FACTORS INFLUENCING THE ACARICIDAL ACTIVITY OF FLUCYCLOXURON

Contact activities of flucycloxuron on immature stages of the two-spot ted spider mite (Tetranychus urticae (Koch)) and the European red mite (Panonychus ulmi (Koch)) gradually decrease in the successive develop mental stages. The levels of contact activity of flucycloxuron on larv ae and protonymphs of T. urticae and P. ulmi are of the same order. De utonymphs of T. urticae are less susceptible to contact activity than the similar stage of P. ulmi. In adult T. urticae, the transovarial ov icidal activity was used as an indicator for cuticular penetration. Mo re than 90% of the maximal penetration into adult mites occurs within 8 h. Reversibility of the transovarial activity was not observed after 24 h, but did occur after a subsequent 48 h stay on untreated leaves. The ovo-larvicidal activity of flucycloxuron on P. ulmi after treatme nt of apple leaves is strongly negatively influenced by leaf age, part ly by lower retention of the spray liquid on the leaves. Leaf penetrat ion was measured by application of flucycloxuron on leaf uppersides an d assessment of the transovarial activity in mites (P. ulmi or T. urti cae) infested on the undersides, one day after treatment. In this test system, leaf penetration was found to be strongly species dependent. Penetration was high in cucumber, moderate in French beans, cotton, ro ses and strawberry, but low in apple and pepper. Leaf penetration in F rench bean plants is drastically reduced at increasing leaf age. The o verall positive effect of increase in relative air humidity on leaf pe netration, is statistically highly significant (P = 0.001) for French beans and almost significant (P = 0.08) for cucumbers. With T. urticae on French bean it was found that in this test flucycloxuron needs mor e than one day for maximal leaf penetration. Although in apple leaves penetration from uppersides was low, penetration from undersides was m uch higher. The surfactants Arkopal N130, Silwet L-77 and X2-5309 enha nce penetration from leaf undersides.