Binomial Sequential Sampling Methods for Cereal Aphids in Small Grains

Abstract

Seventy-one samples of 200 to 400 tillers each were taken from small grain fields. An equation used to relate the proportion of infested tillers to the mean number of aphids per tiller fit the data well ( r 2 = 0.98). Although the equation was developed from pooled counts of four species of cereal aphids ( Schizaphis graminum (Rondani), Sitobion avenae (F.), Rhopalosiphum padi (L.), and R. maidis (Fitch)), it described the relationship between the proportion of infested tillers and mean number of aphids per tiller adequately for each species individually. When predictions from the equation were compared with independent data, the predicted and actual numbers of aphids per tiller were similar. Required sample sizes for estimation of the mean number of aphids per tiller with fixed average levels of precision (standard error /mean) were determined. Required sample sizes to achieve a precision level of 0.15 ranged from a low of approximately 110 tillers for intermediate aphid populations to >500 tillers for low and high aphid populations. A truncated sequential sampling plan was developed. Using this plan, from 25 to 100 tillers are inspected for the presence or absence of cereal aphids. The average number of tillers inspected to arrive at a control decision ranged from 25 to 76 tillers depending on aphid population density. The frequency of decision errors was high (approximately 0.9) for populations near the action threshold (12.5 aphids/tiller), but was otherwise acceptable.