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Dispersal Patterns and Mark-and-Recapture Estimates of Two Pine Root Weevil Species, pales and picivorus (Coleoptera: ), in Christmas Tree Plantations

LYNNE K. RIESKE AND KENNETH F. RAFFA

Department of Entomology. University of Wisconsin. Madison. Wisconsin 53706

Environ. Entomol. 19(6): 1829-1836 (1990) ABSTRACf The pales weevil. Hylobius pales (Herbst), and the pitch-eating weevil, Pachy­ lobius p1dvorus (Germar), are pests of plantation pines in the eastern United States. Dispersal patterns of these species were studied in the summer of 1989 using pitfall traps baited with ethanol and turpentine, and mark-and-recapture techniques. Approximately 17% of H. pales and 34% of P. picivorus were recaptured. Most pales weevils were recaptured in the im­ mediate vicinity of the release point, whereas pitch-eating weevils appeared to disperse farther before responding to the baits. Marked weevils were recaptured up to 8 wk following the release. No gender differences were found in recapture rates. Pronounced temporal differences in recapture rates were observed, with more weevils attracted to baits in spring than in summer. A separate baited trap was developed to monitor weevil flight. Total weevil numbers, and female H. pales considered singly, were more commonly caught at 81 cm than 160 cm. The role of dispersal and migration in pine root weevil ecology is discussed with respect to the ability of these species to colonize new habitats.

KEY WORDS Insecta, pine root weevils, dispersal. migration

CHRISTMAS TREE PRODUCTION is a major industry the production of plantation pines in the Lake States in Wisconsin, with >3 million trees harvested an­ (Finnegan 1959, Mosher & Wilson 1977). Larvae nually (Wisconsin Christmas Tree Producers Assn. of H. radicis or H. rhizophagus can develop in 1989). These even-aged monocultures, along with healthy hosts, creating potential breeding sub­ increased plantings for timber and pulp produc­ strates for H. pales and P. picivorus. tion, have favored several species which were A method of trapping pine root weevils has been previously unimportant. Among the most preva­ developed using pitfall traps baited with ethanol lent of these pests are the pales weevil, Hylobius and turpentine. These compounds act synergisti­ pales (Herbst), and the pitch-eating weevil, Pachy­ cally, mimicking cues used during insect orienta­ lobius picivorus (Germar). tion and host location (Fatzinger 1985; Fatzinger Adult feeding on stems and branches causes ex­ et al. 1987; Tilles et al. 1986a.b; Phillips et al. 1988; tensive seedling mortality and disfigurement of Raffa & Hunt 1988; Hunt & Raffa 1989). This harvestable pines (Drooz 1985). Larvae of both method may prove suitable for monitoring weevil species develop within roots of stressed or dying populations and timing pesticide treatments. How­ pines or cut stumps. Thinning and harvesting prac­ ever, there are currently no methods for estimating tices provide suitable brood sites for these two wee­ trap efficiency or relating trap catch to weevil den­ vils (Speers 1958. Thatcher 1960, Fox & Hill 1973). sities. Also, the dispersal patterns of these , Both H. pales and P. picivorus have overlapping and the poSSible role of migration in offsetting pre­ generations. Ovenvintering adults emerge in spring, dictive indices, are not well understood. mate, and oviposit in recently cut or highly stressed Because of the ephemeral nature of the larval hosts. Overwintering larvae complete development habitat, adult weevils must migrate to find material in midsummer, but little or no oviposition occurs suitable for oviposition and larval development. until the following spring (Finnegan 1959, Bliss & Both H. pales and P. picivorus are capable of sus­ Kearby 1970). Both species are well-established pests tained flight (Finnegan 1959, Franklin & Taylor in southern forests, but the importance of P. picivo­ 1970, Taylor & Franklin 1970), but most local rus in northern states has only recently been rec­ movement is thought to be by walking. ognized (Hunt & Raffa 1989, Raffa & Hunt 1989). Trap catch varies throughout the season when Together with the pine root collar weevil, Hylobius these vol;ltiles are used as baits, peaking in late radicis Buchanan, and the closely related Hylobius spring and early summer. The subsequent decrease rhizophagus Millers, Benjamin & Warner, they in response suggests that either weevil populations form a weevil complex which significantly limits drop conSiderably as the summer progresses, or the

0046-225X/90/1829-1836$02.00/0 © 1990 Entomological Society of America 1830 ENVIRONMENTAL ENTOMOLOGY Vol. 19, no. 6 weevils' attraction to the ethanol/turpentine baits through two 2-mm holes in the trap wall. The vials is not uniform throughout the season. Previous were suspended 4 cm below ground level. Baits studies have suggested that weevil response to these consisted of 95% ethanol and turpentine. The tur­ volatiles coincides with the period of mating and pentine (Mautz Paint Company, Madison, Wis.) oviposition (Hunt & Raffa 1989). was analyzed by gas chromatography using the Mark-and-recapture techniques have been used method of Raffa & Steffeck (1988) and was found with mixed success to assess insect dispersal and to consist of 46% alpha-pinene, 42% beta-pinene, migration, evaluate mass trapping efforts and at­ 2% beta-phellandrene, 1% limonene, 0.88% cam­ tractant efficacy, and estimate field populations phene, 0.77% myrcene, and <1% unknown com­ (Southwood 1978). The technique has been used pounds. The volatilization rates for a 1:1 volumetric to qualitatively describe Hylobius movement, but ratio under laboratory' conditions (22°C) were 200 no quantitative indices have been computed (Wil­ mg/d of ethanol and 40 mg/d of turpentine. Baits son 1968, Corneil & Wilson 1984). Population es­ were replenished weekly throughout the monitor­ timates that incorporate mark-and-recapture tech­ ing period. niques use variations of the Lincoln or Peterson The weevils used for marking and releasing had indices, which are based on the ratio of marked been trapped from field populations. They were and unmarked individuals trapped (Caughley 1977, stored in plastic holding boxes at :::::23°C and a Southwood 1978). photoperiod of 15:9 (L:D), and fed on Scots pine Several assumptions underlie use of these esti­ twigs. No information regarding their age could mates: (1) no adverse effect of the mark; (2) mixing be assessed. Marking was performed on nonanes­ of marked individuals; (3) random or systematic thetized individuals during daylight hours, during sampling, or equal catchability between marked the period of minimal weevil activity. Before and unmarked individuals; (4) sampling at discrete marking and releasing, the general health of each intervals; (5) no births or ingression; (6) equal death insect was assured, and any which could not right and egression rates among marked and unmarked themselves were not used. individuals; and (7) no effect of capture on future Acrylic artists' paint was used to mark the elytra catchability (Caughley 1977, Southwood 1978). of each insect. The marking system was modified The objectives of this study were to: (1) develop from the 1-2-4-7 system developed for insects by mark-and-recapture techniques for assessing dis­ Ehrlich & Davidson (1960). Separate colors were persal patterns of H. pales and P. picivorus, esti­ used for each gender and species. Preliminary lab­ mate field population densities, and determine the oratory experiments showed that the acrylic paint efficiency of baited pitfall traps; (2) determine had no effect on weevil survival or activity. whether seasonal patterns in trap catch can be re­ Experiment 1. Thirty-six pitfall traps were lated to changes in weevil responsiveness to at­ placed in a 432-m2 plot consisting of 130 trees, with tractants throughout a season, and (3) evaluate six traps in every other tree row. The infestation weevil flight patterns in an area where walking level at this site approached 100%. weevils were also being sampled by pitfall traps. Two hundred and ninety H. pales (118 males and 172 females), 172 P. picivorus (77 males and 95 females), and 13 female H. radicis were re­ leased. Marked H. pales and H. radicis were re­ Materials and Methods leased at dusk (1930 hours CST) on 1 June from a The study was conducted in the summer of 1989 plastic platform (19 by 27 cm with a 7-mm ridge) in Waushara and Portage counties, Wis. Field sites placed at the center of the plot. Twenty-four hours were established in Christmas tree plantations on later, marked P. picivorus were released. The dis­ sandy soils. The trees were Scots pine (Pinus syl­ persion of both species was assessed by monitoring vestris L.) (5.5 and 6.5 yr old) planted 1.68 m apart. the pitfall traps at 24-h intervals for the first 7 d, The pitfall traps were a modification of those and weekly thereafter through 1 October. At each used by Hunt & Raffa (1989) and consisted of 17­ monitoring interval, the weevils were identified, cm sections of plastic PVC drainpipe (10 cm di­ and their distinguishing marks were noted. All ameter). Eleven centimeters from one end, a series marked individuals were re-released in the follow­ of eight holes (7 mm diameter) were drilled about ing monitoring period. The movement of each the perimeter. The trap interior was coated with marked and recaptured insect was monitored liquid Teflon to prevent weevil escape. The traps throughout the season. were capped at each end and inserted into the To analyze dispersal, the study plot was divided ground so that the holes were flush with ground into five concentric zones around the point of re­ level. Two 2-mm holes were drilled in the bottom lease. Zone 1, closest to the release point, contained to allow for drainage. The exposed 6 cm of the four pitfall traps averaging 2.4 m from the release trap was painted flat black to simulate a tree trunk point. Zones 2, 3, and 4 surrounded Zone 1, and image. contained 8, 8, and 16 traps, averaging 4.5 m, 6.5 Baits were dispensed from 2-ml glass vials (0.5 m, and 9.2 m, respectively, from the release point. dram, 12 by 35 mm) and were suspended by thin Zone 5 consisted of 200 traps distributed over a aluminum wire from a stiff 14-gauge wire passed 2.43-ha (6 acre) area of the remainder of the farm. December 1990 RIESKE & RAFFA: PINE ROOT WEEVIL DISPERSAL 1831

The Peterson index, as modified by Bailey (1952) consisted of inverted 3.9-liter plastic milk contain­ to provide a more conservative estimate, was used ers with three sides removed, the fourth side serv­ to estimate field populations of H. pales and P. ing as a strike surface for in-flying insects. A 200­ picivorus at this site: ml polyethylene jar was attached at the bottom of each trap and served as a holding jar for trapped N = M(n + 1)/(m + 1), insects. The interior of the holding jar was coated where N is the population estimate, M is the num­ with liquid Teflon and two 2-mm drainage holes ber of marked individuals released, n is the number were drilled in the bottom. Ethanol and turpentine of individuals in the second sample, and m is the baits were dispensed from two 2-ml glass vials at­ number of marked individuals recaptured in sec­ tached below the strike surface. ond sample. Two traps were attached to wooden stakes (5 by Assumptions underlying the use of mark and 5 by 180 cm) at heights of 81 and 160 cm, respec­ recapture were tested for their validity. The as­ tively. The heights were chosen to coincide with sumption of equal catchability was tested by com­ the grass and tree canopy heights. The direction paring the observed and expected variances of the of the strike surface was randomly assigned to one recapture frequencies (Caughley 1977). This value of the four cardinal directions. Barriers consisting can be tested against a X' distribution with degrees of corrugated plastic (20 by 20 cm) coated with of freedom equal to the sum of the recapture fre­ liquid Teflon were attached to the stake approxi­ quencies minus 1. When N is greater than 30, this mately 55 cm above ground level to prevent can be approximated using the normal deviate. A from walking into the trap. significant P value does not support the assumption Barrier traps were arranged in groups of six stakes, of equal catchability (Caughley 1977). To guard each with two traps, in 432-m' areas. A 432-m' against variation in dispersal based on gender, each buffer zone with no traps was placed between each gender of each species was tested individually. grouping. There were nine groups of six stakes. Because the Peterson estimate is biased upward Traps were oriented in a north-south direction, by birth and immigration, and because these weevil forming a transect through a gradient of weevil­ species are attracted to the ethanol/turpentine baits damaged trees. Foliar symptoms indicative of pine only during the peak of their oviposition periods, root weevil damage were evident throughout, but the population estimates were based on a brief they were most prevalent at the southernmost por­ sampling period of 7 d for H. pales and 6 d for P. tion of the study plot. The infestation level at this picivorus to reduce this effect. site approached 95%. The topography of the site The distribution of marked and recaptured in­ was such that some trap groups were located on dividuals of each species was compared across all hill tops, whereas the remainder were on slopes. zones using a X' analysis. To test the species' dis­ Fifty-four corresponding pitfall traps were 10­ tribution within each zone, a test of proportions catedadjacent to the flight traps, with a 30-m-wide (Snedecor & Cochran 1980) was used. Analysis of buffer strip between them. The pitfall traps were gender differences within each species across these grouped similarly to the barrier traps; they also zones was conducted by a X' analysis. The rela­ transected the gradient of weevil-damaged trees. tionship between trap catch and distance from the Flight trap data were subjected to the general release point was analyzed by the general linear linear model procedure (SAS Institute 1982) using model procedure (SAS Institute 1982): number of the model: number of insects = height location marked insects recaptured = zone. Each gender of height. location. Mean separations were per­ each species was analyzed separately. formed using the Student-Newman-Keuls test. Experiment 2. To assess temporal differences in Trap catch based on trap height was compared each species' attraction to the ethanol/turpentine with Student's t test. Each gender of each species baits, a second set of marked weevils was released was analyzed individually. A comparison of trap on 20 July. This is approximately 6 wk past the catch between flight traps and corresponding pit­ peak of the oviposition period. This release oc­ fall traps was made for each species and each gen­ curred in a plot of the same size and trap arrange­ der using a X' contingency table and test of pro­ ment on a farm well separated from the site de­ portions (Snedecor & Cochran 1980). scribed above. The damage level on this plot was <50%. An additional 600 traps were distributed Results throughout three sites within a 2-km radius. Eighty marked weevils of both H. pales and P. picivorus Experiment 1. The recovery rates were 34% for (40 of each gender) were released at dusk on 20 P. picivorus, 17% for H. pales, and 13% for H. July in the center of the plot. Following this release, radicis. In addition, 7.5% of P. picivorus and 2% captured individuals were not re-released. The pat­ of H. pales were recaptured more than once (Fig. tern of recapture between the 1 June and 20 July 1). One female P. picivorus was trapped four times. releases were compared. Because so few H. radicis were released, this species Experiment 3. Baited barrier traps were used was excluded from subsequent analyses. to monitor flight activity. Barrier traps were mod­ Both genders of both species satisfied the as­ ified from those developed by Klepzig (1989) and sumption of equal catchability (H. pales male: P 1832 ENVIRONMENTAL ENTOMOLOGY Vol. 19, no. 6

30 30 • H.pales H. pales c ~ ------cc 25 ~ P. picivorus W 25 t P. picivorus WW 11. a: l<:a: 0::::1 ------a:::::I 20 a:~ 20 <~ wOo :::ED.. m< 11.< 15 :::E&l 15 O() ::::I a: ~rn z z= ..lrn W> 10 <= 10 ()W ~> OW a:w ~w ~3= 5 ~ 3= 5 o 234 5 10 15 20 25 30 35 FREQUENCY OF CAPTURE DAYS Fig. 1. Recapture frequencies of marked H. pales Fig. 2. Recapture rates of marked H. pales and P. and P. picivorus using pitfall traps baited with ethanol picivoTUS in relation to time following 1 June release. and turpentine. tured individuals was 1:0.81 (male/female). As with = 0.07, female: P = 0.09; P. picivorus male: P = H. pales, this does not differ significantly from the 0.46, female: P = 0.31). Combined with the lab­ expected 1:1 ratio (X 2 = 4.370; df = 4). oratory observations showing no adverse effects of The responses of H. pales and P. picivorus across marking, the brief sampling intervals (24 h) over zones differed greatly (x2 = 34.00; df = 4) (Fig. 3). a short period (1 wk) relative to the insect life cycle Analysis within zones using a test of proportions (1.5 yr), and the pattern and occurrence of multiple showed the lack of uniformity in both species' dis­ captures, the additional assumptions underlying use tribution was significant in Zones 1, 3, and 4 (P < of the Peterson index appear to be validated. Based 0.05). Within Zones 1-4, only Zone 2 showed no on the Peterson index, population estimates for the significant difference (P > 0.05) in the number of date of release are 510 H. pales (203 males: 307 H. pales and P. picivorus recaptured. Because of females), and 476 P. picivorus (205 males: 271 fe­ the small number of insects trapped in Zone 5, males), for a 747-m2 ania (Table 1). species distribution was not tested in that zone. Approximately 87% of the captured H. pales Several marked weevils traveled considerable were recovered in the first 7 d following the release distances from the point of release (Table 2a). There (Fig. 2). Marked H. pales were caught up to 7 wk was no apparent relationship between distance after 1 June. Conversely, only 42% of P. picivorus traveled and time elapsed. The greatest distance were recaptured in the first week. The recapture traveled by recaptured weevils was 200 m north rate of P. picivorus maintained moderate levels by two female P. picivorus, recaptured 18 and 54 nearly 8 wk after the release date, with the last d following the release. marked individual recaptured after 10 wk. Experiment 2. Weevil attraction to the ethano\j The distribution of H. pales was not even across turpentine baits varied throughout the season (Fig. zones (x2 = 47.87; df = 4; P < 0.005). Nearly 83% 4). The overall recovery rate of marked individuals were recaptured within 4.5 m of the release point from the 1 June release was 30%. The recovery (Fig. 3). The observed sex ratio of recaptured in­ rate from the 20 July release was 18.7%. The re­ dividuals was 1:0.85 (male/female) which does not covery rate was greatest immediately following each differ significantly from the expected 1:1 (X 2 = 3.03; release, dropping off the following week. However, df = 4; P < 0.25). recapture rates remained relatively constant for Similarly, P. picivorus was not evenly distributed several weeks following the 1 June release but across zones (X 2 = 12.12; df = 4; P < 0.025). How­ dropped to zero 3 wk following the 20 July release. ever, >78% were recaptured between 4.5 and 9.2 As in the first release, recapture rates were great­ m from the release point. The sex ratio of recap- est in the immediate vicinity of the release. How-

( Table 1. Population estimates and standard error of H. pale. and P. picivoru. using the Peterson estimate

H. pales P. piclvorus

&$ 99 &$ 99 Number of marked individuals released, M 118 172 77 95 Number of individuals in second sample, n 49 49 39 56 Number of marked individuals recaptured, m 28 27 14 19 Population estimate, N 203 307 205 271 Standard error (9'0) 24.1 (12) 37.2 (12) 40.6 (20) 47.6 (18)

Total population - N. + N•. H. pales = 510 total; P. piclvorus = 476 total. December 1990 RIESKE & RAFFA: PINE ROOT WEEVIL DISPERSAL 1833

30 I * I c u..a:W O:J 30 c f-o..f­ W Z<{ a: Wu :J 20 Uw f- a: a: 0.. W 20 <{ o..rn U ...J W w­ a: -w» L== f-w ...J 10 :33: 10 <{ :J f- c -0- June 1 release 0 :Ew :J:.;: f- Ua: ----+-- July 20 release <{ :E o I I I I I I I o o 2 4 6 8 10 2.4 4.5 6.5 9.2 >10.5 WEEK NUMBER MEAN DISTANCE FROM RELEASE POINT (METERS) Fig. 4. Comparison of recapture rates of H. pales and P. picivOTUS in baited pitfall traps following 1 June Fig. 3. Recapture of marked H. pales and P. picivo­ and 20 July releases. TUS at various distances from the release point. Chi-square value (x· = 34; df = 4; P < 0.005) refers to species differences across zones; test of proportions (*, P < 0.05) The flight traps positioned at 81 cm caught sig­ refers to species differences within zones. nificantly more female H. pales and total weevils than the traps at 160 cm (P < 0.05) (Table 3). Height was not a significant factor in determining ever, weevil response was too low for statistical flight activity of male H. pales or either gender of comparisons among recovery zones. The greatest P. picivorus. distance traveled by weevils from this release was 1 km, by two female P. picivorus within 6 d of > 20 T'------, the release (Table 2b). Experiment 3. Hylobius pales constituted 60% Flight traps of the flight trap catch (total n = 129), P. picivOTUS u..C ------H. pales ~ 37%, and H. radicis 3%. Flight periods of H. pales o 15 ------P. picivorus a: 0.. and P. picivOTUS were comparable (Fig. 5), al­ W<{ ala: though the initial flight peak of H. pales did not :Ef- occur with P. picivOTUS. Flight activity for both :J rn 10 Z...J species occurred from mid-May until mid-August ...J- <{> and peaked before mid-July. Preliminary studies f-w OW of flight activity in 1988 using similar trapping f-3: 5 methods (3 traps per stake, 15 stakes) yielded com­ parable species ratio and seasonal data. H. pales constituted 65% of the total flight trap catch (n = 0 72), 35% were P. picivorus, and no H. radicis were 5/13 6/1 7/1 8/1 9/1 caught.

80 Table 2. Recapture of marked H. pale. and P. piciv­ oru. outside the release area (Zone 5) Pitfall traps ------H. pales Days u..C Distance from OW 60 ------P. picivorus Species Gender after 0.. release point, m a: 0.. release W<{ ala: (a) I June release :Ef- :J 40 24 H. pales Male 43 Z...Jrn 26 P. picivorus Female 42 ...J- <{> 40 H. pales Male 26 f-w 128 P. picivorus Male 42 OW 20 128 P. picivorus Female 13 f-3: 133 P. picivorus Female 73 136 P. picivorus Male 68 175 H. pales Male 26 0 200 P. picivorus Female 18 5/136/1 7/1 8/1 9/1 200 P. picivorus Female 54 DATE (b) 20 July release Fig. 5. Seasonal pattern of H. pales and P. picivOTUS 1,000 P. plcivo':us Female 6 1,000 P. picivorus Female 6 capture in barrier and pitfall traps baited with ethanol and turpentine. 1834 ENVIRONMENTAL ENTOMOLOGY Vol. 19, no. 6

Table 3. Mean number of H. pale. and P. picivoru. Table 4. Total numbers of H. pale. and P. picivoru. caught in flight traps at two heights baited with ethanol trapped in pitfall traps versus flight traps and turpentine Pitfall Flight Normal Species Gender Trap height. cm trap trap deviate Species Gender 81 160 H. pales Male 39 38 0.11 NS Female 44 39 0.55 NS H. pales Male 0.91 0.84 1.22 NS Female 0.96 0.79 2.91" P. plcivorus Male 116 25 7.67" Female 148 23 9.57" P. plcivorus Male 0.85 0.79 1.52 NS Female 0.83 0.79 0.84 NS ", P < 0.05, test of proportions; NS, not significant. Total insects 1.36 1.07 3.26"

", P < 0.05, Student's t test; NS, not significant. the distribution of more susceptible host material. Trap catch was higher in the western portion of Location within the farm affected flight trap the release area, where tree mortality was greatest. catch only for total H. pales (P < 0.05). The lo­ The lack of significant differences in recapture cation closest to the source of weevil infestation rates between males and females implies that the caught the greatest number of H. pales. Trap lo­ 1:1 sex ratio found in previous studies using baited cation was not a significant factor in determining pitfall traps (Raffa & Hunt 1989, Hunt & Raffa trap catch for either H. pales gender individually, 1989, Rieske 1990) represents actual population or for either P. picivorus gender. ratios rather than behavioral differences. Equiva­ The total numbers of each species trapped in lent responses by both genders further suggests that pitfall versus flight traps are shown in Table 4. these volatiles are not simply ovipositional cues, Pitfall and flight traps were equally effective in but may also act as feeding or mating stimulants, monitoring H. pales activity. However, pitfall trap or both. catch of P. picivorus was more than five times Differences in recapture rates between the early greater than flight trap catch. Although more in­ and mid-season releases demonstrate temporal sects were captured in the pitfall traps, seasonal changes in weevil response to host volatiles. Weevil patterns were similar (Fig. 5). response to the ethanol and turpentine declines as In addition to monitoring flight activity of Hy­ the season progresses and lends support to the idea lomus and Pachylomus weevils, the flight traps con­ of maximum attraction during the oviposition pe­ sistently caught high numbers of other pests of riod. This appears to relate to seasonal changes in plantation pines, most notably Pissodes weevils. host tree chemistry because ethanol rates are high­ est early in the growing season (Crawford & Baines 1977). . Some long-distance dispersal occurred following Discussion both the 1 June and 20 July releases. However, the The high recapture rates of marked weevils, dur­ shorter time periods over which longer distances ing periods when new attacks are normally initi­ were traveled following the 20 July release (Table ated (Wilson 1973, Corneil & Wilson 1984, Hunt 2) suggests seasonal changes in dispersal behavior. & Raffa 1989, Rieske 1990), suggests that the mark­ That is, the weevils released earlier in the season and-recapture technique may be useful for mon­ were probably undergoing nonmigratory, disper­ itoring dispersal as well as for assaying the efficacy sive, or trivial movements (Dingle 1972) associated of various attractants and trap designs. Our area­ with feeding. This contrasts with the long-distance wide estimate converts to four weevils per infested flight observed with female P. picivorus from the tree, which agrees with results from other sampling second release. The latter weevils seem to be un­ methods. For example, Raffa & Hunt (1989) ob­ dergoing migratory behavior characterized by served that an average of 6.3 H. pales and P. pi­ straightened-out movements and reduced response civorus emerged per tree in which development to environmental stimuli (Dingle 1972). Studies on was successful (3.5 weevils per tree in all infested the closely related European Hylomus ametis L. trees), in hosts somewhat larger than in this study. show that flight activity is strongly influenced by In addition, a direct examination of 19 trees in the weather patterns and is subject to both diurnal and study area yielded a total of 75 weevils of all life seasonal periodicity (Solbreck & Gyldberg 1979, stages. Solbreck 1980). Studies with other insects have In this study, H. pales. appeared to be more re­ shown that physiological age can also Influence in­ sponsive than P. picivorus to the immediate stimuli sect migratory behavior, and that migration func­ of the ethanol/turpentine-baited traps adjacent to tions to maximize current survival and assure op­ "the release point. Pales weevils were more com­ timal habitat for offspring (Dingle 1972, 1980; monly caught in the traps closest to the release Taylor 1986). The female P. picivorus recaptured point, and within a relatively shorter time period, 1 km from the release point in'this study were than were pitch-eating weevils. The effects of dis­ possibly migrating to new habitats for over-win­ tance from the release point were confounded by tering and subsequent host colonization. December 1990 RIESKE & RAFFA: PINE ROOT WEEVIL DISPERSAL 1835

Flight trap catch generally coincided with sea­ (Raffa & Hunt 1989), greater mobility may trans­ sonal pitfall trap catch (Fig. 5). The numerical late into greater success. similarity between the pitfall and flight trap catch­ -Knowledge of the dispersal and migratory flight es for H. pales suggests that the nonmigratory patterns of these weevils should help in the devel­ movements of this species involve frequent flight opment of management techniques for root-in­ (Table 4). Considerably more P. picivorus respond­ festing pests. Accurate population estimates are es­ ed to the ethanol/turpentine bait by walking rather sential for developing economic thresholds. The than flying, suggesting that flight activity in this ability to detect migrating infestations will allow species may be more confined to migratory phases. for control of the pine root weevil complex before The low capture rates of H. radicis in flight traps mortality or disfigurement occurs. '- may support the view that this species is an infre­ quent flier (Wilson & Millers 1983), but this con­ Acknowledgment clusion is tentative because pitfall trap catches were also low. Unlike baited pitfall traps in which only We thank the Kirk Company of Wautoma, Wis., for female H. radicis are caught (Hunt & Raffa 1989), the study sites and assistance with trap installation, and both genders were caught in flight traps. Because L. Zastoupil for his valuable advice. M. Bleck, J. Graetz, our study did not include unbaited traps, however, and L. Kellner assisted with data collection. We also thank D. B. Hogg and D. K. Young for reviewing this the possibility that male catches represent simple manuscript. This research was supported by the Christ­ passive impact cannot be discounted. Additional mas Tree Producers Associations of Wisconsin, Minne­ research is needed to fully characterize nonmigra­ sota, Michigan, and lllinois; the Wisconsin Department tory flight of these three species. of Agriculture; Trade & Consumer Protection Sustain­ The significantly greater catch at 81 cm than at able Agriculture Grant 8825; USDA 86-CRCR-1-2077; 160 cm for both total weevils and female H. pales USDA 86-FSTY-9-0210; Sigma Xi Grants-in-Aid of Re­ demonstrates that weevils fly at relatively low search; the University of' Wisconsin Applied Research heights during most of the season. It also suggests Program; and the University of Wisconsin-Madison Col­ that these species may orient to the grass rather lege of Agricultural and Life Sciences. than to the pine canopy because the average height of understory vegetation was approximately 50 cm References Cited throughout the farm. Weevils were just as likely to be caught in the lower traps in small valleys as on Bailey, N. T. J. 1952. Improvements in the interpre­ tation of recapture data. J. Anim. Ecol. 21: 120-127. hills. Bliss, M. & W. H. Kearby. 1970. Notes on the life Considered together, the flight activity and the history of the pales weevil and Northern pine weevil mark-and-recapture data suggest that H. pales may in central Pennsylvania. Ann. Entomol. Soc. Am. 63: be immigrating into the study area and remaining 731-734. in the area once colonization has been initiated. Caughley, G. 1977. Analysis of vertebrate populations. For example, the large May flight peak (Fig. 5) Wiley, New York. corresponds with the period when weevils emerge Corneil, J. A. & L. F. Wilson. 1984. Dispersionand from overwintering sites. Also, almost all marked seasonal activity of the pales weevil, Hylobius pales weevils were recovered locally. Conversely, P. pi­ (Coleoptera: Curculionidae), in Michigan Christmas tree plantations. Can. Entomol. 116: 711-717. civorus appears to be emigrating out of this area, Crawford, R. M. M. & M. A. Baines. 1977. Tolerance based on the mark-and-recapture results. No large of anoxia and metabolism of ethanol in tree roots. peak in flight trap catch occurred until mid-June, New Phytol. 79: 519-526. even though P. picivorus were active in Mayas Dingle, H. 1972. Migration strategies of insects. Sci­ evidenced by pitfall trap catches (Fig. 5). Of the ence 175: 1327-1335. 12 individuals trapped outside the release area (Zone 1980. Ecology and evolution of migration, pp. 1-79. 5), 9 were P. picivorus. This suggests that P. pi­ In S. A. Gauthreaux- [ed.], migration, orien­ CiVOTUS and H. pales are most successful at different tation, and navigation. Academic, New York. levels of host degradation. Differential dispersal Drooz, A. T. [ed.]. 1985. Insects of eastern forests. USDA, Forest Service Miscellaneous Publication 1426. and migration, in addition to differential responses Ehrlich, P. R. & S. E. Davidson. 1960. Techniques to host volatiles (Rieske 1990), may serve to par­ for capture-recapture studies of Lepidoptera popu­ tition common resources. lations. J. Lepid. Soc. 14: 227-229. These patterns of dispersal and temporal attrac­ Fatzinger, C. W. 1985. Attraction of the black tur­ tion could have important implications in the se­ pentine (Coleoptera: Scolytidae) and other for­ quence of infestation by H. pales and P. picivorus. est Coleoptera to turpentine-baited traps. Environ. The relatively greater distances traveled by P. pi­ Entomol. 14: 768-775. civorus, their ability to colonize less degraded hosts Fatzinger, C. W., B. D. Siegfried, R. C. Wilkinson & J. L. Nation. 1987. Trans-verbenol, turpentine, and (Rieske 1990), and their extended period of re­ ethanol as trap baits for the black turpentine beetle, sponse to host volatiles as shown by the mark-and­ Dendroctonus terehrans, and other forest Coleoptera recapture data, suggest that P. picivorus may be in northern Florida. J. Entomol. Sci. 22: 201-209. more capable of colonizing new areas. Because the Finnegan, R. J. 1959. The pales weevil, Hylobius relative success of each of these species may depend pales (Hbst.), in southern Ontario. Can. Entomol. 91: simply on which arrives in a declining stand first 664-670. ,...., "...

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1836 ENVIRONMENTAL ENTOMOLOGY Vol. 19, no. 6

Fox, R. C. & T. M. Hill. 1973. The relative attraction Solbreck, C. & B. Gyldberg. 1979. Temporal flight of burned and cutover pine areas to the pine seedling pattern of the large pine weevil, L. weevils, Hylobius pales and . (Coleoptera, Curculionidae), with special reference Ann. Entomol. Soc. Am. 66: 52-54. to the influence of weather. Z. Angew. Entomol. 88: Franklin, R. T. & J. W. Taylor, Jr. 1970. Biology of 532-536. Pachylobius picivorus (Coleoptera: Curculionidae) in Southwood, T. R. E. 1978. Ecological methods, 2nd the Georgia Piedmont. Can. Entomol. 102: 962-968. ed. Chapman & Hall, London. Hunt, D. W. & K. F. Raffa. 1989. Attraction of Hy­ Speers, C. F. 1958. Pales weevil rapidly becoming lobius radicis and Pachylobius picivorus (Coleoptera: serious pest of pine reproduction in the south. J. For. Curculionidae) to ethanol and turpentine in pitfall 56: 723-726. traps. Environ. Entomol. 18: 351-355. Taylor, J. W. & R. T. Franklin. 1970. Biology of Klepzig, K. D. 1989. Red pine pocket decline and Hylobius pales (Coleoptera: Curculionidae) in the mortality. M.S. Progress Report, University of Wis­ Georgia Piedmont. Can. Entomol. 105: 123-135. consin, Madison. Taylor, L. R. 1986. The four kinds of migration, pp. Mosher, D. G. & L. F. Wilson. 1977. Scotch pine 265-280. In W. Danthanarayana [ed.], Insect flight: deterioration in Michigan caused by pine root weevil dispersal and migration. Springer, New York. complex. Great Lakes Entomol. 10: 169-172. Thatcher, R. C. 1960. Influence of the pitch-eating Phillips, T. W., A. J. Wilkening, T. H. Atkinson, J. L. weevil on pine regeneration in east Texas. For. Sci. Nation, R. C. Wilkinson & J. L. Foltz. 1988. Syn­ 6: 354-361. ergism of turpentine and ethanol as attractants for Tilles, D. A., K. Sjodin, G. Nordlander & H. H. Eid­ certain pine-infesting beetles (Coleoptera). Environ. mann. 1986a. Synergism between ethanol and co­ Entomol. 17: 456-462. nifer host volatiles as attractants for the pine weevil, Raffa, K. F. & D. W. Hunt. 1988. Use of baited pitfall Hylobius abietis (L.) (Coleoptera: Curculionidae). J. traps for monitoring pales weevil, Hylobius pales (Co­ Econ. Entomol. 70: 970-973. leoptera: Curculionidae). Great Lakes Entomol. 21: Tilles, D. A., G. Nordlander, H. Nordenhem, H. H. 123-125. Eidmann, A. Wassgren & G. Bergstrom. 1986b. 1989. Microsite and interspecific interactions affect­ Increased release of host volatil~s from feeding scars: ing emergence of root-infesting pine weevils (Cole­ a major cause of field aggregation in the pine weevil, optera: Curculionidae) in Wisconsin. Ann. Entomol. Hylobius ametis (Coleoptera: Curculionidae). Envi­ , Soc. Am. 82: 438-445. ron. Entomol. 15: 1050-1054. Raffa, K. F. & R. J. Steffeck. 1988. Computation of Wilson, L. F. 1968. Habits and movements of the response factors for quantitative analysis of mono­ adult pine root collar weevil in young red pine plan­ terpenes by gas-liquid chromatography. J. Chern. tations. Ann. Entomol. Soc. Am. 61: 1365-1369. Ecol. 14: 1385-1390. 1973. Pruning and litter removal or soil scraping con­ Rieske, L. K. 1990. Use of host volatiles for evaluating trols the pine root collar weevil in young red pine population patterns, dispersal, and behavioral re­ plantations. Environ. Entomol. 2: 325-328. sponses of the pine root weevil complex, Hylobius Wilson, L. F. & I. Millers. 1983. Pine root collar pales (Herbst), Pachylobius picivorus (Germar), and weevil-its ecology and management. USDA, Forest Hylobius radicis Buchanan, in pine plantations. M.S. Service Technical Bulletin 1675. thesis, University of Wisconsin, Madison. Wisconsin Christmas Tree Producers Association. SAS Institute. 1982. SAS user's gUide: statistics. SAS 1989. Annual marketing survey. Bruce Neidemey­ Institute, Cary, N.C. er, Marketing Director. Quarterly Journal 4(1). Snedecor, G. W. & W. G. Cochran. 1980. Statistical methods, 7th ed. Iowa State University Press, Ames. Solbreck, C. 1980. Dispersal distances of migrating pine weevils, Hylobius abietis, Coleoptera: Curcu­ Received for publication 13 March 1990; accepted 14 lionidae. Entomol. Exp. Appl. 28: 123-131. June 1990.