducted to determine the efficacy of inspectors in detecting these signs and the amount of time taken to find them. The density, height, and position of oviposition pits and exit holes significantly affected the efficacy, accuracy and duration of time for detecting the sign of attack by inspectors. Presence or absence of leaves had no effect. Generally, an increased probability of detection and a faster time-to-discovery occurred when signs of attack occurred at higher densities and were located lower on the tree. Results established the minimum density and height of signs of attack, and time required to optimize detection efficiency, and showed that: (a) oviposition pits and exit holes located on the bole and branches, respectively, were easier to find than those located on the branches and bole, respectively, and (b) visual inspections are equally effective throughout the year. Therefore, discovered of infested trees during establishment of new infestations can be optimized by appropriately employing ground surveyors vs. tree climbers, and by concentrating examination of trees for oviposition pits on the bole and for exit hole on branches. Furthermore, visual examination for signs of attack can be performed over the entire year without compromising detection efficiency. Collectively, these results are critical to early detection in both eradication and management programs. The amount of time allotted to inspection of each tree can be adjusted and matched to the objective of the survey and to the costs of examination.
Technical Abstract: Surveys for the detection and delimitation of the Asian longhorned beetle, Anoplophora glabripennis (Motschulsky) (Coleoptera: Cerambycidae) currently rely upon visual examination of trees to discover the presence of signs of attack such as oviposition pits and exit holes. Understanding the factors that affect the efficacy of inspectors in finding these signs at low densities is not only critical to eradication and slow-the-spread mitigation programs but also to the design of sampling programs that can adjust the efforts and costs to reflect the survey objectives. This study evaluated the response of inspectors to 32 treatment combinations of oviposition pit and exit hole density, tree position (tree bole or branch), height above ground and presence or absence of foliage by quantifying their efficacy in detecting these signs and the amount of time taken to find them. The density, height, and position of oviposition pits and exit holes significantly affected the probability of detection and search duration, whereas the presence or absence of foliage had no effect. The average probability of detection based on 12 combinations of density, height and position was 0.81 for oviposition pits and 0.74 for exit holes suggesting that under certain conditions it might be easier to discover signs of oviposition rather than emergence. The interaction of density and height influenced detection probability of oviposition pits and exit holes. Generally, an increased probability of detection and a faster time-to-discovery occurred when signs of attack occurred at higher densities and were located lower on the tree. Oviposition pits located on the bole were easier to find than those located on branches whereas the opposite was observed with exit holes. The relationship between the search duration for oviposition pits and exit holes and the probability of detection indicated that even if given unlimited time not all infested trees will be located and that after a certain amount of time, there is little gain in the probability of detecting signs of attack. In conclusion, the amount of time allotted to inspection of each tree can be adjusted and matched to objective of the survey.