A Method for Harvesting and Shipping Live Citrus Rust Mites (Acari: Eriophyidae)

Abstract

Field populations of citrus rust mite, Phyllocoptruta oleivora Ashmead in Florida have shown resistance to dicofol (Omoto et al. 1994) and shifts in susceptibility to abamectin (Bergh et al. 1999). Resistance monitoring of eriophyid mites has not been widely practiced, limiting the availability of reference strains and technical expertise. This study was prompted when a company expressed interest in testing the susceptibility of citrus rust mite populations from Texas to their acaricide. Under normal conditions, citrus rust mites do not live long off of the host (J. C. B., unpublished data), and importing them into Florida on citrus fruit or foliage requires quarantine. However, importing mites off of host plant tissue reduces the risk of introducing a new pest or plant pathogen and does not require their quarantine. Our objective was to develop methods for removing large numbers of citrus rust mites from their host and shipping them live to other locations. Toward this end, we capitalized on two aspects of their biology. First, mites disperse by leaping from the plant and are borne away on air currents (Bergh and McCoy 1997). This behavior also occurs on excised pieces of citrus leaf as the tissue deteriorates (Omoto et al. 1994). Second, rust mites in Florida are regularly submerged in rain or dew and can withstand extended periods of immersion, remaining motionless until dried (J. C. B., personal observation). Mites were harvested from 'Sunburst' mandarin leaves from seedlings maintained in a greenhouse at the Citrus Research and Education Center (CREC), Lake Alfred, FL. To examine the effect of temperature on the harvest of mites, heavily infested leaves were cut into 2 x 2 cm pieces, which were randomly assigned to 4 groups. Each piece of leaf was impaled on an insect pin and the pin was inserted into the side of a rubber stopper. Five stoppers with leaf pieces were placed in each of four translucent plastic boxes lined with wet paper towel. Each piece of leaf was positioned about 1.5 cm above the center of a filter paper disk (Whatman No. 50, 38 mm diam.) placed on the wet paper towel. The boxes were covered and placed in lighted environmental cabinets at 20, 25, 30, and 35?C. The filter paper disks were replaced at 2-h intervals from 09:00 to 17:00 hours, and the mites on each were counted using a dissecting microscope at 20x. The mean number of mites harvested on each of three days was compared among temperatures using PROC GLM of SAS (SAS Institute 1985) and the Tukey multiple range test at the 5% probability level. To examine the effect of light on the harvest of mites, rubber stoppers with impaled leaf pieces were placed in uncovered boxes in chambers set at 30?C, with bright, overhead lights and continuous darkness. The filter paper disks were replaced at 2-h intervals from 08:00-16:00 hours and the mites were counted as described above. The t-test was used to compare the mean number of mites harvested in constant light and dark conditions on each of three days.