The study was carried out in a black oat (Avena strigosa) field cultivated under the no-tillage system in an Oxissol (Dark Red Latosol) with clay texture, in the county of Cruz Alta, Rio Grande do Sul State, to determine the size and number of soil samples for 3rd instar larvae of Diloboderus abderus (Sturm). Considering the average number of larvae/m², time required for sample extraction, and the relative net precision, the sample unit 25 x 25 cm dug to a depth of 30 cm yielded the best result. Results indicated a great heterogenicity in the distribution of the larvae; 67 (with error of 25% of the mean) and 419 (with error of 10% of the mean) sample units were necessary to give an acceptable estimate of the larval population.
Insecta; Scarabaeoidea; population; black oat; tillage system
