Soil application of azadirachtin and 3-tigloyl-azadirachtol to control western flower thrips, Frankliniella occidentalis (Thysanoptera: Thripidae): translocation and persistence in bean plants

To study the systemic effects of active neem ingredients, the substrate of bean plants was treated with a 170 g kg(-1) azadirachtin (NeemAzal-U; Trifolio-M GmbH, Lahnau, Germany, registration pending). This product was used at a dose rate of 10 mg AZA (azadirachtin a) and 1.2 mg 3-tigloyl-azadirachtol (azadirachtin b) per treated bean plant. Afterwards, the translocation and persistence of AZA and 3-tigloyl-azadirachtol and the effects on western flower thrips, Frankliniella occidentalis (Pergande), were studied. Residues of AZA and 3-tigloyl-azadirachtol from substrates with different contents of organic matter [pure culture substrate (CS), CS-sand mixture] and from various plant parts were quantified by high-performance liquid chromatography-mass spectrometry (HPLC-MS). The dissipation trends of AZA and 3-tigloyl-azadirachtol were similar within the same substrates. A slower decline of both active ingredients was measured with CS than with CS-sand mixture. Residue analysis of the bean plants showed that only small proportions of the initial amounts of AZA and 3-tigloyl-azadirachtol applied to the substrate were present in the plant (0.3-8.1%). Variable amounts of residues of the active components in relation to plant parts and time of analysis indicated a different translocation pattern for the two active ingredients. Higher residues of the active ingredients were found in roots and stems after neem application using CS, whereas higher residues were found in leaves after CS-sand mixture treatments. Mortality of F. occidentalis after NeemAzal-U soil applications reached up to 95% on CS-sand mixture, compared with 86% in CS.