Dispersal of Trichogramma ostriniae in Potatoes Anna V. Chapman, Thomas P. Kuhar, Peter B. Schultz Virginia Polytechnic Institute and State University Objective To quantify dispersal of Trichogramma ostriniae Peng and Chen (Hymenoptera: Trichogrammatidae) after innundative releases and determine the number of release points required per acre for effective control of European corn borer (ECB) Ostrinia nubilalis in solanaceous crops. Fig. 1 Commercial Potato field in North Hampton County VA and site of T. ostriniae releases. Rationale Recently, inundative releases of T. ostriniae were evaluated for control of ECB nine fields of sweet pepper in Virginia, Pennsylvania, and Massachusetts (Kuhar et al. 2004a). High rates of parasitism and a significant reduction in cumulative fruit damage has shown T. ostriniae to be a promising biological agent for ECB control in peppers. Determining the effective dispersal ability of T. ostriniae will aid in optimizing release strategies which once developed will help promote the use of T. ostriniae in pepper production. Rather than commercial pepper fields, which are typically small (<2 acres) in size and frequently sprayed with insecticides, this experiment was conducted in commercial potatoes, which have a similar plant spacing and crop architecture, and the necessary attributes to conduct the research. Fig 2 Trichogramma ostriniae on ECB Egg mass Female and Male Ostrinia nubilalis Methods Two releases were made in separate potato fields on the Eastern shore of VA in the summer of In each field, 1-acre square sections were mapped into 24 stations around a single central release point. At each station, a wooden stake bearing a 4x6 in. yellow sticky card (Olson Products, Medina, OH) was placed to capture adult T. ostriniae. Wax paper sentinel strips bearing clusters of 2-4 ECB egg masses were attached on the lower surface of leaves of five neighboring individual plants in a row adjacent to each stake (Wright et al. 2001). Live T. ostriniae parasitoids were shipped from Cornell University via overnight express. Parasitoids were contained in paper cups and fastened to plants in the field following Kuhar et al. (2004a). Approximately 1 million T. ostriniae were released per field from 2 individual release containers positioned in the center of the field. Sentinel eggs and yellow sticky cards were placed in the fields at the time of parasitoid release, and retrieved and replaced every 3-4 days to span a 12d experimental duration. Sticky cards were examined microscopically for Trichogramma. Sentinel egg masses were collected and placed in gelatin capsules to observe for parasitism. Parasitism of sentinel egg masses was quantified as the proportion of retrieved egg masses that were parasitized. Dispersal within the field was mapped as number of T. ostriniae captured on sticky cards as well as proportion of sentinel egg masses parasitized. Egg mass parasitism is the most meaningful measure of dispersal, as this shows how far the wasps traveled and reproduced successfully (Caughley 1980) Central release point l l l ^ l16 m lv l l 14 7l ^ 17 l7 m lv l 15 6l ^ 22 l9 m lv l Fig. 3 Field plot design for Trichogramma ostriniae dispersal study. Each numbered station represent one sticky card and five sentinel egg masses. Results and Discussion Results showed that T. ostriniae dispersed quickly after emergence. Within 1-4 days after emergence, sticky card captures showed T. ostriniae had dispersed to the perimeter 1 acre or at least 45m from a central release point. Four days after emergence, T. ostriniae were uniformly dispersed throughout.5 acres in both fields. In addition, uniform parasitism from 20-80% was observed around.5 acres in field B. Numbers of wasps caught on sticky cards decreased significantly with distance from release point (Fig. 4). Dispersal distance was described by the following equation: y = Ln(x) ; R2 = Within eleven days after emergence cumulative sticky card captures show T. ostriniae dispersed throughout 1 acre in both field plots. Based on these results, a minimum of one release point per acre should be effective for uniform dispersal of Trichogramma ostriniae in solanaceous crops. When applying our results for augmentive control of ECB, it is important to consider dispersal and parasitism in conjunction with ECB suppression. Although T. ostriniae were found over 1 acre, percent parasitism decreased with larger area in both trials. For inundative release strategies, more release points per acre, as well as multiple releases over the season would be needed for effective biological control of ECB in peppers. References Cited Caughley, G Analysis of vertebrate populations. Pitman, Bath, UK. Kuhar, T. P., Barlow, V. M., M. P. Hoffmann, S. J. Fleischer, E. A. Groden, J. Gardner, R. Hazzard, M. G. Wright, S. A. Pitcher, and P. Westgate Potential of Trichogramma ostriniae (Hymenoptera: Trichogrammatidae) as a biological control agent of European corn borer (Lepidoptera: Crambidae) in solanaceous crops. J. Econ. Entomol. 97: Wright, M. G., M. P. Hoffmann, S. A. Chenus and J. Gardner Dispersal behavior of Trichogramma ostriniae (Hymenoptera: Trichogrammatidae) in sweet corn fields: implications for augmentative releases against Ostrinia nubilalis (Lepidoptera: Crambidae). Biol. Contr. 22: