Mealybugs (Pseudococcus longispinus) are a type of unarmored scale insect.
They are soft-bodied, and unlike their armored cousins, they keep their legs (rather than losing them and anchoring in one place) and move about a bit to feed.
Mealybugs are so-called because of the powdery white wax they produce to protect themselves against predators and the elements.
This wax also serves to protect them against some pesticides. [source]
Mealybugs Vary from Place to Place
There are multiple species of mealybugs worldwide. All can be found in moist, humid settings. This is what makes houseplants such a target for them. If you get mealybugs on cactus, may be an indication you are keeping your cacti a bit too moist.
Cactus plants and succulents do not like humid settings. Overwatered cactus become weakened and are subject to infestation of mealybugs, as well as fungal, bacterial, and viral infections.
All Species of Mealybugs Reproduce Rapidly
The mealybugs that bother cactus and other plants are all juveniles or females. Male mealybugs look like little wasps. They have wings and fly from place to place to breed, but they do not eat plants. In fact, they do not have mouths. They live a very short time, and their sole purpose in life is mating.
Some female mealybugs lay eggs. Others produce live nymphs. All female and juvenile mealybugs have penetrating mouthparts, which they use to suck the juice out of houseplants, succulents, and cactus. If they are not stopped, they will reproduce rapidly and kill the host plant.
A mature female mealybug produces between 300 and 600 eggs or nymphs in its short lifetime. Even though female mealybugs only live a couple of months, they breed all year round, so generations overlap. This makes it very difficult to completely eradicate an infestation.
What Damage Do Mealybugs Do To Cactus?
There are several different species of mealybugs that attack cacti. They damage the plants by sucking out the sap or juices. This causes distortion of the cactus and can cause death.
As female mealybugs work steadily to destroy a cactus, they may also lay eggs in a mass of fluffy white wax. Alternately, they may produce live nymphs. Whether they hatch from eggs or are born live, the nymphs will crawl fairly quickly over the cactus in search of feeding places. They may make their way to plants nearby.
When the nymphs begin feeding, they also begin producing waxy white filaments that grow to cover and protect their soft bodies. At this point, they are still able to walk and move about slowly, but they don’t tend to stray far from their feeding places. You’ll see them congregated in crevices on the cactus.
Mealybugs Attract Ants
In addition to damage caused by feeding, mealybugs can damage cactus by spreading honeydew. This is excess sugar, which they excrete as a sticky substance that coats the plant and may even drip to surfaces beneath it. A coating of honeydew can become a coating of sooty mold that blocks the sun and makes it impossible for the plant to conduct photosynthesis.
Another problem with sweet, sticky honeydew is that it attracts ants. If ants discover a colony of aphids or mealybugs producing honeydew, they may gather around them to protect and “farm” them for this dependable source of food. [source]
6 Simple Ways To Tackle A Mealybug Infestation
#1 – H2O
If you find that a sturdy plant or cactus is heavily infested with mealybugs, start by blasting the pests with a strong spray of water. This will knock adults and nymphs off the plant and may even knock off eggs.
Cactus and succulents that tend to drop leaves or plantlets might not respond well to this sort of aggressive treatment, but those that don’t can benefit from it.
Mealybugs can, and often do, hide in the soil (root mealybugs)and in nooks and crannies on pots, so you’ll want to take steps that will eradicate them completely.
When you use the water blast method on a cactus, it’s a good idea to unpot the plant, wash it thoroughly (including roots), and then repot it in a new or sterilized pot using entirely clean, new, sharply draining cactus mix.
#2 – Rubbing Alcohol
Most people have a bottle of rubbing alcohol in the medicine cabinet, and this inexpensive, simple chemical is a very powerful tool against mealybugs. You can apply it to individual bugs using a cotton swab, cotton ball, or soft cloth. You can also spray it on.
Standard, 70% Isopropyl Alcohol applied full strength will not hurt your cactus, but it will penetrate mealybugs’ fluffy protection on contact and cause their swift demise.
Just remember that one application is very unlikely to be enough. Alcohol has no residual effects. It works on contact, so you should apply it once or twice a week until you are sure all mealybugs have been impacted.
Easy Mealybug Infestation Treatment
#3 – Make a Neem Oil Solution
Neem Oil contains a natural insecticide for plants called Azadirachtin, which does have a residual effect. One application will last about a week.
You can purchase Neem Oil concentrate for garden use at your local garden center or online. Read and follow packaging instructions carefully to make a diluted solution to spray on your plants and use as a soil drench to deal with mealybugs in the soil.
Generally speaking, the dilution is about an ounce of Neem Oil concentrate per gallon of water. Remove your cactus from direct sunlight when you apply this product because the oil can magnify the sun’s rays and cause burning.
If you are treating outdoor cacti, Neem Oil is a good choice because it won’t negatively impact beneficial insects. This is especially true if you use the product at dusk so that it has a chance to dry overnight before bees, butterflies and natural predator insects become active.
4. Use Soapy Water
Soaps containing vegetable oil or animal fat can be mixed with water to create a spray that breaks down mealybugs’ fuzzy defenses and smothers them. This is an effective, environmentally friendly, old fashioned solution.
Choose organic soaps such as Dr. Bronner’s Liquid Castile Soap to make your spray. Don’t use detergents because they do not contain oils.
As with Neem Oil spray, you can make soapy water spray with just a small amount of soap. Start off with about a tablespoonful per gallon of water. See how that works. If it doesn’t seem to have much impact on the bugs, increase the amount a teaspoonful at a time until you hit on a good mix.
Insecticidal soap solutions are not as long-lasting as a Neem Oil solution, but they are even less detrimental to beneficial insects. Outdoors, apply at dusk to prevent sun damage. You may need to reapply every couple of days.
Spot treat a small part of your cactus before spraying the entire plant. Some cacti are sensitive to soap and water solutions.
5. Invite Beneficial Insects to Help You
If your cactus is a houseplant, you may not want to invite ladybugs into your home to eat your mealybugs, but if you have a large sunroom or similar setup, that may work fine for you.
If your cactus lives outdoors, it will benefit from the presence of regular ladybugs or the highly specialized Mealybug Ladybird (Cryptolaemus montrouzieri), which makes remarkably short work of mealybugs. [source]
Mealybug Ladybirds are shaped like regular ladybugs, but they are slightly smaller. They are also not as flashy. Instead of red wings with black polka dots, they just have plain brown wings and a modest tan head. In other words, they are all business! They can be purchased at garden centers or online.
6. Use a Mild Permethrin Solution
For the most part, mealybugs can be easily dealt with using the methods described above. If the situation gets away from you and you have a heavy infestation to deal with, you may need to mix up a mild solution of permethrin spray to treat your cactus.
Permethrin will harm beneficial insects, but it is not devastating. Like Neem Oil, you should apply it at dusk to avoid negatively impacting good bugs. On the flip side, if your mealybug infestation has attracted ants, permethrin will kill them along with the mealybugs. In fact, permethrin is effective against a wide variety of insect pests. It works by paralyzing their nervous systems. [source]
Permethrin spray has a long-lasting residual effect and is effective if applied monthly. Mix up a light solution of about one teaspoonful of 10% concentrate per quart of water. Spray your cactus liberally.
How To Control Mealybugs On Cactus?
Clearly, there are many different ways to do away with mealybugs on cactus, but prevention is the best method of control. Prevent mealybug infestations by quarantining all new plants for at least 2 weeks before introducing them to your collection.
Starting out with a good blast of water and repotting new plants into fresh soil and clean containers is also helpful.
It’s a good idea to examine your cactus frequently, even if you don’t think mealybugs are present. Vigilance is an excellent defense against mealybugs.
If you catch the infestation early on, you can easily remove them manually and wash them off with water, but you’ll still need to keep a close eye on your cactus to do away with any second-generation stragglers that might turn up.
Just a few mealybugs can be done away with by wiping them off with a damp cloth and/or saturating them with rubbing alcohol. You can either spray it on or touch the little offenders with a cotton swab soaked in Alcohol.
If your infested cactus is part of a collection, examine all of your plants for mealybugs. It won’t hurt to go ahead and treat them all, even if they don’t seem to be infested.
Separate any infested plants from the rest, and wipe down all surfaces with soap and water followed by rubbing Alcohol.