Biological Control of Mealybugs
Mealybugs can be very difficult to control, so if only a few plants are heavily infested, it is best to destroy the infested plants to minimize further spread. Some of the more common species found in greenhouses and interiorscapes are the citrus mealybug (Planococcus citris) and the longtailed mealybug (Pseudococcus longispines). Other species include the Mexican mealybug (Phenacoccus gossypii), the Maderia mealybug (Phenacoccus maderiensis) and root feeding mealybugs (Rhizoecus spp). For more information see Managing Mealybugs in the Greenhouse on the UConn IPM website and references listed at the end of this fact sheet.
Figure 1: Adult citrus mealybug and egg mass. Photo by L. Pundt
Figure 2: Longtailed mealybug adult. Photo by L. Pundt
Biology and Life Cycle
Mealybugs are soft-bodied, segmented oval- shaped insects. Adult females are from 1/20 to 1/5 of an inch long and covered with white, powdery, waxy secretions. Their life cycle consists of an egg stage (except for the longtailed mealybug that gives birth to live young), immature stages that can move ("crawlers") and adults. Crawlers mature in about 6 to 9 weeks. Eggs hatch in 5 to 10 days, with mature females dying after egg laying. The small winged adult males do not resemble the females and their primary role is to fertilize the female mealybugs.
Early detection of mealybugs can be difficult due to their tendency to hide in protected locations. Look for white flecks or cottony residues along the leaf midribs, on leaf or stem axils, on the underside of leaves and near the base of plants. Focus on those plants that are prone to mealybug infestations such as begonia, citrus, coleus, croton, gardenia, palms, and many foliage plants. Mealybugs may also be found on the inside of containers, or in container drainage holes. Adult females may crawl off plants moving to crevices under benches where they lay eggs. Honeydew, sooty mold and the presence of ants may also be an indication of a mealybug infestation.
- Inspect incoming plants for signs of mealybugs
- Start with clean plant material
- Do not hold over "pet plants" that may be infested, and keep greenhouses as weed free as possible
- Immediately dispose of heavily infested plants
- Power wash infested benches between crop cycles
- Do not reuse pots without thorough cleaning before reuse
- Maintain proper fertility levels for the crop you are growing. High nitrogen fertility favors mealybug reproduction
Host specific parasitic wasps and generalist predators are commercially available. It is important to identify the specific mealybugs species present in order to select the most appropriate natural enemy.
The parasitic wasp, Anagyrus pseudococci, parasitizes citrus mealybug larvae. The parastitized pupa swells becoming a hard yellow brown mummy. After 1 to 5 days (depending upon temperature), the adult parasitic wasp emerges from a hole at the posterior end of the mummy. The first mummies can be seen about two to three weeks after the first release (depending upon temperatures). Optimum temperature is 76˚ F with a minimum temperature of 51˚ F. Anagyrus pseudococcus is commercially available as mummies containing the parasitic wasp pupae mixed in inert material. Consult with supplier on recommended release rates.
Tips for using Anagyrus pseudococci
- Identify mealybug species, only effective against citrus mealybug
- Release in mealybug colonies or hot spots
- Release in the early morning or evening
- Can be used with the mealybug destroyer
- Control ants before releasing
An Australian ladybird beetle, commonly known as the mealybug destroyer (Cryptolamus montrouzieri) is commercially available for use against the citrus mealybug. Cryptolamus can also feed on soft scales and aphids but prefers mealybugs. The mealybug destroyer only reproduces on mealybugs with egg masses so is not as effective against the longtailed mealybugs. Mealybug destroyer adults and larvae are predacious, seizing and consuming prey.
Adults are shiny black beetles with a reddish head and thorax. Larvae resemble mealybugs. But, the mealybug destroyer larvae are longer, and more mobile than mealybugs with longer wax threads than mealybug larvae.
Figure 3: Adult Mealybug destroyer. Photo by L. Pundt
Figure 4: Mealybug destroyer larvae. Photo by L. Pundt
Optimum conditions are temperatures between 72 and 77° F and a relative humidity of 70 to 80 %. Mealybug destroyer eggs are deposited within the egg sac of mealybugs. They are most active during sunny conditions and are less active during short winter days. Cryptolamus are most effective when mealybug density is high and can fly off in search of new prey. Cryptolamus montrouzieri are commercially available as adults packed in plastic tubes with a carrier. They have recently become commercially available as larvae that can be released among infected foliage in the evening individually on the leaves or placed in a distribution box. It is helpful to release both larvae and adults, according to Sarah Jandricic, Greenhouse Floriculture IPM Specialist OMAFRA. Larvae attack all mealybug life stages so are effective in hot spots but do not disperse very far. Adult beetles only eat mealybug egg masses, but can disperse through the crop to lay their eggs which will hatch into mealybug destroyer larvae.
Ants protect mealybugs from Cryptolamus so should be controlled before releasing these generalist predators. Consult with supplier on recommended release rates.
Tips for using Cryptolamus montrouzieri
- Release adults in the evening when vents are closed
- Gently tap beetles out of container onto foliage of infested plants
- Beetles are attracted to white, so you can place white 3 by 5 cards next to mealybug hot spots
- Release larvae in the evening among infected foliage
- It is helpful to release both larvae and adults
- Control ants before releasing as they protect the mealybugs
Green lacewings (Chrysoperla sp), are better known as a aphid predator, hence their common name,” aphid lion, “ but they can also feed upon mealybugs , whiteflies, spider mites and thrips. Lacewings are not relied upon exclusively for control, but they may help suppress mealybugs. Only the larval stage is predacious, adults feed upon pollen, honeydew or nectar. Repeated releases are often needed, but do not release the small larvae when the larger larvae are on the plants, as the larvae are cannibalistic.
Green lacewings are commercially available as eggs glued onto cards, or loose in an inert mixture of rice hulls or as larvae in small individual cells so they don’t eat each other or as adults in a cardboard tube that is screened at both ends. They are active during a wide range of temperatures (54 to 95˚ F). Consult with supplier on recommended release rates.
Figure 5: Lacewing larvae. Photo by L. Pundt
Figure 6: Lacewing adults. Photo by L. Pundt
Tips for using Chrysoperla sp.
- Release in the early morning
- Larvae are cannibalistic, so spread over a wide area
- Control ants. They will eat lacewing eggs off of cards
Ants will protect mealybugs from natural enemies, in order to feed upon honeydew, so identify the type of ant species so you can determine the best type of bait to use.
In summary, parasitic wasps, mealybug destroyers and lacewings can help suppress mealybug populations. It may be necessary to spot treat with a compatible pesticide to manage mealybugs.
By Leanne Pundt, Extension Educator, University of Connecticut, 2014. Revised 2015.
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