Biological combination combats Spodoptera litura

Researchers have demonstrated that the combined use of entomopathogenic fungus beauveria bassiana and the plant compound matrine (alkaloid extracted from Sophora flavescens) causes lethal and sublethal effects in the caterpillar Spodoptera litura. In addition to reducing survival and fertility, the combination alters the insect's genetic expression, affecting metabolic pathways essential for its development.

The study compared the effects of isolated and combined applications of B. bassiana and matrina on eggs, larvae and subsequent generations of the pest.

The combination of the two agents resulted in higher mortality and a reduction in the number of emerged caterpillars, even at lower concentrations. Simultaneous use showed a synergistic effect, with mortality higher than expected from the combination of the treatments alone.

Sublethal effects

Exposing caterpillars to a mixture of the two agents prolonged the larval period, reduced the pupation rate, decreased pupal weight, and shortened adult lifespan. These effects compromised the pest's reproductive success and population growth, both in the treated generation (F0) and the subsequent generation (F1).

In the F1 generation, development time was longer. Fertility fell by up to 53,2% compared to the control group. Life expectancy also decreased, being shorter in the group treated with the combination of matrine and B. bassiana.

genetic alterations

The study used RNA sequencing (RNA-Seq) to analyze gene expression in treated larvae. Differentially expressed genes related to cuticle proteins, transcription factors (zinc fingers), hormone receptors, and proteins linked to metabolism and reproduction were identified.

The presence of matrina and B. bassiana primarily altered genes related to xenobiotic metabolism, the peroxisome pathway, and protein processing in the endoplasmic reticulum. The data indicate that the pest activates molecular mechanisms to counter the effects of the applied agents, but with visible damage to development and reproduction.

Cuticle proteins

Genes linked to cuticle formation, such as LCP-22-like, were significantly activated, suggesting a structural reinforcement response against the applied agents. However, the overload on cuticle formation may have hindered molting processes, prolonging the larval stage and compromising the transition to subsequent stages.

Hormonal reduction

Genes related to vitellogenin proteins, essential for egg development, were repressed. Juvenile hormone was also altered, with reduced expression of binding proteins (JHBPs), affecting the pest's reproductive cycle.

The combination of agents initially caused a sharp decline in these genes, followed by a compensatory response. This dynamic may explain the decline in fertility and egg-laying success observed in the experiment.

Integrated management

The integration of biological control and natural compounds shows promise. The combined use of B. bassiana and matrine interferes with the main population parameters of the pest, with direct effects on mortality and fertility, and indirect effects on hormonal regulation and gene expression.

In addition to being efficient, the strategy is environmentally safe and compatible with integrated pest management (IPM), allowing for a reduction in the use of chemical pesticides and reducing the risk of resistance.

Further information at doi.org/10.1016/j.pestbp.2025.106662