Ladybugs like a lot of real estate, say researchers at Michigan State University. Megan Woltz, a Ph.D. student there, found that planting strips of non-crop plants (buckwheat, in this case) near soybean fields did attract ladybugs — to the buckwheat.

“We always found way more ladybugs in the buckwheat than are usually in field edges,” says Woltz at http://news.msu.edu/story/increasing-predator-friendly-land-can-help-farmers-reduce-costs. “Unfortunately, all of the ladybugs in the buckwheat did little to change their populations in the soybean fields.”

Ladybugs are desirable in soybean crops because they feed on soybean aphids. Perhaps cutting the buckwheat when aphids had built to some critical population level in the soybeans would have worked.

According to MSU, ladybugs and other predatory insects that eat crop pests save farmers an estimated $4.6 billion a year on insecticides. That sounds significant; EPA figures say that in 2006 and 2007 (the most recent years for which data have been compiled), U.S. farmers spent just under $2 billion per year on insecticides (www.epa.gov/opp00001/pestsales/07pestsales/market_estimates2007.pdf).

“But ladybugs can fly or crawl for miles,” say Woltz and MSU entomologists Doug Landis and Rufus Isaacs. They found that the amount of grasslands and forests within 1.5 miles of soybean fields determined how many ladybugs ended up in the field.

So having natural habitat in farming areas to provide food and shelter for ladybugs and other beneficial insects could help increase their abundance in crops, say the researchers.

In other studies, landscapes with at least 20 percent of non-crop habitat showed good pest control, add the researchers. They suggest that neighbors could work together to provide that habitat on a landscape scale — the scale that matters to ladybugs.

In our own landscape, we let goldenrod, milkweed and other plants grow near our vegetable garden, fruit trees, fruiting shrubs and Christmas trees, and we see numerous beneficial insects.

I also interplant some flowers with vegetables to attract insects — and some vegetables have flowers that attract beneficials. This year I let last year’s parsnips go to flower, and in just a few minutes on a recent morning, I saw two kinds of ants, a bee, a wasp and a ladybug on one inflorescence. The ants aren’t beneficials per se, but they may be farming aphids (ants like to eat aphids’ “honeydew” or sugary secretions) and, in turn, supplying the ladybugs with a food source.

In an excellent eight-page paper called “Attracting Beneficial Insects to the Garden with Beneficial Flowers” (at www.reneesgarden.com/articles/Beneficial%20Insects%20Guide.pdf), Professor Emeritus Richard Merrill, a California researcher who has studied beneficials and their relationship to garden ecology, writes that beneficial insects include predators, which either chew pests or pierce them and ingest their body fluids, and parasitoids, which lay eggs in or on other insects. When those eggs hatch, the larvae eat the host insect.

Predators include syrphid fly larvae, lacewing larvae, some true bugs, lady beetles, soldier beetles and spiders (which are not insects but arachnids). Parasitoids include some flies, such as tachinid flies, and some very small, non-stinging wasps, such as Trichogramma wasps.

Merrill lists four plant families that are easy to grow and attract beneficials. They are the carrot family (Apiaceae), including dill, fennel, lovage, angelica and others with the typical umbel-shaped flowers of this family; the daisy family (Asteraceae), including chamomile, goldenrod, sunflower, Mexican sunflower and tansy; the cabbage family (Brassicaceae), including broccoli, sweet alyssum and mustards; and the scabiosa family (Dipsaceae), including scabiosa and cephalaria.

Merrill suggests planting insectary plants, which harbor pests such as aphids that beneficials feed on; perennial borders, windbreaks and hedgerows for refuges and food for beneficials; beneficial flowers for pollen and nectar; and repellent plants — those that give off a strong odor that confuses pests that otherwise target vegetable plants by their odor. “Common repellant plants include strongly pungent vegetables (alliums and tomatoes) and many aromatic herbs,” writes Merrill.

Of course, attracting beneficial insects also means not using pesticides, or using them very sparingly and carefully, so that the beneficials are not harmed along with the pests.