The Time-Concentration-Mortality Responses of Western Flower Thrips, Frankliniella occidentalis, to the Synergistic Interaction of Entomopathogenic Fungus Metarhizium flavoviride, Insecticides, and Diatomaceous Earth

Wenchao Ge; Guangzu Du; Limin Zhang; Zhengyue Li; Guanli Xiao; Bin Chen

doi:10.3390/insects11020093

The Time-Concentration-Mortality Responses of Western Flower Thrips, Frankliniella occidentalis, to the Synergistic Interaction of Entomopathogenic Fungus Metarhizium flavoviride, Insecticides, and Diatomaceous Earth

Insects. 2020 Feb 1;11(2):93. doi: 10.3390/insects11020093.

Authors

Wenchao Ge¹, Guangzu Du¹, Limin Zhang^{1

2}, Zhengyue Li¹, Guanli Xiao³, Bin Chen¹

Affiliations

¹ State Key Laboratory for Conservation and Utilization of Bio-Resources in Yunnan, College of Plant Protection, Yunnan Agricultural University, Kunming 650201, China.
² International Cooperation and exchange Department, Yunnan Agricultural University, Kunming 650201, China.
³ College of Agronomy and Biotechnology, Yunnan Agricultural University, Kunming 650201, China.

Abstract

Western flower thrips (WFT), Frankliniella occidentalis (Pergande), is a highly invasive pest which is harmful to many cash crops globally and resistant to various insecticides. Entomopathogenic fungi (EPF), as biological control agents, have demonstrated a good control effect on WFT. The aim of this study was to evaluate the synergistic and pathogenicity efficacy of the fungal strain Metarhizium flavoviride WSWL51721 when distributed with diatomaceous earth (DE) and the active ingredient imidacloprid using four bioassay methods against adult and second instar larvae of WFT. The data of the four bioassays have been fitted to the time-concentration-mortality (TCM) model. The corrected mortality ranges of WFT adults were 75-100%, 82.69-100%, 78.85-100%, and 92.31-100%, and the corrected mortality ranges of WFT second instar larvae were 72.22-100%, 85.19-100%, 77.77-100%, and 100% in the four bioassays at concentrations of 1.2 × 10⁶ to 1.2 × 10⁸ conidia/mL, respectively. At 1.2 × 10⁸ conidia/mL, assays 2 (M. flavoviride with DE), 3 (M. flavoviride with imidacloprid), and 4 (M. flavoviride with DE and imidacloprid) had the shortest median lethal time (LT₅₀), compared with that of assay 1 (M. flavoviride alone) for adults at 2.26 d, 2.06 d, and 1.53 d, and second instar larvae at 2.45 d, 1.70 d, and 1.41 d, respectively. The median lethal concentration (LC₅₀) in the four bioassays decreased within 3-10 days of inoculation. On the third day, it was found that the lowest median lethal concentrations in assays 2, 3, and 4 were 1.58 × 10⁷, 1.13 × 10⁷, and 3.39 × 10⁶ conidia/mL, respectively, which were significantly different from that in assay 1 for the adults. For the second instar larvae, assays 2, 3, and 4 also had the lowest lethal concentrations and were significantly different from those of assay 1. There were significant differences in sporulation between adults and second instar larvae under the four bioassays. Our results indicate that assays 2 (M. flavoviride with DE), 3 (M. flavoviride with imidacloprid), and 4 (M. flavoviride with DE and imidacloprid) demonstrate synergistic effects on the control of both adult and second instar larvae of WFT under laboratory conditions.

Keywords: Diatomaceous earth; Frankliniella occidentalis; Insecticides; Metarhizium flavoviride; Synergism; Time–concentration–mortality modelling.