Phenacoccus aceris Signoret
-- Elizabeth H. Beers
Apple mealybug on woolly apple aphid root gall (E. Beers, April 2006)
Much of the recent literature on apple mealybug concerns its role as the vector of little cherry virus (specifically, little cherry virus 2). The spread of the virus is regulated in British Columbia, which was first found in 1933. This virus was widespread and devastating in Kootenay cherry growing region. While propagation is thought to be the most common form of spread, control of apple mealybug is also specified.
This pest is currently fairly rare in Washington orchards, but where is occurs, it may be quite abundant. Although the host range includes all tree fruits, recent finds (past 10 years) have been in apple orchards, several of which were under organic management. Known Washington populations occur in Okanogan, Douglas, Chelan, and Grant counties.
Despite the common name of “apple” mealybug, this insect is by no means a specialist. The host range is very broad, including all deciduous fruit and nut trees (apple, cherry, pear, plum, apricot, filbert), small fruits (grape, currant, gooseberry, blueberry) many shade trees (maple, oak, birch, willow, ash, linden, elm, mountain ash) and various ornamentals (cotoneaster, hawthorn, quince, spirea). The alternative common name, the polyphagous tree mealybug, is more indicative of this broad host range.
Apple mealybug eggs (closeup) (E. Beers, June 2007)
Eggs: The eggs are oval, ca. 0.3 mm long, and lemon yellow in color. Eggs are laid in ovisacs or nests consisting of dense cottony material covering a mass of separate eggs. The nests are 4-9 mm long, 1-3 mm wide, and can be found on the trunk, twigs, or leaves of apple. The ovisacs contain up to several hundred eggs. Apple mealybug nests can be distinguished from grape mealybug nests by their appearance: the grape mealybug is a loose, cottony mass, whereas the apple mealybug’s nest is a well-defined cottony cylinder.
Nymphs: The first instar nymph is lemon yellow like the egg, and about the same size (0.3-0.4 mm), but with bright red eyes. Nymphs remain in the nest for a while, and gradually disperse to nearby plant tissues. Soon after they begin feeding, they develop the “mealy” coating (a granular white waxy covering) waxy filaments at the caudal end that is typical of mealybugs. This is well developed in later instars.
Adults: The adult female is 3-4 mm long, with a sage green body color visible through the white waxy coating. The “tails” on the caudal end of the mealybug are shorter than those of grape mealybug, and the body color (green vs pale purple) distinguishes it from grape mealybug, the most common mealybug pest in Washington tree fruits. The male is a typical of the Coccoidea, winged and relatively delicate.
Apple mealybug nymphs by leaf midvein (E. Beers, June 2007)
Apple mealybug females and nests on apple twigs (E. Beers, May 2007)
Apple mealybug nest (closed) (E. Beers, May 2007)
(E. Beers, August 2007)
Sucking sap will to some exent devitalize the tree, although this is probably the least of management concerns. Like most sap-feeders, this insect produces honeydew (a high-sugar fluid excrement) that can serve as a substate for sooty mold. The production of honeydew which can drip on fruit is of more concern, and more likely to require control. In addition, apple mealybug can also directly infest and feed on fruit, possibly becoming a direct pest or quarantine concern.
Apple mealybug mummy (parasitized); with ovisac removed (upper)and with ovisac intact (lower). Note the adult parasitoid's exit holes in the ovisac. (E. Beers, July 2007)
Information on the natural enemy complex in Washington is scarce. A parasitic wasp (probably an Anagyrus sp) was found attacking a heavy infestation of apple mealybug in an organic orchard. A high percentage of the overwintering generation was parasitized. Interestingly, the female mealybug could lay viable eggs despite being the host for one or more adult parasitoids. The females and males of this parasitoid species have very different appearances, and may be mistaken for separate species. Adult parasitoid emergence occurred about the same time as egg hatch of the mealybugs.
British Columbia Ministry of Agriculture and Lands. Apple mealybug, Phenacoccus aceris (Signoret).
British Columbia Ministry of Agriculture and Lands. British Columbia Ministry of Agriculture and Lands. 2007. Little cherry disease in British Columbia.
Chachoria, H. S. 1967. Mortality in apple mealybug, Phenacoccus aceris (Homoptera: Coccidae), populations in Nova Scotia. The Canadian Entomologist 99: 728-730.
Eastwell, K. C., and M. G. Bernardy. 2001. Partial characterization of a closterovirus associated with apple mealybug-transmitted littel cherry diseas in North America. Phytopathology 91: 268-273.
Gilliatt, F. C. 1935. A mealy bug, Phenacoccus aceris Signoret, a new apple pest in Nova Scotia. The Canadian Entomologist 67: 161-164.
Gilliatt, F. C. 1936. Observations on the mealy bug, Phenacoccus aceris Sig. The Canadian Entomologist 68: 133.
Gilliatt, F. C. 1939. The life history of Allotropa utlilis Mues., a Hymentoperous parasite of the orchard mealy bug in Nova Scotia. The Canadian Entomologist 71: 160-161.
Kozar, F., L. M. Humble, R. G. Foottit, and I. S. Orvos. 1989. New and little known scale insect (Homoptera: Coccoidea) from British Columbia. Journal of the Entomological Society of British Columbia 86: 70-77.
Madsen, H. F., and P. J. Proctor. 1982. Insects and mites of tree fruits in British Columbia, pp. 1-70. Ministry of Agriculture and Food, Victoria, B.C.
Marshall, J., and A. D. Pickett. 1944. The present status of the apple mealybug, Phenacoccus aceris Sig., in British Columbia and Nova Scotia [Note]. The Canadian Entomologist 76: 19.
Marshall, J. 1953. A decade of pest control in British Columbia. Proceedings of the Entomological Society of British Columbia 49: 7-11.
Muesbeck, C. F. W. 1939. A new mealybug parasite (Hymenoptera: Scelionidae). The Canadian Entomologist 71: 158-160.
Raine, J., R. D. McMullen, and A. R. Forbes. 1986. Transmission of the agent causing little cherry disease by the apple mealybug Phenacoccus aceris and the dodder Cuscuta lupuliformis. Canadian Journal of Plant Pathology 8: 6-11.
Turnbull, A. L., and D. A. Chant. 1961. The practice and theory of biological control of insects in Canada. Canadian Journal of Zoology 39: 697-753.