Enhancing beneficial insects with native plants

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

For many years, entomologists have recommended conserving insect predators, parasites and pollinators around the farm or garden to help suppress pests and increase crop yields. But what can you do to promote these beneficial insects? Since 2003, we have been investigating the role that native plants may play in helping to enhance the abundance and performance of these helpful anthropods. We were interested in learning if native Michigan perennial plants were attractive to natural enemies and determine if a succession of flowering species could provide floral resources over much of the growing season.

We selected 46 native Michigan plants based on their reported bloom period and ability to survive in agricultural habitats and contrasted them with widely recommended nonnative plants (all annuals). All of the native species selected historically grew in prairie or savanna habitats (scattered trees with an understory of prairie species). Native species were established as plug or 1qt size plants in the fall of 2003 and contrasted to the non-native annuals planted as seed the following spring. During the 2004 and 2005 growing seasons, we counted the number of open flowers at each plant species weekly to determine bloom order and time of peak bloom. We also collected, counted, and identified natural enemy insects at each plant species weekly during peak bloom.

Results from 2005 showed that native perennial plants in their third year of growth were quite attractive to natural enemies with many exceeding the attractiveness of frequently recommended plants. In addition, plant bloom periods did overlap, which means that we can pick a subset of the most attractive plant species and still provide nectar and pollen to natural enemies during the entire summer.

During the early season (May through mid-June), native angelica (Angelica atropurpurea) attracted more natural enemies than any other plant, followed by sand coreopsis (Coreopsis lanceolata), Canada anemone (Anemone canadensis), and golden alexanders (Zizia aurea).

During the mid season (July through mid-August) native Indian hemp (Apocynum cannabinum) attracted more natural enemies than any other plant, followed by the native shrubby cinquefoil (Potentilla fruticosa) and meadowsweet (Spiraea alba).

During the late season (mid-August through early October), the native boneset (Eupatorium perfoliatum) was more attractive than any plant. Native horsemint (Monarda punctata) was the second-most attractive to natural enemies, followed by non-native sweet alyssum (Lobularia maritima) and the native cup plant (Silphium perfoliatum) and Riddell’s goldenrod (Solidago riddellii).

We collected many more natural enemies at all of these plants than in a brome and orchard grass mix with no flowering plants. The total number of natural enemies in a sample increased throughout the growing season. During the early season, up to 32 natural enemies were collected per sample, while during the mid season we collected up to 33, and in the late season up to 200 natural enemies per meter 2 of plants.

After two years of research, we have selected a set of 24 native plant species that we found to be very attractive to natural enemies ( see Table 1). We have initiated on-farm demonstration/research to determine if these plant species can be reliably established as strips in crop fields and if this translates into improved pest management. An additional benefit of this approach is that while formerly common, many of these prairie and savanna species have almost completely disappeared from our agricultural landscapes. If proven effective, we may once again enjoy the subtle beauty of these native Michigan plants in our agricultural landscapes.

Table 1. Michigan native plant species best suited to attract natural enemy insects based on both 2004 and 2005 data. Plants listed in 2005 bloom order. 2005 bloom period is indicated by letters: e = early (May-June), m = middle (July-mid-August), and l = late season (mid-August on). Tolerance indicates plant suitable for wet-dry environments.

Bloom 2005 Peak Bloom Date Common Name Genus and species Plant Type Tolerance
Early 24 May Wild strawberry Fragaria virginiana Duchesne 1 Forb Average
Early 6 June Golden alexanders Zizia aurea (L.) Koch Forb Wet
Early 14 June Canada anemone Anemone canadensis L. 1 Forb Average
Early 14 June Penstemon Penstemon hirsutus (L.) Willd. Forb Average
Early 14 June Angelica Angelica atropurpurea L. 1 Forb Average
Early 21 June Cow parsnip Heracleum maximum Bartr. 1 Forb Average
Early 21 June Sand coreopsis Coreopsis lanceolata L. Forb Dry
Mid 12 July Shrubby cinquefoil Potentilla fruticosa auct. non L. Shrub Average
Mid 12 July Indian hemp Apocynum cannabinum L. 2 Forb Average
Mid 2 Aug. Hoary vervain Verbena stricta Vent. Forb Dry
Mid 2 Aug. Swamp milkweed Asclepias incarnata L. Forb Wet
Mid 2 Aug. Yellow coneflower Ratibida pinnata (Vent.) Barnh. Forb Average
Mid 9 Aug. Evening primrose Oenothera biennis L. 3 Forb Average
Mid 9 Aug. Meadowsweet Spiraea alba Duroi Shrub Wet
Late 16 Aug. Yellow giant hyssop Agastache nepetoides (L.) Kuntze Forb Average
Late 16 Aug Horsemint Monarda punctata L. Forb Dry
Late 23 Aug. Ironweed Vernonia missurica Raf. Forb Average
Late 23 Aug. Cup plant Silphium perfoliatum L. Forb Average
Late 23 Aug. Boneset Eupatorium perfoliatum L. Forb Wet
Late 23 Aug. Blue lobelia Lobelia siphilitica L. Forb Average
Late 30 Aug. Pale-leaved sunflower Helianthus strumosus L. Forb Dry
Late 13 Sept. Riddell’s goldenrod Solidago riddellii Frank ex Riddell 4 Forb Wet
Late 20 Sept. New England aster Aster novae-angliae L. Forb Average
Late 27 Sept. Smooth aster Aster laevis L. Forb Average

1 Although attractive to natural enemies, these species are difficult to establish from seed.
2 Apocynum cannabinum is considered an agricultural weed and should be used with caution.
3 Oenothera biennis attracted large numbers of Japanese beetle in both 2004 and 2005.
4 Solidago speciosa may be substituted in dry environments, but was slightly less attractive to natural enemies and attracted more pests.

Dr. Landis’s work is funded in part by MSU‘s AgBioResearch.

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