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 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.

Geranylacetone and nerylacetone are natural sesquiterpenoids, which play various roles in plant-insect interactions, including the deterrent and repellent effects on herbivores. The structural modifications of natural compounds often change their biological activities. The aim of the study was to evaluate the effect of geranylacetone, nerylacetone and their epoxy-derivatives on the probing and settling behavior of Myzus persicae (Sulz.) (Hemiptera: Aphididae). The no-choice test using the Electrical Penetration Graph (EPG) technique showed that the probes before the first phloem phase were usually shorter than 3 min, which means that they were terminated within the epidermis and/or outer layers of mesophyll. This resulted in a tendency to delay the initiation of the phloem phase in aphids, which reflects a weak preingestive deterrent activity of the studied compounds at the level of non-vascular tissues. Most M. persicae showed bouts of sustained phloem sap ingestion. However, the 24-h free-choice test demonstrated that aphids did not settle on the leaves treated with geranylacetone, nerylacetone, and their epoxy-derivatives. The refusal to settle after the consumption of phloem sap on treated plants indicated that the studied compounds had postingestive deterrent activity. The epoxidation of geranylacetone and nerylacetone did not evoke significant changes in their activity profiles.

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.

Apigenin and luteolin are products of the phenylpropanoid pathway, where apigenin serves as a substrate for the synthesis of luteolin. Apigenin and luteolin are highly bioactive flavones; therefore, in search of prospective biopesticides, the receptiveness of the polyphagous green peach aphid Myzus persicae (Sulzer) (Hemiptera: Aphididae) to apigenin and luteolin was studied. The flavones were applied as 0.1% ethanolic solutions to the host plant leaf surface, and aphid probing and feeding activities were monitored using the Electrical Penetration Graph (EPG) technique. The structural difference between apigenin and luteolin, which was the number of hydroxyl groups in the molecule, had an impact on the activity of these flavones. On apigenin-treated plants, the duration of the first probe was three times as short as on the control and five times as short as on the luteolin-treated plants; the duration of the time to the first ingestion phase within the successful probe was shorter than on the control and luteolin-treated plants; the mean duration of xylem sap ingestion bouts and the proportion of xylem phase in all probing activities were the highest; and the duration of salivation before phloem sap ingestion was the longest. Aphids’ response to luteolin-treated plants was less distinct as compared to apigenin-treated plants.

(1) Background: Genistein is a naturally occurring flavonoid with a rich spectrum of biological activities, including plant-herbivore interactions. The aim of the study was to evaluate the effect of exogenous application of genistein on aphid behavior during probing in plant tissues. (2) Methods: Vicia faba, Brassica rapa ssp. pekinensis, and Avena sativa were treated transepidermally with a 0.1% ethanolic solution of genistein, and the probing behavior of generalist aphid species Aphis fabae, Myzus persicae, and Rhopalosiphum padi was monitored on their respective treated and untreated host plants using electropenetrography (=electrical penetration graph technique, EPG); (3) Results: Genistein did not deter aphid probing activities in non-phloem tissues. In A. fabae and R. padi, a trend towards reduction and in M. persicae a trend towards increase in phloem sap ingestion occurred on genistein-treated plants, but these trends were not statistically significant. (4) Conclusions: Genistein is not a deterrent chemical against generalist aphid species studied; therefore, it is not recommended for practical application.