Methodology for Quantifying Damage Caused by Diabrotica speciosa Larvae to Sweet Potato Tuber Roots ( Ipomoea batatas )

The commercial value of sweet potato tuber root is adversely affected by damage caused by Diabrotica speciosa , whose larvae create holes in the peel and internal tunnels in the flesh as a result of feeding activity. Traditional assessment methods based on visual scoring are subjective and constrain advances in genetic breeding programs. This study aimed to characterize and propose a quantitative methodology for measuring internal and external damage, based on approximating tuber roots to cylindrical geometry. Eight sweet potato genotypes cultivated under field conditions were evaluated. The methodology involved calculating the surface area and volume of each root modeled as a cylinder. External damage (holes) was quantified as the percentage of damaged surface area, whereas internal damage (galleries) was quantified as the percentage of damaged volume. The results demonstrated that damage is predominantly superficial, with a higher proportion of external damage. Susceptibility differed significantly among genotypes. “Beauregard,” “BRS Anembé,” and “BRS Cuia” exhibited the highest total damage indices (> 0.12%) and were classified as susceptible. In contrast, “BRS Cotinga,” “BRS Rubissol,” and “BRS Brazlândia Roxa” showed the lowest damage levels. The geometric method developed proved to be objective and reproducible, representing a substantial methodological advance for evaluating resistance to subterranean pests.