2001 Annual Report for GS00-005
Investigating the potential use of Trichogramma, a hymenopteran egg parasitoid, in the integrated management of lepidopteran pests of cabbage in Puerto Rico
Summary
Experiments examining host choices by Trichogramma pretiosum in a two-host system indicated that T. pretiosum parasitized the eggs of both host species with no obvious preference. Location of eggs of host species on the cabbage plant was determined.
A questionnaire for a farmer survey was prepared in Spanish and interviews begun in the Fall. A grower workshop on Integrated Pest Management in Cabbage was held in the central mountain region of Puerto Rico to introduce the goals of the survey. The information is needed to establish levels of compatibility between the small-scale farming systems and the proposed management strategies.
Objectives/Performance Targets
- Investigate the parasitism of diamondback moth and soybean looper by Trichogramma in small-scale cabbage production in Puerto Rico. Design of laboratory and field experiments will focus on effects of the two-species host system on parasitism of each host species by Trichogramma.
Characterize the local farming systems and vegetable-growing practices using linear programming, with special focus on cabbage production and the integration of Trichogramma into IPM practices.
Accomplishments/Milestones
Established working relations with farmers in the two main cabbage-producing areas in Puerto Rico. With the help of Dr. Ángel Luis González, Carlos Ortiz and local extension agents we met and made acquaintance with a number of farmers in the cabbage-producing areas of the south coast, around Santa Isabel and in the central mountain areas of Barranquitas and Orocovis. Subsequently made regular visits to the farms to follow the growth and development of the cabbage crop and to understand the management system utilized by the farmers in the large-scale intensive farms on the south coast and by the farmer on the small, family-run farms of the mountains. Insects were collected and weed species noted. The main insect problem was the diamondback moth in all farms. At the beginning of the crop, the presence of cutworms was a problem. Cutworms were generally present through the growth of the crop. Soyabean loopers (Psuedoplusia includens) were not always found in cabbage but when present had the potential to do much damage. A specific problem in Orocovis in the mountains was a root aphid that, in some instances, was killing entire fields of cabbage plants.
Parasitoids found included Cotesia spp., Diadegma insulare, Copidosoma floridanum, Trichogramma spp. & Voria ruralis. The Trichogramma found were sent off for identification. The Trichogramma were found in eggs of a leaf-rolling pyralid (Zinckenia fascialis) that infested a local weed called "peseta" or "verdolaga de hoja ancha (horse purslane, Trianthema portulacastrum). Other common weeds include "coquí" (Cyperus rotundus), "leche vana" (Euphorbia heterophylla), "platanito" (Cleome spp.) and "verdolaga" (Portulaca oleracea). The "leche vana" appeared to be the main alternative host for the aphid populations in Orocovis.
Much of this work was conducted during the time that research facilities at the Río Piedras experimental station were being prepared and the paperwork organized. These had to be completed before research could begin. The Memorandum of Understanding was finally signed early this year. Also it was necessary to request permits for the importation of the Trichogramma used in my experiments. Other permits were sought for the importation of Plutella xylostella and Pseudoplusia includens. Equipment for field experiments and for greenhouse work and the insect cultures were made or purchased.
In February, a field experiment was conducted at the Fortuna Research Station on the south coast. The experiment was designed to determine the parasitism patterns of Trichogramma when offered diamondback moth and soyabean looper as hosts, either in single host choice treatment or in treatments containing both species. Although there were problems with obtaining healthy host insects and with heavy rains, data were collected.
A questionnaire for the farmer survey was prepared in Spanish and tested. One presentation to local extension agents and one grower workshop were held in the central mountain region of Puerto Rico. These activities were used to introduce the objectives of the questionnaire and farmer survey. The interviews began in the Fall and the participating farmers completed the first of three parts of the questionnaire.
Richard Pluke gave a presentation, titled: The possibilities and problems associated with introducing IPM strategies into the farming systems of Puerto Rico, at the Natural Resources Institute (NRI), University of Greenwich, London in January 2001.
Field work will be repeated during the next cabbage-growing season at Fortuna experimental station. Percent parasitism for each host species, number and position of eggs of host species, and pattern of parasitism with regard to host species positioning on plant will be determined. Greenhouse experiments using cages will be conducted to simulate host-choice studies conducted in the field. Investigations will be conducted in the laboratory to determine the potential of shifts in host preference from extended exposure to eggs of each host species. The host choice preferences of three different Trichogramma species will be examined in the laboratory.
Further interviews with growers are scheduled. The questionnaire is designed to gather detailed information on family structure, sources of income (on-farm and off-farm), management practices, timing of activities, labor supply (family/non-family), governmental support programs, family/farm expenses and income amongst others. A model of farm activity will be developed from this information using linear programming. Model will be used to attempt an understanding of farmer decisions as they relate to activities chosen and to see how these choices relate to the fulfillment of chosen objectives. Attempts will be made to identify the system's constraints and strengths to help determine how best IPM or biological control practices could be introduced. Based on initial observations, labor availability may be a problem in the introduction of biological control and IPM practices to local, small-scale farming systems.
Impacts and Contributions/Outcomes
The diamondback moth (DBM) is a severe pest of cruciferous crops throughout the world, including the Southern Region. In response to reduced pesticide efficacy, due to insecticide resistance, we are investigating the use of natural enemies, such as the generalist egg parasitoids, Trichogramma, that have the ability to prevent early feeding by DBM larvae. This research is complimentary to research on other DBM parasitoids in the Southern Region. The farming systems analysis (linear programming) portion of the project will help determine the effects of constraints, farmer objectives, and resources of the cabbage-growing farms in Puerto Rico on the successful introduction and sustainability of IPM strategies, such as the use of Trichogramma. The results of this project will contribute to the acceptance of biological control as a management tool for lepidopterous pests of cabbage on small-scale farms, which, in turn, will contribute to a reduction in the use of insecticides and an increase in the sustainability of cabbage production in the Southern Region.