Habitat Reservoirs: 'Home Sweet Home' for Beneficial Insects

Scientists at the Rodale Institute Research Center (RIRC) have been conducting habitat management trials since 1987 in search of plants that attract and sustain populations of beneficial insects for biological pest control. Such plants could one day serve as habitat reservoirs that encourage the establishment of beneficials and help maintain a balance between pest and beneficial populations in and around crops.

Enhancing Biocontrol

The RIRC research is based on biological control, a pest management strategy that uses the natural enemies of pests, i.e. parasites, predators, and pathogens, to decrease pest populations, while reducing the need and cost of pesticide application. The main strategies for enhancing biological control include the following:

Conservation. Leaving natural plant communities undisturbed on field borders and other noncrop areas can help maintain existing populations of beneficial mites, spiders, insects, etc.

Nectar and pollen sources. Alternate food sources provided throughout the cropping season can extend the life span of beneficials, allowing them to produce more eggs and to parasitize more pests.

Alternate hosts and prey. When crop pests are not present, other plants and the insects they host can maintain populations of beneficials. Cover crops, hedgerows, windbreaks, and fieldside weeds are good reservoirs for alternate prey such as aphids and thrips.

Habitat shelter. A plant's architecture can influence its suitability as an overwintering site and can affect microclimate, since windbreaks and shade can modify temperature and moisture conditions. Also, flower shape and size can attract beneficials. For example, many predators and parasites such as ladybugs and wasps have short chewing mouth parts and need shallow flowers to access nectar. In contrast, butterflies have long mouth parts that can extend into deep tubular flowers.

Plant Selection

At RIRC the last three strategies have been integrated to study overall habitat management. A habitat management herbary is used to identify plants that attract beneficials. Plants for screening are chosen based on the following characteristics:

Flowering time. Species that bloom at different times are combined to provide season-long shelter and food for beneficials. Food source. A plant's potential for providing nectar, pollen, alternate prey, and honey dew from aphids is considered.

Survivability. The plant's ability to withstand machinery traffic, grass competition, and low maintenance conditions is important. Hardy per-ennials and self-seeding annuals are prime candidates for good survival.

Few pests. Plants are screened for their potential to harbor many beneficials but few crop pests.

RIRC Habitat Plants

Over 160 species have been evaluated so far, including common ornamentals, wildflower species, and a number of culinary herbs. Most of the plants providing good habitat belong to the families Umbelliferae and Compositae. Other important families are Labiatae and Poly-gonaceae. The habitat plants at RIRC include the following:

White sensation cosmos, (Comp-ositae, Cosmos bipinnatus), draws spiders, ladybugs, wasps, hover flies, insidious flower bugs, and lacewings.

Tansy, (Compositae, Tanacetum vulgare), attracts many flies, ladybugs, lacewings, insidious flower bugs, and small wasps. This plant harbors the tansy aphid in large numbers and provides a good alternate food source for predators.

Caraway, (Umbelliferae, Carum carvi), invites wasps, syrphid flies, lacewings, and insidious flower bugs.

Dill, (Umbelliferae, Anethum graveolens), attracts insidious flower bugs, ladybugs, and hover flies.

Sweet fennel, (Umbelliferae, Foeniculum vulgare), lures hover flies, parasitic wasps, ladybugs, and spiders.

Spearmint, (Labiatae, Mentha spicata), draws various flies, predatory wasps, and spiders.

Buckwheat, (Polygonaceae, Fago- pyrum esculentum), attracts hover flies, minute pirate bugs, predatory wasps, tachinid flies, ladybugs, and syrphid flies.

Principal Beneficial Insects

During trials, weekly samples of insect populations are taken by the sweep net method. Insects are then identified and counted, and population data analyzed. Initially, only visual observations from the herbary were recorded. This year, data has been recorded from replicated plots set up in 1989. The most important parasites and predators follow:

Ladybugs. (Coccinellidae) These insects eat aphids and other species of small insects and eggs.

Insidious flower bugs. (Anthocoridae) Also known as pirate bugs, they feed on insect eggs, small larvae, thrips, and mites.

Parasitic wasps. (Braconidae, Chalcididae, Trichogrammatidae, etc.) There are many different wasp species, the most well-known is Trichogramma. They kill pests by laying eggs inside pest eggs, larvae, or adults.

Lacewings. (Chrysopidae) Adults are not predatory, but their larvae feed on small caterpillars, mealybugs and scale, moth eggs, and aphids.

Flies. (Tachinidae, etc.) Some are pests, some are beneficials, depending on the species. The most valuable beneficial flies are tachinids, which parasitize stink bugs and the caterpillar stages of various moths and butterflies.

Hover flies. (Syrphidae) These flies are commonly known as syrphids; their larvae attack many types of aphids.

Habitat Management; an Inexact Science

Establishing habitat reservoirs to encourage biological control of crop pests is a budding area of research requiring much experimentation. The intention here is to stimulate ideas locally, instead of providing a recipe, because plant/pest/beneficial interactions are specific to a particular ecology and microclimate. Scientists and farmers in any location can observe where beneficial insects live, including certain weeds, and compile their own lists of local plants for field trials.

Information for this article provided by RIRC Entomologist Diane Matthews-Gehringer and Horticulture Technician Ed Lachowski.

For more information:

Ed Lachowski
Rodale Institute Experimental Farm
611 Siegfriedale Road
Kutztown, Pa. 19530 U.S.A.