As a child I remember loving this weird old 1950s science fiction movie "Fiend Without a Face". It was about oval shaped creatures that attached themselves to peoples' necks and sucked out their life force. Mealybugs are the fiends without a face of plants. They suck out the plant's life force.

In this blog post I will try and demystify these fiends without faces and give people information for dealing with this annoying pest. 

Mealybugs 101

What exactly are Mealybugs?

Mealybugs, also called "mealies" for short, are insects belonging to the family Pseudococcidae. They feed on plant juices. They have a straw-like mouth-part called a stylet they use to pierce plants in order to feast on their juices. I found this creepy video of a closeup of a mealybug piercing plastic wrap with its stylet to try and get at a plant. See here. 

Mealybugs effect many different plants and cause serious damage.  They get their name from the waxy secretions that coat and protect them. Mealies are related to other pests: scale and aphids. 

Life Cycle

Mealybugs make cottony white sticky nests where they lay their eggs.  I took the following picture at the succulent house of a botanical garden which shall remain un-named. It shows adult and juvenile mealybugs and the nests:

Depending on the particular mealybug, the white nests are present on the plants or hidden at the base of the plant or on roots, but are also found in the environment the plant is in: in the soil, on the pot the plant is in and even the trays and shelving underneath the plant. Mealybugs can lay up to 600 eggs at a time, and one species even gives birth to live Mealie babies. Most mealybug species can reproduce asexually. This means that a single tiny female mealybug hiding in a plant you just bought can infest your entire collection. 

Contagion 

Mealybugs spread quickly. Many people are perplexed about how this can be because adult mealies barely move.  Recall that an adult mealie can lay up to 600 eggs. These hatch into tiny larval mealies called crawlers. The crawlers look like a small version of the adults but are not covered with white fluff and are often darker colored. Unlike the adults, the crawlers can boogie. They move fast. Their mission is to fan out and find new homes. The crawlers can travel quite a distance and will infect neighboring plants.  What can happen with an infested plant is that it will turn into a mealybug factory and continuously churn out despicable crawlers that spread out and infest neighboring plants. 

Damage

Mealybugs cause damage several ways. First, if populations get large they will literally suck a plant dry. Second, they secrete nectar which can cause sooty mold and other damaging fungi to grow. Third, they are known to transmit viruses that make plants sick. For example, a big problem with the cultivation of pineapple in Hawaii are Mealybug Wilt-Associated Viruses spread by mealybugs that cause leaf tip die-back, stunting and can kill pineapple plants.  You can see a presentation on Mealybug Wilt-Associated Viruses here.   Mealybugs can also transmit viruses in grapevines. Read here. Are you a fan of chocolate? I am. Mealybugs and viruses they spread are a huge  problem now with the cultivation of chocolate in Africa. Read here. 

Diversity 

When people discuss mealybug infestations, especially in social media and online forums, there tends to be an underlying assumption that all infestations are equivalent. But there is no one mealybug. According to the Bugguide website there are more than 2,200 different species of mealybugs. Different mealybug species vary in their host range, plant preferences and the damage they can inflict. I've seen all kinds of different mealybugs on succulents: slightly different sizes, different feeding habits, slightly different colors and different levels of white fluff, and differences in how difficult they were to eradicate.

There are some mealies that live exclusively on plant roots, These are called "root mealies" and can be especially damaging because they are obviously less visible than above ground mealybugs. One sign of root mealie is that the plant will easily become un-anchored and can easily be removed from the soil because the mealies stunt the roots.  My first Euphorbia came with weird yellow mealies that only lived on the roots (never made an appearance above the soil level) and made blue, not white,  cottony nests. Some mealies will colonize both the plant and the base of the plant underneath the soil and the roots.

Severity of infestations

I divide mealybug infestations into two categories: opportunistic stray mealies that wander onto plants and more serious infestations involving mealie bugs adapted to the infected plant. I should say this is an hypothesis based on my observations; it's not an observation I have seen others make. And there are likely gradations in severity between these two possibilities. The take-home message is every infestation is different and some will be harder to eradicate than others.

Opportunistic stray mealies

Say you see a mealybug on one of your plants. It could be a mealie that made its way onto your plant from a tree in your backyard. For example I've seen mealies on tree leaves the wind blows onto my deck where I have plants. This kind of mealybug may not be a species adapted to life on your particular plant. It may feed on your plant, but may not be able to efficiently infect and get a foothold on the plant. This infestation will be easy to deal with. Many years ago, I worked in a place where I had succulents on a windowsill. Suddenly, mealybugs showed up. I was perplexed because these were plants I had raised from seed and were mealybug free. This was during the holidays and a coworker made beautiful garlands with fresh red peppers and squash which were strung above the succulents. Upon close inspection, I saw that the garlands had mealybugs which had infested my succulents. These mealybugs were on vegetables but were able to infest my Dorstenias. The infestation was not severe, and I was able to cure it by moving the plants away from the mealybug garlands and repeatedly spraying them with pyrethrin. 

More serious infestations

Mealybugs adapted to living on succulents are much harder to eradicate. In greenhouses where succulents are mass produced for the big box stores and in botanical gardens that grow succulents, populations of mealies evolve over time that are very well adapted to feeding on succulents (again, this is my hypothesis,  this has not been researched in any great detail). These mealybugs are likely to come in with new plants recently acquired from a big box store or from a botanical garden plant sale or from a mail order nursery.  This kind of infestation will be challenging to get rid of. When I first started growing succulents, I remember dealing with an especially stubborn infestation on a Rhipsalis and a  Brachystemla. This mealybug was pink in color and not as fluffy as some, and had lots of fast moving red crawlers. I would treat the plants intensively to kill the mealies and think they were cured, but three weeks later the fiends would be back. It was a very frustrating experience. I ended up ditching the Rhipsalis, and the Brachystlma succumbed to a combination of the mealybug infestation and spider mites.  

How can one distinguish between a stray opportunistic mealie and a potentially stubborn infection? If you have had a plant for many years and suddenly a mealie appears it is likely an opportunistic mealie.  If you move your plant outdoors recently and suddenly see a mealie, it is probably opportunistic. 

If you recently acquired a new plant and mealies show up, this could signal a more serious infestation that will require more work to eradicate. If a plant is covered with mealies like the picture from the botanical garden above, it is likely a serious infestation. Root mealies should be treated as a serious infestation.

Prevention 

The best way to deal with mealybugs is to prevent them from infesting your collection in the first place. Many new succulent aficionados buy plants at big box stores. Though inexpensive and convenient to purchase, these often come with unwanted hitchhikers. But all new plants are suspect - I have received mail order plants from reputable nursereys that came with mealies, and I have had to mail them back.  Thoroughly inspect all new plants. Mealybugs are experts at hiding in nooks and crannies and crevices. When I was first getting into succulents many years ago, my co-worker Marilyn, a more experienced succulent mentor, told me: for every one mealybug you see there are 10 you don't see.

QUARANTINE

All new plants should be QUARANTINED away from your other plants for 3 to 4 weeks. Quarantine is a pain - much easier said than done - because space is an issue for many (I venture to guess most) of us, but just do it. Find a quarantine space and reserve it for new plants. It will save you so many headaches. One mealie or spider mite or scale hiding in a new plant can wreak havoc on your collection. If you should see a plant with mealybugs, immediately quarantine it and carefully inspect neighboring plants. 

Dealing with stray mealies

If you only see one mealybug and believe it is opportunistic based on the criteria discussed above, quarantine the plant and spray the entire plant thoroughly with a pyrethrin-based spray. Then keep an eye on the plant for one month. If no additional mealybugs, appear the plant can be taken out of quarantine.   

Pyrethrin is a insecticide isolated from chrysanthemums and formulations are available for home use. USE GLOVES WHEN USING PYRETHRIN INSECTICIDES. Though formulated for home use, pyrethrin is neurotoxic.  You will notice the toxic effects if any gets on your hands  -your hands will go slightly numb. 

Dealing with serious infestations

First, evaluate how much you value the plant. Is it rare or a particularly nice specimen? Is it especially dear to you? If the answer to these questions is no, then consider throwing the plant out and replacing it. If the answer is yes and you want to save the plant, you need to hit the mealybugs hard. Q-tips dipped in alcohol and dish soap are not enough. I recommend what I call the one-two punch for dealing with stubborn mealies.

One-two punch to knock out mealies for good

The one-two punch involves first treating the plant with a contact insecticide to kill mealybugs and crawlers. But this is not enough. In my experience, the mealybug eggs are resistant and enough can survive being sprayed with insecticides and alcohol that they will reinfect your plants in a few weeks. I recommend treating the sprayed plant with a systemic insecticide which will be taken up by the plant and will kill any newly hatched crawlers.   

Punch #1: If it's not too much trouble, I recommend un-potting the plants and discarding the soil, which may contain mealie eggs. Wash the pots well with hot water - mealies sometimes make their cottony nests on the pots. Douse the plant thoroughly with a pyrtherin-based spray. Make sure to get any nooks and crannies where mealies are hiding.  Allow to dry.

Punch #2: Re-pot the plants and water them with a good dose of Imidoclaprid.  Imidoclaprid is a systemic insecticide available in most garden stores in the US as a Bayer product (look for Imidoclaprid as the active ingredient). Systemic means the insecticide is absorbed by the plant. When the insects suck the plants juices they die. Imidoclaprid is a neo-nic (the chemical compound is related to nicotine in structure) insecticide. It's safer than the earlier generation on systemic insecticides and is even used in pet products. This insecticide is controversial because of its effects on bees, but you can take steps to prevent it from affecting bees: if you have treated a plant in the last 6 months and is accessible to bees, cut off any flowers that form or put the plant in a place where bees can't get to the flowers. This insecticide is not available in the EU, which is too bad because it's quite effective.  

After treatment, continue to monitor the plants. 

 A word about pesticides: 

When using any insecticide read and follow the precautions on the label. Remember, these are poisons. But, if you grow plants, sometimes you have to use them.  Exposure to older generation insecticides has been liked to increased risk of Parkinson's disease and other conditions. The newer insecticides are safer but BE CAREFUL AND MINIMIZE YOUR EXPOSURE! 

Other treatments

On social media you will read all manner of home remedies for mealybugs, including dish soap and diatomacous earth (from diatom fossils). I doubt these will work against serious infestations though they may work against the opportunistic stray mealies.

Biological control

By this point you can surmise that meaybugs are one of my least favorite insects.  What are some of my favorite insects? One of them is "Mealybug Destroyer". These delightful creatures devour mealybugs and other pests. "Mealybug destroyers" look like giant fast moving mealybugs. This can be a problem because they are sometimes incorrectly misidentified as mealybugs and killed. I have never used them but will never forget the first time I saw them in action nearly 20 years ago on a citrus tree outside of Chez Panisse restaurant in Berkeley. They are my heroes. Read more here for more information. 

Mealybug fun facts: 

Mealybugs are like cows for ants

Humans aren't the only farmers on Earth. Ants will farm mealybugs, scale and aphids. The ants will tend to colonies of these pests, clean them, protect them from enemies and move them to fresh plants. In exchange, the pests secrete drops of nectar that the ants consume. Watch this video on YouTube of ants farming mealybugs. This is one reason why you want to keep ants away from your plants. 

Want some Mealybug with your strawberry yogurt?

A mealybug relative, cochineal, that grows on Opuntia cacti is used to make a red dye used as food coloring and added to products like strawberry yogurt, soft drinks and other foods. Read more here.