Summary: The purpose of this study is to assess the repellent activity of lemongrass (Cymbopogon citratus) essential oil (EO), grown in Serbia under greenhouse conditions, against four prevalent stored product pests: Plodia interpunctella (larvae), Sitophilus oryzae, Acanthoscelides obtectus and Tribolium castaneum (adults). The lemongrass EO repellency was tested using filter paper in Petri dishes and a Y-tube olfactometer. According to the repellency index (RI), the lemongrass EO repellency was divided into 5 classes. Prior to biotesting, the chemical characterization of lemongrass EO was performed and the following main compounds were detected: myrcene (31.0%), geranial (30.0%), and neral (23.6%). The C. citratus EO considered was found to exhibit the Class III repellent activity against P. interpunctella larvae only at the highest concentration (namely 0.5%). This is the very first report on the C. citratus EO repellent activity against this pest. The lemongrass EO examined showed strong repellency (Class IV) against S. oryzae (0.2% and 0.5% of EO), A. obtectus (0.1% and 0.2%), and T. castaneum (0.05-0.1%). Moreover, higher lemongrass EO concentrations (0.5%) were found to exhibit extreme repellency (Class V) against A. obtectus and T. castaneum. The results obtained were confirmed in the bioassays performed, indicating the great potential of lemongrass EO as a bio-repellent when applied in higher concentrations to all the insects considered, regardless of the exposure period.

The biological activity (contact and contact-digestive toxicity, repellent and fumigant effects, effect on the insect’s development and life cycle parameters) of industrial hemp (Cannabis sativa L.) ethanolic extract was assessed against Plodia interpunctella, the most destructive storage pest of sunflower. Additionally, the study aimed to examine the phytotoxic activity of the extract in order to assess its potential as a sunflower grain protectant. Phytotoxicity assessment was based on the effect on germination energy and seed germination and the activity of antioxidative enzymes, enzymes of the polyphenolic metabolism, and the intensity of lipid peroxidation in sunflower seedlings. The antioxidant capacity and content of phenolic compounds (total phenolics and total tannins) were also measured in seedlings. In the experiments, 70% ethanolic extract of dried flowering buds of industrial hemp (variety Helena) was applied at 0.5%, 1.0% and 2.0% concentrations directly on sunflower seeds. Ethanol solution (70%) was the control. The hemp extract (1% and 2%) revealed medium repellence for P. interpunctella larvae (L_3–4) while at 2% concentration it caused 42.5% larval mortality after 72 h. Moreover, the insect’s development was prolonged and fecundity significantly reduced in hemp treatments. The extract did not exhibit fumigant activity. Germination energy and germination of sunflower seeds were stimulated in treatment with 2% hemp extract, while most biochemical parameters of the seedlings were not significantly affected by the hemp extract.

Using the standard method, we studied the germination energy of seed of seven different sunflower genotypes (five hybrids and two cytoplasmically male sterile female lines) developed at the Institute of Field and Vegetable Crops in Novi Sad. The seed was treated with the fungicides benomil, metalaxyl and fludioxonil and the insecticides thiamethoxam and imidacloprid and kept for a year in a storage facility. Analysis of variance showed that there were highly significant differences among the genotypes, chemical treatments, and storage periods. Highly significant differences were also recorded for all the interactions among the factors studied. On average, the highest germination energy was found in the hybrid H2 (93.45%), whose values of this parameter were highly significantly higher than those of the rest of the genotypes, except for the hybrid H1. Also, each of the hybrids had highly significantly higher germination energy than either of the two lines, and the differences among the hybrids themselves were highly significant. Looking at the chemical treatments, the control had the highest germination energy by a highly significant margin (80.39%). The largest difference was observed in relation to the treatments with insecticides (5.48 and 9.56%). These treatments had highly significantly lower values of germination energy than those involving fungicides. Germination energy increased in the first nine months of storage, peaking at 81.29%. After that, there was a sharp drop to 68.94% after 12 months of storing. Differences among the different storage periods were all highly significant except for that between six and nine months of storage, which was not statistically significant.