ANTIFEEDANT EFFECT OF NEEMAZAL-T/S ON THE LARGE PINE WEEVIL HYLOBIUS ABIETIS L.

The paper presents three laboratory experiments aimed to establish how long NeemAzal-T/S can protect the seedlings against the weevils, and if the effective lifespan of insecticide could be prolonged by mixing the emulsion with the adjuvant Nu-Film 17. Tests with mature as well as with young, immature insects, have established the efficiency of protection against the damages caused by the large pine weevil when the treatment was conducted with 5 %, 10 % and 20 % NeemAzal-T/S (having 1 % azadirachtin A), as well as with a mixture of 20 % NeemAzal and 10 % Nu-Film 17. The insect feeding has been affected by all treatments and the magnitude of effect has increased with the concentration of insecticide, but it has also been influenced by the gender and physiological state of the weevils. In mature, post oviposition insects, females have been more sensitive to insecticide than males, and the opposite was true in young, immature weevils, as well in mature insects during oviposition. The best results have been achieved with 20 % NeemAzal and 10 % Nu-Film 17 against the male young weevils. A good protection (efficacy higher than 75 %) is possible only a few days after treatment, but sufficient protection is achieved after two weeks, because most of the wounds are superficial, without severe impact on the plants. Consequently, we suppose that treating the seedlings with 20% NeemAzal (or higher concentrations) at time intervals shorter than two weeks, during the periods with high rates of feeding, will keep the damages and seedling losses at a normal level. The efficiency could be improved and the period between treatments prolonged by mixing NeemAzal with Nu-Film. Field experiments are necessary to validate our conclusions.