Quantifying Pest and Beneficial Insects in Insectary Hedgerows
Final Report - September 2001
Principal Investigator:
Rachael Long
UC Cooperative Extension
70 Cottonwood
Woodland, CA 95695
(530) 666-8734, rflong@ucdavis.edu
Other Investigators:
Coring Pease, UCCE, Yolo County
Cliff Fong, UCCE, Yolo County
Blake Harlan, Harlan Farms
Fred March, March Farms
Jack Meek, Meek Farms
Location of project: Field Crop Farms, Yolo County, Sacramento
Valley, California
Funding:
FY 1999-2000: $7,000
FY 2000-2001: $7,000
Objective
The purpose of our study was to monitor insect activity in hedgerows of flowering plants to quantify the diversity and abundance of beneficial insects and pests using these plants.
In a two-year study, four insectary hedgerows were monitored bimonthly for pest and beneficial insect activity throughout the growing season. Insectary plants refer to plants that provide food (nectar and pollen) for beneficial insects. These 5-year old hedgerows that we sampled are located on field crop farms in California's Sacramento Valley. Plants sampled included toyon, milkweed, elderberry, coyotebrush, coffeeberry, Ceanothus, buckwheat, and yarrow (Table 1). Beneficial insects observed included minute pirate, big-eyed, damsel, and assassin bugs, parasitic wasps, syrphid and tachnid flies, lacewings, and lady beetles (Table 2). Pests observed included cucumber and flea beetles, Lygus, and stinkbugs (Table 3).
Research results showed that insectary hedgerows favored beneficial insects over pests by a ratio of three to one, in both years of our study. Buckwheat consistently had the highest numbers of beneficial insects per square foot, Ceanothus, the lowest. These data were expected because buckwheat has the longest flowering period of the "insectary" plants and produces nectar, a preferred food source for many beneficial insects. Ceanothus, in contrast, has a short flowering period, and the pollen provided by these flowers is hard to digest for many beneficial insects, so not a preferred by some insects.
Some pests were found in the hedgerows, but usually mid- to late in the season, so the hedgerow plants were not contributing to the build-up of early season pests. For example, stinkbugs, a tomato pest, were mostly found feeding on ripened elderberries in the fall. Few immature insects were found on the hedgerow plants, which indicated that pests were not reproducing on them. One exception was buckwheat, which had numerous Lygus bug nymphs (a cotton and strawberry pest). However, Lygus nymphs also provide a food source for minute pirate and big-eyed bugs, which outnumbered the Lygus bugs by ten to one on buckwheat.
We believe that few pests were found in our hedgerows early in the season because these plants lacked seedpods at this time. Many insect pests need the high-energy source provided by seeds for reproduction. The insectary plants in the hedgerows are perennials that set seed later in the season, so were likely not preferred by pests until this time. Hedgerows may serve as replacement vegetation for plants such as mustard, radish, and cheeseweed, which set seeds early in the spring, providing an ideal food source for pests at this time.
Monitoring for pest and beneficial insects was done by visually inspecting two plants of each species in each of four hedgerows for 3 to 5 minutes and recording the types and numbers of insects that visited each plant. Flower heads were tapped onto a collection board to look for smaller insects that hide in them. Care was taken to observe the entire plant. Insect activity was recorded per square foot of plant material to standardize differences in plant size. Plant measurements were taken in the spring and fall.
Average numbers of beneficial and pest insects per plant per site are shown in Figure 1. Seasonal phenology of the different insect species sampled on the plants throughout the growing season is shown in Figures 2 and 3. The following information provides a summary of the types and numbers of beneficial and pest insects found in the hedgerows.
California buckwheat
California buckwheat flowered from June to October. Beneficial insects that were most abundant on this plant included syrphid and tachinid flies, minute pirate and big-eyed bug nymphs and adults, and assassin bugs. Halictid bees, which are important pollinators in some crops, were extremely abundant on this plant when it was blooming. Lygus nymphs and adults (primary pests of cotton, strawberries, and beans) were abundant mid-June to August.
Ceanothus (California lilac)
Ceanothus flowered from March to April. In general, insect counts were low on this plant. The primary floral resource in Ceanothus is pollen, which is not digestible for many beneficial insects. Lacewings, syrphid flies, and honeybees are pollen feeders so these were the most numerous beneficial insects found on this plant. Few pests were found on this plant, although some stinkbugs were observed feeding on the seed-pods late spring.
Coffeeberry
Coffeeberry flowered from May to June. During this time, syrphid and tachinid flies, wasps, and lady beetles were observed feeding on the flowers. In two-years of data collection, coffeeberry attracted the most assassin bugs of all the perennial shrubs. Adults were found in April, then eggs, nymphs, and adults in September and October. Some stinkbugs were found on this plant when berries were ripe in the summer.
Coyote brush
Coyote brush flowered from October to November. Beneficial insects found feeding on the flowers included syrphid and tachinid flies, wasps, minute pirate bugs, and lady beetles. Coyotebrush also hosted aphids that served as prey for lady beetles, lacewings, and wasps throughout the season. Cucumber beetles were the most abundant pests on coyote brush during bloom
Narrow leaf milkweed
Milkweed has a relatively short flowering period in June. During this time syrphid and tachinid flies, minute pirate bugs, lady beetles and wasps were found feeding on the flowers. Milkweed also attracted oleander aphids, which served as prey for lady beetles and wasps throughout most of the growing season. We also found monarch butterflies (larvae and adults) on these plants.
Toyon
Toyon flowered in June and attracted syrphid and tachnid flies, minute pirate bugs, and cucumber beetles. Assassin bug adults and nymphs were observed on toyon mostly from September to November. A few Lygus bug adults and cucumber beetles were found on this plant during its flowering period.
Elderberry
Elderberry flowered from April to October. Syrphid flies and lacewings, and were observed on this plant throughout the flowering period. Elderberry hosted aphids as alternative prey for predators in addition to flower resources. Assassin bugs were present from September to November. Stinkbug adults and nymphs were found feeding on ripened elderberries in the fall, after nearby tomato fields were harvested. Cucumber beetles were found feeding on flower heads early and late in the growing season.
Yarrow
Yarrow flowered from May through July. Syrphid and tachinid flies, minute pirate bugs and wasps were observed from May to June, during peak bloom. Big-eyed bugs were observed from June to October. Some Lygus bug nymphs and adults were found on yarrow from April to June. Flea beetles were present from August to October. This plant was sampled during the first year only because there were not enough flowers at each hedgerow site in the second year of our study.
Potential Benefits/Impacts on Agriculture
California farmers are interested in planting insectary hedgerows to attract beneficial insects for better biocontrol of pests in adjacent crops (Long et al. 1998). However, farmers are also concerned about attracting pests to their farms with hedgerow plantings. While some pests are found in the hedgerows, our data show that perennial insectary plants are not contributing to a build-up of pests on farms. Most pests were found mid-to late in the season, and few were found to reproduce on the plants, especially early in the season. Instead, the insectary hedgerows in our study favored beneficial insects over pests, by a ratio of three to one.
In 2002, our research will focus on whether pest insects over-winter in the hedgerows (with a grant from the Yolo County Resource Conservation District). Preliminary data suggest that stinkbugs over-winter in the deergrass; however, we also find aggregations of lady beetles in these plants. Future research will also focus on whether insectary hedgerows on farms result in better biological control of pests in adjacent field crops. Preliminary data suggest that parasitism of stinkbug eggs by wasps occurs more quickly in tomato plants adjacent to insectary hedgerows than those further away.
This report will be distributed to ATTRA (Appropriate Technology Transfer for Rural Areas) in Davis. Copies will also be given to our local Resource Conservation Districts, which provide on farm assistance to growers interested in planting hedgerows. We are also currently writing a paper for California Agriculture on the results of this research.
I am frequently invited to give talks on insectary hedgerows. Currently, I am scheduled to talk about insectary hedgerows at an upcoming multi-county grape growers' meeting in Mendocino County, as well as at a Pest Management meeting at UC Berkeley.
I am also a statewide resource on hedgerows and frequently receive calls from the agricultural industry to provide information on pest and beneficial insects associated with hedgerow plantings.
Literature Cited
Long RF, Corbett A, Lamb C, et al. 1998. Movement of beneficial insects from flowering plants to associated crops. California Agriculture. 52(5): 23-26.
Hedgerow plants monitored for pest and beneficial insects, 1999-01, Sacramento Valley, CA.
| California lilac | Ceanothus spp |
| California buckwheat | Eriogonum fasciculatum |
| Coffeeberry | Rhamnus californica |
| Coyotebrush | Baccharis pilularis |
| Yarrow | Achillea millefolium |
| Narrow leaf milkweed | Asclepias fascicularis |
| Toyon | Heteromeles arbutifolia |
| Blue elderberry | Sambucus mexicana |
Beneficial insects sampled in the hedgerow plants, 1999-01, Sacramento Valley, CA.
| Minute pirate bug | Orius spp. |
| Assassin bug | Zelus spp., Sinea diadema |
| Big-eyed bug | Geocoris spp. |
| Soldier beetle | Cantharis spp. |
| Green lacewing | Chrysoperla spp., Chrysopa spp. |
| Colops | Colops spp. |
| Lady beetle | Hippodamia convergens |
| Damsel bug | Nabis spp. |
| Hymenoptera | Ichnuemonidae, Braconidae, Vespidae (Polistes spp., Vespula spp.), Sphecidae |
| Hoverflies | Syrphinae |
| Tachinid flies | Archytas apicifer, Gymnosoma spp., Tricopoda pennipes, Cylindromia spp. |
Pest insects sampled in the hedgerow plants, 1999-01, Sacramento Valley, CA.
| Stinkbugs (consperse, Uhler's, red shouldered, and southern green) | Euchistus conspersus, Thyanta pallidovirens, Nezara viridula, Chlorochroa uhleri |
| Lygus bug | Lygus spp. |
| Flea beetle | Chrysomelidae |
| Spotted cucumber beetle | Diabrotica undecimpunctata |
Figure 1. Pest and benefical insects observed on hedgerow plants, Sacramento Valley, CA, 2000.
Figure 2. Seasonal phenology of beneficial insects on hedgerow plants, Sacramento Valley, CA. 2000.
Figure 3. Seasonal phenology of insect pests on hedgerow plants in the Sacramento Valley, CA. 2000.
