Chemically-mediated insect behavior in an herb-vegetable sustainable cropping system
2008
Calumpang, S.M.F., Philippines Univ. Los Banos, College, Laguna (Philippines). National Crop Protection Center
Laboratory and small plot field trials were conducted to generate information on the plant-insect interaction, as influenced by head space volatile chemicals, found in a mixed crop (herb/vegetable) sustainable cropping system. Insect bioassays were conducted in caged conditions to assess on oviposition preference of two major insect pests in vegetables: cutworm and eggplant fruit shoot borer to various vegetables (pechay, cauliflower and eggplant) and herbs which included lemon grass, marigold, onions, among others. Choice tests were conducted using 2-3 day old cutworm moths in cages with the potted plants. Egg mass counts on each plant were made 48 hr or 72 hour after introduction. Shoot damage of eggplant seedlings by eggplant fruit shoot borer was assessed 1 week after introduction. Field experiments of selected vegetables and herbs grown together by organic agriculture were conducted at the Institute of Plant Breeding, UPLB. The population dynamics of insect pests and natural enemies were monitored to provide the science behind mixed vegetable gardening without pesticides in the presence of selected herbs. The cropping system involved eggplant and cauliflower. Cage experiment on eggplant, where fruit shoot borer adults were introduced showed that the presence of Thai and Vietnam basil, chives, and non-flowering tarragon did not reduce insect damage. The presence, however, of marigold and bunching onions reduced damage of eggplants. Olfactometric y-tube assays were conducted to assess response of corn borer moths to volatile chemicals of Vietnam basil and vegetables (corn, eggplant and broccoli). Basil extract reduced the attractancy of corn extract to corn borer moths. Broccoli extract was attractive to corn borer moths. Marigold would also be a good companion plant for pechay as the number of cut worm egg masses on pechay is reduced and more are laid on marigold. In addition, cutworm larvae that emerged from eggs laid on marigold did not survive. Field insect pest populations were monitored in a mixed herb vegetable garden consisting of eggplants, sweet and hot pepper, tomato, and ampalaya bordered by basil, bunching onions, red balsam, sunflower and marigold. insect pests found were flea beetles, leafhoppers and mealy bugs while beneficial insects included: ants, dragon flies, spiders, and coccinellid beetles. Fruit borer damage in the mixed vegetable-herb plot was comparable to damage in plots treated with synthetic insecticides. A second cropping system consisting of eggplant intercropped with chives and cauliflower intercropped with dill plant while celery and lemon grass were planted between cauliflower and eggplant during the wet season. This cropping system did not give rise to fruit shoot borer damage but was not able to reduce leaf hopper populations.
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