Fall Newsletter: Attack of the Mealybugs
As we move into the fall, we have received a spike of inquiries detailing mealybug outbreaks.
With that in mind, we would like to share some information on the subject, hoping we can shed some light on a fairly common pest. There are two main species of Mealybug that we see here in the US. Longtailed mealybug (featuring tails that can protrude as long as the main body of the insect) and citrus mealybug(does not feature long tails). There is also a species of mealybug that can reside in soil so checking root balls can be crucial for plant care.
Mealybug Hosts
Longtailed Mealybug hosts: Dracaena, avocado, citrus, grapes, pear, persimmon, pineapple, tropical/subtropical plants, cycads, orchids, jade, oleander, beans, flax, guava, apple, potato, lemon, begonia, sedum, sempervivum and other ornamentals.
Citrus Mealybug hosts: As the name suggests, these are primarily pests of citrus but also enjoy ornamentals, vegetables, and fruits. They seem to prefer grapefruit over other citrus but other hosts include amaryllis, asparagus, begonia, cactus, coconut, coleus, croton, cucurbits, cyclamen, dahlia, yams, ficus, strawberries, gardenia, impatiens, poinsettia, sweet potato, mango, bananas, avocado, guava, pomegranate, pineapple, pear, apple, eggplant, tulips, milkweed, rosemary, and the list goes on!
Needless to say, these pests have a very wide host range and can attack many houseplants. Production growers should be vigilant of these pests and should consistently ship out clean material. It is always a good idea to inspect plants thoroughly, even the soil, before sending them off to customers.
Pictured are 3 different developmental stages of mealybugs right next to each other. Smaller nymphs leading up to a full grown female adult mealybug.
Photo by Brendan Kelly
Mealybug Damage: Signs to Look Out for
Mealybugs and other insects with piercing-sucking mouthparts, like aphids, feed directly from the host plant vascular system. Feeding from this pest can lead to wilted, yellowed chlorotic leaves, premature leaf drop, stunted growth, and even death!! The sugary honeydew secreted from mealybugs as a byproduct of their feeding habit can cause sooty mold to grow on plant surfaces, hindering photosynthetic capability. The honeydew can also attract ants to the situation which can lead to distribution of the mealy pest.
Options for Control:
For small infestations, a light isopropyl alcohol solution spray can help kill some of these pests on contact without damaging your plants. Mechanical removal by washing plants with water can help significantly as well. These pests are great at getting down into plant crevices and hidden points in new growth that will help keep the covered from sprays and washes, not to mention their waxy coating can also act as a barrier to sprays. Another defensive behavior that has been observed is the egg laying, adult female Mealybug covering stage 1 and 2 instars when sprays are being conducted.
Commercially, we can offer an entomopathogenic fungi such as Beauveria bassiana to help with mealybug outbreaks. Some of the products that we offer including this fungi are Velifer, Botanigard MAXX, Mycotrol, and BioCeres. Another successful biopesticide that we offer is the beneficial fungus product NoFly. This contains the fungal organism Isaria fumosorosea and works wonders for mealybug control. Long Shadow does include mealybug on its label but comes with caveat that cinnamon oil can be highly phytotoxic, so use caution and do a test before spraying everything.
Cryptolaemus montrouzieri are the best biocontrol option. These adults and their larvae are both predacious and a single Cryptolaemus can eat up to 250 small mealybugs over its lifetime. Their larvae do look oddly similar to the mealybug, although they appear a bit “harrier”, are much larger, and eventually turn into an adult Ladybird Cryptolaemus. They spend about 2-3 weeks as larvae and can live over a month as an adult. This gives them close to 50 days of life, which is pretty long compared to other beneficial predators. They may be more effective against citrus mealybug because they are known to lay eggs in cottony masses. The long tailed mealybug is still a good prey option for the Cryptolaemus but are not known to lay eggs which is an easy target for the predator. The predators will likely go after younger mealybugs first. The Cryptolaemus is a specialized predator so its’ main focus will be the Mealybug.
Chrysoperla rufilabris, or the Green Lacewing is a generalist predator that will eat just about anything (including its own kind!). These predators have shown success in controlling mealybugs and can be a cheap option for coverage of multiple pest issues.
Mealybugs can reproduce without mating, like aphids and each female can lay up to 350-600 eggs. The mealybugs can each live for around a month and will do damage the entire time. Some mealybugs can also be found colonizing in soil so scouting root masses can be an integral part of monitoring and control.
Sources of this information are:
-New Zealand Landcare Research
-NC State Extension
-University of California IPM
-University of Florida Entomology Department
Cryptolaemus montrouzieri is the most commonly used biological control for mealybugs. Cryptolaemus is used to control mealybugs mainly in interior plantscapes. They can be used outdoors, but will not survive sub-freezing temperatures. To keep mealybug populations down to acceptable levels in greenhouses, several releases of Cryptolaemus may be necessary, particularly during winter months. They are less effective on longtailed mealybug (Pseudococcus longispinus) because this species lacks the cottony masses Cryptolaemus requires for egg laying.
Adults and young larvae prefer to eat mealybug eggs, but older larvae will feed on all stages of mealybugs. The adults can fly and cover large areas to search for food. If food is scarce they will also eat soft scales and aphids.
BioCeres WP targets common insect pests such as aphids, whiteflies and thrips.
BioCeres WP is a contact biological insecticide that contains the entomopathogenic fungus Beauveria bassiana. This particular strain, ANT-03, was isolated from Lygus bugs in Canada. It works by germinating into the cuticle of insects and releasing toxins while also consuming the hemolymph.
One of the advantages of BioCeres is that it is an i-502 allowable product containing B. bassiana without the pyrethrins. BioCeres WP can also be tank mixed with several other biorational pesticides (check the technical info for specific combinations).
NoFly WP is a naturally occurring fungi strain which acts as a natural pesticide. The concentrated spores of Isaria fumosoroseus strain FE 990. Highly effective under humid conditions, this microbial fungal spore germinates and infects a select group of pests, including aphids, whitefly, thrips, mealy bugs and more. Beneficial predator mites that may be in your growing system are not affected. See the link for additional label and important application instructions. NoFly WP is also compatible with many chemicals making it an excellent tool for use in an integrated pest management (IPM) program.