Studies in the Resistance of Strawberries to Mites. IV. Effect of Season on Preference or Nonpreference of Strawberries to Tetranychus urticae1

Abstract

Leaf disks from field grown strawberry cultivars ‘Dixieland,’ ‘Surecrop,’ and ‘Citation’ and clones of Ky 22-61-9 and Ky 17-61-15 were utilized in laboratory studies to observe the influence of season on the acceptability of foliage to Tetranychus urticae Koch. Preference and non preference responses were measured by number of female mites active and trapped in a sticky barrier ringing the leaf disk. Fecundity also was measured to observe possible manifestation of antibiosis. Foliage was generally attractive to the mites in spring and early summer but not during July and August. Foliage was again attractive to the mites in September but reverted to a relatively unattractive condition in October and November. Cultivars Dixieland, Surecrop, and Citation were significantly preferred over Kentucky clones 22-61-9 and 17-61-15. The basis for resistance of these selections to mites apparently precluded antibiosis as a factor. A lack of tolerance was apparent in Citation; this cultivar appeared to be suffering from a deficiency of water when injured by mites. Generally, resistance was manifested as a behavioral response of the mites to some component of the leaf disk that either attracted or repelled them; the variables were strawberry selection and seasonal influcnce on the plant.