Hawai‘i Herald Columnist
One day you are checking your plants and notice white fluff. Upon closer inspection, you notice some of the white fluff is traveling up and down the stem while other white fluff is just hanging out in the leaf axils. These may be two different insects that look alike but do very different things.
GOOD BUG: Mealybug destroyer (cryptolaemus montrouzieri)
This insect does what its name says. It feeds on mealybugs (and other pests). The insect goes through a complete metamorphosis, meaning the larvae stage looks different from the adult. The adult is a lady beetle with a blackish body and orange-brown head that is 3-4mm long (1/8in – 1/6in). The larval stage looks similar to a mealybug but is twice the size of an adult mealybug and actively moves around in search for food. It is covered in shaggy white “hairs” or filaments, which makes them look like they are having a bad hair day. Both the adults and young larvae feed on insect eggs while the older larvae (pictured here) will eat mealybugs and some aphids and scale. See the links in the resources below for more information.
BAD BUG: Mealybug (family pseudococcidae)
This insect goes through several molts from egg to adult. Adults are 3-4.5mm (1/8in-1/ in) with short “hairs” or filaments around the sides of the body and two to four longer filaments at their rear. The newly hatched nymphs are in the “crawler” stage where they actively move around in search of a place to feed. The older nymph stages and adults can move, but tend not to travel very far or quickly. All life stages feed on plants by sucking plant juice from the leaves. As a result, mealybugs excrete a sticky “honeydew” that ants feed on and sooty mold likes to grow on leaving a black film on leaves.
Control of mealybugs
Treat your plants after you have accurately identified the pests as mealybugs. If the infestation is really bad, it may be worthwhile to cut off the heavily infested areas and disposing it in the trash (not compost pile). Hosing the pest off with sharp streams of water may temporarily solve the problem. If you only notice a few on your houseplant, you can try dabbing it with rubbing alcohol. Appropriate insecticidal soaps or horticultural oils can also be used once you tested to see if it is safe to use on your plants without damage. Check and follow all label instructions.
Beneficial insects in the garden: #15 Mealybug Destroyer (tamu.edu):
Mealybug Destroyer/UC Statewide IPM Program (UC IPM) (ucanr.edu): ipm.ucanr.edu/PMG/PESTNOTES/pn74174.html
Cryptolaemus montrouzieri (cornell.edu): biocontrol.entomology.cornell.edu/predators/Cryptolaemus.php
Hawaii Master Gardener Program: FAQ:
Amy Tsuneyoshi grew up playing in the mud and still finds joy in getting her hands in the soil. She grows a variety of edible and ornamental plants in her urban jungle as well as Native Hawaiian plants. She has a degree in horticulture from the University of Hawai’i at Mänoa and is currently the President of the Friends of Hälawa Xeriscape Garden.