It still amazes me how many plant people are obsessed with insects. After Doug Tallamy’s first book, Bringing Nature Home, was published in 2007, the plant-obsessed people in my life became bug-obsessed overnight. dr Tallamy’s work supported the movement towards more native plants in our gardens by highlighting the importance of native plants in wildlife conservation. It’s really a simple premise. Native plants support insects and birds feed insects to their young. Plant more native plants, support more birds and thus other wildlife.
When I first started studying horticulture, the “All bugs are evil” camp had more members than the “This bug is really cool and such an important pollinator” camp. Now it’s completely reversed. Gardening professionals are more likely to celebrate insects than worry and reach for a pesticide. Home gardeners can follow suit by embracing the role of beneficial insects (insects, fungi, bacteria) in our gardens. When used as biological controls, beneficial organisms can help us control pests both indoors and outdoors.
What is a biological control?
Many of us have vivid memories of caterpillar droppings raining down on backyard picnics in the mid-1980s when gypsy moths (formerly gypsy moths, Lymantria dispar) invaded. Then, after a weird few summers, the moths magically disappeared. For more than thirty years, the sponge moth was little of a problem in the Northeast, thanks to a fungus (Entomophaga maiimaiga) and a virus (nucleopolyhedrosis virus) that kill developing caterpillars. Drought in New England a few years ago brought back sponge moths for a season or two. Their disappearance once again demonstrates the power of natural enemies to combat harmful insect pests.
Another local insect pest successfully controlled by biological controls is the winter moth (Operophtera brumata), an introduced moth from Europe that emerges from the ground to lay eggs in mid-November. Eggs overwinter and in early spring newly hatched caterpillars feed on many forest trees including maple, oak, cherry, beech and hickory. University of Massachusetts entomologists released a tachinid fly (Cyzenis albicans) whose larvae invade the intestines of developing winter moth caterpillars and parasitize them. The winter moth is now kept in check and is no longer considered a significant forest pest.
Biological controls are also used to control invasive plant species. Purple loosestrife (Lythrum salicaria) inhabits sensitive wetlands across North America and harms biodiversity. Because loosestrife infests wetlands where it forms dense monocultures, it can be difficult to control using traditional methods. Fortunately, a pair of beetles (Galerucella calmariensis and G. pusilla) that feed exclusively on purple loosestrife can help control their populations.
Using biological controls at home
Biological controls can be a sustainable way to control a variety of plant pests in our home gardens. As with any pest control, the most important first step is identification. Without accurately identifying the pest, any effort, biological or otherwise, can be at best unsuccessful or at worst harmful.
For those in search of the perfect lawn, the milk spore is a bacterium (Bacillus popilliae) that kills larvae. A single application of milky spores can create a self-sustaining population of soil bacteria that will control maggots for decades. Mosquito larvae can also be fought with bacteria (Bacillus thuringensis israelensis).
Many common houseplant pests can be controlled with biological controls. Unfortunately, many biocontrol agents are not necessarily welcome indoors. Because as much as I love ladybugs—an excellent biological pesticide for aphids—I’d rather not have them in my living room. One pest that can be effectively controlled indoors with biological controls is fungus gnats. The larvae of these pesky flying insects feed on organic matter in the soil and damage plant roots. Fortunately, beneficial nematodes (Steinernema feltiae) can be applied to potting soil to keep fungus gnats at bay. You can ask the UMass Extension office, a regional farming and gardening resource, for tips on where to find beneficial insects for your home and garden.
We’ve moved well beyond the days of better living through chemistry, when the only good bug was a dead bug. Whether you are a horticulturist, gardener or houseplant enthusiast, there are countless examples of better life through biodiversity. And lots of good bugs we can take on to help us control the bad ones.
Gardening Central Mass. was written by the team at the New England Botanic Garden in Tower Hill. Located on 171 acres in Boylston, the New England Botanic Garden is one of the region’s finest horticultural resources. Throughout the year, garden visitors experience the wonders of plants, learn about the natural world, and make joyful connections. There is so much growing in the garden. Discover it today at www.nebg.org. The column appears on the third Sunday of the month.
