Submitted to: Southwestern Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/7/2000
Publication Date: 9/1/2000
Interpretive Summary: Bird cherry-oat aphid infestations were sampled from hard red winter wheat fields in Oklahoma 115 times between 1997 and 1999. A statistical model for developing sequential sampling plans was constructed. Sequential sampling stop lines were calculated for economic thresholds (ET) of 3, 9, and 15 bird cherry-oat aphids per tiller. It was found that statistical models for rpresence/absence sampling explained over 95% of the variance in the number of bird cherry-oat aphids per tiller in relation to the number of tillers with one or more bird cherry-oat aphids on them. Sequential sampling plans were developed based on the presence/absence models. The models will be useful to wheat growers and crop consultants because they will make it easier and less time consuming for them to determine whether bird cherry- oat aphid infestations are high enough in a field that it is cost effective to spray the field with insecticide. Stop lines for presence/absence sequential sampling schemes are presented.
Technical Abstract: From 1997 to 1999, Rhopalosiphum padi L. (Homoptera: Aphididae), population intensity (number per tiller) was estimated on 99 occasions in hard red winter wheat fields located throughout Oklahoma. We investigated the relationship between the mean number of R. padi per tiller (m) and the proportion of infested tillers (PT). The PT-m linear model provided a strong fit for data on R. padi at tally thresholds (T) of 0, 1, 2, 3, 4, and 5. A regression model with a tally threshold of T = 0 was the most precise for classifying R. padi populations during growth of winter wheat because it explained 97% of the variation in the PT-m relationship. The parameters of this model were significantly different from previously published models, suggesting the need for a separate sampling plan for R. padi in winter wheat in the Southern Plains. Sequential sampling stop lines based on sequential probability ratio tests were calculated for economic thresholds (ET) of 3, 9, and 15 R. padi per tiller at a tally threshold of T = 0. Operating characteristic and average sample number functions were also generated. With P0 and P1 equal to +/- 16.7% of PET, and alpha and beta error rates set at 0.1, the average sample number required to reach a decision on R. padi populations varied from 112 (ET = 9) to 160 (ET = 15). Stop lines for binomial sequential sampling schemes are presented.