Lethal and sub-lethal effects of three microbial biocontrol agents on Spodoptera litura and its natural predator Rhynocoris kumarii

Authors: SAHAYARAJ, KITHERIAN - Central Plantation Crops Research Institute; SUBASH, NATARAJAN - Central Plantation Crops Research Institute; ALLINGHAM, ROBERT - Fungal Centre - Netherlands; KUMAR, VIVEK - University Of Florida; AVERY, PASCO - University Of Florida; MEHRA, LUCKY - Kansas State University; McKenzie, Cindy; OSBORNE, LANCE - University Of Florida

Submitted to: Insects
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/9/2018
Publication Date: 8/14/2018
Citation: Sahayaraj, K., Subash, N., Allingham, R.W., Kumar, V., Avery, P., Mehra, L., McKenzie, C.L., Osborne, L.S. 2018. Lethal and sub-lethal effects of three microbial biocontrol agents on Spodoptera litura and its natural predator Rhynocoris kumarii. Insects. 9(3):101. https://doi.org/10.3390/insects9030101.
DOI: https://doi.org/10.3390/insects9030101

Interpretive Summary: The cutworm, Spodoptera litura (Fab.) (Lepidoptera: Noctuidae), known to attack over 120 plant species among vegetables, fruits, and ornamentals worldwide, is a serious pest of field crops in India. The indiscriminate and large-scale use of synthetic chemical pesticides to manage this pest has resulted in development of resistance against many synthetic insecticides. Thus, in order to offer growers alternates to harmful insecticides, in this study we evaluated the efficacy of three entomopathpogenic micorbes as biocontrol agents of the cutworm¸ and also assessed their impact on a generalist predator Rhynocoris kumarii, commonly found in the cotton fields. Results showed that three entomopathogenic microbes altered the feeding behavior and subsequent food consumption and weight gain, fecal pellet production and relative growth rate of the cutworm. Our findings indicate that one of the microbes, Pseudomonas fluorescens, could potentially be integrated with the R. kumarii predator in an integrated pest management program for management of cutworm in cotton agroecosystems.

Technical Abstract: Entomopathogenic microbes like, Spodoptera litura nucleopolyhedrovirus (SpltNPV), Metarizhium anisopliae and Pseudomonas fluorescens are biological agents used for the control of multiple arthropod pests. The objective of this study was to assess their effects on the biological parameters of Spodoptera litura (Lepidoptera: Noctuidae) larvae, and its natural reduviid predator Rhynocoris kumarii (Hemiptera: Reduviidae) under laboratory conditions. Results suggested that Pseudomonas fluorescens reduced the food consumption index, relative growth rate, approximate digestibility, efficiency of conversion of ingested food, and the efficiency of conversion of digested food of Spodoptera litura third instar larvae compared to prey infected with Metarizhium anisopliae and SpltNPV. Both SpltNPV and Metarizhium anisopliae caused similar mortality of Spodoptera litura life stages after 96 h of observation. To observe the effect of an infected diet on predator behavior, infected Spodoptera litura larvae were offered to the third, fourth, and fifth instar nymphs of Rhynocoris kumarii, and their prey handling time, predation rate (number/day/predator), developmental period and the survival rate was recorded. The predator Rhynocoris kumarii when offered Pseudomonas fluorescens-infected Spodoptera litura larvae consumed more prey compared to the other treatments and untreated control. The juvenile predator feeding on Pseudomonas fluorescens-infected Spodoptera litura larvae had a significantly longer developmental period (2–4 days) compared to those fed on infected with other microbial agents. However, feeding on Pseudomonas fluorescens did not affect the predator nymphal survival rate or the adult sex ratio. The outcome of this study suggests that the integration of reduviids with Pseudomonas fluorescens are compatible and potentially effective for the management of Spodoptera litura population. However promising, this combined strategy needs to be tested under field conditions to confirm the laboratory findings.