Characterisation and localisation of plant metabolites involved in pharmacophagy in the turnip sawfly

Abstract

Several herbivorous insects consume certain metabolites from plants for other purposes than nutrition, such as defence. Adults of the turnip sawfly, Athalia rosae take up specific terpenoids, called clerodanoids, from Ajuga reptans. These metabolites are slightly modified by the sawflies and influence their mating behaviour and defence against predators. We characterised these metabolites and investigated their localisation in the insect and the specificity of the uptake and metabolite modification. Therefore, we performed feeding assays with adults and larvae of A. rosae as well as larvae of Spodoptera exigua, followed by chemical analyses. Two main clerodanoid-derived metabolites were detected in the abdomen and thorax but also on the surface of the adults. Small amounts were also found in larvae of the sawfly, while they were not detectable in S. exigua. Our findings provide new insights into the peculiarities of pharmacophagy and specialised metabolism in A. rosae.

Plant metabolites modulate animal social networks and lifespan

“…From each bucket only the feature with the highest intensity was used. We focussed on two metabolites which are likely taken up from A. reptans and metabolised by the sawflies (Brueggemann et al . 2023), putative clerodanoid 1 eluting at 16.3 min ( m/z 529.229 [M+HCOOH-H] - ) and putative clerodanoid 2 eluting at 18.2 min ( m/z 527.214 [M+HCOOH-H] - ), with the monoisotopic masses of 484.231 Da (proposed sum formula C 24 H 36 O 10 ) and 482.214 Da (C 24 H 34 O 10 ), respectively.…”

“…After centrifugation, supernatants were dried and resolved in 8 100 µl of methanol with mefenemic acid (Sigma-Aldrich GmbH, Taufkirchen, Germany) as internal standard. Samples were filtered and analysed using an ultra-high performance liquid chromatograph (UHPLC; Dionex UltiMate 3000, Thermo Fisher Scientific, San José, CA, USA) equipped with a Kinetex XB-C18 column (1.7 µm, 150 × 2.1 mm, with guard column, Phenomenex) kept at 45 °C, coupled to a quadrupole time of flight mass spectrometer (QTOF-MS/MS; compact, Bruker Daltonics, Bremen, Germany) in negative electrospray ionisation mode, following Brueggemann et al (2023; for details see Supplement).Samples were separated with a gradient from 0.1% formic acid (p.a., eluent additive for LC-MS, ~98%, Sigma-Aldrich) in deionised water (eluent A) to 0.1% formic acid in acetonitrile (LC-MS grade, Fisher Scientific, Loughborough, UK; eluent B) at a flow rate of 0.5 ml min -1 , starting eluent B at 2%, increasing to 30% within 20 min, and then to 75% within 9 min, followed by column cleaning and equilibration. The settings for the MS mode were capillary voltage 3000 V, end plate offset 500 V, nebuliser (N2) pressure 3 bar, dry gas (N2, 275 °C) flow 12 L min -1 , quadrupole ion energy 4 eV and collision energy 7 eV.…”

“…From each bucket only the feature with the highest intensity was used. We focussed on two metabolites which are likely taken up from A. reptans and metabolised by the sawflies (Brueggemann et al 2023)…”

“…The adults of A. rosae feed on floral nectar, usually from Apiaceae plants. In addition, they visit non-food plant species such as Ajuga reptans (Lamiaceae), on which they exhibit pharmacophagy by taking up specialised metabolites, neo-clerodane diterpenoids (hereafter called 'clerodanoids'), which they further metabolise slightly (Brueggemann et al 2023). These (metabolised) clerodanoids can serve as a resource for A. rosae adults in multiple ways (Paul et al 2022).…”