Effects of Varying Ethanol and Turpentine Levels on Attraction of Two Pine Root Weevil Species, Hylobius pales and Pachylobius picivorus (Coleoptera: Curculionidae)
L. K. RIESKE .\NO K. F. RAFFA Department of Entomology. University of Wisconsin. ~ladison. Wisconsin 53.06
EnvirOlL Entomol. 20< 1): 48-52 (1991) ABSTRAcr The pales weevil. Hylobius pales (Herbst). and the pitch-eating weevil. PachlJ lohim picicorus (Gennar), are part of a.weevil cOmplex causing extensive damage to plan tation pines throughout the Lake States. A means of monitoring w~l populations has been developed using pitfall traps baited with ethanol and turpentine. The relative attractiveness of six combinations of ethanol anc;I turpentine were compared. Traps were monitored through out the 1988 and 1989 growing seasons in a Scots pine Christmas tree farm. Both species were more strongly attracted to ethanol/turpentine ratios above 1:1. Pales weevils preferred slightly higher ethanol/turpentine ratios than did pitch-eating weevils. Within species. both sexes responded equivalently among treatments. The implications of these behavioral re sponses to weevils' locating stressed trees. the role of chemical ecology in niche partitioning, and IPM of pine root weevils are discussed. .
KEY WORDS Insecta. HlJlobius spp., PtichlJlobius spp., host volatiles
THE PALES WEEVIL, Hylobius pales (Herbst), and Olfactory stimulation is an important aspect of the pitch-eating weevil Pachylobius picifJOTtJS host location and recognition (Mustaparta 1984). (Cermar), are part of a root-feeding complex that Volatile compounds emanating from host plant tis threatens plantation pine production in the Great sues are known to attract many insect species. Both Lakes region (Finnegan 1959, Mosher & Wilson ethanol and turpentine are recognized as important 1977). These species share a common host range host location and recognition cues in a variety of and are morphologically, behaviorally, and ec0 pine-infesting insects (Moeck 1970, Fatzinger 1985), logically similar (Drooz 1985). Larvae of both spe including Hylobius and Pachylobius spp. (Tilles cies develop within roots of hosts weakened or re 1986a,b; Raffa &- Hunt 1988; Hunt & Raffa 1989). cently harvested. Adult weevils feed nocturna1ly . Turpentine is composed of host monoterpenes, of on pine branches and stems. This feeding can dam which a-pinene and p-pinene are the major com~ age harvestable pines, as well as cause extensive ponents. a-Pinene is thought to be the primary seedling mortality (Davis & Lund 1966; Wilson attractant (Chenier & Philogene 1989). Ethanol is 1968a,b). The pine root collar weevil, H. ,adieU a product of anaerobic plant -and microbial me Buchanan, geographically overlaps H. pales and tabolism and is present in varying levels in all pine P. picifJOTtJS, and shares a common host range (Wil species. Ethanol levels vary seasonally in Scots pine, son & Millers 1983). However, these larvae breed Pinus syltJeStris L., reaching their peaks in late in healthy hosts. Infestation and subsequent tissue April and May (Crawford & Baines 19i7). In ad degradation of a healthy host by H. .rad~ may dition to these seasonal changes, ethanol levels rise render trees suitable for subsequent development in response to plant stress (Kimmerer & Koz!owski by H. pales or P. piciV01US. 1982). . Traditional control measures consist of preven Previous studies of the pine root weevil compie:< tive applications of highly toxic, persistent insec have shown that a 1:1 ratio of ethanol to turpentine ticides (Benyus 1983, Drooz 1985), Preplant dip in pitfall traps attracts weevils Blank traps or traps_ ping of seedlings or stump applications of lindane with either compound alone show no attraction. are used most commonly. Because of thc sandy Etf-~r:ol :md turpentine act synergistically. and ap soils characteristic of much of the pine-producing parently mimic cues used during insect orientation regions of Wisconsin. the threat of groundwater (lUffa & Hunt 1988. Hunt & Raffa 1989). Better contamination from these chemic:lls is gre:lt. Mon determination of the cues governing host attraction itoring pine root weevils could potentially reduce could help in developing a monitoring system. insecticide usage to those situations where damage which could le:ld to reduced insecticide use in con- was imminent. -~:olling these weevils.
OO-l6-~X;9IiOO-l1!-OO~2S02-00/f) c: 1991 Entomoingic:>i Socletv "f .-\meric:> February 1991 RIESKE'& R.-\FF.-\: PI:\E ROOT \VEE\"lL .\TTRACTIO:\ TO ETH.-\:\OL Tl'RP~:\ .
.\lthough ;, 1:1 mi: 60 \988 Q III ... 0 0.. o~ 0.. ~ «" a:: ...... ::: ... 2'- lIO ~~ :;....I . ~ :> III ...... III ...... ~ 2~ ....I ...~ ...0 1:10 I:S 1:1 S:1 10:1 75:1 ElMAHOL:TURPEKTlME RATIO ~ Itlin soeciea failcMwcl by tN SMte leM' ar. not s-gnlficanCfy June j dill (P < 0.05, Duncan', mum.,. l'3n9- :HI). Fig. 2. Mean number of· H. pales and P..picivorus 1989 attracted per treatment to varying ratios of eth.anol and 160 turpentine for 1988 anel 1989 pooled (n - 30). Means Q III followed by the same letter are not significantly different ...0.. (P < 0.05; Duncan's multiple range test. SAS Institute ~... 120 [1982D· • H. pale3; .. P. pi.cioortJ3. ID ....I:;: The significantly higher trap catches in baits with III .90 III high levels of ethaool may reflect weevil behavioral ~ strategies for locating suitable hosts. In particular. attraction to higher ethanol levels may orient wee vils to degrading plant tissue. Because ethanol is produced by a variety of plants (Kimmerer & Koz o-I-...... _....-...... _~.,::::;:==-- __...... L,.-.,-.-...,..,....-\ lowski 1982). the turpentine compclnent may be June 1 July 1 Aug I Sepll' required for species recognition. Peak activity by Fig. 1. Cumulative seasonal tr2p catch of H. paW H. pa~ and P. pfcioorus occurred in early sum and P. picifX11U$ across all treatments in ethanol and mer, coinciding closely with peak seasonal ethanol turpentine baited pitfall traps. -+-. H. pain; emissions. Crawford & Baines (1977) showed peak ~, P. picifX11U$. seasonal ethanol emission by Pinus sylvestris 0c curred in late spring. This synchrony of insect be The ratio of females to males was 1.1 for H, havior with host plant phenology may reflect an pales and 1.6 for P. pIcfvOnU. For H. pales, the evolved response to emission patterns. These results sex ratio did not differ significantly (P < 0.05) from support the view that insects may increase their the expected 1:1 ratio Table 1. H. pale# and P. piciPOrtu ca~t ;>er ~.tmeDt iD pitfall tr.Ips baited ...ith various volumetric ethanol turpeDtiDe ratios (n - 15) f :\0. w~vils, tr""ement \.=5D) 1988 1989 . Ratio EtaH : Turp. . d d H. pales 1:10 0.:20 (0.41)e 0.13 (O.35)b 0_33 (0.72le 0_1:3 (O.35)e 1:5 0.13 (O.35ie ~ 0.20 (0.56)b 0.40 (O.63ie 1:1 0.47 (l.13)bc 0.33 (1.re)b 0.93 (1.12)bc 1.17 (2.40Ibc ~'7 5:1 1.27 (1.91)a (1.62)a 1.10 (1.01)b 1.53 (1.l9)ab 10:1 1.07 (l.12)ab 1.33 (1.72)a 3.13 (2.79)a 3.40 (3.81)a 75:1- 1.27 (1.91)a 1.Bi (2.833) 4.07 (4.74)a 3.33 (2.69)a P. pirirorw 1:10 0.13 (Q.35lc 0..27 (0.461d 1.60 (l.59)b 0.93 (1.391b 1:5 0.13 (o.351e Q.80(1.l5)cd" 1..27 (1.87)b 1.73 (4.09)b 1:1 O.Bi (Q.64)b 1.80 (1.78)b" 5.93 (5.84)a 8.47 (7.79)a" 5:1 2.47 (3.83)ab 4.13 (3.46)a" 6.27 (5.34)a 6.80 (4.11)a 10:1 3.47 (3.18)a 4.80 (3.23la" 8.13 (5.33)a 8.60 (5.07)a 75:1" 1.20 (l.32)b 1.33 (l.re)bc 6.47 (6.41)a 6.73 (5.02)a Means withiu columns followed by the same letter are not significantly different (P < o.re; Duncan's multiple range test.. 5AS Institute 1982). Deviations from 1:1 sex ratios (P < o.re) are iDdicated by a ", aud are not significant elsewhere. " I>ispemed from a 5-<:m-diameter cootaiDer. These results have implications to our under- . for developing field monitoring systems. However, standing of the chemical ecology and sequence of because actual release rates of ethanol and turpen infestation by closely related species exploiting a tine were not manipulated, weevil preferences common resource. H. radicis, which breeds in based on the perceived relative proportions carmot healthy host tissue, was plentiful (43%) in trap be quantified. Because ethanol is more volatile than catches in 1987 (Hunt & Raffa 1989), but W2S rel turpentine, maximum chemosensory responses atively rare in 1988 and 1989 «1%). P. pidfJoTus probably occur at higher ethanol/turpentine ratios 'was common in 1987 (57"), with gradually in than thosereported here. Likewise, we cannot yet creasing numbers in 1988 (70%) and 1989 (77%), distinguish whether weevil responses reflect pref ,uthough its proportion of the total weevil complex erences to increased ratios, or increased. levels, of leveled. In 1987, H. pales W2S absent, but has grad- . ethanol ually become more abwxlant (30'5 in 1988, 23" in 1989). Infestation by H. radicU may degrade host plant tissues so as to attract and allow devel- Acknowledgment opment by H. pales and P. J1icit'orw. By 1989, - We would like to thank the Kirk Company of Wau- most trees at this site were probably degraded to' loma. Wis., for the study sites and assistance with trap an extent that they were lessattractive·to H. nulicis installation, and 1.. Zastoupil for his valuable advice. M. or unable to sustain H. rad1cU brood development, Bleclt, J. Graetz, and 1.. Kellner assisted with data col or both, at least in the presence of competition from lection. We also thank D. B. Hogg and D. K. Young for H. nnlu and P. nirivonu. H. pales and P. ptcit;orr.&$ -- r.eviewing thi;s ~pt. This research was supported r- r-- thr gh al by the ChristuiiIs Tree Producers Associations of-Wis.. may partition common resources ou tempor MinD. h. · the'l'r' colonization sequence, that are " ,Mic, and Ill, the Wisconsin Department of differences m Agriculture, Trade ;\ Consumer Protection Sustainable reflected in behavioral responses to volatiles. For Agriculture Grant 8825. USDA 86-CRCR-1-2077. USDA example, P. picivonu showed stronger attraction 86-FSTY-9-0210. Sigma Xi Grants-in-Aid of Research. to 1:1 ethanol/tu.pent:ne level! ~han did H. pales the University of Wisconsin System Applied Research (Fig. 2). Converseiy, responses of P. picioorus, but Program, ami the University of Wisconsin-Madison., Col not H. pales, declined at very high ethanol/tur- lege of Agricultural and Life Sciences. pentine levels. 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