Essential Oil Composition of Seven Bulgarian <i>Hypericum</i> Species and Its Potential as a Biopesticide

<i>Hypericum</i> species and especially <i>H. perforatum</i> L. are well known for their therapeutic applications. The present study assessed the essential oil (EO) composition, and antifungal and aphid suppression activity of seven Bulgarian <i>Hypericum</i> species. The EOs were analyzed by GC–MS–FID. Two experiments were conducted. In the first experiment, <i>H. perforatum</i>, <i>H. maculatum</i>, and <i>H. hirsutum</i> were used. Additionally, the EO composition of <i>H. perforatum</i> extracted via hydrodistillation (ClevA) and via commercial steam distillation (Com) were compared. The second experiment compared the EOs of <i>H. perforatum</i>, <i>H. cerastoides</i>, <i>H. rumeliacum</i>, <i>H. montbretii</i>, and <i>H. calycinum</i> (flowers and leaves) extracted via hydrodistillation and collected with <i>n</i>-hexane. Overall, the EO constituents belonged to four classes, namely alkanes, monoterpenes, sesquiterpenes, and fatty acids. The main class for compounds in <i>H. maculatum</i> and <i>H. perforatum</i> (section <i>Hypericum</i>) were sesquiterpenes for both experiments except for <i>H. perforatum</i> (Com). <i>Hypericum montbretii</i> (section <i>Drosocarpium</i>) EO had monoterpenes (38.09%) and sesquiterpenes (37.09%) as major groups, while <i>H. hirsutum</i> EO (section <i>Taeniocarpium</i>) contained predominately alkanes (67.19%). <i>Hypericum hirsutum</i> EO contained cedrol (5.04%), found for the first time in <i>Hypericum</i> species. Fatty acids were the main compounds in <i>H. cerastoides</i> (section <i>Campylopus</i>), while monoterpenes were the most abundant class in <i>H. rumeliacum</i> and <i>H. calycinum</i> EOs. <i>α</i>-Pinene and germacrene D were the major EO constituents of all analyzed <i>Hypericum</i> species except for <i>H. hirsutum</i> and <i>H. cerastoides. Hypericum perforatum</i> EO (Com) had significant repellent and insecticidal activity against two aphid species, <i>Rhopalosiphum padi</i> (Bird Cherry-oat aphid) and <i>Sitobion avenae</i> (English grain aphid) at concentrations of 0%, 1%, 2.5%, 3.5%, 4.5%, and 5%. The tested EOs did not show significant activity against selected economically important agricultural fungal pathogens <i>Fusarium</i> spp., <i>Botrytis cinerea</i>, <i>Colletotrichum</i> spp., <i>Rhizoctonia solani</i>, and <i>Aspergillus</i> sp. The EO of the <i>Hypericum</i> species found in the Bulgarian flora could be utilized for the development of new biopesticides for aphid control.