Manipulate Habitats to Increase Beneficial Organisms

Monarda punctata, spotted horsemint, attracts beneficial bugs. Source: Karan A. Rawlins, University of Georgia, Bugwood.org

Growers often use the IPM technique of increasing the complexity and diversity of vegetation to fight bad bugs (plant damaging insects). While this technique has been around for a long time, scientists continue to test new ways to implement it.

For example, flowering conservation strips and beetle banks, made up of specific types of plants, provide food resources such as pollen and nectar or alternate prey, shelter, and overwintering sites for good bugs.¹ Using native plant species could serve a dual function of fighting the bad bugs by enhancing the beneficial ones, while also promoting other valuable ecosystem services.

Attractive Research

For example, Steven Frank, Paula Shrewsbury, and Okemeteri Esiekpe evaluated ten native plant species for their attractiveness to good bugs at the University of Maryland. Plants that showed the most promise were Monarda punctata or spotted horsemint (Lamiaceae), Pycnanthemum tenuifolium or mountain mint (Lamiaceae), and Eupatorium hyssopifolium or hyssopleaf thoroughwort (Asteraceae), all of which generally harbored the greatest number of predators and parasitoids dwelling and foraging among the plant foliage.

This IPM technique is considered by scientists to be a branch of conservation biological control—using nature’s tactics to fight pests. Specifically, scientists are studying ways to manipulate habitats—changing the composition of plants and other organisms—to fight attackers. There is evidence going back over twenty years that increasing plant species diversity and vegetation complexity of habitats and therefore the abundance of food resources can increase the longevity and fecundity of natural enemies.

In Europe, beetle banks, composed of bunch grass or Dactylis glomerata, provide shelter for ground foraging predators such as carabid beetles, staphylinid beetles, and spiders. Studies in Maryland found similar results.

"Providing overwintering habitat allows good bugs to remain in fields or landscape beds rather than retreating to edges and may lead to more robust populations of natural enemies over time," said Shrewsbury. "We go so far as to say that increasing vegetative complexity in general could benefit ground-dwelling predators."

Common flower species, those that have been proven attracters through research, and that are recommended in habitat manipulation programs, are sweet alyssum, Lobularia maritima L. (Brassicaceae), buckwheat, Fagopyrum esculentum Moench (Polygonaceae), phacelia, Phacelia tanacetifolia Benth. (Hydrophyllaceae), and umbelliferous herbs such as coriander, Coriandrum sativum L. (Apiaceae), fennel, Foeniculum vulgare Miller (Apiaceae), and dill, Anethum graveolens L. (Apiaceae).

One strong performer is mountain mint, Pycnanthemum tenuifolium Schrader (Lamiaceae). Another two are the above-mentioned Monarda punctata and Eupatorium hyssopifolium. Spiders and parasitoids thrived around these species of plants.

Bring It On

Heteropteran predators such as bigeyed bugs, Geocoris spp. (Lygaeidae), minute pirate bugs, Orius spp. (Anthocoridae) and predatory stink bugs (Pentatomidae) made up a small population, but were important predators of aphids, eggs and larvae of lepidopteran pests, and other small plant feeding arthropods. Coccinellid lady beetles have been shown to reduce aphids and other pests.

Home Defender

The IPM strategy of habitat manipulation could shape up to be a big game-changer for homeowners and gardeners in the match against the brown marmorated stink bug (BMSB), an invasive plant-feeding insect and home invader in the fall and winter months.

In 2015, researchers found that in production nurseries the availability of fruit on trees affected the abundance of that pest.² It turned out that although BMSB is a generalist herbivore, the availability of ripe fruit serves as a key resource and attractant for the insect. Removal of fruits from trees suppressed stink bug populations. During their study, H. halys successfully moved about, tracking ripe fruit as it became available throughout the season.

The researchers suggest that for homeowners, gardeners, or ornamental tree growers, removal of fruits from trees could be an effective stink bug population control tactic. Since this tactic is impractical in most cases, another strategy might be to plant non-fruiting varieties of trees as ornamentals, to reduce stink bugs in landscapes, reduce risks to crops, and limit home invasions by the bug. Clearly, fruit growers will have to use other IPM tactics.

No Use for Stink Bugs

In the first outbreak of BMSB in North America in 2010, growers faced multimillion dollar losses in apples and peaches; vegetables such as sweet corn, peppers, and tomatoes; row crops including field corn and soybeans; vineyards; small fruit; and ornamental plants. In the 2011 growing season farmers applied repeated pesticide applications to suppress damage by BMSB while researchers searched for alternative management strategies. BMSB also invaded homes and structures by the thousands in the fall. Pest control companies responded to demand by spraying eaves, windows, and doorways of buildings where BMSB aggregate and enter.

In North Carolina and Virginia natural woodland edges, the greatest numbers of BMSB were found on tree of heaven (Ailanthus altissima), catalpa (Catalpa spp.), yellowwood (Cladrastis kentukea), paulownia (Paulownia tomentosa), wild cherry (Prunus spp.), walnut (Juglans spp.), and redbud (Cercis spp.).

In a study published in 2016, Erik Bergmann and coauthors identified 88 commercially available host plants used by BMSB and 43 plants that did not support BMSB at any life stage.³ The authors suggest that planting non-hosts, especially gymnosperms—including conifers, cycads, and ginkgo—may help to reduce the intensity of the pest’s presence in landscapes providing a further example of habitat manipulation.

IPM to the rescue, again: By avoiding plants that favor BMSB and incorporating non-hosts into landscapes, homeowners could perhaps reduce the need for treating structures and plants with insecticides, and reduce the likelihood of home invasions.

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