such as verbenone have a shielding effect around the 

 tree under attack and are the main cause of switch- 

 ing, or if their function is to regulate attacks once 

 beetles are on or very near the tree surface, playing a 

 more localized role in the switching process. If indeed 

 verbenone has a shielding effect, vmknown parameters 

 include the size of the shielding plume and timing of 

 its influence. The main objective of this study was to 

 collect information on the spatial and temporal se- 

 quence of the mountain pine beetle switching process. 

 Original motivation for the study was to obtain quan- 

 titative information for parameterization of a math- 

 ematical model of mountain pine beetle dispersal that 

 includes chemical ecology and spatial interaction be- 

 tween beetles and host trees (Powell and others 1996). 

 Data at the fine spatial and temporal resolution neces- 

 sary for deriving model parameters were unavailable 

 in published literature. In this study we did not meas- 

 ure pheromone emission, but rather the effect of phero- 

 mones on beetle behavior. SpecificaUy, we asked sev- 

 eral questions: (1) How long after attacks are initiated 

 on a focus tree does switching to surrounding trees 

 occur? (2) What is the distance from the initial focus 

 tree within which surrounding trees are protected from 

 beetle attacks (the shielding affect)? (3) What affect 

 does tree diameter have on the switching process? 



Methods 



Three plots in lodgepole pine (Pinus contorta Douglas 

 var. latifolia Engelmann) stands in the Gold Creek 

 drainage of the Sawtooth National Recreation Area, ID, 

 were selected. Species composition in the drainage is 

 approximately 80 percent lodgepole pine and 20 per- 

 cent Douglas-fir {Pseudotsuga menziesii [Mirb.] Franco) 



and subalpine fir (Abies lasiocarpa [Hook.] Nutt.). 

 Cturently there is a sub-epidemic mountain pine beetle 

 population that has been slowly bmlding during the 

 last 4 to 5 years. All plots were at an elevation of 

 approximately 2,073 m, and at least 100 m apart. On 

 August 6, 1995, a mountain pine beetle pheromone 

 tree bait (Phero Tech Inc., Delta, BC, Canada) was 

 placed on the north side of a single tree in each plot. 

 Based on emergence data fi*om a nearby experiment 

 (Bentz 1995), beetle flight in the area had just begun. 

 The bait was left on each focus tree for 24 hours, then 

 removed. All trees within a radial distance of 10 m (20 m 

 diameter) fi-om the focus tree were monitored for 

 beetle attacks xintil August 18 at which time coloniza- 

 tion of trees within the plots had, for the most part, 

 stopped. Attacks were tallied twice per day (approxi- 

 mately 8:00 a.m. and 5:00 p.m.), by height on the bole 

 (0 to 1.2 m, 1.2 to 1.8 m, and 1.8 to 2.4 m) and aspect of 

 the bole (N, E, S, W) where the attack was located. An 

 attack was counted once the nesting hole was initiated 

 and resin or frass was noticed; landing rates were not 

 included. Each entry was marked with a colored push 

 pin, and later tallied. Because our intent was to moni- 

 tor the "natural" attack process of mountain pine 

 beetle on lodgepole pine, those trees attacked while 

 the bait was on the focus tree were removed from data 

 analysis. A stem map was developed for each plot 

 including diameter of each tree at 1.5 m above the 

 ground (d.b.h.). 



Results 



Due to a lack of attacks in plots 2 and 3, only results 

 from plot 1 are reported (fig. 1 ). 'Tl' represents the first 

 tree in the attack process, and similarly, 'T7' is the 



N. 



10 

 8 

 6 

 4 

 2 

 

 -2 

 -4 

 -6 

 -8 

 -10 









s 





e 



©a 





o 

 o 



® 



e 



e 



O © 





O 











-2 



Figure 1 — Spatial map (in meters) 

 of all trees in plot 1 . -sir is the baited 

 tree at plot center, © are success- 

 fully attacked trees, with the num- 

 ber representing the day in the at- 

 tack sequence, © are strip-attacked 

 trees, and O are live trees at the 

 end of the attack period. Size of 

 circle indicates relative diameter at 

 breast height of each tree. 



2 



