ADULT AND LARVAL BIOASSAYS FOR DETERMINING RESISTANCE OF SWEETPOTATO GENOTYPES TO Diabrotica SPP.

Abstract

Production of sweetpotatoes is severely limited by several insect pests, and new pest management approaches for this crop are needed. A host plant resistance research program typically depends on reliable bioassay procedures to streamline evaluation of germplasm. Thus, bioassay procedures were developed for both adults and larvae of two cucumber beetle species (Diabrotica balteata and D. undecimpunctata). For the adult bioassay, a piece of sweetpotato peel (periderm & cortex with stele removed) was embedded periderm-side up in plaster in a Petri dish, and a single adult was placed on it. Plugs were changed as needed and adult longevity was measured. A laboratory bioassay also was developed for Diabrotica larvae. Plugs (0.9 cm diameter) of sweetpotato peel or stele were placed periderm-side up into sterile microcentrifuge tubes (1.5 mL) containing 0.5 mL water-agar to prevent desiccation. One second instar Diabrotica was added to each micro centrifuge tube, which was held at 25 °C for 12 days. Surviving larvae were weighed. Diabrotica larvae grew larger when they were fed stele than when they were fed peels of any sweetpotato genotype. Larval growth was not different among genotypes for any of the stele treatments. However, larval growth on the peel of the resistant genotypes (Regal and W-375) was significantly lower than for the susceptible cultivars Beauregard or SC1149-19. These bioassays were consistent with field results, indicating that these techniques could be useful for evaluating pest resistance in sweetpotato genotypes for Diabrotica and other insect species.