A FOOD-WEB APPROACH TO ECONOMIC THRESHOLDS - A SEQUENCE OF PESTS PREDACEOUS ARTHROPODS ON CALIFORNIA COTTON
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The value of an adequate food base for predaceous arthropods as provided by Tetranychus is relevant for the development of economic thresholds for this group and also for pests that occur later in the season. A higher predaceous potential was reflected in greater levels of Geocoris and of Orius on untreated plants with abundant food, as compared with lower predator numbers on insecticide-treated plants having lower food levels. The higher numbers of Geocoris and Orius were significant because they persisted through July-August. In the San Joaquin Valley, an increase in predators during this period is highly beneficial, because Lygus and lepidopterous worms may damage cotton at this time. Policy guidelines on effects from chemicals on arthropods need re-evaluation. The assessment of disruptive effects of chemicals must include their impact on the arthropods that constitute the principal sources of food for predaceous arthropods. The indirect effect of chemicals against beneficial-predaceous insects via disruption of their food chain is highly significant because a considerably longer time-interval is required to replenish the food supply, than is needed for beneficial-predaceous adults to reinvade a field. Results from this study support our contention that at least four components must be considered seasonally in developing economic thresholds for pest management programs: 1) the plants. 2) the complex of key pests, 3) the complex of beneficial arthropods, and 4) sources of food in the form of minor pests required to support significant numbers of predaceous arthropods in agricultural crops. 1982 Balthazar Publications.
