Blueberry Bud Mite, Acalitus vaccini (Keifer) on Southern Highbush Blueberry in Florida1
The blueberry bud mite (blueberry bud mite), Acalitus vaccinii (Keifer), is an important pest of Vaccinium spp. Lowbush, highbush and rabbiteye blueberries are known hosts to this mite. It was first described by H. H. Keifer in 1939 as Eriophyes vaccinii Keifer, but had caused considerable damage in cultivated blueberries in North Carolina for several years previously (Fulton 1940). This publication provides some guidelines for the recognition and control of the blueberry bud mite.
The blueberry bud mite is common throughout its range in eastern North America among Vaccinium spp. from Canada to Florida, and among blueberry plantings in the mid-west including Michigan, Ohio, and Indiana (Isaacs et al. 2004).
The blueberry bud mite belongs to a group of microscopic mites known as eriophyid mites. Eggs are about 55 microns long, and 35 microns thick, colorless or clear to slightly whitish and translucent. Late in development the embryo becomes evident through the cuticle. Protonymphs are about 100 microns long, about 35 microns thick, oblong, transparent and colorless to whitish. Deutonymphs are about 150 microns long, about 40 microns thick, and of similar shape and color (Figure 1). Adults are about 200 microns long, cigar-shaped, of worm-like appearance, transparent and colorless to whitish. Typical for eriophyids, the two body regions are the mouthparts or stylet-like chelicera (gnathosoma), and the rest of the body (idiosoma) with two pairs of short and chunky legs bunched toward the wider head end. The idiosoma resembles the abdomen of an insect, and has several pairs of sensory setae projecting from it.
Like other eriophyids, all four life stages of the blueberry bud mite live together in large clusters and reproduce rapidly within the scales of the blueberry bud. At 19°C, 15 days are required from oviposition to the adult stage. The female is known to lay up to 200 eggs (Baker and Neunzig 1970). In Florida and other south-eastern states, the population has been observed to peak as early as February then decline during the hot summer months of June through September (Weibelzahl and Liburd 2009). Epizootics by the acarine fungal parasite, Hirsutella thompsonii (Fisher), are at least partially responsible for the decline, and multiple species of predatory mites are commonly found in the presence of blueberry bud mite (Baker and Neunzig 1970; Weibelzahl and Liburd 2009). During fall and early winter, all four life stages are present in low numbers between the preferred large and succulent scales of dormant flower buds. Eriophyids disperse primarily by air, however, dispersal by walking and phoresy through honey bees has been observed (Baker and Neunzig 1970).
Damage and Economic Importance
The mites remain almost continuously in the protective confines of the bud. Here, they feed on the epidermal region of the developing leaf, floral parts, and the developing fruit, transferring a substance or toxin, causing the tissue to become roughened and blistered in appearance (Baker and Neunzig 1970; Weibelzahl and Liburd 2009). Persistent feeding by large numbers of mites results in reddening and swelling of the base of the bud scales. Buds appear rosetted and may desiccate due to mite feeding and fail to open (Figure 2a and 2b). Flowers and berries developing from buds with few mites usually have small blisters and pimples (Figure 3). Summer generations cause retarded leaf growth, reducing the vegetative growth that impacts the following years crop. An average of 66% of bud infestation was recorded for highbush blueberries in Georgia (Cromroy and Kuitert 2005).
From January through May the presence of blueberry bud mite is relatively easy to detect by looking for the distinctive red blisters on bud scales, flowers, or fruit. From June through December, bushes exhibiting desiccated or swollen buds are more likely to harbor blueberry bud mite. The symptoms of blueberry bud mite infection are often confused with winter injury. These symptoms may be noticed first since the mites are not visible without magnification. Infestations can be confirmed by examining the scales of dissected buds under a microscope at 4O X magnification.
Because of their cryptic nature of feeding and breeding within the blueberry buds, blueberry bud mite are very difficult to control using acaricides and can be devastating to plantings if populations are allowed to develop in the fields. Hirsutella thompsonii can play an important role in regulating populations of blueberry bud mite in southern highbush blueberries in Florida (Weibelzahl and Liburd 2009). Since the full extent of the damage caused by blueberry bud mite, and the frequency of epizootics by H. thompsonii is still unknown, disease and blueberry bud mite management programs should consider H. thompsonii when selecting fungicides for foliar disease control. McCoy and Lye (1995) demonstrated that copper sprays applied in citrus, reduced the magnitude of the epizootic of H. thompsonii on citrus rust mites. Although some blueberry cultivars are less likely to be infested, there are no fully resistant cultivars identified. Recommendations for the control of blueberry bud mite are limited to pruning of older and removing of infected branches, and post-harvest application of acaricides. Reduced-risk pesticides, such as abamectin and horticultural oils, are less hazardous and perform with high efficacy against blueberry bud mite.
Baker, J. R. and Neunzig, H. H. 1970. Biology of the blueberry bud mite. Jour. Econ. Ent. 63: 74–79.
Cromroy, H. L. and Kuitert, L. C. 2005. Blueberry bud mite, Acalitus vaccinii (Keifer) (Arachnida: Acari: Eriophyidae). Gainesville: University of Florida Institute of Food and Agricultural Sciences. https://edis.ifas.ufl.edu/in343
Fulton, B. B. 1940. The blueberry bud mite, a new pest. Jour. Econ. Ent. 33: 699.
Isaacs, R., Morrone, V. and Gajek, D. 2004. Potential acaricides for management of blueberry bud mite in Michigan blueberries. Hort. Technology 14(2): 18–21.
Keifer, H.H. 1939. Eriophyid Studies V. Bulletin of California Department of Agriculture 28:329.
McCoy, C. W., Lye, B. H. 1995. Effect of copper sprays on the population dynamics of the citrus rust mite, Phyllocoptruta oleivora (Acari: Eriophyidae) and its fungal pathogen, Hirsutella thompsonii. Proc. Fla. State Hort. Soc. 108: 126–129.
Weibelzahl, E. and Liburd O. L. 2009. Epizootic of Acalitus vaccinii (Acari: Eriophyidea) caused by Hirsutella thompsonii on southern highbush blueberry in north-central Florida. Florida Entomologist 92: 601–607.