Epizootic of Acalitus vaccinii (Acari: Eriophyidea) Caused by Hirsutella thompsonii on Southern Highbush Blueberry in North-Central Florida

Abstract

The blueberry bud mite (BBM), Acalitus vaccinii (Keifer), is gaining importance as a pest of southern highbush blueberries. During a BBM population development study in a north-central Florida location, an epizootic was observed, and the mesothermic acarine mycopathogen, Hirsutella thompsonii (Fisher), was identified as the causal organism. In order to better understand the progression of an epizootic resulting from H. thompsonii ,the area was extensively sampled from Mar 2007 until Apr 2008. Terminal buds of the following developmental stages were collected, as follows: (1) tightly closed buds, (2) symptomatically swollen and reddened buds, and (3) separating or opened buds. A red food coloring staining technique commonly used to stain phyto-parasitic nematodes in or on roots was used to improve the visibility of the microscopic mite. Within 1 year, the population declined from 50% of the flower buds infected (up to 2,000 BBM per bud) to less than 5% of the flower buds infected (about 20 BBM per bud). During the summer, fall, and winter months, the preferred flower buds are scarce, causing low numbers of BBM to colonize less favorable leaf buds. At this time, infection by H. thompsonii remained above 50%. In months with average temperatures below 25°C (Dec through Mar), the frequency of the disease was reduced to 50% and less, allowing the BBM population to recover slightly.