Laboratory evaluation of insecticidal activity of three wood ashes and diatomaceous earth against maize weevil (Sitophilus zeamais Motschulski, Coleoptera, Curculionidae)

V laboratorijskih razmerah smo preučevali insekticidno delovanje treh lesnih pepelov navadne smreke (Picea abies H.), navadne bukve (Fagus sylvatica L.) in navadne robinije (Robinia pseudoacacia L.) in diatomejske zemlje (pripravek SilicoSec®) na koruznega žužka (Sitophilus zeamais M.). V prvem delu poskusa smo preučevali kontaktno delovanje snovi, v drugem delu pa insekticidno delovanje preizkušanih snovi, zmešanih z zrnjem ozimne pšenice. Pripravke smo na zrnje pšenice nanesli v različnih koncentracijah. Smrtnost odraslih osebkov smo preučevali pri treh temperaturah (15, 20 in 25 °C) in dveh vrednostih relativne zračne vlage (55 in 75 %). Smrtnost hroščev smo v prvem delu poskusa ugotavljali 1., 2., 3., 4. in 7. dan, nato pa smo še 8., 9., 10., 11. in 14. dan spremljali smrtnost hroščev z zamikom. V drugem delu poskusa pa smo smrtnost hroščev spremljali 7., 14. in 21. dan po izpostavitvi. Ugotovili smo signifikanten vpliv preučevanih snovi na smrtnost odraslih osebkov koruznega žužka. Smrtnost imagov je bila v vseh delih poskusa signifikantno najvišja v obravnavanjih \u27Silicosec\u27 in \u27Smreka\u27. Smrtnost hroščev je bila signifikantno višja pri kombinaciji višje temperature in nižje relativne zračne vlage. Čas izpostavljenosti je prav tako vplival na smrtnost hroščev, in sicer se je le ta s časom izpostavljenosti višala. Ugotavljamo, da je lahko lesni pepel učinkovita snov za zatiranje koruznega žužka, vseeno pa bodo potrebne še nadaljnje raziskave za določitev ustreznih koncentracij lesnega pepela pri zatiranju navedenega in drugih skladiščnih škodljivcev. Lesni pepel, ki je v Evropi zelo dostopna surovina, je zato zagotovo snov, ki jo je potrebno v prihodnje bolj intenzivno preučevati tudi v varstvu rastlin, saj rezultati naše in številnih drugih raziskav kažejo na njegov velik pomen pri zatiranju skladiščnih škodljivcev.Laboratory experiment was carried out to evaluate the insecticidal efficacy of three different natural wood ashes Norway spruce (Picea abies H.), European beech (Fagus sylvatica L.), and Black Locust (Robinia pseudoacacia L.) and diatomaceous earth (SilicoSec®) against maize weevil (Sitophilus zeamais M.) adults. In the first part of experiment we tested a contact activity of the substances, and in the second part we evaluated the insecticidal activity of the substances mixed with winter wheat grains. The substances were applied at different concentrations, and bioassays were carried out at three different temperatures (15, 20 and 25 °C), and two different relative humidity (Rh) levels (55 and 75%). In the first part of the experiment the adult mortality was evaluated after the 1st, 2nd, 3rd, 4th and 7th day, and after the 8th, 9th, 10th, 11th, and 14th day delayed mortality was established. In the second part of the experiment the adult mortality was recorded after 7th, 14th, and 21st day of exposure. We confirmed the significant effect of tested substances on mortality of maize weevil adults. In both parts of experiment the mortality of adults was significantly the highest in treatments SilicoSec® and \u27Norway spruce\u27. Adults\u27 mortality was significantly higher with the combination of higer temperature and lower relative humidity. Also time of exposure had an impact on adults\u27 mortality, namely with each day of exposure, the mortality was higher. We can conclude that wood ash can be an efficient substance in controlling maize weevil, however further surveys should focus on the impact of the wood ash dose rates. Due to the high percentage of area covered with forest in some European countries, the main ingredient is present locally, but additional surveys are needed to help improve the practical use of wood ash