Caterpillar-Induced Plant Volatiles Attract Adult Tortricidae
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J Chem Ecol (2017) 43:487–492 DOI 10.1007/s10886-017-0847-7 Caterpillar-Induced Plant Volatiles Attract Adult Tortricidae D. M. Suckling1,2 & A. M. El-Sayed1 Received: 31 October 2016 /Revised: 9 April 2017 /Accepted: 13 April 2017 /Published online: 6 May 2017 # Springer Science+Business Media New York 2017 Abstract Binary and ternary combinations of volatile organic Keywords Kairomone . Tortricidae . phenylacetonitrile . compounds identified earlier from caterpillar-infested apple 2-phenylethanol . Benzyl alcohol . Acetic acid . Eye-spotted foliage caught more than one thousand individuals of both budmoth . Spilonota ocellana . Oblique-banded leafroller . sexes of several adult tortricid leafroller species in several Choristoneura rosaceana . Three-lined leafroller . days of trials conducted in apple orchards in southern British Pandemis limitata Columbia. A series of combinations with phenylacetonitrile, benzyl alcohol, and/or 2-phenylethanol and acetic acid en- abled substantial catches of both sexes of eye-spotted Introduction budmoth, Spilonota ocellana, oblique-banded leafroller, Choristoneura rosaceana and three-lined leafroller, Herbivore-induced plant volatiles that arise after insect herbi- Pandemis limitata. These findings suggest that new monitor- vore attack on plants are used for host location by parasitoids ing aides can be developed to seasonally track populations, (Turlings et al. 1990). These volatiles have been well studied enabling practical applications in surveillance of female leaf- and reviewed because they have complex and sometimes un- roller populations for the first time. It may also be possible to predictable effects at more than one trophic level (Dicke and develop suppression tools based on combinations of kairo- Baldwin 2010; Poelman et al. 2012). However, the application mone compounds originally identified from leafroller larval- of synthetic volatiles to manage natural enemies has proven damaged apple trees, given the level of attraction. The discov- more complex than expected (Kaplan 2012). In addition, there ery of these adult tortricid attractants (aromatic compounds has been surprisingly little field investigation of the attraction plus acetic acid) raises new ecological questions about of herbivore pest insects, the group that is of most direct eco- evolved direct plant defences against herbivores. Larval nomic interest. The discovery of confamilial attraction (El- feeding-induced attraction of adult herbivores produces sig- Sayed et al. 2016) suggests an evolutionary advantage for nals that are potentially harmful to the plant by increasing the plant, although evidence for effects on plant fitness from herbivory in the same family and probably feeding guild, such signalling remains elusive. but evidence for effects on plant fitness is needed. In fact, whole groups of pest insects of many perennial crops have received comparatively little investigation thus far. A number of species of Tortricidae (leafrollers) are orchard pests, particularly favored by the habitat and conditions pro- duced in s deciduous tree fruit orchards (Beers et al. 2003). * D. M. Suckling Populations can occur with webbing of nests between leaves [email protected] and fruit, providing a risk of live larvae associated with exported fruit (Lo et al. 2000). Decades of insecticidal control 1 The New Zealand Institute for Plant & Food Research Limited, have led to selection for insecticide resistance (Lowery and Gerald Street, Lincoln 7608, New Zealand Smirle 2000), non-target impacts on beneficial insects mea- 2 School of Biological Sciences, University of Auckland, Tamaki surable as reduced biodiversity (Epstein et al. 2000), residues Campus, Building, Auckland 733, New Zealand on fruit unwanted by consumers, and consequent adoption of 488 J Chem Ecol (2017) 43:487–492 pheromones for reduced reliance on insecticides in some compounds emerging with behavioral activity share an aro- countries (Walker et al. 2017). matic ring. This led us to focus here on phenylacetonitrile, The development of trapping and direct control systems for benzyl alcohol and 2-phenylethylalcohol, together with acetic Tortricidae based on sex pheromones has included a wide acid. Having discovered the activity first on adult array of innovations including mating disruption (El-Sayed E. postvittana in New Zealand (El-Sayed et al. 2016), we set 2017). Some multi-species systems have been developed to out to explore the effect of combinations of these compounds target ecosystem level pest management in North America on economically-important North American leafroller species with a single pheromone release device (Judd and Gardiner the oblique-banded leafroller (OBLR), Choristoneura 2008). In New Zealand, the pheromone-based systems rosaceana (Harris), and eye-spotted bud moth (ESBM), target nil or low residues on fruit combined with no insects Spilonota ocellana (Denis and Schiffermüller), as well as oth- present, the stringent standard needed for market access er species present in lower density such as three-lined leafroll- (Walker et al. 2017). However, these literally disruptive tech- er, Pandemis limitata (Robinson)(TLLR), European leafroller nologies can make pest surveillance more difficult, by Archips rosana, (Linnaeus, 1758)(ELR) and fruit-tree leafroll- preventing the operation of sex pheromone traps baited with er, Archips argyrospila (Walker, 1863) (FTLR). the same compounds (Judd and Gardiner 2008). Several tortricid pests are undergoing geographic range expansion (Suckling et al. 2016). These include the Materials and Methods European grapevine moth, Lobesia botrana Denis & Schiffermüller, in the USA and Chile (Varela et al. 2010) Chemicals Chemical purities of compounds used in trapping and the light brown apple moth, Epiphyas postvittana experiments were as follows: glacial acetic acid (>99%), ben- (Walker), now established in Hawaii, California, Great zyl alcohol (>99%), phenylacetonitrile (>99%), and 2- Britain and several European countries (Suckling and phenylethanol (>99%) (Sigma Aldrich, St. Louis, MO, Brockerhoff 2010). Hence, there is a need to develop new USA). Glacial acetic acid was stored under ambient tempera- technologies for surveillance, and potentially new control ture while all other compounds were stored at −20 °C until tactics to support leafroller pest suppression in existing and used. Aromatic lures were prepared in sealed polyethylene new jurisdictions. sachets, with acetic acid in a Nalgene vial (Nalg-Nunc Like other plants (Schittko et al. 2001; Turlings et al. 1990) International, Rochester, NY, USA). Lures containing apple, Malus domestica Borkhausen, have apparently co- phenylacetonitrile, benzyl alcohol and 2-phenylethanol were evolved chemical communication with their insect herbivores. made as reported elsewhere (El-Sayed et al. 2016), by dis- Chemical attraction of herbivores to apple fruit involving vol- pensing each compound into a permeable polyethylene bag atile organic compounds (VOC) has long been recognised that was then heat-sealed. In the final experiment, (Sutherland 1972; Wearing and Hutchins 1973). Some fruit phenylacetonitrile was added directly to the 3 mL of acetic volatiles compounds have been successfully incorporated into acid in the vial, as well as being presented separately in a trapping systems for female codling moths (Landolt et al. sachet. A trap with a blank lure without chemical was used 2007; Light et al. 2001). The potential now exists to do this as negative control in all trials. for other tortricids. A particular chemical signalling pathway was identified to Field Experimental Protocol All field experiments were con- result from a fatty acid-amino acid conjugate elicitor released ducted in a mixed variety organic apple orchard (49° 13′N, during caterpillar feeding on foliage (Alborn et al. 1997). Fatty 119° 58′W) in Cawston, British Columbia, Canada during acid amino acid conjugates also occur in many families of 2015. Large white delta traps (Pherocon VI, Trécé Inc., Lepidoptera, including leaf feeding Tortricidae (Yoshinaga Adair, OK) were used all trials. Traps baited with different et al. 2010). Volatiles induced from apple foliage from leaf- blends of host-induced plant volatile (HIPV) compounds were roller larval feeding were attractive to a braconid wasp haphazardly assigned to five rows as replicates, each contain- (Suckling et al. 2012), which appears to be a general phenom- ing treatments tested in a randomized complete block design. enon for other leafroller species on other hosts than apple, All trials had five replicates. Traps were positioned 1.7 m where the same wasp locates and parasitizes the larvae above the ground in each trap tree, and were spaced 20 m apart (Suckling et al. 2001). We recently reported attraction of in each row. The polyethylene sachets and vials containing host-induced plant volatiles which were discovered to be acetic acid were attached at the center and on the side, inner highly attractive for adult moths of several species of surface, of a delta trap using a 2.5-cm length of Velcro® in- Tortricidae (El-Sayed et al. 2016). This reinvestigation of dustrial sticky-back tape (Canadian Tire, Penticton, BC, leafroller-damaged apple foliage showed additional com- Canada). Counts were made of common tortricid moths, in- pounds not reported earlier, identified acetic acid and its role cluding S. ocellana, C. rosaceana and P. limitata,aswellas in odor combinations for attracting adult moths. The A. rosana, and A. argyrospila