Predator [Metaseiulus occidentalis] — Prey [Pronematus spp.] interactions under sulfur and cattail pollen applications in a noncommercial vineyard

The effect of sulfur and cattail pollen applications on predatory and phytophagous mite species was investigated in a noncommercial vineyard for a full growing season. Populations of tydeids (Pronematus spp.) increased earlier in pollen and control plots that received no sulfur than in plots treated 4- and 10-times with sulfur. Predatory mite populations [Metaseiulus occidentalis (Nesbitt)] responded quickly to this increase in tydeid numbers in all plots. However, peak densities achieved by this phytoseiid in the pollen and control replicates (1.6/leaf and 1.1/leaf, respectively) were twice that attained in the sulfur treated plots (0.6/leaf), although comparable numbers of tydeids were present in all plots. Further evidence of the inimical effect of sulfur was provided by tarsonemid populations which increased quickly in late summer in those plots receiving no sulfur, but increased only slightly in plots treated with sulfur. The numbers of tetranychid mites remained extremely low throughout the season. In bud samples taken during the winter 1971–72, the numbers ofM. occidentalis found per bud, as well as the number of buds in which they were present, were similar in all treatments, except the 10-treatment sulfur plots where a much lower overwintering population was found. A close ecological relationship betweenM. occidentalis and tydeid mite species was revealed by this study. The data suggest that the maintenance of a tydeid —M. occidentalis predator—prey interaction throughout the year, and especially in the late fall months to allow a greater number of predators to enter overwintering sites, would contribute to improved spider mite control.