In press: Correspondence to:

Oecologia Matthew P. Ayres Department of Biological Sciences Dartmouth College Hanover, NH 03755 USA (603) 646-2788 FAX (603) 646-1347 [email protected] Resource partitioning and overlap in three sympatric species of bark (Coleoptera: Scolytidae)

Bruce D. Ayres, Great Lakes Institute for Pine Ecosystem Research, Colfax, WI, USA 54730 Matthew P. Ayres, Department of Biological Sciences, Dartmouth College, Hanover, NH, USA 03755-3576 Mark D. Abrahamson, Plant Pest Survey/Biocontrol Program, Minnesota Department of Agriculture, St. Paul, MN, USA 55107 Stephen A. Teale, Environmental Science and Forestry, State University of New York, Syracuse, NY, USA 13210-2778

Abstract. The bark beetles Ips pini, I. perroti and I. grandicollis are sympatric in pine forests of the north central United States. They share the same limited phloem resource and often coexist within the same host trees. We tested whether phloem resources are partitioned in time and space by measuring spatial and seasonal colonization of logs. Differences among species in flight phenology, development time, voltinism and spatial colonization patterns within logs reduce, but do not eliminate, species overlap. The bark species share predation by dubius () and Platysoma cylindrica (Histeridae), which exploit pheromone signals for prey location. We employed pheromone traps to test for chemical communication among species. Heterospecific signals tend to be deterrents when they are added to conspecific signals but attractants when they are alone, indicating that the communication system can both reduce and increase species overlap in resource use depending upon relative abundance of the species. Deterrence by heterospecific signals is probably a result of selection for minimizing interspecific competition. However, individuals may sometimes benefit from joining aggregations of other species because of (1) predator swamping, (2) improved success in attacking live trees, and (3) location of suitable, recently dead, trees. These benefits should be greatest for males (which locate and colonize host trees before signalling females) and indeed males tended to be more attracted by heterospecific signals than females. Shared resources, shared predators, and heterospecific pheromone communication all contribute to species interactions in this guild of bark beetles, but it remains difficult to predict whether the removal of one species will tend to increase or decrease the abundance of remaining species. It seems likely that species interactions are conditional and that coexistence is promoted by benefits to rare species of multispecies associations.

Keywords: interspecific competition; pheromones; conditional interactions; chemical communication; information theory Ayres et al. Page 2

INTRODUCTION whether semiochemical interactions promoted or In forests throughout the world, bark beetles reduced resource overlap. The absence of mechanisms (Coleoptera: Scolytidae) lie at the center of complex for avoiding interspecific competition could imply that communities that exploit the resources provided by dead the species assemblage is unstable or that the species and dying trees (Saveley 1939; Howden and Vogt 1951; accrue benefits from association that offset the costs of Moser et al. 1971; Dajoz 1974; Wood 1982a; Herard competition. Determining whether these species and Mercadier 1996; Kaila et al. 1997; Amezega and interactions are antagonistic or beneficial is of Rodriguez 1998). Multiple species of bark beetles considerable importance to forest managers who need to frequently live and feed within the phloem of trees judge whether particular species should be considered (Birch et al. 1980; Flamm et al. 1987; Flamm et al. pests or biological controls on congeneric species that 1989; Paine et al. 1981; Reid 1955; Smith et al. 1990). are pests. Multi-species aggregations can be structured by airborne host volatiles and by pheromones (Birch METHODS 1978; Svirha et al. 1980; Wood 1982a; Savoie et al. Field experiments were conducted in pure red pine 1998) which can convey multiple species-specific (Pinus resinosa) plantations in Dunn County, west messages (Blum 1996). Interspecific responses to central Wisconsin, USA. All study sites were planted pheromones range from strong deterrence (Lanier and between 1957 and 1967, had been thinned within the Wood 1975; Byers and Wood 1980; Borden et al. 1992; last 5 years, and were being maintained at a basal area Miller and Borden 1992), suggesting an antagonistic of 27 - 46 m2 / ha. All plantations had little or no relationship, to strong attraction (Hedden et al. 1976; undergrowth, and study sites were selected to avoid Cane et al. 1990), which suggests the potential for what little there was. mutualism (Svihra et al. 1980; Smith et al. 1990). Suitable phloem is frequently a limited resource for Pheromone production of Ips perroti bark beetles (Berryman 1973; Anderbrandt et al. 1985) Ips perroti were collected in Dunn County, and competition among bark beetles can limit parental Wisconsin, in early May, 1995. Because preliminary fecundity and reduce the survival and fecundity of studies indicated that this species was attracted to the progeny (Kirkendall 1989; Light et al. 1983; Rankin combination of ipsenol and ipsdienol, beetles were and Borden 1991; Gara et al. 1995; Robins and Reid caught in Lindgren funnel traps baited with commercial 1997). However, offsetting benefits of interspecific formulations of both compounds (Phero Tech, Inc., attraction could accrue from increased success in mass Delta, B.C.). After capture, 120 male beetles were attacks of trees, exploiting host material located by placed on damp paper toweling and shipped overnight other species (De Jong and Sabelis 1988), or predator to Syracuse, NY. Volatiles were collected by aerating swamping. a pooled sample of males feeding on red pine for 5 Ips pini (Say) (Coleoptera: Scolytidae) occurs days (Teale et al. 1991). The adsorbent was extracted throughout pine forests of temperate North America. In daily. A coupled gas chromatograph/mass spectrometer Wisconsin, Ips pini coexists with I. grandicollis (Hewlett Packard models 5890 and 5971) fitted with a (Eichhoff) and I. perroti (Swaine). These three species 30 m HP-Wax column was used to identify and quantify can be found in mixed assemblages feeding on the same the components. The GC conditions were 0.5 min phloem resource within the same region of the tree bole. splitless injection at 209 °C, oven 40 °C for 1 min, ramp Ips pini produces the pheromone ipsdienol 5° / min, 20 min at 210 °C. The ipsdienol enantiomeric (2-methyl-6-methylene-2,7-octadien-4-ol; Stewart 1975; composition of individual males was determined by Lanier et al. 1980), and the attractant synergist lanierone solvent extraction of frass followed by chiral GC-MS (Teale et al. 1991), which function in aggregation and (Teale et al. 1994; Hager and Teale 1996). mate attraction. Ips grandicollis produces and is attracted to the related compound ipsenol Flight phenology and seasonal abundance (2-methyl-6-methylene-7-octen-4-ol) (Vite and Renwick In 1994 and 1995, we used three-trap arrays of 1971). Pheromone production of Ips perroti was Lindgren funnel traps to assay the flight phenology, analyzed as part of this study. Of the three species, I. relative abundance, and pheromone preferences of wild pini is most frequently implicated in pine tree mortality . Within each array, traps were hung 2 m above (Sartwell et al. 1971; Goulding et al. 1988) but we have ground and configured as an equilateral triangle 20 m also observed I. grandicollis and I. perroti participating on a side. Each array contained one trap baited with in attacks of live trees. each of three pheromone lures; ipsdienol, ipsenol, or We conducted experiments to determine how these ipsdienol plus ipsenol. The ipsdienol was a 50% (+): three species of Ips maintain sympatry while apparently 50% (-) enantiomeric blend, which approximates the sharing a single limited food resource and habitat. We preferred blend for this population of I. pini (Herms et tested for phenological segregation and spatial al. 1991; Seybold et al. 1995a). The pheromone lures segregation within and among trees, and evaluated were 20-mg bubblecaps with elution rates of 0.2 mg / Ayres et al. Page 3 day (Phero Tech Inc., Delta, British Columbia, Canada). days, when emergence had largely ceased, the bark was In 1994, we used one three-trap array. In 1995, we peeled from all bolts to count living, unemerged Ips. repeated the trial with eight three-trap arrays: two in We compared development time of the three Ips each of four plantations. Plantations were separated by species in the laboratory at 25 °C by introducing adults 10 - 15 km. Arrays within plantations were separated into sections of fresh phloem (6 x 25 cm) sandwiched by 200 m. Traps were emptied weekly from 15 April within plexiglass (Schmitz 1972) and monitoring the thru 15 October. The position of pheromone lures development of their progeny. Bark and phloem were within trap arrays was rotated weekly to guard against peeled from freshly cut red pine logs. We introduced spurious spatial effects. In two of the plantations, one adult male into each of three 3-mm holes in the lanierone was added (elution rate = 0.01 mg / d) to the plexiglass of each sandwich (4 - 10 sandwiches per ipsdienol and the ipsdienol + ipsenol lures at one array. species). After 24 hours, two females were placed with The lanierone was alternated weekly between the two each male that had begun a nuptial burrow. Each arrays within those plantations. No lanierone was used resulting progeny was individually monitored every 24 at the other two plantations hours through hatching, larval development, and A small parallel study was conducted in two pine pupation. plantations in west central New Hampshire, USA, to Egg volume for each species was estimated using a test for regional stability in the interspecific patterns of microscope micrometer (± 0.01 mm) to measure the pheromone preferences. From May - October 1995, we length and width of 16 - 79 eggs from 6 - 24 mothers sampled Ips pheromone preferences with one three-trap from each species (assuming a prolate spheroid). A array in each of two pine plantations separated by 2 km. subset of 20 eggs were measured, dried and individually Array configurations and sampling protocols were as in weighed to allow a conversion to dry mass. Average Wisconsin. Traps within each array were baited with adult dry mass was estimated from 30 - 40 adults per either ipsdienol, ipsenol, or ipsdienol plus ipsenol. species. From 1989 thru 1995, five to 18 funnel traps baited with 20-mg ipsdienol bubblecaps (elution rates of 0.2 Species associations mg / day) were emptied weekly from spring snow melt We tested for natural spatial separation of Ips species thru the first snowfall. All scolytids and coleopteran within entire felled trees. On 14 May, 1994, we cut predators were counted and identified. Daily high and down seven red pines and mapped the subsequent low air temperatures were recorded from on-site colonization of logs by Ips. All trees were 13 - 18 m thermometers. tall, 15 - 22 cm diameter at 1 m, and separated from the closest felled tree by 30 - 100 m. After two weeks, and Development time at three day intervals for the next two weeks, Ips Freshly cut logs and emergence traps were used to colonization galleries were counted and mapped on each compare generation times of the three Ips species under tree. One month after felling, three 1-m long sections ambient field temperatures. On 16 May, 1995, we were cut from each tree, one within 1 m of the butt, one induced synchronous colonization of 12 logs (0.5 m in just above the first live branch, and the third from length, 15 - 17 cm in diameter) by wrapping each log midway between. The bark was peeled from these with screen to enclose 25 - 50 adults of either Ips pini, I. sections, and the colonizers identified. On 8 June, perroti, or I. grandicollis (four logs per species). Logs seven more trees were felled, and on 25 July, five were cut from mid bole of 4 codominant trees (3 galleries within each of three regions (butt, lower sequential logs from each tree starting 1 m above crown, and midpoint) on each tree were sampled. ground) selected for uniform size and thick phloem. We tested for spatial separation of Ips species among Bolts from all trees were mixed and then randomly logs. Between 5 May and 6 July, 1995, we peeled the assigned to species. Insects were taken from pheromone bark from 61 logs that had been naturally colonized by traps that day. Insects were not sexed, but concurrent Ips and determined the species occupying each gallery. pheromone captures showed a significant male bias, All logs were 0.5 - 1.0 m long, 10 - 30 cm diameter, and (431 vs 272 for I.pini; 1844 vs 226 for I perroti; I. separated from the nearest such log by >20 m. grandicollis not sexed ) which assured that female oviposition would not be limited by availability of Analyses mates. Seven days after colonization, the screen was We compared the flight phenology of species with removed and logs were placed in emergence traps (20 chi-square tests of the null hypothesis that equal cm diameter PVC tubing with four mesh-covered holes, proportions of each species would be captured each 100 mm diameter, to provide air circulation). All traps month. We used a one-way ANOVA to test for from all sites were hung under a rain shelter in one of differences among species in egg development, larval the study plantations. Insects emerging from the bolts development, pupation time, and adult mass, and a were removed and counted twice weekly. After 92 nested ANOVA to test for differences in egg volume among species and among individual mothers within Ayres et al. Page 4

species. Spatial patterns of colonization within felled where R = beetle response, Nwith = number of captures trees were evaluated with (1) a general linear model that with the heterospecific signal, Nwithout = number of included tree as a class variable and distance from butt captures without the heterospecific signal, and Nconspecific as a continuous variable and (2) a chi-square test of the = number of captures with conspecific signal alone. R hypothesis that equal proportions of all species can range from -100%, indicating high deterrence, to 0, occupied the butt, mid-tree, and lower live crown indicating no effect, to 100%, indicating high attraction. regions of the bole. We evaluated species associations This parameter is similar to that suggested by Lanier among logs with a G-test based on the null hypothesis (1975) but more readily accounts for the possibility of that occupancy of a log by one species was independent both attraction and deterrence. For each species, R was of occupancy by other species. calculated for each possible combination of Contingency analyses (SAS 1990, CATMOD heterospecific pheromones in both the presence and procedure) were used to compare pheromone absence of the conspecific pheromones (values for Nwith preferences of the three Ips species and to test for and Nwithout were either with or without the conspecific effects of season, lanierone, and sex on pheromone signal). Because we had not anticipated that a preferences. For each main effect and interaction, the parameter such as R would be required, the present null hypothesis was that the source had no effect on the research lacked a treatment with unbaited funnel traps proportion of beetles captured with ipsdienol vs. ipsenol (the basis for calculating Nwithout in the absence of vs. ipsdienol + ispenol. By design and necessity, the conspecific signals). However, we know from previous experiment was a partial factorial (because the effects sampling at the same sites that Ips captures in unbaited of lanierone were only tested in two of the four pine traps are very rare (9 captures of I. pini in unbaited traps plantations, and because it was impractical to sex one of vs. 1289 captures in paired traps baited with racemic the species, I. grandicollis). Consequently, we ipsdienol; Herms et al. 1991). So, for the purposes of developed orthogonal contrasts to test each hypothesis calculating R in the absence of conspecific signals, we for main effects and interactions using the most data used this result (9 vs. 1289) to estimate expected that could be applied while still retaining a balanced captures in unbaited traps. We used chi-square statistics design structure. This involved four different statistical to evaluate departures from the null hypothesis of no models. In model 1, we tested for differences among effect on captures of adding a heterospecific signal (R = the three Ips species, effects of season (spring = 1 May 0). Tests for effects of heterospecific signals in the to 14 June, mid summer = 16 June to 31 July, late absence of conspecific signals were approximate summer = 1 August to 9 October), and species x season because they depended on previously collected data interactions (Ntotal = 6619 Ips captured in 6 3-trap arrays and, in the case of I. perroti and I. grandicollis, within 4 plantations; trap arrays with lanierone were assumed that these species have the same probability of excluded). In model 2, we tested for effects of being captured in unbaited traps as I. pini. All other lanierone and interactions of lanierone with season and tests were statistically rigorous in being based on species (Ntotal = 6233 Ips captured in 4 trap arrays within planned comparisons of treatment combinations within 2 plantations; 2 plantations without lanierone were the present data. For each Ips species, we controlled for excluded). In model 3, we tested for effects of sex, and experimentwise error in the family of tests regarding interactions of sex with season and species (Ntotal = 5784 responses to heterospecific pheromone signals (Dunn - Ips captured in 6 trap arrays within 4 plantations; I. Šidák adjustment, Sokal and Rohlf 1995). grandicollis and trap arrays with lanierone were excluded). In model 4, we tested for interacting effects RESULTS of sex and lanierone (Ntotal = 5926 Ips captured in 4 trap Pheromone production of Ips perroti arrays within 2 plantations; I. grandicollis and Of the 120 male beetles introduced to the red pine billet, plantations without lanierone were excluded). This 97 successfully bored in and excavated mating galleries. family of tests was controlled for experimentwise error The average production of ipsenol was 4.7 µg · male-1 · with the Dunn - Šidák adjustment (Sokal and Rohlf day-1 (range = 3.3 - 7.6) and of ipsdienol was 1.0 µg · 1995). male-1 · day-1 (range = 0.7 - 1.7). The ipsenol to Results suggested that interspecific effects of one ipsdienol ratio increased from 3.9:1 on day 1 to 5.3:1 on pheromone could depend upon other signals within the day 5 and increased each day except for day 3 which same pheromone plume (from other Ips species that was unchanged from day 2. The average enantiomeric might or might not be colonizing the same log). We composition of ipsdienol (± SE) was 11.6 + 1.7 % summarized the response of each species to R-(-)-ipsdienol and ranged from 4.4 to 21.0 % heterospecific pheromone signals as R-(-)-ipsdienol (N = 13).

N - N Flight phenology and seasonal abundance R = with without ×100, Eq. 1 Funnel traps captured a total of 1133 Ips in 1994 and Nconspecific 10350 in 1995 (Fig. 1). Of these, I. pini, I. perroti and Ayres et al. Page 5

I. grandicollis constituted 49% , 40% and 11% behaviors constituted a substantial proportion of respectively in 1994, and 39%, 51%, and 10% in 1995. development time. After eclosion, adults spent 1 - 2 d The phenological pattern varied among species (Fig. 1; within their pupal chamber, then began wandering and chi-square = 638.37 for 1994 and 2379.95 for 1995, P < feeding throughout the sandwich. 0.0001 and df = 8 for both years). In both years I. Insect development time is partly a function of the grandicollis, and I. perroti were most abundant in May growth that must be accomplished from neonate to adult but showed second peaks in July. Within this spring (Ayres and Scriber 1994). Ips grandicollis adults were flight, I. perroti and I. pini tended to fly earliest, with the largest of the three species (mean ± SE = 2.17 ± high captures in the first week of May followed by four 0.07 mg dry mass, N = 50). Males were larger than weeks of decline. In contrast, I. grandicollis captures females in both I. pini (mean ± SE = 1.99 ± 0.07 vs. were low until the third week of May, but 63% of total 1.77 ± 0.06 mg, t = 2.44, P < 0.01, df = 58) and I. annual captures occurred in the next two weeks. Adult perroti (mean ± SE = 1.45 ± 0.04 vs. 1.11 ± 0.05 mg, t activity of all three species declined following the = 5.21, P < 0.001, df = 54). Egg volumes of I. pini and spring flight (minimum during the second week of I. grandicollis were larger than those of I. perroti (mean June). Thereafter, the abundance of I. grandicollis ± SE =0.111 ± 0.004, 0.104 ± 0.006, and 0.073 ± 0.008 3 adults remained low but measurable through September. mm , respectively; F2,30 = 7.87, P = 0.0023). There was The abundance of I. perroti rebounded in July to levels additional variation in egg size among galleries within near those of the spring flight, but then declined species (F30,137 = 4.68, P = 0.0001). Average dry mass throughout the remainder of the summer. In contrast, for eggs of I. pini, I. grandicollis, and I. perroti was the abundance of I.pini adults remained quite stable 27.9, 24.5, and 18.7 µg, respectively. Thus, larval from May through August and peaked in September. development in I. pini and I. perroti requires an increase Seven species of predators were captured in 1989 - in biomass of 59 - 64 fold, compared to 88-fold for I. 1995, five species of Cleridae and two Histeridae, but grandicollis. only one species from each family was abundant. In 1995, we captured 492 Thanasimus dubius (Cleridae) Species associations within logs and 501 Platysoma (= Cylistix) cylindrica (Histeridae). In June 1994, three weeks after trees were felled, the The peak flights of both predators tended to occur in number of colonizing female adults per tree equaled, in

June, but in some years they were also abundant later in rank order, 1, 23, 25, 47, 52, 89, and 326 (F5, 78 = 45.67, the summer (Fig. 2). P < 0.0001 for effect of tree, excluding the tree with only one colony). Colonization was densest at the

Development time stump end and decreased toward the crown (F1, 78 = Under natural temperatures (mean of daily temperatures 135.25, P < 0.0001), especially on trees with the most

± SD = 19.4 ± 3.8 °C; maximum daily high = 36.6 and Ips galleries (F5, 78 = 20.76, P < 0.0001 for distance x minimum daily low = 0.2), the median development tree interaction: slopes ± SE = -2.96 ± 0.29 vs. -0.32 ± time of I. pini was 65 d, compared to 76 and 78 d for I. 0.08 galleries / m for trees with 326 vs. 23 colonies). grandicollis and I. perroti, respectively (N = 630, 131, We identified 225 colonizing adults (109 I. pini, 71 I. and 82 adults). There were no living larvae after 92 d grandicollis, and 45 I. perroti). Species overlapped but 30% of the I. perroti adults still remained within the within the logs, but differed in their relative abundance logs while all I. pini and I. grandicollis had emerged. along the length of the logs (chi-square = 58.92, df = 4, At constant temperatures, I. pini eggs hatched faster P < .001). The majority of I. grandicollis colonies than I. grandicollis, both of which hatched faster than I. were near the butt of the log (59% compared to 25% in perroti (mean ± SE = 3.08 ± 0.05, 3.60 ± 0.16, 3.85 ± the mid bole and 15% at the lower live crown). One

0.08 d, respectively; F2, 136 = 26.23, P = 0.0001; Fig. 3). third (35%) of I. pini colonies occurred near the butt of Larval development was relatively rapid in I. pini and I. the logs, 61% in the mid bole, and 5% at the lower live grandicollis compared to I. perroti (mean ± SE = 9.59 ± crown. Only 2% of the I. perroti colonies were in the

0.23, 9.86 ± 0.23, 15.61 ± 0.43 days; F2, 81 = 103.04, P = butt, compared to 62% in the mid bole and 36% in the 0.0001). Similarly, pupal development time was nearly lower live crown. Thus I. perroti and I. grandicollis identical for I. pini and I. grandicollis and 35% longer tended to be spatially separated within trees, while I. in I. perroti (mean ± SE = 3.07 ± 0.07, 3.09 ± 0.06 , pini overlapped extensively with both species. In July

4.15 ± 0.10 days; F2,167 = 56.02, P = 0.0001). Each 1994, we identified Ips from 90 galleries in three zones larval molt was preceded by the insect reversing its of seven trees felled on 8 June: all were I. pini, with the orientation within the feeding chamber and compacting exception of two I. grandicollis (both located in the frass to seal the burrow behind them. Prior to pupation, basal region), and one I. perroti (located in the crown). larvae stopped feeding and spent 24 - 36 h thrashing in a manner that resulted in slow rotation within the Species associations among logs feeding chamber and created a circular barrier of Of 61 logs that were naturally colonized in 1995, 45 compacted frass around them. These pre-molting were colonized by I. pini, 21 by I. grandicollis and 10 Ayres et al. Page 6 by I. perroti. Fifteen bolts were colonized by two absence of conspecific signals and more deterred by species and one was colonized by all three species heterospecific signals in the presence of conspecific (Table 1). Ips grandicollis were significantly more signals (Fig. 5). This matches the pattern of stronger likely to occur alone and less likely to occur with I. pini segregation in naturally colonized logs (Table 1). By than would be expected by chance (Table 1). I. pini itself, ipsdienol + lanerione was barely any more co-occurred with I. perroti at about the frequency attractive to I. grandicollis than an unbaited funnel trap expected by chance (6 vs. 6.3 logs). Logs were rarely (R = 1.2). However, ipsdienol was a strong deterrent shared equally; in all but four logs, a single species when added to a pheromone plume that already comprised > 85% of the colonizing population. contained ipsenol (R = -84.9 for addition of signal from I. perroti, chi- square = 536.24 for 151 captures vs. Pheromone interactions 684). I. grandicollis were similarly deterred by the Species differed strongly in their pheromone addition of a signal from I. pini, which added lanierone preferences (Fig. 4, Table 2). Each species was most as well as ipsdienol (R = -91.7 for signals 3 or 4 in Fig. attracted to the pheromone signal produced by that 5). species: I. grandicollis to ipsenol alone, I. pini to In the absence of their own pheromone signal, I. ipsdienol + lanierone, and I. perroti to ipsenol + perroti were somewhat attracted by the signal of I. pini ipsdienol. However, there were interactions with (Fig. 5; R = 2.5 for responses to signal 3, chi-square = season and the effects of any particular pheromone 23.81; 153 captures with ipsdienol + lanierone vs. 35 signal often depended upon the presence or absence of captures expected if R = 0). In the absence of their own other signals (Table 2, Figs 4-5). With three Ips signal, I. perroti, especially males, were also attracted species, there are seven possible permutations of by the signal of I. grandicollis (R = 13.0 and 3.1 for species within a tree, which give rise to four possible males and females; chi-squares = 146.78 and 29.60 for composite signals that might be encountered by an male and female captures, respectively, of 320 and 92 individual beetle searching for host material. In vs. expected captures of 19 and 17 if R = 0; chi-square general, beetles were attracted to heterospecific signals = 121.06 for contrast between sexes). Lanierone tended in the absence of their conspecific signal, but deterred if to deter I. perroti, especially females (captures with and the heterospecific signal was added to the conspecific without lanierone = 701 vs. 1035 for females and 451 signal (Fig. 5). vs. 528 for males; chi- square = 64.26 for females, not Ips pini were somewhat more likely to be captured significant for males). Consequently, the combined in traps baited with the heterospecific signals of I. signal of I. pini and I. grandicollis was not quite as grandicollis (ipsenol) than to unbaited traps (captures attractive as the conspecific signal (R = 85 and 67 for with ipsenol = 69 compared to 16 expected under the males and females in Fig. 5, lower left), and the hypothesis of no effect, R = 2.3 in Fig. 5, chi-square = addition of a signal from I. pini to the conspecific signal 20.27). Conspecific signals from I. perroti (or I. perroti tended to reduce captures of I. perroti (R = -15 and -32 + I. grandicollis) were even more attractive to I. pini for males and females, Fig. 5, bottom right; note that the (624 captures vs. 12 expected if there was no effect, R = signal from I. grandicollis is qualitatively redundant 54.4 in Fig. 5, chi-square = 551.04). Ips pini females with the conspecific signal, so again, R = - 15 and -32). were deterred by signals from I. grandicollis and/or I. Ips perroti were less discriminating earlier in the perroti if the plume already contained their conspecific season, with significantly more choosing either ipsenol signal (R = -20.4, chi-square = 16.68 for 574 captures or ipsdienol over the combination in the spring than in vs. 721) while males were unaffected or even attracted the summer (322 of 1331 vs. 343 of 3978; chi square = by addition of the same signal (R = 16.6, 484 captures 161.00). Chi-square statistics in this paragraph were all vs. 416; chi-square for difference between sexes = significant when controlled for experimentwise error 19.01). With lanierone, captures of I. pini were about with a Dunn - Šidák adjustment for six post hoc tests. 5-fold higher during the spring and mid summer than in Patterns of pheromone attraction and deterrence were replicate arrays without lanierone (106 vs. 23 captures similar in New Hampshire except that we captured no I. in spring and 1053 vs. 271 captures in mid summer). perroti. Ipsenol had little or no deterrent effect on I. During late summer, captures were still higher with pini responses to traps already baited with ipsdienol lanierone than without (1055 vs. 460 captures), but the (812 vs. 914 I. pini at one site and 89 vs. 80 I. pini at effect of lanierone was significantly reduced relative to the other site), but ipsdienol was a strong deterrent to I. earlier in the summer (chi-square for season x lanierone grandicollis (captures of I. grandicollis with ipsenol interaction = 36.18). Chi-square statistics in this alone vs. ipsenol + ipsdienol = 38 vs. 4 at one site and paragraph were all significant at P < 0.05 when 19 vs. 2 at the other site). controlled for experimentwise error with a Dunn - Šidák adjustment for five post hoc tests. Predator responses to Ips pheromones Compared to I. pini, I. grandicollis were less Both T. dubius and P. cylindrica were more attracted to attracted by heterospecific pheromone signals in the the combination of ipsenol and ipsdienol than to either Ayres et al. Page 7 by itself (captures during 1995 with ipsenol, ipsdienol, resources throughout the summer even though it is and ipsenol + ipsdienol = 101, 164, and 227 for T. univoltine. I. perroti has the slowest relative growth dubius, respectively, and 88, 129, and 284 for P. rate and longest larval development time of the three cylindrica; chi-square for differences among signals = species. Furthermore, I. perroti adults continue feeding 48.4 and 1501.36). Lanierone had little or no effect on within the phloem for weeks after eclosion (perhaps to responses of T. dubius but appeared to increase captures acquire energy reserves for overwintering or to become of P. cylindrica: captures in paired arrays with and inoculated with mutualistic fungi). The relatively small without lanierone = 101 vs. 124 for T. dubius and 109 larval galleries of I. perroti suggested a nutritional vs. 161 for P. cylindrica (chi-square = 10.01). dependency upon fungi (Ayres et al. 2000), which Chi-square statistics in this paragraph were significant would make them unique within this community. at P < 0.05 when controlled for experimentwise error Resource overlap between Ips species is reduced by with a Dunn - Šidák adjustment for three post hoc tests. partial spatial segregation on trees, as has been reported for some other bark beetle communities (Wagner et al. DISCUSSION 1985; Birch 1978; Svirha et al. 1980; Paine et al. 1981; Spatial and temporal overlap among species Hui and Xue-Song 1999). I. grandicollis most often Differences among species in the timing of spring colonized the base of the tree, while I. perroti tended to emergence, development rate, and number of annual colonize near the crown, and I. pini colonized the generations reduce, but do not eliminate, interspecific mid-bole. Spatial colonization patterns are flexible competition for phloem. Of the three species, I. pini has (presumably mediated by pheromones) because I. pini the largest egg size and most rapid development. I. pini spread themselves evenly throughout the tree in late in this system are multivoltine, as are other populations summer, when I. grandicollis and I. perroti were absent. (Reid 1955; Schenk and Benjamin 1969). I. grandicollis are multivoltine in the southern United Pheromone communication among species States (Coulson et al. 1986) and I. perroti have been Interspecific responses to pheromones can both reported to be bivoltine in Alberta (Reid 1955), but we reduce and increase species overlap in resource use. A found very few I. perroti or I. grandicollis colonizing pheromone from a congener can act as a deterrent when trees or bolts after June in either 1994 or 1995, added to a conspecific signal, or as an attractant when suggesting that they are chiefly univoltine in our system. alone (Fig. 5, compare left and right panels). The A small second peak in flight activity in July (Fig. 1) deterrence must contribute to segregation of species suggests that some fraction may initiate a second within and among resource patches (logs), while the generation, but some Ips still respond to aggregation attraction must contribute to species overlap. pheromones after reproduction has ceased for the Interspecific chemical communication is ubiquitous in season (Teale 1991), so this second flight may also bark beetle communities (Birch et al. 1980; Wood represent some poorly understood post-reproductive 1982a; Cane et al. 1990; Smith et al. 1990; Borden et al. behavior. It makes sense that I. grandicollis and I. 1992; Savoie et al. 1998), even though it is seldom perroti would be univoltine because of their relatively reported in other taxa (London and Jeanne 1996; long development time. Annual degree day Chivers et al. 1997). Ips pini in the western United accumulations (10 °C base) from 1989 thru 1995 States are deterred by ipsenol (Furniss and Livingston reached their mid-point from 11 - 20 July. In 1995, the 1979; Borden et al. 1992), which is produced by date of median adult emergence from the first sympatric populations of I. paraconfusus (Lanier) , and generation was near midsummer for I. pini (20 July), I. paraconfusus are deterred by R-(- )-ipsdienol which is but after midsummer for I. grandicollis, and I. perroti produced by sympatric populations of I. pini (Birch and (31 July and 3 August, respectively), so multivoltinism Wood 1975). Similarly, the attraction of I. latidens to only appears to be viable for I. pini (immatures of any its pheromone, ipsenol, is inhibited by the ipsdienol species are unlikely to survive the winter; Clemens produced by I. pini (Miller and Borden 1992). 1916; Reid 1955; Lombardero et al. 2000). Temporal Conversely, Ips avulsus (Eichhoff), I. calligraphus overlap among species is increased by intraspecific (Germar), I. hoppingi (Lanier), I. montanus (Eichhoff), variation in reproductive phenology. Although most of Dendroctonus frontalis (Zimmermann), Hylastes the mating and oviposition in I. perroti and I. gracilis (LeConte), and knechteli (Swaine) grandicollis was during early May and mid May, are all attracted to pheromones produced by sympatric respectively, there was additional flight activity, host species of bark beetles (Lanier and Wood 1975; Hedden colonization, and mating in both species during June et al. 1976; Svihra et al. 1980; Cane et al. 1990; Smith (apparently from that had overwintered because et al. 1990; Poland and Borden 1994). Ours seems to the first adult progeny did not appear until mid-July). be the first report of heterospecific responses switching The relatively late spring flight of I. grandicollis (Fig. from attraction to deterrence depending upon the 1) further increases temporal overlap with I. pini. presence of conspecific signals. This indicates that the Similarly, I. perroti continues to compete for phloem information content of a pheromone plume is more Ayres et al. Page 8

complex than predicted from the additive effects of (beyond mating opportunities) that would not also be individual pheromones. This increases the information accrued from heterospecific aggregations. Sometimes, that can be transferred with a limited number of signals bark beetle individuals will suffer less from competition (in this case, ipsdienol, ipsenol, and lanierone), and with heterospecifics than from an equivalent number of therefore represents an example of semiochemical conspecifics (e.g., if the heterospecifics develop at a parsimony (sensu Blum 1996). In terms of information slower rate). Furthermore, there are at least three theory, the Ips communication system has higher mechanisms by which bark beetle individuals could entropic properties (McCowan et al. 1999). The benefit from multispecies associations: predator information content of a pheromone plume may be even swamping, group attack, and host location. The Ips greater because additional information is probably species share a guild of predators (Fig. 2; Raffa and transmitted by pheromone quantity (Birgersson et al. Klepzig 1989, Raffa 1991), so per capita survival is 1984; Renwick and Vite 1969), the enantiomeric probably higher on logs where the total number of bark composition of ipsdienol (Teale et al. 1994; Miller et al. beetles is higher (Reeve et al. 1995). Abrams et al. 1996), and undiscovered pheromones or synergists that (1998) described a similar situation as apparent are produced in low quantity (Miller et al. 1990). mutualism. When bark beetles attack live trees, per Presumably, the potential for species interactions is capita reproductive success is enhanced by high attack increased when there is overlap between species in rates (Raffa and Berryman 1983). Potential attack rates pheromone production. In our system, lanierone is the are greater for multispecies aggregations, so presumably only chemical signal that is unique to a single species; per capita reproduction can sometimes be enhanced if ipsenol is produced by both I. grandicollis and I. beetles produce and respond to heterospecific signals. perroti, and ipsdienol is produced by both I. pini and I. Ips also depend upon locating recently dead host perroti. Signal overlap within bark beetle guilds is material. All three species exploit this same ephemeral relatively common (Wood 1982a). It is also common resource, so pheromone plumes from any species will for bark beetle species to have chemoreceptors that indicate suitable host material, and individuals that can detect compounds they do not use as pheromones. For orient to heterospecific pheromones should have an example, the antennae of both I. pini and I. grandicollis increased probability of finding food resources. In this respond to numerous volatile molecules that function as context, the responding beetle is a parasite or pheromones in other species of bark beetles (Mustaparta commensalist. The attraction of Ips for heterospecific et al. 1977; Ascoli-Christensen et al. 1993). Species pheromones could result from selection to exploit these overlap in pheromone production and response is benefits. Differences among species could be the result probably enhanced because pine-feeding bark beetles of asymmetrical competition (e.g., weaker cross-specific share a limited set of suitable precursors in their host attraction in I. grandicollis and stronger cross-specific plants (chiefly monoterpenes) and share common deterrence suggests that they may suffer more from biochemical pathways by virtue of common descent competition with other species than other species suffer (Francke et al. 1995; Seybold et al. 1995b). from competition with I. grandicollis). Nonetheless, the family Scolytidae employs at least 20 It makes sense that males, the colonizing sex in these different molecules as pheromones (Wood 1982a; three species, would be more strongly attracted to Francke et al. 1995), so even species-rich guilds could heterospecific signals than females because they derive be organized to eliminate overlap in pheromones. the most benefit from participating in mass attacks and Species with pheromone signals that overlap most with from pirating previously located host material. Females sympatric species (e.g., I. perroti) should tend to would not normally accrue these benefits, but would experience the strongest interspecific interactions. still suffer the negative effects of interspecific competition among larvae. If heterospecific attraction Are there benefits of multispecies aggregations? has been favored by natural selection, then it should be The Ips community that we studied occurs in pine strongest among sympatric species, where it may tend to forests across a broad geographic area, suggesting that it counteract selection for reproductive isolation (Lanier is a stable assemblage. Indeed, most coniferous forests and Wood 1975). An alternative hypothesis is that harbor diverse communities of bark beetles with very heterospecific attraction is an evolutionary anachronism similar ecological requirements (Wood 1982b). Such or a biochemical artifact of coincidental overlap in communities would be more likely to persist if there signaling molecules and chemoreceptors (Lewis and were sometimes benefits of multispecies associations Cane 1990). that mitigate the costs of competition. Adaptive Regardless of whether or not heterospecific attraction explanations for communication systems have to be is an evolved attribute of bark beetle communities, the reconciled with benefits to the individuals that are effect is to strengthen interactions among species. It producing the signals and/or those that are responding remains difficult to predict whether removing a species (Alcock 1982). Unlike eusocial insects, bark beetles from our system would increase or decrease the derive no benefit from conspecific aggregations abundance of remaining species. This question has Ayres et al. Page 9 practical as well as theoretical value because it Anderbrandt O, Schlyter F, Birgersson G (1985) determines whether species- specific control program Intraspecific competition affecting parents and (e.g., Bakke 1989) would tend to increase or decrease offspring in the bark beetle Ips typographus. Oikos the abundance of other bark beetle species. The effect 45:89-98 Ascoli-Christensen A, Salom SM, Payne TL (1993) of changing the abundance of one species could depend Olfactory receptor cell responses of Ips upon the abundance of shared predators, the severity of grandicollis (Eichhoff) (Coleoptera: Scolytidae) to food limitations, reliance on attacking live trees, and the intra- and interspecific behavioral chemicals. J relative abundance of the different bark beetle species. Chem Ecol 19:699-712 This would be an example of conditional interactions Ayres MP, Scriber JM (1994) Local adaptation to (Abrams 1987) such as reported for some communities regional climates in Papilio canadensis of plants and fungi (Bronstein 1994a, b; Johnson et al. (Lepidoptera: Papilionidae). Ecol Monogr 1997; Brooker and Callaghan 1998). It seems likely 64:465-482 that rare species would tend to accrue the strongest Ayres MP, Wilkens RT, Ruel JJ, Lombardero MJ, benefits of interspecies associations. For example, an Vallery E (2000) Nitrogen budgets of phloem-feeding bark beetles with and without individual of species A would receive greater benefits symbiotic fungi (Coleoptera: Scolytidae). Ecology from species B (in predator swamping and mass attacks) 81:2198-2210 if that individual is without conspecifics than if it is Bakke A (1989) The recent Ips typographus outbreak in associated with many conspecifics (with conventional Norway--experiences from a control program. assumptions regarding functional responses of predators Holarctic Ecol 12:515-519 and mortality responses of trees). If so, this frequency Berryman AA (1973) Population dynamics of the fir dependence of conditional interactions would tend to engraver, Scolytus ventralis (Coleoptera: stabilize the community by increasing the reproductive Scolytidae). I. Analysis of population behavior success of rare species relative to common species. and survival from 1964 to 1971. Can Entomol 105:1465-1488 Conditional interactions mediated by pheromone Birch MC (1978) Chemical communications in pine communication provides a promising hypothesis to bark beetles. Am Scientist 66:409-419 explain the persistence and prevalence in coniferous Birch MC, Svihra P, Paine TD, Miller JC (1980) forests of diverse guilds of bark beetles with very Influence of chemically mediated behavior on host similar resource requirements. tree colonization by 4 cohabiting species of bark beetles. J Chem Ecol 6:395-414 ACKNOWLEDGMENTS Birch MC, Wood DL (1975) Mutual inhibition of the Thanks to Alice Shumate for her insight and efforts, attractant pheromone response by two species of Bob Haack for his confidence and inspiration, and Ilo Ips (Coleoptera: Scolytidae). J Chem Ecol 1:101-113 Ayres for her tolerence and criticism. Thanks also to Birgersson G, Schlyter F, Lofqvist J, Bergstrom G the management and employees of Woods Run Forest (1984) Quantitative variation of pheromone Products for the time and space to do this work. Some components in the spruce bark beetle Ips funnel traps were generously provided by USDA Forest typographus from different attack phases. J Chem Service, North Central Forest Experiment Station. The Ecol 10:1029-1056 manuscript was improved by comments from Mike Blum MS (1996) Semiochemical Parsimony in the Bohne, Greg Eaton, Rich Hofstetter, and Fina Arthropoda. Annu Rev Entomol 41:353-374 Lomberdero. We thank two anonymous reveiwers, who Borden JH, Devlin DR, Miller DR (1992) Synomones each devoted considerable effort to helping us improve of sympatric species deter attack by the pine this work. engraver, Ips pini (Coleoptera Scolytidae). Can J Forest Res 22:381-387 Bronstein JL (1994) Conditional outcomes in REFERENCES CITED mutualistic interactions. 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Cane JH, Merrill LD, Wood DL (1990) Attraction of Ips pini (Scolytidae) and Thanasimus dubius pinyon pine bark beetle Ips hoppingi to conspecific (Cleridae). J Chem Ecol 17:1705-1714 and Ips confusus pheromones (Coleoptera Howden HF, Vogt GB (1951) Insect communities of Scolytidae). J Chem Ecol 16:2791-2798 standing dead pine (Pinus virginiana Mill.). Ann Chivers DP, Kiesecker JM, Wildy EL, Anderson MT, Entomol Soc Amer 44:581-585 Blaustein AR (1997) Chemical alarm signalling in Johnson NC, Graham JH, Smith FA (1997) Functioning terrestrial salamanders: intra- and interspecific and mycorrhizal associations along the responses. Ethology. 103: 599-613 mutualism-parasitism continuum. New Phytol 135: Clemens, WA (1916) The pine bark beetle. Cornell 575-586 University Agricultural Experiment Station Bulletin Kaila L, Martikainen P, Punttila P (1997) Dead trees 383 left in clear-cuts benefit saproxylic Coleoptera Coulson RN, Flamm RO, Pulley PE, Payne TL, Rykiel adapted to natural disturbances in boreal forest. EJ, Wagner TL (1986) Response of the southern Biodiversity & Conservation 6:1-18 pine bark beetle guild (Coleoptera: Scolytidae) to Kirkendall LR (1989) Within-harem competition among host disturbance. Environ Entomol 15:850-858 ips females an overlooked component of Dajoz, R. (1974) Les insectes xylophages et leur role density-dependent larval mortality. Holarctic Ecol dans la degradation du bois mort. In: Pesson, P. 12:477-487 (eds) Ecologie forestiere. Gautiers-Villars, Paris, Lanier GN, Wood DL (1975) Specificity of response to pp 257-307 pheromones in the genus Ips (Coleoptera: De Jong MCM, Sabelis MW (1988) How bark beetles Scolytidae). 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Environ study of interspecific and intraspecific competition Entomol 16:390-399 within and between two sympatric bark beetle Francke W, Bartels J, Meyer H, Schroder F, Kohnle U, species, Ips pini and I. paraconfusus. Z ang Baader E, Vité JP (1995) Semiochemicals from Entomol 96:233-241 bark beetles: New results, remarks, and reflections. Lombardero MJ, Ayres MP, Ayres BD, Reeve JD J Chem Ecol 21:1043-1063 (2000) Cold tolerance of four species of bark beetle Furniss MM, Livingston RL (1979) Inhibition by (Coleoptera: Scolytidae) in North America. Environ ipsenol of pine engraver attraction in northern Entomol 29:421-432 Idaho USA. Environ Entomol 8:369-372 London KB, Jeanne RL (1996) Alarm in a wasp-wasp Gara RI, Werner RA, Whitmore MC, Holsten EH nesting association: do members signal cross- (1995) associates of the spruce beetle specifically? Insectes Sociaux 43: 211-215 Dendroctonus rufipennis (Kirby) (Col., Scolytidae) McCowan B, Hanser SF, Doyle LR (1999) Quantitative in spruce stands of south-central and interior tools for comparing communication Alaska. J Appl Entomol 119:585-590 systems: information theory applied to bottlenose Goulding, H A, Hall, D J, Raffa K F, and Martin A J dolphin whistle repertoires. Animal Behaviour (1988) Wisconsin woodlands: Identifying and 57:409-419 managing pine pests in Wisconsin. Agricultural Miller DR, Borden JH (1992) (s)-(+)-ipsdienol - Bulletin G3428, University of interspecific inhibition of Ips latidens (Leconte) by Wisconsin-Extension, Madison, WI Ips pini (Say) (Coleoptera - Scolytidae). J Chem Hager, B J, Teale, S A (1996) Genetic correlation of Ecol 18:1577-1582 pheromone production and response in the pine Miller DR, Borden JH, Slessor KN (1996) engraver beetle, Ips pini. Heredity 77:100-107. Enantiospecific pheromone production and Hedden R, Vite JP, Mori K (1976) Synergistic effect of response profiles for populations of pine engraver, a pheromone and a kairomone on host selection and Ips pini (Say) (Coleoptera: Scolytidae), in British colonization by Ips avulsus. Nature 261:696-697 Columbia. J Chem Ecol 22:2157-2172 Herard F, Mercadier G (1996) Natural enemies of Miller DR, Gries G, Borden JH (1991) E-myrcenol a Tomicus piniperda and Ips acuminatus (Col.; new pheromone for the pine engraver Ips pini (Say) Scolytidae) on Pinus sylvestris near Orleans, (Coleoptera: Scolytidae). Can Entomol 122 France: temporal occurrence and relative :401-406 abundance, and notes on eight predatory species. Moser JC, Thatcher RC, Pickard LS (1971) Relative Entomophaga 41:183-210 abundance of southern pine beetle associates in Herms DA, Haack RA, Ayres BD (1991) Variation in East Texas. Ann Entomol Soc Amer 64:72-77 semiochemical-mediated prey-predator interaction: Mustaparta H, Angst ME, Lanier GN (1977) Responses of single receptor cells in the pine engraver beetle Ayres et al. Page 11

Ips pini (Coleoptera: Scolytidae) to its aggregation chemotaxonomic character of North American pheromone ipsdienol and the aggregation inhibitor populations of Ips spp. in the pini subgeneric group ipsenol. J Comp Phys A 121 :343-348 (Coleoptera: Scolytidae). J Chem Ecol 21:995-1016 Paine TD, Birch MC, Svihra P (1981) Niche breadth Seybold SJ, Quilici DR, Tillman JA, Vanderwel D, and resource partitioning by 4 sympatric species of Wood DL, Blomquist GJ (1995) De novo bark beetles (Coleoptera: Scolytidae). Oecologia biosynthesis of the aggregation pheromone 48:1-6 components ipsenol and ipsdienol by the pine bark Poland TM, Borden JH (1994) Semiochemical-based beetles Ips paraconfusus Lanier and Ips pini (Say) communication in interspecific interactions (Coleoptera: Scolytidae). Proc Natl Acad Sci USA between Ips pini (Say) and Pityogenes knechteli 92:8393-8397 (Swaine) (Coleoptera: Scolytidae) in lodgepole Smith MT, Payne TL, Birch MC (1990) pine. Can Entomol 126:269-276 Olfactory-based behavioral interactions among five Raffa, K F (1991) Temporal and spatial disparities species in the southern pine bark beetle group. J among bark beetles, predators, and associates Chem Ecol 16:3317-3332 responding to synthetic bark beetle pheromones: Sokal, R. R. and Rohlf, F. J. (1995) Biometry. W. H. Ips pini (Coleoptera: Scolytidae) in Wisconsin. Freeman and Company, San Francisco Environ Entomol 20:1665-1679 Stewart, T. E. (1975) Volatiles isolated from Ips pini: Raffa KF, Berryman AA (1983) The role of host plant isolation, identification, enantiomeric composition, resistance in the colonization behavior and ecology biological activity. Dissertation. State University of bark beetles (Coleoptera: Scolytidae). Ecol of New York, Syracuse, NY Monogr 53:27-49 Svihra P, Paine TD, Birch M C (1980) Interspecific Raffa KF, Klepzig KD (1989) Chiral escape of bark olfactory communication in southern pine beetles. beetles from predators responding to a bark beetle Naturwissenschaften 67:518-529 pheromone. Oecologia 80:566-569 Teale SA, Hager BJ, Webster FX (1994) Rankin LJ, Borden JH (1991) Competitive interactions Pheromone-based assortative mating in a bark between the mountain pine beetle and the pine beetle. Animal Behaviour 48:569-578 engraver in lodgepole pine. Can J Forest Res Teale SA, Webster FX, Zhang A, Lanier GN (1991) 21:1029-1036 Lanierone: a new pheromone component from Ips Reeve JR, Ayres, MP, and Lorio, PL, Jr (1995) Host pini (Coleoptera: Scolytidae) in New York USA. J suitability, predation, and bark beetle population Chem Ecol 17:1159-1176 dynamics. In: Cappuccino, N and Price, PW (eds) Vité JP, Renwick JAA (1971) Population aggregating Population dynamics: New approaches and pheromone in the bark beetle Ips grandicollis. J synthesis. Academic Press, San Diego, CA, pp Insect Physiol 17:1699-1704 339-357 Wagner TL, Flamm RO, Coulson RN (1985) Strategies Reid RW (1955) The bark beetle complex associated for cohabitation among the southern pine bark with lodgepole pine slash in Alberta. Can Entomol beetle species: Comparisons of life-process 87:311-323 biologies. USDA For Serv Gen Tech Rep Renwick, J. A. A. and Vite, J. P. (1969) Bark beetle SO-56:87-101 attractants: mechanism of colonization by Wood DL (1982a) The role of pheromones kairomones Dendroctonus frontalis. Nature 224:1222-1223 and allomones in the host selection and Robins GL, Reid ML (1997) Effects of density on the colonization behavior of bark beetles. Annu Rev reproductive success of pine engravers: Is Entomol 0-8243-0127-7:411-446 aggregation in dead trees beneficial? Ecol Entomol Wood SL (1982b) The bark beetles and ambrosia 22:329-334 beetles of North America and Central America Sartwell C, Scmitz RF, Buckhorn WJ (1971) Pine (Coleoptera: Scolytidae), a taxonomic monograph. engraver, Ips pini in the western states. Forest Pest Great Basin Naturalist Memoirs 6:1-1359 Leaflet 122. USDA Forest Service, Washington, DC SAS (1990) SAS/Stat User's Guide: Version 6, Fourth Edition. SAS Institute Inc., Cary, North Carolina Savely HE (1939) Ecological relations of certain animals in dead pine and oak logs. Ecol Monogr 9:321- 385 Savoie A, Borden JH, Pierce HD, Jr, Gries R, Gries G (1998) Aggregation pheromone of Pityogenes knechteli and semiochemical-based interactions with three other bark beetles. J Chem Ecol 24:321-337 Schenk JA, Benjamin DM (1969) Notes on the biology of Ips pini in central Wisconsin jack pine forests. Ann Entomol Soc Amer 62:480-485 Seybold SJ, Ohtsuka T, Wood DL, Kubo I (1995) Enantiomeric composition of ipsdienol: A Ayres et al. Page 12

Table 1. Associations of Ips pini, I. perroti, and I. grandicollis in 61 logs that were naturally colonized in summer 1995. 4444444444444444444444444444444444444444444444444444444444444444444 Number of logs )))))))))))))))))))))))) Ips species present Observed Expecteda )))))))))))))))))))))))))))))) )))))))))) )))))))))) I. pini alone 32 28.5 I. perroti alone 2 2.0 I. grandicollis alone 11 4.9 ** I. pini & I. perroti 6 6.3 I. pini & I. grandicollis 7 15.0 ** I. perroti & I. grandicollis 2 1.1 All three Ips species 1 3.3 )))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))) a Based on the null hypothesis of no association between species. * P < .05; ** P < .01; *** P < .001 (G -tests).

Table 2. Contingency analysis comparing the pheromone preferences of three Ips species in three seasons (spring, mid summer, and late summer), with and without the presence of lanierone. For each line of the table, the null hypothesis is that the source had no effect on the proportion of beetles captured with ipsdienol vs. ipsenol vs. ipsdienol + ispenol. Data are summarized in Fig. 4. 444444444444444444444444444444444444444444444444444444444444444444444444 Source df Chi-square ))))))))))))))))))) ))) )))))) Species 2 3423.10** Season 2 182.51** Lanierone 1 7.31 Species x Season 4 191.96** Species x Lanierone 2 11.22 Season x Lanierone 2 11.22 Species x Season x Lanierone 4 63.91** Sex 1 0.00 Sex x Species 1 8.02 Sex x Season 2 0.13 Sex x Lanierone 1 0.50 Sex x Species x Season 2 4.33 Sex x Species x Lanierone 1 2.11 Sex x Season x Lanierone 2 6.23 Sex x Species x Season x Lanierone 2 3.63 )))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))) ** P < 0.01; controlled for experimentwise error with Dunn - Šidák adjustment for 15 tests.

100 Ips grandicollis 50 -1 0 200

150 ¥ fortnight

-1 100 Ips perroti

50

0

100 Ips pini 50 Beetles ¥ trap array 0 1-May 1-Jun 1-Jul 1-Aug 1-Sep 1-May 1-Jun 1-Jul 1-Aug 1-Sep 1-Oct Date in 1994 Date in 1995

Figure 1: Seasonal captures at pheromone traps of Ips grandicollis, I. perroti, and I. pini in 1994 and 1995.

Thanasimus 300 1989 dubius 200 100 Platysoma 0 cylindrica

2000 1990 1000

0 -1 400 1991 200 month ¥ 0 -1

600 1992 300 trap array

¥ 0 100

50 1993 Predators 0

200 1994 100

0

50 1995

0 Apr May Jun Jul Aug Sep Oct

Figure 2: Total monthly captures at pheromone traps of the two most abundant species of Ips predators. Traps in 1989-1993 were baited with ipsdienol only. Trap arrays in 1994-95 also included ipsenol and ipsdienol + ipsenol.

Oviposition Pupation and and hatch Larval eclosion development

Ips x ± 1SE pini

Ips perroti

Ips grandicollis

0 5 10 15 20 25 Development time at 25 °C (d)

Figure 3: Generation time at 25%C of Ips pini, I. perroti, and I. grandicollis. ipsdienol ipsenol both

No lanierone With lanierone 600 1855 609 94 306 106 100 80 60 40 spring (%) Captures in 20 0

180 1535 479 50 696 1073 100 80 60 40

Captures in 20 mid summer (%) 0

55 608 718 22 329 1055 100 80 60 40

Captures in 20 late summer (%) 0 Ips Ips Ips Ips Ips Ips grand. perroti pini grand. perroti pini

Figure 4: Relative preferences of three Ips species for ipsdienol alone, ipsenol alone, and ipsdienol + ipsenol. Percent captures at each blend are shown for spring, mid summer, and late summer (upper, middle, and lower panels), with and without the presence of lanierone (right vs. left panels). Values above each set of bars indicate total captures of each species in each season with no lanierone (6 trap arrays) or with lanierone (2 trap arrays). See Table 2 for corresponding analyses Absence of Presence of Heterospecific conspecific conspecific signal signal signal

M 4 I. grand. 1 * F M I. perroti 2 F 4 M I. grand. I. perroti 2 F 4

I. pini 3 * 4 I. perroti 2 2

I. pini I. perroti 4 4

M 4 I. pini 3 * F M I. grand. 1 F 2 M I. pini I. grand. 4 F 4 -100 0 100 -100 0 100 Beetle response

Figure 5: Response of Ips pini, I. grandicollis, and I. perroti to heterospecific semiochemicals in the presence and absence of conspecific signals. Beetle response is expressed as numbers of beetles relative to that attracted by the conspecific signal alone (equation 1). Values can range from strong deterrence (- 100) to strong attraction (100), with a value of 0 indicating no effect. Numbers to the left and right of each bar indicate the composite pheromone signal: 1 = ipsenol, 2 = ipsenol + ipsdienol, 3 = ipsdienol + lanierone, and 4 = ipsenol + ipsdienol + lanierone. Asterisks indicate three cases where the bars are very small but where R is significantly positive. "M" and "F" represent males and females, respectively.