Fumigant toxic effect of essential oils on larvae of yellow mealworm (Tenebrio molitor L.)

Veliki brašnar (Tenebrio molitor L.) štetni je kornjaš koji ošteduje uskladišteno brašno i proizvode od brašna, žito, mliječni prah i meso, a ličinke ošteduju i ambalažu. Nedostatak djelatnih tvari za suzbijanje, ali i problem razvoja rezistentnosti uslijed učestalog korištenja istih fumiganata, dovele su do potrebe za novim strategijama suzbijanja. Eterična ulja pokazuju insekticidno djelovanje na kukce, a ujedno su i ekološki proizvodi. U radu je istražen fumigantni toksični učinak eteričnih ulja bosiljka, lavande, eukaliptusa, zvjezdastog anisa i limunske trave na ličinke velikog brašnara. Na komercijalno nabavljenim ličinkama velikog brašnara testiran je toksični učinak deset koncentracija (2, 4, 8, 16, 32, 200, 400, 600, 800 i 1000 μl/l zraka) eteričnim uljima bosiljka, lavande, eukaliptusa, zvjezdastog anisa i limunske trave. U staklene posude (750 ml) postavljeno je po 10 ličinki, a na donju stranu poklopca zalijepljen je filter papir tretiran onom količinom ulja kojom je se postigla zadana koncentracija u volumenu 750 ml. Svaka koncentracija i kontrola (voda) postavljena je u pet ponavljanja (ukupno 51 varijanta). Očitavanje mortaliteta provedeno je svakih 24 sata tijekom pet dana. Za svaku varijantu i ponavljanje izračunata je korekcija mortaliteta po formuli Schneider-Orelli, a dobiveni podatci obrađeni su statistički analizom varijance. Najbolje rezultate pri koncentracijama od 200, 400, 600, 800 do 1000 μl/l zraka pokazalo je eterično ulje eukaliptusa s učinkom od gotovo 100 % ved nakon prvog dana od postavljanja pokusa. Iste koncentracije bile su učinkovite i kod eteričnih ulja bosiljka, lavande i zvjezdastog anisa četiri do pet dana od postavljanja pokusa, dok je učinak eteričnog ulja limunske trave bio slabiji (oko 28 %). Svih pet eteričnih ulja u koncentracijama od 2, 4, 8, 16 i 32 μl/l zraka pokazala su izrazito nizak fumigantni toksični učinak (manje od 6 %) na ličinke velikog brašnara.Yellow mealworm beetle (Tenebrio molitor L.) is pest beetle which damages stored flour and flour products, grain, milk powder and meat, and the larvae also damage the packaging. The lack of active substances for control, but also the problem of developing resistance due the frequent use of the same fumigants, led to the need for new control strategies. Essential oils show insecticidal activity on insects, and are also ecological products. The fumigant toxic effect of essential oils of basil, lavender, eucalyptus, star anise and lemongrass on the larvae of the yellow mealworm beetle was investigated in the work. The toxic effect of ten concentrations (2, 4, 8, 16, 32, 200, 400, 600, 800 i 1000 μl/l air) of essential oils of basil, lavender, eucalyptus, star anise and lemongrass was tested on commercially acquired yellow mealwormlarvae. Ten larvae were placed in glass containers (750 ml), and filter paper treated with the amount of essential oil that reached the desired concentration in the volume of 750 ml was glued to the underside of the lid. Each concentration and control (water) was set up in five replicates (51 variants in total). Mortality readings were taken every 24 hours for five days. For each variant and repetition, the mortality correction was calculated according to the Schneider-Orelli formula, and the obtained data were processed by statistical analysis of variance. Eucalyptus essential oil showed the best results at the concentration of 200, 400, 600, 800 and 1000 μl/l of air, with an effect of almost 100% already after the first day of setting up the experiment. The same concentrations were effective with essential oils of basil, lavender and star anise four to five days after setting up the experiment, while the effect of essential oil of lemongrass was weaker (around 28%). All five essential oils in concentrations of 2, 4, 8, 16 and 32 μl/l of air showed very low fumigant toxic effect (less than 6 %) yellow mealworm larvae