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AN ABSTRACT OF THE THESIS OF
Joseph Francis Cacka
for the degree of Master of Science in Entomology
presented on February 1 1982,
Oregon State University

This study of the strawberry root weevil, Otiorhynchus ovatus (L.), on peppermint, Mentha piperita (L.), in central Oregon provided biological information to assess economic importance and to develop a sequential sampling plan.

Teneral adult weevils emerged from the soil from late May until late July. Oviposition of new generation adults commenced in early July. A minimum 12 day egg incubation period was observed. Larvae were present in peppermint fields all year and were the dominant life stage from late August until midMay the following year. Pupation commenced during early to mid-May and was completed by late June. Over wintered adults were found in spring samples at densities not greater than 11.6% of the sampled population.

Developed ova were observed in the overwintered adults in late May. A carabid beetle, Pterostichus vulgar is (L.). was predaceous on larval, pupal and adult strawberry root weevils, no other predators or parasites were observed.

Fall plowing of peppermint fields increased the depth at which weevils were found the following spring. When fields are sample in midMay, a minimum depth of 15 cm is suggested for fall plowed fields and ten cm for unplowed fields.

Strawberry root weevil adults, pupae, larvae and the total of all these life stages have a clumped distribution that fit the negative binomial distribution when sufficient data were available to determine frequency distributions.

Statistically significant negative relationships were found between pupae, larvae and the total strawberry root weevil population and peppermint oil yields.

A modified sequential sampling plan was developed for the total strawberry root weevil population using a common K value (0.411) and a tentative estimate of the economic injury level (ca. 8.19 weevils/1000 cm²) .