Neuroptera: Chrysopidae)
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View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Online Research @ Cardiff Conspecific and Heterogeneric Lacewings Respond to (Z)-4-Tridecene Identified from Chrysopa formosa (Neuroptera: Chrysopidae) 1 1 2 2 2 Sándor Koczor & Ferenc Szentkirályi & József Vuts & John C. Caulfield & David M. Withall & John A. 2 2 1 Pickett & Michael A. Birkett & Miklós Tóth Abstract Green lacewings (Chrysopidae) are predators of soft-bodied pest insects and are among the most important biological control agents in crop protection. Chrysopa spp. are of special importance since, unlike most green lacewing species, adults are also predatory. The current study was undertaken in search of Chrysopa formosa compounds with semiochemical activity. Using coupled gas chromatography-electroantennography (GC-EAG), head and thorax extracts of C. formosa elicited EAG responses to a compound subsequently identified by coupled GC/mass spectrometry, microchemistry, chemical synthesis and GC peak enhancement as (Z)-4-tridecene. In field experiments, this compound decreased attraction of adult C. formosa to (1R,4aS,7S,7aR)-nepetalactol and that of Chrysoperla carnea species-complex to a ternary floral lure, with the inhibitory effect found to be dose-dependent. Our results suggest that (Z)-4-tridecene may serve as a general warning signal among multiple green lacewing species. Perspectives for potential practical applications are discussed. Keywords Chrysopa formosa Chrysoperla carnea species-complex (Z)-4-tridecene (1R,4aS,7S,7aR)-nepetalactol . Synthetic ternary floral bait Repellency Biological control Predator Introduction Chrysoperla spp., Chrysopa spp. are also of importance for biological control since, unlike most green lacewings, Green lacewings (Chrysopidae) comprise a species-rich fam- adults are also predatory (Bozsik 1992; Canard 2001). ily with more than 1200 taxa described worldwide (Brooks To maximize the control impact of green lacewings, de-tailed and Barnard 1990). Their larvae are predatory and are of in- knowledge of their chemical ecology is of key importance terest for biological control of agricultural pests (Pappas et al. (Aldrich and Zhang 2016). To date, studies have mainly reported 2011). Chrysoperla spp. for instance, are considered impor- on behavioral responses of lacewings to plant or aphid tant agents of biological control (Pappas et al. 2011), and are semiochemicals (e.g., Flint et al. 1979; Hooper et al. 2002; Tóth available commercially. Nevertheless, it is important to note et al. 2006). Despite the identification of several compounds from that the taxon previously referred to as ‘Chrysoperla carnea’ is different green lacewing species (e.g., Aldrich et al. 2009), composed of several species (Henry et al. 2001); hence, the reports on the behavioral responses of green lacewings to these name C. carnea species-complex or C. carnea s. lat. Besides semiochemicals are scarce. (1R,2S,5R,8R)-Iridodial from extracts of male Nearctic lace-wings Chrysopa oculata Say, 1839 (Zhang et al. 2004) and C. nigricornis Burmeister, 1839, was reported as a male attrac-tant (Zhang et al. 2006), and it has also been found to be attractive to other green lacewing species (Aldrich and * Sándor Koczor Zhang 2016). Interestingly, Aldrich et al. (2016) found that this [email protected] com-pound was not produced by laboratory-reared C. oculata, but only by field-collected individuals. Zhu et al. (2000) identified 1 Plant Protection Institute, Centre for Agricultural Research, (Z)-4-tridecene (TRIDEC) from a Nearctic Chrysoperla sp. and HAS, H-1022 Herman Ottó u. 15, Budapest, Hungary reported that it elicited arrestment in a Y-tube olfactometer, and 2 Department of Biointeractions and Crop Protection, Rothamsted decreased attraction to 2-phenylethanol, a floral volatile, in a Research, Harpenden, Hertfordshire AL5 2JQ, UK preliminary field experiment. Reduced oviposition of Chrysopa commata Kis & Újhelyi, 1965, C. oculata, C. perla was used with a constant humidified airflow of ca. 0.7 l.min−1. (Linnaeus, 1758) and ‘C. carnea (Stephens)’ on surfaces where An antenna was freshly amputated at the base from a live lace- hatched first-instar larvae had been present has been reported wing and mounted between two glass capillary electrodes con- (Ruzicka 1994, 1996, 1998, 2010). However, poten-tial taining Ringer solution. The antennal preparation was placed ca. semiochemicals have not been identified. Interestingly de- 3 mm from the effluent airflow. One of the electrodes was spite the reports on the effect of freshly hatched larvae on grounded, while the other was connected to a high-impedance DC oviposition, later studies conducted with Chrysoperla species amplifier (IDAC-232, Syntech, Kirchzarten, Germany). Aliquots did not verify the effect of previously laid eggs on oviposition (10 μl) of head, thoracic or abdominal extracts were administered onto a 10 mm diam. Rotilabo filter disc (RKTech Kft., Budapest, by females (Fréchette et al. 2006; Koczor et al. 2017). Previous work has shown that Chrysoperla spp. green lace- Hungary) inside a Pasteur pipette. Methyl sa-licylate (10 μl of 1 wings respond to plant volatiles (e.g., Flint et al. 1979; Tóth et μg.μl−1 hexane solution) was used as a standard, and was tested al. 2006 and references therein). For instance, a ternary plant before and after the other stimuli, for normalizing response volatile blend was more attractive to males and females of amplitudes. Solvent (hexane) and air were the controls. For a European populations of the C. carnea species-complex (i.e., stimulus, 1 ml of air was pushed through the Pasteur pipette into C. carnea complex) than previously published attractants the airstream flowing toward the antenna. Stimuli were (Tóth et al. 2009). The ternary blend, also, was found to administered at ca. 20–30 s intervals. increase oviposition in the vicinity of baits (Jaastad et al. 2010; Koczor et al. 2015a), and adults preferred overwintering Coupled Gas Chromatography- shelters baited with the blend (Koczor et al. 2015a). Electroantennography (GC-EAG) The current study focused on C. formosa Brauer 1850, one of the most common Chrysopa species in Hungary, which is also of A thoracic extract was purified on silica gel (hexane) to remove significance in agroecosystems of arable crops and orchards contamination from high molecular weight contaminants, and throughout Europe and Asia (Duelli 2001; Szentkirályi 2001). was subjected to coupled GC-EAG using an Agilent 6890 N gas Given the important ecological role that C. formosa has, as a chromatograph equipped with a DB-WAX column (J&W predator of soft-bodied insects, our aim was to investigate semio- Scientific, Folsom, CA, USA, 30 m × 0.32 mm i.d.). Helium was chemicals from C. formosa with a view to using the identified the carrier gas and injection was performed in the splitless mode. compounds as potential tools in ecological pest management. The temperature program started at 60 °C and increased to 220 °C by 10 °C.min−1. The column effluent was split be-tween the flame ionization detector (FID) and a heated transfer line to the Methods and Materials EAG apparatus. For each test, 1 μl aliquots of an extract and 10 ng tetradecyl acetate in 1 μl hexane as internal standard, were co- Preparation of Lacewing Extracts injected. A compound was defined as EAG-active if it evoked an antennal response, distinguishable from background noise, in at Male C. formosa were collected in the field at Halásztelek least three replicates. (Hungary) with CSALOMON® VARL+ funnel traps (Plant Protection Institute, CAR, HAS, Budapest, Hungary, http:// Coupled GC/Mass Spectrometry (GC/MS) Analysis www.csalomontraps.com) baited with (1R,4aS,7S,7aR)- nepetalactol (NEPOH; Botanix Ltd., Paddock Wood, Kent, UK) Thoracic extracts were analyzed on an HP 6890 GC, equipped in PVC rope formulation (5% loading w:w; Agrisense-BCS Ltd., with a cool-on-column injector and FID, and fitted with a 30 Pontypridd, Wales, UK). This trap design and for-mulation is m × 0.32 mm inner dia. × 0.5 μm film thickness polar DB- effective at catching C. formosa males (Koczor et al. 2010, WAX column, or a 50 m × 0.32 mm inner dia. × 0.52 μm film 2015b). For the preparation of extracts, 25 live males were frozen thickness non-polar HP-1 column (J & W Scientific, Folsom, at −20 °C, dissected into head, thorax and abdomen, which were CA, USA). The oven temperature was maintained at 30 °C for then immersed in hexane at room tem-perature. The supernatant 2 min and then programmed at 10 °C.min−1 to 250 °C. The was placed in glass microcapillaries, which were closed by heat carrier gas was hydrogen. For tentative identification of EAG- sealing, and stored at -20 °C until required for active peaks from thoracic ex-tracts, GC/MS analysis was electrophysiological and chemical studies. performed on a Micromass Autospec Ultima magnetic sector mass spectrometer (Waters, Milford, MA, USA), attached to Electrophysiology (EAG) an Agilent 6890 N GC (fitted with a 30 m × 0.32 mm inner dia. × 0.5 μm film thickness polar DB-WAX column, J & W Extracts were tested for EAG activity with antennae from male C. Scientific, Folsom, CA, USA) equipped with a cool-on- formosa in a preliminary screening. For presenting the stim-uli to column injector. Ionization was by electron impact (70 eV, the antenna, a stainless steel tube (teflon coated inside) 220 °C). The GC oven temperature was maintained at 30 °C for 5 min and then programmed at 5 BuLi solution (32.2 ml, 43.40 mmol) and the mixture stirred for −1 °C.min to 250 °C. Tentative identifications were obtained 60 min. Iodine (11.00 g, 43.40 mmol) in Et2O (100 ml) was by comparison of mass spectra with the NIST mass spectral added slowly to the mixture before being allowed to warm to database (2011), and confirmed by comparison of KI values room temperature over 3 h.