MF3001 Mealybug

i Mealybug Management in Greenhouses and Interiorscapes Mealybugs are major insect pests of greenhouse and interiorscape environments (including conservatories) where they feed on a wide range of plants and are difficult to manage (suppress) with insecticides. Host plant range depends on the particular mealybug species but includes herbaceous annuals or perennials, foliage plants, orchids, vegetables, and herbs. Specific plants include aglaonema, begonia, chrysanthemum, coleus (Solenostemon scutel- larioides), croton (Codiaeum variegatum), dracaena, false aralia (Dizygotheca elegantissima), ficus, grape ivy (Cissus rhombifolia), marigold, poinsettia (Euphorbia pulcherrima), pothos (Epipremnum aureum), and transvaal daisy (Gerbera jamesonii). A number of mealybug species may be found in green- Figure 3. Mealybug life cycle houses and interiorscapes, but the predominant species are the citrus mealybug, Planococcus citri and the longtailed (Figure 4), and do not mealybug, Pseudococcus longispinus. In addition to these have to mate to repro- two species, which feed aboveground, root mealybugs duce (this is referred (Rhizoecus spp.) are of concern because they are extremely to as parthenogen- difficult to detect and manage with available insecticides. esis). Eggs hatch into Biology and Damage crawlers that actively move around seeking Mealybugs are elliptical in shape with white, waxy protru- places to settle and feed. sions extending from the body (Figure 1). Females are Crawlers are yellow- white, wingless and 2 to 5 mm long when full-grown, Figure 4. Long-tailed mealybugs orange (Figure 5), even- (Figure 2). Males are tually turning white af- typically smaller. Most ter each successive molt. mealybug species Once settled, mealybugs reproduce asexually progress through several (lay eggs). The typi- growth stages before cal female mealybug becoming adults. Male life cycle consists of mealybugs eventually five growth stages: an become winged indi- Figure 1. Mealybugs feeding egg, three nymphs or viduals (Figure 6), mate Figure 5. Crawler crawler stages, and with females, and die adult (Figure 3). Males after 2 to 3 days. undergo six growth Females continue de- stages including two velopment and die after pupal stages: prepupa depositing eggs. Eggs and pupa. Before adult remain protected under females die, they lay the body of the dead eggs underneath the female until they hatch body cavity. Longtailed (Figure 7). A single mealybug females give citrus mealybug female Figure 6. Winged male Figure 2. Female citrus mealybug birth to live offspring Kansas State University Agricultural Experiment Station and Cooperative Extension Service is capable of produc- mealybug populations early. Workers should wear dispos- ing up to 600 eggs. able rubber gloves when handling highly susceptible plants. Only the adult males Management and newly emerged crawlers actively Cultural Management disperse. This involves implementing practices such as weed re- Mealybugs, in gener- moval, proper fertility, and old plant material disposal. al, have a longer de- Favorable environmental conditions (e.g., temperature) and velopmental period Figure 7. Eggs plant growth may increase the mealybug population. For (egg to adult) than example, plants irrigated frequently that receive high con- most other green- centrations of a nitrogen-based fertilizer tend to be more house insect and mite pests such as aphids, spider mites, susceptible to mealybugs. Water-stressed plants may also thrips, and whiteflies. The life cycle from egg to adult takes be more susceptible to mealybugs. Furthermore, mealybug approximately 60 days, depending on temperature and host females feeding on plants receiving high concentrations of plant. The primary means by which mealybug crawlers a nitrogen-based fertilizer may lay more eggs than usual. It disperse within a greenhouse or interiorscape are wind or is also important to immediately discard heavily infested air currents, workers handling infested plants and inadver- plants, especially those that have been around for several tently transferring mealybugs to uninfested plants, water- years (“grandmother plants”), which tend to harbor mealy- ing equipment, plant leaves touching that allow crawlers bug populations. If feasible, a forceful or high-pressure to move among plants, introduction of infested plant water spray, conducted regularly (e.g., twice per week) is material, and ants transporting crawlers among plants. The effective in dislodging or removing all life stages (eggs, lateral waxy protrusions help protect mealybugs from natu- crawlers, and adults) quickly, thus preventing outbreaks ral enemies (e.g., parasitoids and predators) and promote from occurring. the spacing of individuals in a colony. Mealybugs seem Insecticide Management almost invisible during early stages of infestation, and then Factors that may impact suppression of mealybug popula- suddenly populations become noticeable, resulting in out- tions with insecticides include: breaks. It is usually too late then to implement an effective management strategy. • Mealybugs have a cryptic behavior or clumped spatial distribution, and tend to aggregate or establish them- Mealybugs cause direct plant injury by feeding on plant selves in concealed/protected areas of plants. fluids or sap in the vascular tissues—primarily the phloem or mesophyll or both—with their piercing-sucking mouth- • Frequent overlapping generations with an age structure parts. They may also inject a toxin. This may cause leaf yel- consisting of all the life stages present (eggs, crawlers, lowing, plant stunting, and wilting. In addition, mealybugs and adults) simultaneously. excrete a clear sticky liquid called honeydew, which serves • Hydrophobic (water-hating) waxy body covering repels as a growing medium for black sooty mold fungi. Mealy- hydrophilic (water-loving) insecticides. bugs are also capable of transmitting diseases, including • The mealybug life cycle and need to apply insecticides viruses. Mealybugs tend to congregate in large numbers frequently increases the development of resistance. at leaf junctures where the petiole meets the stem, on leaf undersides, on stem tips, and under the leaf sheaths of cer- • Certain insecticides may stimulate development and tain plants such as orchids and the prayer plant (Maranta reproduction of mealybugs. leuconeura). • Many insecticides are not compatible with natural Scouting enemies (e.g., parasitoids and predators) and repeated insecticide use will kill existing natural enemies. Mealybugs do not fly, except for the adult male, so they are not captured on yellow sticky cards. Visual plant The types of insecticide applications include foliar sprays inspections are the only way to detect early mealybug and those directed toward the growing medium (drench or infestations. Because of their cryptic behavior and small granule). Adult mealybugs are difficult to manage because size, scouting via visual inspections is labor intensive and they form a white, waxy protective covering that is nearly impractical. Scouting efforts should be focused on plant impervious to most insecticides. And because most insec- species highly susceptible to mealybugs. This can be done ticides have no activity on eggs (with the possible excep- by tagging a number of plants (five to 10 per plant spe- tion of petroleum-based or neem oils), at least two to three cies) and inspecting them regularly, which may help detect weekly applications usually are required to achieve satisfac- 2 tory suppression, especially when dealing with overlapping dactylopii (Figure 9). generations. The crawler stage, which does not possess a The larval stages of the waxy covering, is most susceptible to insecticides includ- mealybug destroyer ing insect growth regulators (e.g., azadirachtin, buprofezin, resemble mealybug adults and kinoprene), insecticidal soaps (potassium salts of fatty (Figure 10). Leptomastix acids), horticultural oils (petroleum-based), and possibly dactylopii females only insect-killing fungi (Beauveria bassiana). Although very attack the third instar few (if any) insecticides are able to penetrate the waxy and young adult female covering of mealybugs, those containing ethyl alcohol life stages. Both natural Figure 8. Mealybug destroyer (ethanol), such as some oil-based insecticides, may allow enemies may be effective the material to penetrate through the waxy covering, kill- in suppressing or regu- ing mealybugs. lating citrus mealybug When applying high-volume sprays, thorough coverage populations, and they can is imperative, especially when using contact insecticides, be used together under because mealybugs are commonly located in areas that are certain systems and situ- not easily accessible, such as the base of leaf petioles, leaf ations. The waxy cover- sheaths, and leaf undersides. Adding a spreader-sticker to ing of later life stages a spray solution may be helpful in improving coverage and may provide protection penetration. Table 1 lists insecticides that are registered for against these natural Figure 9. Leptomastix dactylopii use on mealybugs in both greenhouses and interiorscapes. enemies. In addition, For highly susceptible plants, it may be prudent to routine- mealybugs may encapsu- ly spray with either an insecticidal soap or horticultural oil late (smother) the eggs to prevent mealybug populations from reaching outbreak laid by the parasitoid, proportions. Also, it is essential to make multiple applica- and the cryptic behavior tions when crawlers are present

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