Pollinators and pests in your garden: How to save one, get rid of the other

A Monarch butterfly
A monarch butterfly pauses on a native milkweed plant, which is not as showy as the bright orange flowers of the tropical milkweed but safer for the butterfly, conservationists say.
(Ron Vanderhoff / Roger’s Gardens)

Pollinators play an important role in our ecosystem. Here’s how to care for them while getting rid of the pests in your garden, like dreaded stink bugs.

Bugs are a big part of gardening — pro and con — and scientists spend entire careers looking at ways to either shut them down or, in the case of pollinators, help them thrive.

Their research can help even the most modest gardens, so we’re going to share some of their findings to help you and your garden play its role in our evolving ecosystem. Today’s lessons involve monarch butterflies, mosquito eradication and (bleah) stink bugs.

Protect monarchs with native milkweed

Monarch butterflies are fussy eaters that dine only on milkweed, so to boost the graceful pollinator’s dwindling numbers, woke SoCal gardeners have been busy sowing milkweed plants in their yards. All well and good, except now there’s news that some milkweeds are more hindrance than help, according to Ron Vanderhoff, general manager of Roger’s Gardens nursery in Corona del Mar and a board member of the Orange County chapter of the California Native Plant Society.

The most common milkweed in California gardens is a non-native known as tropical milkweed (Asclepias currassivica), which blooms profusely with rich orange flowers the monarchs love, but also harbors microscopic protozoans that survive on the plants during winter and sicken the caterpillars who eat them in the spring, Vanderhoff wrote in a recent article on the Roger’s Gardens website.

So Roger’s Gardens has stopped selling tropical milkweed. The Xerces Society, an invertebrate conservation group, recommends that home gardeners plant native milkweed species instead, such as narrow-leaf milkweed (Asclepias fascicularis), “a relatively showy plant reaching about 3 feet in height, with pale pink to cream-colored flowers.” Unlike the tropical variety, the native plants die down to the ground in the winter, so overwintering critters aren’t an issue, Vanderhoff says.


If you must keep your tropical milkweed (which have more showy flowers), Vanderhoff says gardeners should cut it to the ground in December, and once more in February, to ensure no nasty protozoans survive.

These mini-donut-sized Mosquito Dunks contain BTI, a bacterium that’s lethal to mosquito larvae, black flies and fungus gnats for up to 30 days, but won’t harm plants or animals (including humans). Use them in ponds, bird baths or even bromeliads to keep mosquitos from breeding.
(Summit Responsible Solutions)

Act now to eradicate mosquito hangouts

Our wet spring was a boon to our garden plants but it also created a lot of watery nooks for mosquitoes to breed. The voracious skeeters need ridiculously little moisture to reproduce, so take time to wander your estate to look for any sources of standing water, no matter how small.

Be sure to check shallow drip saucers under your garden pots, discarded cans or tires, and even big-throated plants like bromeliads, which accumulate water in their centers.

Toss the trash and keep the saucers emptied (it’s not good for your plants to stand in water anyway). But don’t tear out your bromeliads. Instead, try washing out the tank — a.k.a. the center — where water accumulates, and add a few drops of cooking oil to suffocate any larvae, according to Horticulture magazine.

Another option for water troughs, bird baths and even bromeliads is a product such as Mosquito Dunks, which uses BTI (short for Bacillus thuringiensis subspecies israelensis), a biological or naturally occurring bacterium found in soils. According to the Environmental Protection Agency, BTI is lethal to mosquito larvae, black flies and fungus gnats but does not harm humans or other animals (including honeybees) or plants.

Stink bugs will literally suck your plants dry, as you can tell from this shriveled peach, but if you plant the right flowers in your garden, a tiny parasitoid wasp could come to your rescue.
(Kristie Graham/USDA ARS)

Encourage stink bug doom with nectar-producing plants

Is there anything more frustrating than an army of shield-shaped stink bugs sucking the strength out of your tomatoes or zucchini?

One day your plants look healthy, and the next they are decimated by this aptly named garden pest. (One good squish and you’ll know what we mean.) There haven’t been many deterrents aside from dousing them with chemicals or picking them off by hand, said Glynn Tillman, a U.S. Department of Agriculture scientist in the Agricultural Research Service.

Happily, Tillman and her ARS colleagues have found a promising parasitoid champion that — literally — nips stink bugs where it hurts.

The heroes are tiny wasps, such as the Trissolcus japonicus, a.k.a. samurai wasps, which lay their teensy eggs on stink bugs eggs. When the samurai larvae hatch, they eat up the stink bug larvae inside, crawl out of the eggs and then fly away to start the cycle anew.

Some species even lay their eggs on the backs of stink bugs, Tillman said, so their larvae feed on the living bug until (shiver) the bug is living no more.

“It’s pretty cool but gross,” she said, but that’s how parasitoids roll — parasites that actually kill their hosts instead of just sharing their calories and space.

This Trissolcus basalis, one type of parasitoid wasp, is as tiny as a gnat but it’s a giant in destroying the stink bugs intent on devouring our gardens.
(Elijah Talamas / University of Florida)

These non-stinging wasps are smaller than gnats, so they’re hard to see, but they’re prolific and extremely effective at killing stink bugs, Tillman said. The wasps originated in East Asia but now can be found all over the United States.

The trick is attracting them to your yard.

Turns out parasitoid wasps have a serious sweet tooth: “They have to have sugar to reproduce,” Tillman said. So farmers and gardeners can lure the wasps by planting nectar-producing flowers among their crops.

If you plant the right flowers, the wasps will come, she said. Their favorites include wild milkweed, alyssum, buckwheat, sunflowers and two herbs, dill and cilantro, which should be allowed to flower.