L.A. at Home

Design, Architecture, Gardens,
Southern California Living

« Previous Post | L.A. at Home Home | Next Post »

Master gardener in training: Ladybugs are good, but lacewings and mantises may be better

June 9, 2010 |  7:30 am


The question is when, not if, aphids will find your tomatoes, or caterpillar holes will appear on the eggplants. For dealing with the inevitable pest incursion, my UC Extension Master Gardener class has been taught integrated pest management, which considers plant selection, physical barriers, trapping, biological controls and, as a last resort, the least-toxic pesticides.

Defending your planted real estate is possible only with a broad view. A knee-jerk reaction won’t help. So take a deep breath and consider the long-term potential of beneficial insects.

The goodwill ambassador of biological controls is the ladybug — cute, available at nurseries and able to eat 50 aphids a day. Ladybugs should be released at night, when they’re less likely to fly away for the garden next door (though they may do that the next day anyway).

Lesser known is the green lacewing, a.k.a. the aphid lion, pictured above. Lacewings may not be icons like ladybugs, but they can eat soft-bodied insects 20 times faster. Lacewing eggs — 1,000 fit in a pea — will hatch quickly, and because they lack wings, they will stay put in vegetable beds or in container plantings. 

MG609_pestsjeffIMG_0045 Praying mantises will eat anything that comes their way. Do not let the eggs hatch before you put them out (in the crotch of a tree, preferably). Mantises have terrible eyesight and will eat the first thing in their path — including siblings. Like lacewings, mantises do not fly. (That's a mantis egg sack, at right.)

The pint-sized king of the beneficial insects, however, is trichogramma, a genus of  parasitic wasp less than 1 millimeter long, or one-quarter the size of a grain of pepper. They are widely used in commercial agriculture, effective for controlling 200 kinds of moths and caterpillars, including horn worms and the cabbage loopers ravaging my dinosaur kale. The trichogramma kills — and I love this — by laying its eggs within its prey’s eggs. The wasp egg consumes its host from within and then emerges, alien-like, out of the back of the carcass, leaving behind a brown shell. The larva then goes on to eat more eggs. It is a killing machine.

It’s a bug-eat-bug world, Paula White from Orcon told my class. “Pick the right bug for the job.”

Choices abound. If you have spider mites, a praying mantis may not take care of it, but one type of predatory mite will. Although lacewings do eat whitefly larvae, a tiny parasitic wasp, Encarsia formosa, is so effective that it’s also widely used commercially. Several insects target mealybugs, but the Australian ladybug, Cryptolaemus montrouzieri, eats only mealybugs and is one of the oldest biological controls in use.

MG609_jeffIMG_0057 Decollate snails, at right, live mostly under the soil and attack and kill the common brown garden snail and its eggs.

Beneficial nematodes go after flea larvae, white grubs, cutworms, gypsy moth larvae and more than 225 other soil-dwelling and wood-boring pests. They don’t bother other beneficial insects and are safe for humans, pets and plants.

MG609_jeffIMG_0067You can incorporate certain types of plants to attract beneficial insects. Anise, dill, carrot and fennel may attract helpful wasps. Mustard flowers draw lacewings. Sunflowers will bring in birds, the best defense against caterpillars.

If you’re using beneficial insects, be patient. There’s a time lag before the population gets big enough to have a visible effect. (That's a team of ladybugs being released, at right.)

And remember that another strategy is simply to plant more than you’ll need and just accept the damage from pests, sacrificing some crops to save others.

Finally, be a good horticulturist. Collect and discard all diseased foliage. Healthy plants have fewer problems. And be mindful with watering. Too much water is the leading cause of pests.

-- Jeff Spurrier

Photo credits: Lacewing by Ricardo DeAratanha / Los Angeles Times; all others by Jeff Spurrier

More advice: Get recommendations, event notices and more by joining our Facebook page.