Density and distribution of the flat mite (Brevipalpus yothersi) (Acari: Tenuipalpidae) on four Hibiscus varieties: do leaves tell the full story?

The flat mite, Brevipalpus yothersi (Baker, 1949) is widely distributed in the southern United States. This mite is associated with a citrus leprosis virus ((CiLV-C2) Cilevirus colombiaense strain hibiscus) infecting ornamental hibiscus (Hibiscus rosa-sinensis) in Florida and Hawaii. Because hibiscus is a highly traded ornamental plant, CiLV-C2 has the potential to spread. In laboratory experiments, the abundance and distribution of B. yothersi were studied on four varieties of tropical hibiscus. Plants, grown from cuttings, were infested with female mites, and held in environmental chambers (25 °C, 75% RH). After 3 months, the plants were divided into strata representing the top, middle and bottom of the plant. All mites (including eggs) found on the leaves and woody parts (main stems and side branches) were counted, and the surface area of each part calculated. The number and surface area of leaves and woody parts varied between hibiscus varieties; however, the differences between varieties with respect to total number of mites/plant and mites/cm² were not statistically significant. There were twice as many mites on the woody parts than on the leaves. Most mites were found in the bottom stratum of the plants, and they showed an aggregated spatial distribution. The implications of mite distributions for assessing population sizes of B. yothersi were analyzed with the purpose of optimizing sampling without damaging the plant. The efficient sampling protocol developed is an important tool for managing the vector and thereby the disease.