Beyond the Mortality Effect: Spodoptera frugiperda Multiple Nucleopolyhedrovirus Promotes Changes in Feeding and Inhibits Larval Growth and Weight Gain in Fall Armyworm

TL;DR

This study shows that a virus infecting fall armyworm larvae not only kills them but also reduces their growth and feeding at low concentrations.

Contribution

The study reveals sublethal effects of SfMNPV on larval growth and feeding behavior in fall armyworm.

Findings

Low concentrations of SfMNPV inhibit larval weight gain and body growth.

Leaf consumption is reduced at low SfMNPV concentrations but increases at higher concentrations among surviving larvae.

The virus's impact on fall armyworm extends beyond mortality to include developmental and feeding dysfunctions.

Abstract

Infection by Spodoptera frugiperda multiple nucleopolyhedrovirus (SfMNPV) profoundly alters the physiology of S. frugiperda (Lepidoptera: Noctuidae), promoting molecular responses that activate genes related to cellular defense. These responses demand substantial energy and lead to feeding dysfunction. Knowledge about the effects of SfMNPV on weight gain and leaf consumption rate is still incipient; in this context, we evaluated the survival rate, weight gain, leaf consumption rate, and body size of S. frugiperda exposed to different concentrations of SfMNPV. A completely randomized design was used in the laboratory. Treatments consisted of SfMNPV from the commercial product Cartugen®, diluted at different concentrations and applied on a Petri dish: 9.00 × 103, 1.80 × 104, 3.75 × 104, 7.50 × 104, 1.35 × 105, 2.25 × 105, and 3.75 × 105 occlusion bodies (OBs)/mL. Fifty first-instar larvae were used per treatment. The median lethal concentration was estimated at 1.32 × 105 OBs/mL (95% confidence interval = 1.22 × 105–1.43 × 105 OBs/mL). Nonlinear regression analysis of sublethal effects showed that the expected weight of the control (W0), the angular parameter (B), and the effective concentration capable of reducing larval weight by 50% (EC50) were 47.40 mg, 1.42, and 1.16 × 104 OBs/mL, respectively. Leaf consumption was inhibited at lower concentrations and increased at higher concentrations among surviving larvae, and larval growth (measured by head diameter, body length, and body width) was lower when larvae were exposed to SfMNPV than in the control. Our data suggest that SfMNPV at low concentrations causes dysfunctions that prevent normal development in surviving individuals, resulting in reduced consumption rate, body growth, and weight gain. Overall, our analysis indicates that the impact of SfMNPV extends beyond mortality; low concentrations can affect larval growth and feeding consumption rate in S. frugiperda.

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