Evaluation of Pheromone-Based Management Strategies for Dogwood Borer (Lepidoptera: Sesiidae) in Commercial Apple Orchards TRACY C. LESKEY,1 J. CHRISTOPHER BERGH,2 JAMES F. WALGENBACH,3
J. Econ. Entomol. 102(3): 1085Ð1093 (2009)
ABSTRACT The dogwood borer, Synanthedon scitula (Harris) (Lepidoptera: Sesiidae), is a serious wood-boring pest of apple in eastern North America. The recent identiÞcation of its sex pheromone and systematic documentation of the effect of a potent behavioral antagonist affords the opportunity to develop pheromone-based management strategies for this important pest. Here we evaluated the potential of pheromone-based mass trapping of males to reduce dogwood borer infestations and conducted preliminary evaluations of an antagonist-based pheromone blend for disruption of dogwood borer mate Þnding in commercial apple orchards in North Carolina, Virginia, and West Virginia. In the mass trapping study, treatments included a conventional trunk-drench application of chlorpyrifos, a low-density mass trapping regime of 5 traps/ha, a higher-density mass trapping regime of 20 traps/ha, and an untreated control. We removed large numbers of males from orchards at all locations, with 27,155, 8,418, and 7,281 removed from high-density trapping plots in North Carolina, Virginia, and West Virginia, respectively, over 2 yr. After 2 yr under each of these treatment regimes, infestation in high- and low-density mass trapping plots was not reduced to the level of chlorpyrifostreated plots. An antagonist-based dispenser deployed at a rate of 250/ha effectively disrupted mate-Þnding by male dogwood borer. In plots with mating disruption dispensers, captures in pheromone-baited traps were virtually eliminated, and no males were captured in traps baited with virgin females. KEY WORDS dogwood borer, mass trapping, antagonist-based mating disruption, Sesiidae, apple
The dogwood borer, Synanthedon scitula (Harris) (Lepidoptera: Sesiidae), is an important wood boring pest of apple, Malus domestica Borkhausen, in eastern North America (Riedl et al. 1985, Warner and Hay 1985, Kain and Straub 2001, Bergh and Leskey 2003, Kain et al. 2004). The increased severity of dogwood borer infestations in apple orchards is similar to an earlier scenario in Europe with the apple clearwing moth, Synanthedon myopaeformis Brkh, which emerged as a serious pest of apple after the introduction of clonal, size-controlling rootstocks (Dickler 1976). Clonal rootstocks promote the formation of adventitious root initials (burr knots) on exposed porMention of trade names or commercial products in this publication is solely for the purpose of providing speciÞc information and does not imply recommendation or endorsement by the U.S. Department of Agriculture. 1 Corresponding author: USDAÐARS, Appalachian Fruit Research Station, 2217 Wiltshire Rd., Kearneysville, WV 25430-2771 (e-mail: [email protected]
). 2 Virginia Polytechnic Institute and State University, Alson H. Smith, Jr. Agricultural Research and Extension Center, Winchester, VA 22602. 3 North Carolina State University, Mountain Horticultural Crops Research and Extension Center, Fletcher, NC 28732. 4 USDAÐARS, Invasive Insect Biocontrol and Behavior Laboratory, BARC-W, 10300 Baltimore Ave., Beltsville, MD 20705.
tions of the rootstock and on the trunk and scaffold limbs (Marini et al. 2003). Burr knots are an excellent food resource for developing S. myopaeformis larvae (Dickler 1976) and also serve as the primary point of infestation of apple trees by dogwood borer (Riedl et al. 1985, Kain et al. 2004, Leskey and Bergh 2005). Ongoing infestations of sesiid larvae in apples have resulted in declined yields in the case of S. myopaeformis (Dickler 1976), and tree death in the case of dogwood borer (Weires 1986, Howitt 1993). The organophosphate insecticide chlorpyrifos has provided the most consistent (Riedl et al. 1985) and highest level of control of dogwood borer in apple orchards (Kain and Straub 2001, Kain et al. 2004). A single trunk-drench application at half-inch green or petal fall (early season phenological growth stages) provided season-long control in New York apple orchards (Kain et al. 2004). However, the review of tolerances for organophosphate pesticides under the 1996 Food Quality Protection Act has resulted in cancellations and increased restrictions on the use of chlorpyrifos, highlighting the importance of developing alternative management tactics for this pest. IdentiÞcation of the sex pheromone of dogwood borer (Zhang et al. 2005) and documentation of its attractiveness and species speciÞcity (Zhang et al. 2005,
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Leskey et al. 2006) provides the opportunity to explore pheromone-based management strategies such as mass trapping and mating disruption. A recently published review of mass trapping indicated that this approach holds signiÞcant potential for suppressing or even eradicating isolated invasive lowdensity pest populations (El-Sayed et al. 2006), and studies have shown the efÞcacy and viability of pheromone-based mass trapping for control of endemic lepidopteran pests. For example, damage caused by the Chinese tortrix, Cydia trasias (Meyrick), a pest of Chinese scholar-trees, Saphora japonica L., in urban landscapes, was reduced by using a mass trapping strategy (Zhang et al. 2002). Similarly, populations of pink bollworm, Pectinophora gossypiella (Saunders), in cotton Þelds (Mafra-Neto and Habib 1996) and the rice stem borer, Chilo suppressalis Walker, in rice paddies (Su et al. 2003) were suppressed and damage was reduced using a mass trapping strategy. Among sesiids, two studies targeted S. myopaeformis as a candidate for mass trapping in European apple orchards (Trematerra 1993, Bosch et al. 2001). Bosch et al. (2001) reported that, after 3 yr of mass trapping S. myopaeformis males in apple orchards in Spain, captures were reduced in two orchards by 96.3 and 51.9%, respectively. However, mass trapping for managing North American sesiids has never been evaluated. The effectiveness of traps baited with the dogwood borer sex pheromone blend at capturing very large numbers of males (Zhang et al. 2005, Leskey et al. 2006) suggested that this approach for suppressing dogwood borer populations in commercial apple orchards merited investigation. Pheromone-based mating disruption has proven successful against two sesiid species that are closely related to dogwood borer, the lesser peachtree borer, S. pictipes (Grote and Robinson) (Pfeiffer et al. 1991, Agnello and Kain 2002), and peachtree borer, S. exitoisa (Say) (Agnello and Kain 2002, Alston et al. 2003). The only published mating disruption trial for dogwood borer was conducted before identiÞcation of its pheromone and involved deployment of Isomate-P (peachtree borer) disruption dispensers (Shin-Etsu Chemical, Tokyo, Japan) that contained ⬇90% (Z,Z)3,13-octadecadienyl acetate (ODDA) and 10% other ODDA isomers in 2-ha plots of ÔGalaÕ apples in Virginia (Pfeiffer and Killian 1999). Although capture of male dogwood borer in pheromone traps was reduced in the disrupted block by nearly 100%, the percentage of burr knots with dogwood borer larvae, pupal exuviae, or fresh frass was not reduced compared with nondisrupted untreated blocks. Chemical synthesis of (Z,Z)-3,13-ODDA on a commercial scale commonly yields a product that contains the (E,Z)-3,13-ODDA and other geometric isomers as impurities (Henrick 1977, Chisholm et al. 1978, Uchida et al. 1979). Karandinos et al. (1977) and GreenÞeld and Karandinos (1979) concluded that the response of dogwood borer to (Z,Z)-3,13-ODDA alone was reduced by the addition of (E,Z) 3,13-ODDA. Zhang et al. (2005) conclusively showed that low concentrations of (E,Z)3,13-ODDA can act as a potent behavioral antagonist
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of dogwood borer; in Þeld trials using pheromone traps, as little as 0.5% (E,Z)-3,13-ODDA added to the complete dogwood borer pheromone blend signiÞcantly reduced male captures in traps (Zhang et al. 2005). Consequently, it is likely that failure of mating disruption reported by Pfeiffer and Killian (1999) was caused by the disruption dispensers and pheromone lures for monitoring ßight containing sufÞcient amounts of (E,Z)-3,13-ODDA to render them less attractive and species-speciÞc to dogwood borer in the Þeld. Despite having identiÞed the dogwood borer sex pheromone, the difÞculties associated with synthesizing pure (Z,Z)-3,13-ODDA, the main component of the dogwood borer pheromone, have impeded the development of mating disruption for this pest. However, perception of antagonistic compounds by male moths that results in reduced upwind orientation or pursuit of attractive pheromonal stimuli (Linn and Roelofs 1995) may provide another alternative for dogwood borer management. Mating disruption blends based on behavioral antagonists have been evaluated in the Þeld for a number of Tortricidae (Evenden et al. 1999a, b). Given that the electroantennogram (EAG) response of male dogwood borer antennae to (E,Z)-3,13-ODDA is as strong as to its major sex pheromone component, (Z,Z)-3,13-ODDA (Nielsen et al. 1979, Zhang et al. 2005) and that extremely small amounts of this compound signiÞcantly reduced captures in traps baited with the sex pheromone blend (Zhang et al. 2005), an antagonist-based mating disruption formulation containing predominantly (E,Z)-3,13-ODDA, as is the case for the Isomate-LPTB (lesser peach borer) dispenser, may effectively disrupt mate-Þnding by dogwood borer. As an indirect pest of apple, we believe the dogwood borer is a prime candidate for exploring the potential of mass trapping and antagonist-based mating disruption as management options based on behavioral manipulation. Here we describe a 2-yr mass trapping study, a Þrst for North American sesiids, and preliminary evaluations of an antagonist-based blend for disruption of mate Þnding of dogwood borer in commercial apple orchards in North Carolina, Virginia, and West Virginia. Materials and Methods Mass Trapping Orchards. Commercial apple orchard blocks (⬇3Ð7 ha) were selected in Lincoln County, NC; Frederick County, VA; and Berkeley County, WV. Each block was of approximately square dimensions and consisted of trees on size-controlling rootstock with a high percentage showing active dogwood borer infestation in burr knot tissue. Horticultural details of each orchard are provided in Table 1. Treatments. Each orchard block was divided into four relatively square plots of equal area (⬇1Ð2 ha) and subjected to a single treatment regime from late April to early May 2005 through late October to early
LESKEY ET AL.: PHEROMONE MANAGEMENT FOR DOGWOOD BORER
Table 1. Horticultural characteristics and trapping details of experimental plots located in commercial apple orchards in North Carolina, Virginia, and West Virginia Block size (ha)
Davis Orchard, Lincoln County, North Carolina
Marker Orchard, Frederick County, Virginia Orr Bros. Orchard, Berkeley County, WV
No. traps/plot Varieties
ÔBraeburnÕ, ÔFujiÕ, ÔGalaÕ, ÔGolden DeliciousÕ, and ÔGoldrushÕ ÔGolden DeliciousÕ, ÔGranny SmithÕ, ÔIda RedÕ, and ÔYorkÕ ÔSuper Chief Red DeliciousÕ and ÔGolden DeliciousÕ
November 2006. Treatments included (1) a trunkdrench application of Lorsban 4E (Dow AgroSciences, Indianapolis, IN) (chlorpyrifos) at 3.5 liters/ha in ⬇65 liters/ha within 3 wk of petal fall in 2005 and 2006 (conventional control); (2) a low-density mass trapping regime of 5 traps/ha; (3) a high-density mass trapping regime of 20 traps/ha; and (4) a nontreated control. In the nontreated control and Lorsban plots, 2 traps/ha were used to monitor populations. Delta-style sticky traps baited with rubber septa lures formulated with a 1-mg load of the complete dogwood borer sex pheromone blend (Zhang et al. 2005) were used in all plots. Traps deployed in the two mass trapping treatments were uniformly distributed within their respective plots, and the two plots were located diagonally to one another such that each was bordered by the control and conventional plots on one side. Outside each orchard at North Carolina and West Virginia, three baited traps also were deployed ⱖ50 m into an adjacent forest to provide an indication of the potential inßuence of moth immigration. Traps in all plots were deployed before the onset of adult emergence and ßight (late April to early May) and maintained until emergence and ßight ended (late October to early November). The number of male moths captured in each trap was counted, and all moths were removed weekly. Evaluation of Treatment Efﬁcacy. The effect of two mass trapping treatments and the conventional insecticide treatment on infestation levels were evaluated against a nontreated control plot. Evaluations of the percentage of trees showing signs of current dogwood borer infestation (i.e., fresh “frass” on burr knot tissue at the base of trees) were made twice annually: in spring (before deployment of pheromone traps and Lorsban application) and fall in 2005 and 2006. A sample unit consisted of 20 consecutive trees in a row. Each plot contained six sample units (120 trees/plot) in North Carolina and Virginia and nine sample units (180 trees/plot) in West Virginia. Data Analysis. Each orchard served as a replicate for evaluation of the effect of mass trapping treatments on the capture of males per trap and the percentage infestation among plots. A generalized linear model (GLM) procedure used treatment and location as class variables, followed by TukeyÕs honestly signiÞcant difference (HSD) if signiÞcant differences were detected (SAS Institute 2003). Moth captures were
compared among treatments based on weekly captures per trap per plot and on total captures per plot for 2005 and for 2006. Moth capture data were not transformed because homogeneity-of-variance assumptions were not violated according to BartlettÕs test for homogeneity (SAS Institute 2003). Percentage infestation was subjected to an ARCSIN SQRT transformation. Infestation was compared across treatment plots for samples taken at the start of the experiment in spring 2005 and at the conclusion in fall 2006. A two-sample t-test was performed to determine whether there was a signiÞcant difference in the mean percentage of infested trees within each treatment plot at the start of the experiment in spring 2005 and at the conclusion in fall 2006. All statistical analyses were considered signiÞcantly different at ␣ ⫽ 0.05. Antagonist-based Disruption. In 2006, IsomateLPTB (lesser peachtree borer) disruption dispensers (CBC America, Commack, NY) were deployed in three orchard locations, North Carolina, Virginia, and West Virginia, to test the hypothesis that dogwood borer mate-Þnding can be disrupted using a formulation based on the behavioral antagonist, (E,Z)-3,13ODDA. Each 50-mg dispenser contained 60.5% (E,Z)3,13-ODDA (the behavioral antagonist of dogwood borer), 22.7% (Z,Z)-3,13-ODDA (the main pheromone component of dogwood borer pheromone), and 16.8% other ODDA isomers. Dispensers were deployed in commercial orchard blocks of at least 2 ha in size at a rate of 250/ha in late April to early May and compared with 2-ha nontreated blocks. Each orchard location consisted of apple trees planted on size-controlling rootstock with abundant burr knot tissue and active dogwood borer infestations. In all orchards, disruption was assessed with traps baited with lures containing 1 mg of the complete dogwood borer sex pheromone blend (Zhang et al. 2005) deployed in treated and control blocks (three traps per block in Virginia and West Virginia, two traps per block in North Carolina). Traps baited with virgin females were deployed for 2 wk (during peak periods of dogwood borer ßight in late August) in treated and nontreated blocks in West Virginia; two female-baited traps were deployed in both treated and control blocks, and females were replaced weekly. All traps were checked weekly from mid-May to late October, and the number of male moths captured were recorded and removed. A two-sample t-test was per-
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formed to determine whether there was a signiÞcant difference between the mean number of males captured per pheromone-baited trap in mating disruption and control plots in Virginia and West Virginia, but not in North Carolina, where only two traps per plot were deployed. Results Mass Trapping Trap Captures. Differences in mean weekly trap captures were signiÞcant in both 2005 (F ⫽ 7.23; df ⫽ 5,6; P ⫽ 0.016) and 2006 (F ⫽ 11.92; df ⫽ 5,6; P ⫽ 0.004). Trap captures were not signiÞcantly different among treatments (P ⫽ 0.253 in 2005, P ⫽ 0.213 in 2006) but were signiÞcantly different among locations (P ⫽ 0.004 in 2005, P ⫽ 0.001 in 2006). There were significantly more males captured per trap in North Carolina and Virginia compared with West Virginia in 2005 and in North Carolina compared with Virginia and West Virginia in 2006. The model for total captures was signiÞcant in 2005 (F ⫽ 4.64; df ⫽ 5,6; P ⫽ 0.044), but the effect of treatment (P ⫽ 0.052) and location (P ⫽ 0.062) were not signiÞcant at P ⬍ 0.05. In 2006, the model for total captures was signiÞcant at P ⫽ 0.0523 (F ⫽ 4.29; df ⫽ 5,6). In North Carolina, the total number of males captured increased by 1.5Ð2.0 times from 2005 to 2006 in all treatment plots. In total, 27,155 and 10,446 males were removed from the high- and low-density trapping plots, respectively (Fig. 1). In Virginia, the total number of males captured in each treatment plot did not differ substantially between years (Fig. 1). In total, 8,418 and 3,137 males were removed from the highand low-density trapping plots, respectively. Large increases in total captures were observed in West Virginia; 1,803 and 5,478 males were captured in the high density trapping plot in 2005 and 2006, respectively. In total, 7,281 and 3,816 males were removed from the high- and low-density trapping plots, respectively. Infestation. At the start of the experiment in spring 2005, the GLM was signiÞcant (F ⫽ 31.06, df ⫽ 5,6; P ⬍ 0.0001), with a signiÞcant effect of location (P ⬍ 0.001) but not treatment (P ⫽ 0.773). Among the states, the mean percentage infestation (% infested trees ⫾ SE) across all treatments before the initiation of mass trapping was signiÞcantly greater in the North Carolina orchard (81.80 ⫾ 2.46%) compared with the Virginia (46.83 ⫾ 2.74%) and West Virginia (16.68 ⫾ 2.83%) orchards, with infestation in Virginia being signiÞcantly greater than in West Virginia. At the conclusion of the experiment in fall 2006, the effect of location was not signiÞcant, and it was removed from the model. The subsequent one-way analysis of variance (ANOVA) showed signiÞcant differences among treatments (F ⫽ 5.66; df ⫽ 3,8; P ⫽ 0.022). The mean percentage of infested trees was signiÞcantly greater within the high-density trapping plots compared with plots treated with Lorsban, with infestation in low-density trapping and control plots not
Fig. 1. Total number of males captured in high trap density, low trap density, Lorsban-treated, and control plots in North Carolina, Virginia, and West Virginia apple orchards in 2005 and 2006.
signiÞcantly different from any of the treatments (Table 2). In the high-density trapping plots (t ⫽ 0.582; df ⫽ 4; P ⫽ 0.592), low-density trapping plots (t ⫽ 0.983; df ⫽ 4; P ⫽ 0.381), and control plots (t ⫽ 1.1602; df ⫽ 4; P ⫽ 0.310), there was no signiÞcant change in the percentage of infested trees from spring 2005 to fall 2006. Within the Lorsban-treated plots, infestation was reduced nearly 10-fold (Table 2) by fall 2006, although the effect was not signiÞcant at P ⱕ 0.05 (t ⫽ 2.64; df ⫽ 4; P ⫽ 0.057). In North Carolina, the per-
LESKEY ET AL.: PHEROMONE MANAGEMENT FOR DOGWOOD BORER
Table 2. Mean percentage of infested trees ⴞ SE in highdensity trapping, low-density trapping, Lorsban-treated, and control plots in spring 2005 and fall 2006 Treatment
High-density trapping Low-density trapping Lorsban Control
51.9 ⫾ 21.4 a 46.7 ⫾ 20.1 a 50.2 ⫾ 16.7 a 44.8 ⫾ 17.3 a
37.5 ⫾ 12.6 a 26.9 ⫾ 2.1 bc 5.7 ⫾ 2.4 c 24.2 ⫾ 3.2 bc
Means in the same column from the same location followed by the same letter are not signiÞcantly different according to TukeyÕs HSD (P ⬍ 0.05).
centage of infested trees was reduced in all treatment plots from spring 2005 to fall 2006. The percentage of infested trees increased in the high-density trapping plot in Virginia and in high-density trapping, lowdensity trapping, and control plots in West Virginia from spring 2005 to fall 2006 (Fig. 2). Antagonist-based Disruption. In blocks treated with the LPTB pheromone dispensers containing the antagonist for dogwood borer, moth captures in pheromone-baited traps were almost completely eliminated throughout the entire season (Fig. 3). SigniÞcantly more males were captured in monitoring traps deployed in control plots compared with disrupted plots in Virginia and West Virginia (Table 3); numerically more males were captured in control plots in North Carolina, but a t-statistic could not be calculated because of the number of traps deployed. No males were captured in traps baited with virgin females deployed during periods of peak ßight activity in the West Virginia orchard (Table 3). Discussion Here we report the Þrst attempt to manage a North American sesiid species using mass trapping. One of the reasons we pursued mass trapping for dogwood borer management was because it was potentially far less expensive than conventional mating disruption based on the amount of pheromone required; this same factor was highlighted as a critical consideration in studies of other species reviewed by El-Sayed et al. (2006). Our estimates of the density of pheromonebaited traps required to reduce dogwood borer populations were based on the densities of traps used for S. myopaeformis in mass trapping studies in Europe; Trematerra (1993) and Bosch et al. (2001) deployed traps at 12/ha in Italian and 2.1Ð3.3/ha in Spanish apple orchards, respectively. Thus, mass trapping required ⬍0.2% of the pheromone required for conventional mating disruption based on these trap densities. In our mass trapping studies, large numbers of moths were removed from orchards: 47,319 in North Carolina, 15,964 in Virginia, and 13,111 in West Virginia. The largest captures were in the high-density trapping plots, exceeding captures in the control, Lorsbantreated, and low-density plots by 5.2Ð7.8, 3.0 Ð 6.7, and 2.0 Ð2.5 times, respectively, across orchards. However, this did not translate into reduced infestation levels; in no instance was the infestation level in the high-den-
Fig. 2. Percentage of infested trees in high trap density, low trap density, Lorsban-treated, and control plots in North Carolina, Virginia, and West Virginia apple orchards in 2005 and 2006.
sity plot reduced below that of the control plot. Although infestation levels declined from the beginning to the end of the experiment across all treatments in North Carolina, this trend was not consistent with results in Virginia or West Virginia. As would be anticipated, based on the known efÞcacy of chlorpyrifos against dogwood borer (Potter and Timmons 1983, Kain et al. 2004), the only consistent trend across all study sites was that Lorsbantreated plots had the greatest reduction in percentage of infested trees from the beginning to the end of the study. A single application of Lorsban at half-inch green or petal fall provided season-long control in
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Fig. 3. Mean number of males captured per week in monitoring traps baited with complete pheromone blend and deployed in untreated blocks or blocks treated with a mating disruption blend based on a behavioral antagonist in commercial apple orchards in North Carolina, Virginia, and West Virginia in 2006.
New York apple orchards (Kain et al. 2004), and in our study, despite intense season-long dogwood borer activity lasting from May through late October.
The failure of mass trapping to reliably reduce infestation of dogwood borer in apple orchards likely can be explained in part by the principles of compet-
LESKEY ET AL.: PHEROMONE MANAGEMENT FOR DOGWOOD BORER
Table 3. Total no. and mean no. of males captured in monitoring traps deployed in blocks treated with an antagonist-based disruption blend or untreated and in commercial apple orchards in North Carolina, Virginia, and West Virginia in 2006
North Carolina Virginia West Virginia a b
Total captures in pheromone-baited traps
Mean no. males ⫾ SE captured per pheromone-baited trap
Total captures in virgin female-baited traps
Disrupted Control Disrupted Control Disrupted Control
1 928 25 4,846 65 6,129
0.5 ⫾ 0.5 464.0 ⫾ 460.0a 8.3 ⫾ 1.2 1615.3 ⫾ 56.6b 23.7 ⫾ 17.7 2045.0 ⫾ 144.6b
Ð Ð Ð Ð 0 75
Means based on two traps. Could not perform two-sample t-test. SigniÞcant difference between traps deployed in disrupted and control blocks based on two-sample t-test (P ⬍ 0.05).
itive attraction (Miller et al. 2006a, b), a mechanism used to describe communication disruption. This mechanism assumes that mate Þnding is reduced when males are diverted from orienting to calling females, because of proximity to sources of attractive or arrestive synthetic pheromonal stimuli (Miller et al. 2006a). Thus, the same principles govern the efÞcacy of mass trapping and mating disruption. For efÞcacious disruption based on competitive attraction theory, it is hypothesized that the pheromone formulation be optimized to match the natural blend produced by female moths, that the release rate of dispensers generally matches or exceeds those produced by females, and that dispenser density exceeds female density by 100 times, although it can be somewhat lower if dispensers are markedly more attractive than females (Miller et al. 2006b). Assuming that mass trapping would operate similarly by diverting mateseeking males from calling females, our pheromone blend was optimized to closely resemble the natural blend produced by females, and our release rate should have been competitive; a 1-mg lure was ⬇28 times more attractive than calling females (Zhang et al. 2005). However, assuming a 50:50 ratio of female to male moths, it is also likely that our dispenser density was far too low to adequately divide the attention of a majority of mate-seeking males from calling females. Even in the high-density plots where traps were deployed at 20/ha, the predicted population density of females based on the average number of males captured per day was ⬇17, 23, and 82 females/ha in West Virginia, Virginia, and North Carolina, respectively. Another factor that could have contributed to our inability to show consistent reductions in infestation is movement of mated females into our test plots from other nearby orchards and orchard blocks. All locations had other apple orchard blocks nearby with at least some detectable level of dogwood borer infestation present. There have been no published studies on the distance mated females may ßy to locate acceptable oviposition sites. Therefore, it is also possible that mated females could have moved from other surrounding orchard blocks into our mass trapping plots and contributed to the lack of differences observed among treatment plots. We also surmise that dogwood borer immigrating from wooded habitats surrounding orchard blocks did not pose a threat to
apple orchards. On average, less than two males per week were captured in traps deployed 50 m away from orchards in wooded habitats in North Carolina and West Virginia orchard locations (T.C.L. and J.F.W., unpublished data). These results are in agreement with Bergh et al. (2006) who found that season long captures of males in apple orchards exceeded those captured in woodland habitats by 219 times and in managed urban landscapes by 16 times. It is likely that virtually all dogwood borers trapped in this study were from resident populations within the orchards and not immigrants from adjacent habitats. Ultimately, the only signiÞcant reduction in infestation was observed in the North Carolina orchard, and this reduction extended to all plots, including the control, indicating that other factors must have been responsible for decreased infestation over the course of the study. One potential factor could be resource availability. Leskey and Bergh (2005) found that the amount of available burr knot tissue had the greatest impact on dogwood borer populations; i.e., increasing amounts of available burr knot tissue resulted in higher infestation levels. The North Carolina orchard consisted of a number of varieties planted on Mark rootstock. Although this rootstock does produce burr knots (Lawes 1999, Marini et al. 2003), infestation levels could decline if all available burr knot tissue were consumed. T.C.L. (unpublished data) observed that infestations in orchard plots with apples on M.26 rootstock declined from 95 to ⬍50% in 1 yr, likely because of lack of available burr knot tissue. The North Carolina orchard had an extremely high population density of dogwood borer at the start of this experiment that could have consumed all available burr knot tissue resources resulting in the observed decline in infestation levels. A more promising approach for pheromone-based management of dogwood borer seems to be mating disruption. Dispensers formulated with an antagonistbased blend were deployed and disruption was assessed with traps baited with the complete pheromone blend and, in West Virginia, with calling virgin females. Based on trapping evidence, elimination of captures in traps baited with pheromone lures known to be highly attractive to males is considered to be the strongest evidence for effective mating disruption (Miller et al. 2006b) although subsequent studies eval-
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uating damage caused by the target pest are also necessary. In blocks treated with the antagonist blend, moth captures in pheromone-baited traps were almost completely eliminated, indicating that ⬎99% of the mate-Þnding activity of males was disrupted. Furthermore, no males were captured in traps baited with calling virgin females deployed during periods of peak ßight activity in West Virginia. These preliminary results indicate that mate-Þnding behavior of male dogwood borer can be successfully disrupted by using a formulation based on a high percentage of the behavioral antagonist, (E,Z)-3,13ODDA in combination with the main pheromone component, (Z,Z)-3,13-ODDA. We do not yet know if a pure formulation of (E,Z)-3,13-ODDA would successfully disrupt mate-Þnding by male dogwood borer. In the few other published studies, formulations using only the behavioral antagonist were successful for some species (Evenden et al. 1999a) but not others (Suckling and Burnip 1996). By deÞnition, antagonists reduce upwind orientation or pursuit of attractive pheromonal stimuli. If male attraction to pheromone lures or virgin females is eliminated or greatly reduced in the presence of behavioral antagonist alone, one can assume that disruption is based on a noncompetitive mechanism (Miller et al. 2006a). Future research to compare disruption formulations for dogwood borer based on the complete sex pheromone blend, the antagonist, and an antagonist-based blend will be necessary to identify the most efÞcacious formulation for mate-Þnding disruption and reductions in infestation levels and to identify the behavioral mechanism of disruption associated with each. Acknowledgments We thank D. Kain and C. Myers for reviewing an earlier version of this manuscript; S. Wright, T. Hancock, J. Engelman, S. Schoof, and J. Nie for excellent technical assistance; and M. Orr, Orr Bros. Orchard, A. Davis, Davis Orchards, and J. Marker, Marker-Miller Orchards, for allowing us to conduct studies in their commercial apple orchards. This research was supported primarily by Grant 2005-3410315592 from the USDAÐCSREES Southern Region IPM Grants Program.
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