No abstract

Thujone is a natural biologically active monoterpene ketone component of essential oils of numerous plants. The aim of the study was to evaluate the effect of β-thujone and β-thujone derivatives bisulfite adduct, lactone, oxime, and lactam application on behavior of Myzus persicae (Sulz.) (Hemiptera: Aphididae) during probing and settling. The choice and no-choice tests (aphid settling and Electrical Penetration Graph (EPG), respectively) revealed that stereochemistry of thujone was important for biological activity (β-thujone caused changes in aphid behavior while α-thujone did not) and that cyclopentane ring modifications and functional groups addition gave derivatives that possessed stronger and more durable deterrent effects. The most effective modification was the incorporation of a lactam moiety into the β-thujone molecule. Application of β-thujone lactam limited aphid settling for at least 24 h, caused restlessness in aphids and a delay or failure in reaching phloem phase by M. persicae. β-Thujone lactam can be considered a deterrent of medium potency with activity expressed at preingestive phase of aphid probing. Other compounds did not restrain aphid stylet penetration in non-phloem tissues but slightly limited sap ingestion (lactone, oxime), and restrained aphid settling for a period of less than 24 h (β-Thujone, bisulphite adduct, lactone).

The small-seeded legumes are important forage crops for grazing animals and contribute nitrogen to succeeding crops in crop rotation systems. However, the susceptibility of several of the forage legumes to the specialist pea aphid Acyrthosiphon pisum (Harris) has never been investigated. The present study on aphid probing behaviour using the Electrical Penetration Graph technique revealed that the forage legumes studied were (i) highly acceptable (common vetch Vicia sativa L.), (ii) acceptable (wooly vetch Vicia villosa Roth), (iii) moderately acceptable (fodder galega Galega orientalis Lam., crimson clover Trifolium incarnatum L., Persian clover Trifolium resupinatum L., white clover Trifolium repens L.), (iv) barely acceptable (common bird’s-foot-trefoil Lotus corniculatus L., yellow lucerne Medicago falcata L., alfalfa Medicago sativa L., sand lucerne Medicago × varia Martyn, common bird’s-foot Ornithopus sativus Brot., alsike clover Trifolium hybridum L., red clover Trifolium pratense L., common sainfoin Onobrychis viciifolia Scop.), and (v) unacceptable (white melilot Melilotus albus Medik.) to the pea aphid. On (i) plants, probing occupied 85% of experimental time, all aphids (100%) succeeded in feeding on phloem sap, phloem phase occupied 50% of probing time, sap ingestion periods were long (mean duration: 100.8 ± 28.2 min.) and engaged 97% of the phloem phase. On (ii) plants, probing occupied 73% of exp. time, feeding activity occurred in 66.7% of aphids, phloem phase occupied 30% of probing time, sap ingestion periods were long (mean duration: 115.5 ± 46.7 min) and engaged 80% of the phloem phase. On (iii) plants, probing ranged from 53% of exp. time on T. repens to 70% on T. incarnatum and T. resuspinatum, feeding occurred in 35.3% of aphids on T. resuspinatum up to 54.5% on T. incarnatum, phloem phase occupied 10% of exp. time on G. orientalis, T. incarnatum, and T. resuspinatum and 20% on T. repens, sap ingestion periods were from 9.8 ± 1.8 min. on G. orientalis to 51.9 ± 20.7 min. long on T. resuspinatum and engaged from 30% of phloem phase on G. orientalis to 80% on T. incarnatum. On (iv) plants, probing occupied 25% of exp. time on O. viciifolia up to 38% on O. sativus and T. hybridum, feeding occurred in 6.7% of aphids on T. hybridum to 28% on O. sativus, phloem phase occupied less than 1% of probing time on all plants except O. viciifolia (4%) and O. sativus (5%) and it consisted mainly of salivation. On M. albus (v), probing occupied 22% of experimental time, the probes were short (1.8 ± 0.3 min), and no aphid on M. albus showed feeding on phloem sap. M. albus can be recommended for intercropping, ‘push-pull’ strategies, or as a barrier crop against A. pisum in sustainable agricultural practices.

Considering the need for reduction in insecticide use, we studied the potential for antibiosis and the potential for antixenosis in seven highly yielding winter Brassica napus L. cultivars against Myzus persicae (Sulz.). We found evidence for antixenosis, i.e., disruption in probing in non-phloem tissues and a failure in reaching sieve elements in cultivar ‘Alister’. We found evidence for antibiosis, i.e., reduced ability of the plant to serve as a host, in cultivar ‘Florida’. On ‘Alister’ and ‘Florida’, net reproduction and reproductive period duration of M. persicae were the lowest of all studied cultivars. ‘Adriana’, ‘Andromeda’, ‘Gladius’, and ‘Kolumb’ are intermediately susceptible to M. persicae infestation with medium values of net reproduction and reproduction period duration, and slight disturbances in aphid probing and feeding. ‘Artoga’ is highly susceptible. On ‘Artoga’, reproduction period was the longest, daily fecundity and net reproduction of M. persicae were highest, and probing and feeding behaviors were unaltered. Glucoallysin, glucobrassicanapin, gluconapin, gluconapoliferin, progoitrin, glucobrassicin, and 4-OH-glucobrassicin occurred in the leaves of all rapeseed cultivars in similar quantities and proportions and did not affect aphid performance and phloem sap ingestion by M. persicae.

The effect of structurally related sesquiterpenoids (E,E)-farnesol and cis-nerolidol on the host-plant selection behaviour of the peach potato aphid Myzus persicae (Sulz.) was evaluated using electrical penetration graph (EPG) technique. No repellent effects of (E,E)-farnesol and (Z)-nerolidol to M. persicae were found but aphid probing activities on (E,E)-farnesol- and cis-nerolidol-treated plants were restrained. During non-phloem phases of probing, neither (E,E)-farnesol nor (Z)-nerolidol affected the cell puncture activity. On (E,E)-farnesol-treated plants, the total duration of phloem phase, the mean duration of individual sustained ingestion periods were significantly lower, and the proportion of phloem salivation was higher than on control plants. On (Z)-nerolidol-treated plants, the occurrence of the first phloem phase was delayed, and the frequency of the phloem phase was lower than on control plants. The freely moving aphids were reluctant to remain on (E,E)-farnesol- and (Z)-nerolidol-treated leaves for at least 24 h after exposure. (E,E)-Farnesol and (Z)-nerolidol show complementary deterrent properties, (E,E)-farnesol showing ingestive and post-ingestive activities and nerolidol showing pre-ingestive, ingestive, and post-ingestive deterrent activities.