Some Factors Influencing the Abundance of the Predaceous Mite Amblyseius hibisci in Southern California (Acarina: Phytoseiidae)1

Abstract

Mite population surveys carried out in 3 avocado orchards from 1961 through 1963 showed that the predaceous mite Amblyseius hibisci (Chant) often attained its highest population density of the season in the spring or early summer, when mite prey densities were very low. The crawler stage of the latania scale, Hemiberlesea lataniae (Signoret), was a suspected source of food but no correlation was found between the abundance of A. hibisci and that of scale crawlers or crawler-producing females. Another suspected food was pollen. Rapid increases of A. hibisci followed the the beginning of blossoming and egg production peaks showed a close correlation with peaks in flowering intensity. In another orchard the predaceous mite population reached unusually high levels, apparently as a result of large quantities of pollen drifting from adjacent plants of Ricinus communis L. Marked population increases of A. hibisci were induced artificially by dusting caged branches with pollen at weekly intervals. Laboratory tests showed that mites confined on excised avocado leaves fed and reproduced on avocado pollen applied at an average density of only 6.6 pollen grains per square inch of leaf surface. The characteristic of pollen feeding in relation to the potential effectiveness of A. hibisci as a predator is discussed.