Evaluation of Beneficial Insect Habitat for Organic Farms
Data were collected in 2003for a project to study the value of beneficial insect habitats that are increasingly being employed by growers on organic farms in the South. There are few data to support farmers in their attempts to increase natural control of pest insects, resulting in a scarcity of guidelines. Some growers are developing their own beneficial insect habitat based on anecdotal information, while others are turning to purchased habitat seed mixtures. While these commercial mixtures appear to offer some of the life sustaining resources needed by beneficial insects there are no data demonstrating seed quality, growth, beneficial insect attraction, or value to nearby crops in the southern United States. The objectives of this project are to 1) examine the purity, germination and on-farm growth characteristics of these commercial seed blends; 2) determine what insects (beneficial or otherwise) are attracted to select cut flower crops, cover crops, and commercial beneficial seed blends, and 3) to construct and evaluate a simple beneficial insect habitat based on existing literature. Composition of samples examined for objective 1 was variable, and often included weed seeds. Germination of the seeds under lab conditions was also variable, with some seeds not germinating because of previous insect damage. Samples collected to satisfy objective 2 indicate that a wide variety of insects are attracted to the seed mixes studied. Although these samples are still being processed, preliminary examination indicates significant differences in species and numbers of insects attracted to the various plant mixes. These insects fell into a variety of feeding categories, and in some cases, most were not beneficial. One interesting portion of this study examined night-flying pests such as hornworm and fruitworm moths. One of the commercial mixes actually had plants with flowers that were extremely attractive to these pest insects, thus potentially creating greater pest problems. The experiment conducted to satisfy the third objective showed no differences in pest numbers, crop damage or yield.. It also revealed no difference in parasitism or predation of fruitworm eggs or hornworm larvae between the plots with commercial habitat surrounding them and the plots with no habitat.
1) To monitor the communities of insects, both beneficial and otherwise, that are attracted to commonly planted cut flowers and cover crops on organic farms.
2) To examine the purity, composition, germination and growth characteristics of commercial seed mixtures sold as beneficial insect habitat.
3) Based on currently available literature, construct and evaluate a simple beneficial insect habitat designed to attract and build populations of the indicator species Trichogramma spp. and Cotesia congregata, egg and larval parasitoids, respectively, for suppression of tomato fruitworm and hornworms
Accomplishments to Satisfy Objective 1: A very wide variety of insects were attracted to the different plant mixes studied. Although these samples are still being processed, preliminary examination indicates significant differences in species and numbers of insects attracted to the various mixes. These insects had a wide range of feeding behaviors. These included beneficial insects such as predators, parasitoids, and pollinators, but also plant feeding pest insects, as well as predators and parasitoids of beneficial insects. In addition to insects attracted to the plants during daylight, we also looked at insects attracted at night. Some of the flowers present in the study plots were highly attractive to night-flying pests such as hornworm and fruitworm moths.
Accomplishments to Satisfy Objective 2: Composition of samples examined for objective 1 was variable, and often included weed seeds. Germination of the seeds under lab conditions was also variable, with some seeds not germinating because of previous insect damage. The germination and purity data are currently being analyzed. A field study looking at season-long growth characteristics of selected commercial beneficial insect habitats is currently underway.
Accomplishments to Satisfy Objective 3: A field experiment to determine if surrounding tomato plots with beneficial insect habitat had any effect on the activity of beneficial insects and pests. A commercial beneficial insect habitat seed mix was used in the study. Plants were started in the greenhouse and transplanted to the field to create an optimal mix of plants, rather than depending on germination and growth in the field.. The beneficial insects primarily examined were Trichogramma wasps and Cotesia congregata, well-known parasitoids of eggs and larvae, respectively, of tomato fruitworms and hornworms. The data have not yet been analyzed, but seasonal charts of egg fate (Fig.s 1a,b) and hornworm larval parasitism (Fig. 2) do not reveal any major differences between plots surrounded by commercial habitat and those surrounded by millet. Data on pest numbers, crop damage and yield were also collected, but have not yet been analyzed.
Figure 1. A = Mean percentage of hornworm (tomato + tobacco) larvae
parasitized by C. glomerata, CEFS, July 2003. B = Mean umber of
hornworm larvae present in tomato plots, CEFS, July 2003.
Figure 2. Mean fate of tomato fruitworm eggs recruited into tomato
Plots, CEFS, July 2003. H = hatched; A = abraded from leaf; P =
Partasitized; Pr = chewing predator; SU = sucking predator; U= unknown;
ST = sterile (unhatchable) eggs
Impacts and Contributions/Outcomes
This ongoing work has already produced information that will ultimately provide organic growers with sorely needed information on insect management. Specifically, it will begin to provide organic growers with guidance on selecting commercial beneficial habitat seed mixes, cut flowers, and cover crops to influence both beneficial and pest insect populations on their farms.
North Carolina State University
Dept. of Entomology
Raleigh, NC 27695-7613
Office Phone: 9195158424
North Carolina State University
Dept. of Crop Science
Raleigh, NC 27695
Office Phone: 9195155644