Efficacy of entomopathogenic fungi, nematodes and spinetoram combinations for integrated management of Thrips tabaci

Abstract

Background: Two consecutive field trials using a blend of entomopathogens in combination with a new chemistry insecticide were conducted to determine treatment effects on onion thrips (Thrips tabaci Lindeman) populations, crop damage, plant development, crop yield and impact on natural enemies. Products were tested in an onion cropping system and included the insect pathogenic fungus Beauveria bassiana (isolate WG-11), an entomopathogenic nematode Heterorhabditis bacteriophora (strain VS) and the new-chemistry chemical insecticide spinetoram.

Results: In all treatments, a significant decrease in thrips per plant population was detected in both trials. Overall, dual application of entomopathogens and insecticide was more effective than singly applied treatments. The lowest number of thrips larvae (1.96 and 3.85) and adults (0.00 and 0.00) were recorded when treated with dual application of B. bassiana and spinetoram at 7 days post application (DPA) after the second spray application in 2017and 2018, respectively. Damage on onion plants was considerably decreased in all treatments relative to the control. The lowest damage was observed on onion plants treated with B. bassiana + spinetoram at 7 DPA after the second spray application during both years. A significant decrease in the number of natural enemies (beetles, spiders, mites, lacewings, ants and bugs) on onion plants was recorded during both years. Insect pathogens when applied alone and in combination with each other considerably protected arthropod natural enemies compared to insecticide application applied alone. Significant increase in plant agronomic traits was observed compared to the control. Among all the treatments, B. bassiana + spinetoram produced maximum leaf length, leaf weight, total leaves, neck diameter, bulb diameter, number of rings per bulb, bulb weight, dry matter and plant yield following the 2017and 2018 applications, respectively.

Conclusion: The findings of the study reveal the potential of using insect pathogens and insecticide for control of T. tabaci. However, combinations containing spinetoram are harmful to nontarget organisms, whereas biological control agents help in protecting biodiversity in onion agroecosystems. © 2023 Society of Chemical Industry.

Keywords: Beauveria bassiana; Heterorhabditis bacteriophora; Thrips tabaci; damage assessment; field efficacy; natural enemies; spinetoram.