The goals of this project were successfully accomplished. First, release of T. thalense parasitoids into BIORAPP fields during the 1998 production seasons added detectable mortality of APM eggs in the field with the highest APM infestation rates (field B2). Additionally, a six-month insecticide-free period was achieved in all BIORAPP fields in the first project season (June 1998 to March 1999-, field B2 was sprayed in March 1999), and in the second year BIORAPP fields did not receive any pesticide applications. Our results demonstrate that we can successfully rear a wild, adapted Trichogramma species in the laboratory, release it into a commercial production field (free of insecticide stress), and collect parasitized APM eggs in the release area. While costs of this program are currently prohibitively high, future improvements in efficiency could make the program economically feasible for growers.
Based on data from the field B5 in 1999, it appears that APM population sizes and damage levels in an annual artichoke production system are similar to those in the perennial system, and that the BIORAPP system was effective in the annual system. However, the annual site in this study was located in a different production area, with different levels of APM pressure, than the rest of the fields in the study. Unfortunately, an annual control site was not available to us in the current study.
There are several ways in which the BIORAPP approach could be further optimized. First, the degree-day model did not consistently result in accurate predictions of APM, perhaps because of low APM numbers, insecticide applications in the C fields, and/or use of long-ten-n temperature averages in the second project year. Second, the percent APM parasitism by laboratory-reared parasitoids reported here is lower and less consistent than those obtained in prior years of our research. Parasitization rates could possibly be increased by improving Trichogramma colony quality. Enhancing the efficiency of release organisms could improve control of APM larval hatch and damage to buds, and would help make mass release of Trichogramma an economically viable control option. Trichogramma effectiveness also needs to be assessed against APM in an annual (six month) artichoke production system; in such a system, the relationships between the timing of artichoke bud maturation, APM generations, and Trichogramma development differ from those of a perennial system, and Trichogramma control strategies may need to be rethought.
Additionally, artichoke yields were not measured in this project. While it is probable that any yield differences would be directly proportional to differences in bud damage between BIORAPP and control fields, a direct determination of yields would be a preferable measurement method. The BIORAPP production systems project results suggest that biorational techniques (parasitoid release, pheromone ropes, mass trapping) can contribute to the suppression of APM damage at an acceptable level for North Coast artichoke -rowers interested in biorational and organically acceptable techniques and monitoring. Further studies are necessary for BIORAPP program optimization and to study the efficacy of this program in an annual artichoke production system.