What are mealybugs and what do they look like?
Mealybugs are closely related to scale insects but do not produce a hard, protective covering. Instead mealybugs produce soft waxy secretions giving them a white, fluffy (or "mealy") appearance from whence they get their name. Immature mealybugs (nymphs) are soft-bodied with few distinguishing features. In fact, to the untrained eye they don't really look like insects at all. They are small (less than one quarter inch) oval-shaped blobs with body segmentation usually apparent when looked at under magnification. The first nymphal stage, which hatches from the egg, is called a crawler, because unlike the other nymphal stages, they have well-developed legs and antennae. Crawlers are the primary means of mealybug dispersal, moving from one spot to another on the plant and they are easily spread by wind (as well as on farm equipment). Adult male and female mealybugs are completely different from each other. Adult females are wingless with few distinguishing features, looking just like nymphs only bigger, while adu lt males are much smaller, barely visible without a hand lens, have wings and well developed legs and antennae. Furthermore, adult males lack functional mouthparts, so they do not feed. Their role in life is to fly and find a female with which to mate.
Female vine mealybugs release a pheromone to attract the winged males. This pheromone was recently identified and synthesized by Dr. Jocelyn Millar at UC Riverside. Currently only UC and other state personnel have access to pheromone traps that can be used for monitoring, but hopefully these traps will become commercially available.
Mealybugs have sucking mouthparts and are phloem feeders. Phloem is the tissue that is just under the bark of the vine. Like aphids and many other sucking insects, mealybugs must take in great quantities of plant fluids, and therefore secrete a lot of liquid waste called "honeydew." Honeydew promotes the growth of a black fungus called sooty mold, so a significant infestation of mealybugs creates a black, sticky mess.
There are four mealybug species that are capable of causing economic damage to Californian winegrape vineyards: grape mealybug, obscure mealybug, longtailed mealybug and vine mealybug. Two other species, the pink hibiscus mealybug and the citrus mealybug, have the potential to become economic problems on wine-grapes but either do not occur in vineyards yet or are found infrequently on grapes.
What is the vine mealybug, where did it come from and where is it now?
The vine mealybug, Planococcus ficus, is native to the Mediterranean region. It has spread to Pakistan, South Africa, Argentina, the southeastern United States and now California. It feeds on all parts of the grapevine, including the roots, setting it apart from the other grape mealybug species, which feed on all parts of the vine except the roots. All life stages are present throughout the year. During the winter, eggs, crawlers, nymphs and adults are found under the bark, within developing buds and on roots. Most are found on the lower trunk near the soil and on roots.
as temperatures warm in the spring, vine mealybug numbers increase and become more visible. By late spring and early summer they have moved to all parts of the vine. When looking for vine mealybug infestations, look for white fluffy material on and under bark, on canes and in bunches, and also look for copious amounts of honeydew, which gives bark a water-soaked appearance. Vine mealybugs produce much more honeydew than do the other mealybug species and heavy infestations produce cone-shaped deposits that look like candle wax or little stalactites. Another distinguishing feature is that the other three species have a "tail" that is created by elongated waxy filaments, while this is not elongated on the vine mealybug.
The vine mealybug was first found in California in 1994 on table grapes in the Coachella Valley. It spread to southern Fresno County in 1998. In 2000 and 2001 it was found in several vineyards in the Central Coast region in Santa Barbara and San Luis Obispo counties. In August of this year a vineyard in Sacramento County was found infested with vine mealybugs. Within two weeks of this find, vine mealybug-infested vineyards were found in Sonoma and Napa counties, too. Infested vineyards have also been found in the Clarksburg area in Yolo County.
The sudden recent spate of findings begs the questions, "Why does the vine mealybug seem to be spreading quickly all of a sudden, and how is it spreading?" Some of these infestations have most likely been present for more than one year and are just now becoming noticeable. Until a vine mealybug infestation gets large enough to produce noticeable amounts of honeydew it is not easy to find.
Regarding how it is spreading, experts feel that the most common way it has reached winegrape vineyards in Northern California is on the roots of potted grape vines that were grown in vine mealybug-infested areas in the southern San Joaquin Valley. The move from Coachella Valley to southern Fresno County was thought to be via contaminated farming equipment.
Damage caused by the vine mealy-bug is similar to, but more severe than that caused by other mealybug species. Grape bunches on infested vines become a sticky, sooty mold-infested mess. More importantly, heavy infestations of vine mealybugs severely stress vines and significantly reduce yield (Dr. Kent Daane, pers. comm.).
How can vine mealybugs be controlled?
Several types of insect natural enemies prey upon the vine mealybug. The most important appears to be a parasitic wasp, Anagyrus pseudococci, which has achieved up to 20% parasitism in some vineyards in the Coachella Valley. A. pseudococci was introduced throughout California in the 1940s to control citrus mealybug. Dr. Dan Gonzalez at UC Riverside has been doing research on new strains of A. pseudococci that may be better adapted to the environmental conditions in the Coachella and San Joaquin valleys. He also introduced Leptomastidea abnormis, another species of parasitic wasp that attacks vine mealybugs.
The presence of mealybug "mummies" is evidence of parasite activity. Mummies are the dead outer skins of parasitized mealybugs that remain after the parasite has developed inside the mealybug. Mummies are hard shells, usually round or oval and somewhat puffed-up looking. There will be one or more perfectly round holes in the mummy if the wasp parasites have emerged.
Other insects also attack vine mealybug, such as brown lacewings, minute pirate bugs and a species of lady beetle called the mealybug destroyer (Cryptolaemus montrouzieri). The larvae of the mealybug destroyer resemble mealybugs themselves because they are covered with waxy filaments, too.
Ants are associated with vine mealybug colonies because they are attracted to and feed on the honeydew. Ants are a big problem in vine mealybug management because they move mealybugs from one place to another and chase away parasites and predators.
The most important cultural pest management strategies are directed at keeping vine mealybugs from moving from an infested vineyard to a noninfested one. Infested leaves, bunches and bits of cane can travel on farm equipment from one site to another. It is extremely important that all farm equipment used in an infested vineyard is cleaned before it leaves the site. Vine mealybugs can also be transported on clothing. Therefore vineyard workers should not move from an infested vineyard to a noninfested one on the same day.
Vine mealybug management is very problematic. Ants interfere with natural enemies so that untreated populations sooner or later reach unacceptable levels. Furthermore, the vine mealybug is difficult to control with insecticides because many individuals are found underneath the bark, on the roots or on other protected areas on the vine. So far, UC research has shown that the most efficacious treatment is with a combination of chlorpyrifos (Lorsban) and imidacloprid (Admire). Unfortunately, Lorsban is disruptive to vineyard integrated pest management programs and Admire is expensive. For the most up-to-date information on recommended treatments visit the UC Statewide 1PM Program Web site at ipm.ucdavis.edu and look for UC Pest Management Guidelines for the vine mealybug.
The most important thing that growers and pest control advisors can do at the moment about vine mealybugs in California is to limit their spread to new areas and vineyards. Therefore be on the lookout for anything that might resemble a vine mealybug infestation and bring it to the attention of your farm advisor and your county Agricultural Commissioner's Office. All the mealybug species resemble each other to the untrained eye, so it is very important that an expert is brought in to identify the mealybug species involved.
The following resources were used in writing this column and contain more detailed information: Godfrey et. al. 2002. "Mealybugs in California Vineyards," Univ. Calif. Agric. Nat. Res. Publ. 21612; Peacock, et. al. "Vine mealybug: A serious new pest in the San Joaquin Valley," Univ. Calif. Agric. Nat. Res. Publ. IPM6-00 at b://cetulare.ucdavis.edu/pubgrape/ipm600.1 and UC Pest Management Guidelines-Vine Mealybug at pm.ucdavis.edu/PMG/r3023 01911 html.
RELATED ARTICLUS: Citrus Pest Now After Grapes
The citrus peel miner, formerly a problem strictly for citrus growers in Kern County, Calif., has been branching out to damage other crops including grapes. Entomologists say this change in behavior may be for one of two possible reasons: a new species of citrus peel miner may have entered California's Central Valley or there may be a cyclical, 10-to 15-year population explosion of the insects.
No chemicals are effective to control the pests, although the wasp Cirrospilus coachellae is a natural parasite. The wasp was released in 40 Kern and Tulare County citrus orchards in 2001 and is expected to spread throughout the San Joaquin Valley within one to two years.
The citrus peel miner has shown a preference for large-berried table grape varieties such as Red Globe, but may attack other varieties as well. In Vineyards it attacks shoots, leaf petioles, tendrils, bunch rachis and berries. Vines near citrus, cotton and bean fields may be at high risk. Morning glory and purslane weeds should be removed from vineyards, because they, too, are attractive to the pest.