Efficacy of entomopathogenic nematodes against western flower thrips Frankliniella occidentalis at different pupation depths

摘要

To study the effects of the pupation depth of western flower thrips (WFT), Frankliniella occidentalis (Pergande), on the efficacy of entomopathogenic nematodes (EPN), Heterorhabditis indica strain LN2 and Steinernema bicornutum were applied at dose rates of 100 and 400 infective juveniles (IJ) cm~(-2) to WFT that had pupated at different depths. Additionally, the effects of EPN concentrations and thrips densities were tested on the pupation depth of WFT. A higher concentration of H. indica was required when the thrips pupated deeper. Yet applications of S. bicornutum even at a high concentration resulted in a significantly lower WFT mortality at greater rather than at shallower depths. Generally, WFT control levels of 5-57% were obtained depending on depth of pupation, EPN species, and concentrations. The results clearly indicate that WFT at high EPN concentrations seem to remain at a certain soil depth in order to avoid EPN attraction by moving around. Without or at low EPN concentrations, up to 80% of WFT pupated at the deepest depth of 3-5 cm. However, at higher thrips densities and EPN concentrations, 45-48% of WFT pupated in the medium depth of 1-3 cm. Thus, depth of pupation is an important factor in WFT control using EPN.