The combined effect of soil-applied azadirachtin with entomopathogens for integrated management of western flower thrips

Abstract

Performance of soil application of azadirachtin products with entomopathogens was evaluated as single treatments, in multiple combinations and in different concentrations against the soil stages of western flower thrips, Frankliniella occidentalis (Pergande), in French beans Phaseolus vulgaris L. Treatments consisted of NeemAzal-T solution, neem pellets, Steinernema carpocapsae (Weiser) Nemastar®, isolates of Metarhizium anisopliae (Metschnikoff) Sorokin (IPP 2539 and ICIPE-69) and Beauveria bassiana (Balsamo) – Naturalis®. All treatments were analysed for the number of emerging adults, while emerged adults in fungi-based treatments were analysed additionally for the retarded development of mycosis as a possible cause of secondary mortality. Possible interactive effects in combined treatments were analysed using a generalized linear model (GLM) approach, and three levels of dose–response combinations of the selected treatments were further tested. Bioassay results of the single treatments indicated between 43% and 60% reduction in adult emergence with NeemAzal-T solution thus proving to be the most efficient. However, most cadavers with entomopathogenic fungi (EPF) treatments showed the development of mycosis. Therefore, the reduction in adult emergence attributed to the EPF was altogether >87%. Combined treatments with Steinernema, Metarhizium (ICIPE-69), NeemAzal-T and neem pellets resulted in total reduction in adult emergence of 95–97% when late mortality by mycosis was considered. Of the treatment combinations, two showed synergistic, four additive and one an antagonistic response. Combining low concentration of entomopathogenic nematode (EPN) (100 IJ/cm2) with NeemAzal-T resulted in satisfactory control compared to the operational dose of EPN, while the highest concentration of M. anisopliae (108 conidia) combined with Steinernema showed the best performance with 74% reduction in adult emergence.