Foliar-Feeding Mealybugs

Mealybugs (family Pseudococcidae) develop through three life stages: egg, nymph, and adult. Adult females appear grayish to whitish and are soft-bodied, wingless, and about 1/20 to 1/5 inch long. Females and settled nymphs are elongate to ovoid, segmented, and covered with pale, powdery wax of varying thickness that at least partly obscures the body of females and older nymphs. Many mealybugs have wax filaments around their margin that help distinguish among species; characteristics are based on the relative length of filaments, mostly those at the rear end as summarized in the table Distinguishing common mealybugs in floriculture and ornamental nursery crops. Mealybugs often occur where foliage is dense or touching and in other partly hidden areas of plants. Some species feed on roots.

Adult male mealybugs are rarely seen and do not feed. Males are tiny and delicate, gnat-like with one pair of opaque wings and long antennae. The body is commonly brownish to reddish.

Mealybugs can be confused with adelgids and woolly aphids that sometimes infest leaves and shoots of woody perennials. Aphids can be distinguished by their pear-shaped body and long legs, and those that produce pale wax generally occur only on deciduous broadleaved plants. Adelgids also produce cottony wax-like material but infest only conifers, which are not commonly infested by mealybugs.

Generally it is not necessary to determine the species of mealybug because cultural practices, exclusion and sanitation, and pesticides are similar for all. However, where biological control will be employed, correct identification of the species is necessary.

Mealybugs generally are a problem only on perennial or long-term crops. They suck phloem sap and excrete sticky honeydew, which supports the growth of blackish sooty mold and attracts ants. Mealybugs tend to feed in groups, and their waxy bodies and white egg masses (of some species) on leaves and green shoots can be especially apparent. Feeding causes leaves to yellow and sometimes drop prematurely. Mealybug feeding on new growth can cause leaf and shoot distortion. Infested plants may decline in vigor and young plants may be killed.

Inspect plants regularly for mealybugs and signs of their presence. Management is easier and more effective if infestations are detected and managed early before crop foliage becomes dense, mealybugs and their protective wax become abundant, and the crop is damaged. Practice excellent exclusion and sanitation to avoid introducing mealybugs into production areas, and when they are present to help avoid their spread.

If not disrupted, resident parasitic wasps and predators commonly control longtailed mealybug and sometimes certain others. Avoid application of broad-spectrum, persistent insecticides for any pests where feasible, especially early in crop production cycles. Control dust that disrupts the activity of many natural enemies, and control ants that carry mealybugs among plants and protect them from natural enemies. See BIOLOGICAL CONTROL and Protecting Natural Enemies and Pollinators for more suggestions.

The mealybug destroyer (Cryptolaemus montrouzieri), a lady beetle, is commercially available for control of mealybugs that produce egg sacs. The beetle lays eggs in the egg masses of their host; the progeny (larvae) of these provide the control and feed on all mealybug life stages. For best results, release adults of the mealybug destroyer where mealybug egg masses are present. Mealybug destroyers will also control certain other ovisac-forming insects, such as green shield scale. Since longtailed mealybug females give live birth to young and produce no egg masses the mealybug destroyer will not reproduce or be effective against this species. Releases of mealybug destroyer must begin early during the crop's production cycle. Where mealybug eggs are available as food, female Cryptolaemus lay numerous eggs. The larvae resemble mealybugs, but mature to a larger size (1/4 to 1/2 inch), and when not feeding can move quickly (unlike mealybugs). If carefully observed, their chewing mouthparts can be seen.

Parasitic wasps specific to certain mealybug species can also be released. The Leptomastix dactylopii parasite has been effective for control of citrus mealybug in greenhouses and is sometimes released in combination with the mealybug destroyer. See Natural Enemy Releases for Biological Control of Crop Pests for more information.

Practice excellent exclusion and sanitation. Mealybugs readily spread as crawlers (mobile, first instars) on contaminated containers, equipment, tools, workers, and the wind and move among nearby plants and surfaces before settling to feed. Mealybug adults and nymphs can also walk slowly throughout their life and spread within the crop.

Carefully inspect new plants and temporarily place new stock in quarantine or isolation until it is apparent that they are not infested; re-inspect new plants to ensure they are pest free before moving them into production areas. When disposing of infested plants, place them in covered containers to prevent them from becoming sources of infestation for other plants.

Brief exposure to dry heat or hot water can disinfest many crops of insects and certain plant pathogens. Carefully control the conditions as recommended. Before extensively employing heat, test the method on a small portion of each particular variety to ensure plants are not sensitive. See Some Pests Controlled by Heat Treatment of Plants for more information.

Biological control, including the mealybug destroyer lady beetle and parasitic wasps, and cultural controls are organically acceptable management methods. Certain formulations of the botanicals azadirachtin (e.g., Azatin) and neem oil, the microbial Beauveria bassiana, and narrow-range oil (Organic JMS Stylet Oil) are organically acceptable.

Regularly inspect plants for honeydew, sooty mold, and whitish wax. Look for ants, which can indicate mealybugs or other phloem-sucking insects are present. Concentrate monitoring for mealybugs on the basal stems, branch crotches, underside of foliage, and where plant parts touch. Sticky tape traps wrapped around infested stems can be useful to time insecticide applications for when crawlers are active and to compare mealybug activity before versus after pesticide application. Pheromone-baited sticky traps that attract male mealybugs are available for monitoring males of at least the grape mealybug (Pseudococcus maritimus) and vine mealybug (Planococcus ficus). Contact trap suppliers to learn what products are available and how to use them.

Early instars, especially crawlers, are most susceptible to insecticides. Crawler emergence generally occurs over a shorter time period earlier in the growing season; making treatments then can reduce the total number of warranted applications. To monitor crawler activity for timing applications or evaluating results, use traps of double-sided sticky tape wrapped around twigs in late winter placed near where egg masses or groups of mealybugs are observed. Since not all crawlers emerge at the same time, multiple insecticide applications may be needed depending on the crawler emergence period and the pesticide used. See Sticky Tape Traps for how to effectively use this technique.

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