Chemical composition and toxic effects of an ethanolic extract of Senecio rudbeckiaefolius on Diatraea saccharalis larvae

Diatraea saccharalis Fabricius (Lepidoptera: Crambidae), known as sugarcane borer, is the most damaging pest of sugarcane (Saccharum officinarum L., Poaceae) in northwestern Argentina and it causes significant losses in sugar and ethanol production. Currently, chemical and biological controls are used, along with host plant resistance, but there is a clear trend toward adoption of integrated pest management strategies. Considering the potential environmental and health risks associated with using agrochemicals, our study focuses on utilizing bioactive natural products, specifically plant secondary metabolites. Senecio rudbeckiaefolius Meyen & Walp (Asteraceae) is a perennial shrub found in southern Peru, Bolivia, and northwestern Argentina, valued for its use in traditional medicine. The main compounds of the genus Senecio are sesquiterpenes, with some species containing pyrrolizidine alkaloids (PAs), known for their harmful effects on herbivorous insects and vertebrates. Plant extracts exhibit several modes of action, encompassing confusion, feeding deterrence, growth regulation, insecticidal, and repellent effects. Our goal was to analyze the chemical composition of an ethanolic extract (EE) of S. rudbeckiaefolius and evaluate its lethal and sublethal effects on D. saccharalis larvae. We also investigated the potential target sites affected by the ingestion of an alkaloidal fraction from the EE (AFEE) through a midgut histological study. The main secondary metabolites identified were the PAs and phenolic compounds, with the highest concentrations found in the flowers and leaves. The majority of the PAs identified were senecionine and integerrimine. Toxicity bioassays were carried out with larvae fed on a diet supplemented with an EE of S. rudbeckiaefolius. Concentration-dependent mortality and a marked inhibition of larval growth were recorded. We described the midgut histological structure and compared it with that of AFEE-fed larvae. Various morphological changes were observed in the intestinal epithelium, especially an increase in the number of goblet cells and pronounced acidophilic secretion in the lumen. These results suggest that the EE of S. rudbeckiaefolius could be promising for D. saccharalis control.