Post-diapause overwintered larvae and neonates of any generation of the peach twig borer, Anarsia lineatella (Zeller), seek suitable sites to bore into and mine tissue of their host plants, including almond and peach. We tested the hypothesis that larvae are attracted to the same almond volatiles that elicit antennal responses from adult moths. Of five candidate almond semiochemicals [β-bourbonene, (E,E)-α-farnesene, (E)-β-ocimene, nonanal, decenal] tested singly or in binary combination (nonanal, decenal) in laboratory Y-tube olfactometers, only β-bourbonene attracted neonate larvae. β-bourbonene in combination with (EE)-α-farnesene was as attractive as the complete almond volatile blend, indicating that they are key semiochemicals for foraging larvae

Danci, Adela

Gries, Gerhard

Gries, Regine

Judd, Gary J. R.

Sidney, Mark

English

Journal of the Entomological Society of British Columbia

J. ENTOMOL. SOC. BRIT. COLUMBIA 103, DECEMBER 2006  3  Almond volatiles attract neonate larvae  of Anarsia lineatella (Zeller) (Lepidoptera: Gelechiidae) MARK SIDNEY1, REGINE GRIES1, ADELA DANCI1,  GARY J.R. JUDD2 and GERHARD GRIES1,3 ABSTRACT Post-diapause overwintered larvae and neonates of any generation of the peach twig borer, Anarsia lineatella (Zeller), seek suitable sites to bore into and mine tissue of their host plants, including almond and peach.  We tested the hypothesis that larvae are at-tracted to the same almond volatiles that elicit antennal responses from adult moths. Of five candidate almond semiochemicals [β-bourbonene, (E,E)-α-farnesene, (E)-β-ocimene, nonanal, decenal] tested singly or in binary combination (nonanal, decenal) in laboratory Y-tube olfactometers, only β-bourbonene attracted neonate larvae.  β-Bourbonene in combination with (E,E)-α-farnesene was as attractive as the complete almond volatile blend, indicating that they are key semiochemicals for foraging larvae.  Key Words: Semiochemicals, β-bourbonene, (E,E)-α-farnesene, (E)-β-ocimene, nonanal, decanal, olfactometer bioassay  INTRODUCTION The peach twig borer, Anarsia lineatella (Zeller) (Lepidoptera: Gelechiidae), is a worldwide pest of almond and stone fruits (Marlatt 1898, Jones 1935, Bailey 1948, Ahmad 1988, Ponomarenko 1990). Almond and peach are the principle crop host plants, but apricot, nectarine, plum and prune (Summers 1955), and even sweet and sour cherry, apple and persimmon are attacked (Ponomarenko 1990). There are three generations of A. lineatella in the Okanagan Valley of British Columbia (BC) (Sarai 1966) and two gen-erations and a partial third in the Simil-kameen Valley of BC. Larvae predomi-nantly enter buds and terminal shoots, bor-ing a path toward the centre, and then downward, often until they reach the previ-ous year’s wood (Ponomarenko 1990). In peach orchards, most economic damage is caused when larvae burrow into fruits. Lar-vae typically mine cavities just beneath the skin, discolouring the fruit and causing exu-dation of gum mixed with frass. Even when only minor damage is inflicted, cosmetic alterations reduce the fruit’s value and in-crease picking and culling costs. Fruit dam-age also increases putrefaction and suscep-tibility to other pests (Curtis 1983). In both peach and almond orchards, severe shoot damage can stunt and kill small trees (Summers 1955). Host-foraging and selection by A. lineatella is likely achieved by both female moths and larvae. Five almond-derived volatiles [β-bourbonene, (E,E)-α-farnesene, (E)-β-ocimene, nonanal, decanal] elicit an-tennal responses from female A. lineatella moths (Sidney 2005), and thus may be be-haviourally active semiochemicals to forag-ing adults. When females lay eggs on sites other than a new shoot or fruit, larvae must search for a site to enter host plant tissue.  Overwintered larvae emerging from hiber-1 Department of Biological Sciences, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada 2 Agriculture and Agri-Food Canada, Pacific Agri-Food Research Centre, Summerland, British Columbia  V0H 1Z0, Canada 3 To whom correspondence should be addressed; E-mail: gries@sfu.ca  4  J. ENTOMOL. SOC. BRIT. COLUMBIA 103, DECEMBER 2006   Experimental Insects. Insects were collected from peach orchards in Keremeos, BC, and reared according to protocols de-veloped and modified, respectively, by McElfresh and Millar (1993) and Sidney (2005). Acquisition of Fruit and Shoot  Volatiles. Freshly collected early season fruits and shoots of almond and peach were aerated separately for 3-7 d in a cylindrical Pyrex® glass chamber (15.5 × 20 cm).  Charcoal-filtered air was drawn at 2 L/min with a water aspirator through the chamber and a glass column (14 × 0.40 cm ID) con-taining 3 cm of 50-80 mesh Porapak Q (Waters Associates Inc., Milford, MA).  Volatiles were eluted from the Porapak Q with 3 ml of redistilled pentane and refrig-erated (4 ˚C) until use. Olfactometer Bioassays. Anemotactic responses of neonate larvae to test stimuli were assessed in a vertical Y-shaped Py-rex® glass olfactometer (Fig. 1) at 20 ± 3 ˚C and 35% ± 5% relative humidity. The olfactometer was placed vertically and illu-minated from above with tubes of fluores-cent “daylight” and “wide spectrum grow light” (Osram Sylvania Ltd., Mississauga, Ontario) because A. lineatella larvae are both negatively geotactic and positively phototactic. Two pieces of 20-gauge steel wire were suspended inside Y-tubes to fa-cilitate movement of larvae (Landolt et al. 1998), with one piece connecting the open-ing of each side arm, and a linear piece sus-pended therefrom (Fig. 1). Visual cues were standardized by enclosing the olfactometer on three sides with black poster board. Treatment and control test stimuli were micropipetted onto Whatman No. 2 filter paper discs (1.27 cm diameter) inserted 1 cm into the orifice of each side arm. All pipetting was done in a separate room to avoid contamination. For each replicate, a freshly-cleaned and oven-dried Y-tube with new steel wire, insect and filter paper were used, with test stimuli randomly assigned to side arms. Air drawn through the apparatus at 0.1-0.2 L/min with a water aspirator was humidified before entering the side arms.  Nalgene® tubes running from the humidifi-ers to the side arms were dedicated as treat-ment or control tubes to avoid contamina-tion. Thirty seconds after placement of stimuli, a neonate was introduced into the Y-tube on the linear piece of wire. All neo-MATERIALS AND METHODS nacula may need to move considerable dis-tances to locate new growth in spring (Bailey 1948). Larval foraging behaviour may be medi-ated in part by airborne semiochemicals, as shown for codling moth, Cydia pomonella L. (Bradley and Suckling 1995, Landolt et al. 1998, Knight and Light 2001), and pars-nip webworm, Depressaria pastinacella (Duponchel) (Carroll and Berenbaum 2002). Lepidopteran larvae can detect semiochemicals from host plants (Dethier 1980, Landolt et al. 1998, 2000, Singh and Mullick 2002) with semiochemical recep-tors residing on rudimentary antennae or maxillae (Dethier and Schoonhoven 1969, Dethier and Kuch 1971, Dethier 1980). However, such antennae are difficult to prepare for electrophysiological screening of potential host plant semiochemicals. Thus, we used adult moth antennae instead (Sidney 2005), working under the assump-tion that olfactory receptors are conserved across life stages, and that larval and adult antennae respond to the same semiochemi-cals. Our objectives were (1) to determine whether neonate A. lineatella larvae orient chemo-anemotactically toward Porapak Q extracts of almond and peach shoot vola-tiles; and (2) if so, to determine the semio-chemical(s) responsible for attraction of larvae. In this paper, we focus on bioassays with almond volatiles because β-bourbonene, the most abundant component, was present only in almonds, rendering it potentially useful for attraction of A. lineatella in peach orchards having no natu-rally occurring competing sources of the compound.  J. ENTOMOL. SOC. BRIT. COLUMBIA 103, DECEMBER 2006  5  nates were less than 5 h old at the time of bioassay. Neonates that travelled more than 2 cm up a side arm within 10 min were classed as responders; all others were classed as non-responders and were not included in statistical analyses.  Stimuli tested in experiments 1-11 are listed in Tables 1 and 2. Experiments 1 and 2 tested Porapak Q extract of peach and almond shoots, respectively, and experi-ments 3-11 tested five synthetic or plant-derived almond volatiles that elicited re-sponses from adult moth antennae (Sidney 2005). Experiments 3-6 tested three of those five components singly, and nonanal and decanal in combination. To determine whether β-bourbonene, as the most attrac-tive of the five components, was solely re-sponsible for attraction of neonates to Pora-pak Q almond extract, experiment 7 tested β-bourbonene versus Porapak Q almond extract. Because Porapak Q extract was more attractive than β-bourbonene, experi-ments 8-10 tested β-bourbonene singly ver-sus binary combinations of β-bourbonene with (E,E)-α-farnesene (Exp. 8), (E)-β-ocimene (Exp. 9), or with nonanal plus de-canal (Exp. 10). Experiment 11 tested β-Figure 1.  Vertical Y-tube olfactometer used for testing chemoanemotactic responses of neo-nate Anarsia lineatella larvae to test stimuli in experiments 1–11.  Neonates were placed on the steel wire and classed as responders when they crawled > 2 cm up a side arm within 10 min; all others were classed as non-responders and were not included in statistical analyses.  6  J. ENTOMOL. SOC. BRIT. COLUMBIA 103, DECEMBER 2006   Table 1. Name, amount, chemical purity, and source of stimuli tested in experiments 1-11.   1 Amount is the sum of all antennally active compounds present in 5 µL of Porapak Q extract 2 Amounts of almond volatiles used were equivalent to the amounts present in 5 µL of Porapak Q almond twig and fruit extracts. 3 Saje, Delta, BC (geranium essential oil); absolute configuration of β-bourbonene unknown 4 Purified by high-performance liquid chromatography 5 Purified to 99% by preparative gas chromatography 6 TCI = Tokyo Chemical Industry, Portland 7 IFF = International Flavours and Fragrances, New York, NY 8 3.2 ng of nonanal were combined with 3.2 ng of decanal  Stimuli Amount  (ng / lure) Chemical purity  (%) Source Porapak Q peach twig extract1   85.0   Porapak Q almond twig + fruit extract2   39.4   β-Bourbonene   12.0 99 Saje3,4,5  (E,E)-α-Farnesene   3.0 99 TCI5,6  (E)-β-Ocimene   3.0 99 IFF5,7  Nonanal   3.28 95 Aldrich Decanal   3.28 95 Aldrich Table 2. Stimuli tested in Y-shaped Pyrex® glass olfactometer experiments and number of neonate larvae responding.  1 Number of responding insects given in parenthesis  2 Porapak Q almond twig/fruit extract Experiment  no.  Test stimuli Treatment Control 1 Porapak Q peach twig extract  Pentane 175 (106)  2 Porapak Q almond twig/fruit extract  Pentane 170 (105)  3 β-bourbonene  Pentane 260 (155)  4 (E,E)-α-Farnesene  Pentane 60 (37)  5 (E)-β-Ocimene Pentane 60 (38)  6 nonanal + decanal Pentane 90 (59)  7 β-Bourbonene Porapak Q extract2 60 (34)  8 β-Bourbonene + (E,E)-α-farnesene  β-Bourbonene  80 (58)  9 β-Bourbonene + (E)-β-ocimene  β-Bourbonene  60 (45)  10 β-Bourbonene + nonanal + decanal  β-Bourbonene  60 (37)  11 β-Bourbonene + (E,E)-α-farnesene  Porapak Q extract2 150 (115)  Larvae tested (n)1  J. ENTOMOL. SOC. BRIT. COLUMBIA 103, DECEMBER 2006  7  RESULTS AND DISCUSSION In Y-tube olfactometer bioassay experi-ments, more larvae responded to Porapak Q extracts of peach shoots (χ2 = 8.2, P < 0.005; Fig. 2, Exp. 1) or almond shoots and fruits (χ2 = 18.9, P < 0.001; Fig. 2, Exp. 2) than to solvent controls, demonstrating that A. lineatella neonate larvae orient chemoanemotactically to host volatiles. Of the five almond volatiles [β-bourbonene, (E,E)-α-farnesene, (E)-β-ocimene, nonanal, decanal] that were bioas-sayed in experiments 3-6, only β-bourbonene was attractive to neonate larvae (χ2 = 22.1, P < 0.001; Fig. 2, Exp. 3).  How-bourbonene plus (E,E)-α-farnesene (the only binary combination more attractive than β-bourbonene alone) versus Porapak Q almond extract. Data Analysis. Data were analyzed with the χ2 goodness-of-fit test using Yates cor-rection for continuity to determine whether observed frequencies deviated significantly from expected frequencies, under the null hypothesis that A. lineatella neonate larvae did not prefer either treatment or control stimuli (Zar 1996).  Figure 2.  Anemotactic responses of neonate Anarsia lineatella larvae in Y-tube olfactometer experiments to Porapak Q extracts of peach twigs (Exp. 1), almond twigs and fruits (Exp. 2), or to specific candidate semiochemicals (Exps. 3-6).  For each experiment, bars with asterisks (*) indicate a significant preference for a particular treatment; χ2 test with Yates correction for continuity, treatment versus control; * P < 0.005; ** P < 0.001.  8  J. ENTOMOL. SOC. BRIT. COLUMBIA 103, DECEMBER 2006   Figure 3.  Anemotactic responses of neonate Anarsia lineatella larvae in Y-tube olfactometer experi-ments 7-11 to Porapak Q extracts of almond twigs and fruits (Exp. 7), or to specific candidate semiochemicals (Exps. 8-11).  For each experiment, bars with asterisks (*) indicate a signifi-cant preference for a particular treatment; χ2 test with Yates correction for continuity, treatment ever, β-bourbonene was not as attractive as Porapak Q extracts of almond shoots and fruits (χ2 = 5.4, P < 0.05; Fig. 3, Exp. 7), suggesting that the almond volatiles con-tained at least one additional semiochemi-cal.  Of the potential synergistic compo-nents [(E,E)-α-farnesene, (E)-β-ocimene, or nonanal plus decanal] that were bioassayed in experiments 8-10, only (E,E)-α-farnesene enhanced attractiveness of β-bourbonene (χ2 = 5.3, P < 0.05; Fig. 3, Exp. 8). No dif-ference in attractiveness between almond Porapak Q extract and β-bourbonene plus (E,E)-α-farnesene (Fig. 3, Exp. 11) indi-cated that the latter two components medi-ate attraction of neonate larvae to almond extract. (E,E)-α-Farnesene is also a component of ‘Granny Smith’ apples, and attracted C. pomonella larvae in Petri dish bioassays (Bradley and Suckling 1995). The (E,E)-isomer in ‘Granny Smith’ apples accounts for 99.5% of the total α-farnesene content (Bradley and Suckling 1995) and it is also the predominant isomer in Porapak Q ex-tracts of almond volatiles.  Neonate A. lineatella larvae seeking a feeding site are probably susceptible to pre-dation and poor weather, as are neonate C. pomonella larvae under similar circum-stances (Jackson and Harwood 1980). Through oriented movement toward β-bourbonene and (E,E)-α-farnesene, A. lineatella larvae would likely increase the chances of successful almond shoot or fruit location, host penetration, and survival.  In integrated pest management programs for peaches, neonate A. lineatella could possi-bly be controlled by depositing bait droplets impregnated with attractive β-bourbonene and (E,E)-α-farnesene and laced with insec-ticide on tree twigs. However, this “attract and kill” tactic would be effective only if larvae were attracted over a considerable distance, and if both sesquiterpenes became commercially available.  J. ENTOMOL. SOC. BRIT. COLUMBIA 103, DECEMBER 2006  9  ACKNOWLEDGEMENTS  We thank Eberhard Kiehlmann for re-viewing the manuscript. The research was supported by a Research and Development grant from the Natural Sciences and Engi-neering Research Council of Canada, Agri-culture and Agri-Food Canada, and the B.C. Fruit Growers’ Association to G.G. and G.J.R.J.  REFERENCES Ahmad, T.R.  1988.  Predicting emergence and flight activity of peach twig borer (Lepidoptera: Gelechii-dae) by heat unit accumulation.  Insect Science and its Application 9: 197-200. Bailey, S.F.  1948.  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Almond volatiles attract neonate larvae of Anarsia lineatella (Zeller) (Lepidoptera: Gelechiidae)

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Almond volatiles attract neonate larvae of Anarsia lineatella (Zeller) (Lepidoptera: Gelechiidae)

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