M. O. Petrova

Investigation of the biological activity of Litsea cubeba essential oil and its main component citral to assess the possibility of their use in biologized protection of greenhouse crops was the aim of this research. The study was carried out on a laboratory population of the two-spotted spider mite on bean plants. The toxic action under the contact-intestinal application and fumigation, and repellent action against the spider mite females and their o spring were evaluated. When using L. cubeba oil and citral at a concentration of 0.25%, a signi cant decrease in the reproduction index by 2.8 and 2.5 times, respectively, was recorded. The activity of the essential oil under fumigation at doses of 7.5 and 6.0 μl/l of air was close to 100%. After reducing the dosage to 4.5 μl/l, the mortality in the experiment exceeded 50%, and the suppression rate of reproduction was 84.5%. The negative e ect on fertility remained above 60% at 3.75 μl/l. The citral application at a dosage of 3.0 μl/l resulted in the mite mortality above 80% and a decrease in the number of eggs laid by female by more than 90%. Females ignored leaves treated with 0.25% solutions of the studied substances, and the decrease in the number of eggs was more than 90% (repellent e ect). The use of citral at 0.125 and 0.06 % concentrations prevented the colonization of leaves by mites also, and at a concentration of 0.045 %, it reduced the number of eggs laid by 3.1 times. Thus, L. cubeba oil and citral may be perspective as natural acaricidal agents with di erent modes of action.

Surveys were carried out in 2019 and 2020 to study the effects of weather conditions (temperature and humidity) on the dynamics of degradation of various t

The fungus, Alternaria sonchi is considered to be a potential agent for the biocontrol of perennial sowthistle (Sonchus arvensis). A new chlorinated xanthone, methyl 8-hydroxy-3-methyl-4-chloro-9-oxo-9H-xanthene-1-carboxylate (1) and a new benzophenone derivative, 5-chloromoniliphenone (2), were isolated together with eleven structurally related compounds (3–13) from the solid culture of the fungus, which is used for the production of bioherbicidal inoculum of A. sonchi. Their structures were determined by spectroscopic (mostly by NMR and MS) methods. Alternethanoxins A and B, which were reported in A. sonchi earlier, were re-identified as moniliphenone and pinselin, respectively. The isolated compounds were tested for phytotoxic, antimicrobial, insecticidal, cytotoxic and esterase-inhibition activities. They did not demonstrate high phytotoxicity (lesions up to 2.5 mm in diameter/length at a concentration of 2 mg/mL) when tested on leaf disks/segments of perennial sowthistle (Sonchus arvensis) and couch grass (Elytrigia repens). They did not possess acute toxicity to Paramecium caudatum, and showed moderate to low cytotoxicity (IC₅₀ > 25 µg/mL) for U937 and K562 tumor cell lines. However, chloromonilicin and methyl 3,8-dihydroxy-6-methyl-4-chloro-9-oxo-9H-xanthene-1-carboxylate (4) were shown to have antimicrobial properties with MIC 0.5–5 µg/disc. Compound 4 and chloromonilinic acid B were found to have contact insecticidal activity to wheat aphid (Schizaphis graminum) at 1 mg/mL. Compounds 2 and methyl 3,8-dihydroxy-6-methyl-9-oxo-9H-xanthene-1-carboxylate displayed selective carboxylesterase inhibition activity at concentration of 100 µg/mL. Therefore, the waste solid substrate for production of A. sonchi spores can be re-utilized for the isolation of a number of valuable natural products.