Grape Mealybug

Grape mealybug is found in many pomegranate orchards, but it only occasionally becomes a serious pest. Natural enemies usually keep grape mealybug numbers below economically significant levels.

Life Cycle

Grape mealybug females lay several hundred yellow to orange eggs in white, cottony egg masses that are typically located on the trunk under bark. The grape mealybug has two generations a year and usually overwinters in the egg stage. Just before or after budbreak in March, the eggs hatch and most of the crawlers move out to young shoots, where they nestle between the leaf petioles and the shoots. In late May to early June, mealybugs begin returning to the trunks where they mature and immediately begin depositing eggs.

The second generation hatches in early June through early July and the crawlers begin migrating to leaves and fruit. Many can be found in the sucker growth at the base of trees. Second-generation grape mealybugs mature and lay eggs under bark or on fruit beginning in August. If there is no fruit, they return to the trunks and lay eggs that will overwinter.

Appearance

Crawlers are light yellow to orange-brown and initially free of a waxy cover, but they soon begin secreting wax. Adults are about 0.2 inch (5 mm) long, flat, oval shaped, and have a white waxy covering with wax filaments sticking out from the circumference of the body. Longer filaments from the posterior end make these mealybugs appear to have "tails."

Damage occurs when the mealybugs settle where two fruit touch, or inside the calyx of the fruit. Rot or discoloration can occur where the mealybugs deposit honeydew. Sometimes rot can start inside the calyx and spread to the interior of the fruit. Mature mealybugs or egg masses hidden in the calyx may also cause culling or could be missed and reach the consumer.

Chemical control is best achieved with long-residual pesticides. Natural enemies often reduce the grape mealybug in pomegranates to numbers that are not economically significant.

Grape mealybug is attacked by a complex of parasites and predators in pomegranates. These natural enemies are often capable of providing sufficient control alone or when integrated with pesticide applications.

The parasites of grape mealybugs are all wasps in the family Encyrtidae. Parasites such as Acerophagus notativentris and A. angelicus produce multiple generations for each generation of the mealybug. Larger mealybugs host multiple parasites, and adult mealybugs may host as many as 8 to 12. A larger parasite, Chrysoplatycerus splendens, attacks adult mealybugs before they lay eggs. Parasitized mealybugs, called mummies, are yellow and the emergence holes may be seen with a hand lens.

Several predators feed on mealybugs. The predaceous gall midge Dicrodiplosis californica (Cecidomyiidae) feeds on all stages of mealybugs and is a key predator in the San Joaquin Valley. The adult resembles a small mosquito. The maggot starts out white and becomes red as it feeds. So far, this midge has only been observed in pomegranates near vineyards. It has a life cycle of about one month and is active in grapes from May until at least September.

A tiny brown lady beetle, Nephus sordidus (Cocinellidae), also feeds on all stages of mealybugs. The waxy larvae look superficially similar to mealybugs.

Green lacewings (Chrysopidae) are generalist predators that feed on mealybugs in addition to aphids and many other pests, contributing to the control of mealybugs in pomegranate. Eggs are laid on stalks, larvae are described as "tiny alligators", and the pupae surround themselves with round white cocoons.

Thinning fruit so none are touching can reduce mealybug damage.

Biological and cultural controls are acceptable in organically managed pomegranate orchards. The neem tree extract, azadirachtin, is effective on immature grape mealybugs.

Grape mealybugs first occur in isolated aggregations before spreading throughout the entire orchard. They should be monitored at different times in the season to gauge their numbers and also the effectiveness of their natural enemies. The larger instars, adults, and egg masses are easy to find under bark in late fall through late winter and in the spring from mid-April to early July. Also look for parasitized mummies and for predators and signs of their feeding.

Mealybugs are not tolerated on exported fruit, whereas a single mealybug on a fruit may be tolerable for some domestic markets. Multiple mealybugs where fruit touch or inside a calyx can lead to rot and discoloration. Thresholds have not been established, so monitor throughout the season and if mealybugs are observed and natural enemy numbers are low, then consider pesticide applications.

Insecticides with a long residual, such as buprofezin (Applaud), are best applied when second-generation crawlers begin moving around in mid-June. Insecticides with short residuals should be applied later, after most of the eggs have hatched, to target the exposed crawlers. Crawlers are hard to find in March, when they hide under leaf bases on the new shoots. In late June and July, they are often most abundant on sucker growth near the base of trees. Therefore, spray applications should include nozzles aimed low as well as directed at the tree.

Soil-applied products containing imidacloprid or clothianidin are effective on mealybugs feeding on leaves, but because they cannot be used during prebloom and bloom to protect bees, apply before bud elongation in early February (before February 15; this would also help control aphids).

Integrate chemical control with natural enemies. Buprofezin is soft on parasites and most predators except predatory beetles. Azadirachtin and rosemary plus peppermint oil are soft on most natural enemies.