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,Zhengyue Li,Guangzu Du,Guanli Xiao,Limin Zhang,Bin Chen

doi:10.3390/insects11020093

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.

Highlights

Western flower thrips (WFT), Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), is an invasive pest in agroforestry worldwide, impacting many economically important greenhouse-grown crops, such as ornamental flowers, vegetables, fruits, and other various plants through their piercing-sucking mouthparts, causing direct feeding damage and transmission of several destructive plant viruses which have caused significant economic losses in many open-field and greenhouse crops [1,2,3,4,5,6].Currently, due to the wide suitable area for WFT, they pose a huge threat to agriculture and forestry crops
The three different dose rates of imidacloprid and buprofezin did not significantly affect the colony growth of M. flavoviride inoculated on Sabouraud Dextrose Agar (SDA) plates, indicating that the two insecticides had good compatibility with M. flavoviride
We found that the corrected mortalities of WFT adults and second instar larvae were 75% and 72.22%, respectively, at 10 days after inoculation of 1.2 × 106 conidia/mL in assay 1 (M. flavoviride alone); while the corrected mortality of WFT adults and second instar larvae was 100%

Summary

Introduction

Western flower thrips (WFT), Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), is an invasive pest in agroforestry worldwide, impacting many economically important greenhouse-grown crops, such as ornamental flowers, vegetables, fruits, and other various plants through their piercing-sucking mouthparts, causing direct feeding damage and transmission of several destructive plant viruses which have caused significant economic losses in many open-field and greenhouse crops [1,2,3,4,5,6].Currently, due to the wide suitable area for WFT, they pose a huge threat to agriculture and forestry crops. Entomopathogenic fungi (EPF) are biological control agents with insecticidal activities against a variety of agricultural insect pests worldwide [16,17,18,19] Most importantly, they do not pollute the environment, are harmless to humans and animals, have an ecologically wide distribution, and target a variety of host species, demonstrating a broad spectrum of insecticidal effectiveness and strong pathogenicity against many insect pests in the agricultural field. They do not pollute the environment, are harmless to humans and animals, have an ecologically wide distribution, and target a variety of host species, demonstrating a broad spectrum of insecticidal effectiveness and strong pathogenicity against many insect pests in the agricultural field They have been widely used and studied throughout the world [17]. As the essential oils (EOs) of botanical insecticides have similar control efficacies on pests as EPF, there have been many studies on EOs in controlling WFT [28,29]

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