AN ABSTRACT OF THE
Stephen Dale Danielson
for the degree of Master of Science in Entomology
presented on June 22 1976,
Oregon State University
Title: DEVELOPMENT AND EVALUATION OF SEQUENTIAL SAMPLING PLANS FOR REDBACKED CUTWORM
LARVAE, EUXOA OCHROGASTER (GUENEE), IN OREGON PEPPERMINT
Field studies were conducted in 1975 and 1976 to evaluate sequential sampling plans for
the red backed cutworm, Euxoa ochrogaster (Guenee), in Oregon peppermint.
Sequential sampling resulted in reliable decisions concerning whether or not cutworm
densities were high enough to justify treatment with insecticides. The use of sequential
sampling reduced the time required to sample fields when compared with stratifiedrandom
sampling. Results indicated that location of samples was simpler and less time was
required with a systematic pattern of sequential sampling than with a random pattern of
sequential sampling. There was no advantage in taking a predetermined minimum number of
samples before decisions regarding the need for insecticide treatment were reached by
sequential sampling, and all decisions were made before the maximum number of samples were
Significant correlations were found between the number of damaged plants/ft and the number
of cutworm larvae/ft2 in most fields in 1975 and 1976. Results suggest, however, that
variation in the correlations between 1975 and 1976 may preclude the use of damaged plants
to estimate cutworm densities.
Larvae were contagiously dispersed and larval
counts fit the negative binomial distribution when population densities were above 0. 50
Negative correlations were found between
peppermint oil yields and cutworm larval densities in artificiallyinfested newly planted
peppermint plots (class I) and naturallyinfested 8yearold peppermint plots (class III).
Significant correlations were not found between larval densities and peppermint oil yields
in artificially and naturallyinfested 2yearold fields (class II).
Modified sequential sampling plans were formulated using revised kvalues and tentative
estimates of economic injury levels for fields of the three age classes: I (<
lyearold), II (2 to 5-yearsold), and III (>6yearsold).