Optimizing Trichogramma ostriniae (Hymenoptera: Trichogrammatidae) releases to control European corn borer, Ostrinia nubilalis (Lepidoptera: Crambidae) in bell pepper
The effective dispersal ability of the egg parasitoid Trichogramma ostriniae Pang and Chen was assessed in potato fields on the Eastern Shore of Virginia in spring 2005 and 2006. Approximately 0.5 million T. ostriniae were released from a central release point in separate potato fields. Dispersal was monitored using yellow sticky card traps and European corn borer, Ostrinia nubilalis HÃ¼bner, egg mass sentinels. Adult T. ostriniae dispersed quickly throughout the 0.4 ha (1 acre) sampling area. Parasitism and sticky card captures were highest close to the release point and decreased with increasing distance. Sticky card data were a good fit to the diffusion model used (r² > 0.90) for all but two sampling dates. In 2005 parasitization peaked at 4 days post release with close to 40% of sentinels parasitized at 30m from the release point. The mean distance encompassing 98% (x98) of T. ostriniae for both fields in 2005 was 27.5 (± 2.4) meters. For fields 1 and 2 in 2005, x98 for parasitism was 21 and 26 meters, respectively. In 2006 sticky card data fit the dispersal model moderately well (r² > 0.77) except for two sampling dates and dispersal was generally lower. The mean x98 value for sticky card data was 12.9 (± 0.9) meters. For parasitism, the x98 distances for field 1 and 2 were estimated at 8 and 10 meters, respectively. Correlation analysis showed no significant difference in the distributions between sticky card captures and sentinel egg mass parasitism.
In 2006, T. ostriniae were released in small pepper plots in Pennsylvania, Maryland and two locations in Virginia to evaluate the number of wasps needed per plant for effective control of European corn borer. Treatments included 0, 5, 20 and 50 wasps per plant. In each plot, parasitism was measured using 30 sentinel egg masses collected on 3 and 6 days post release. Parasitism was relatively low in Pennsylvania and Virginia and no significant effect from release density was observed. High rates of parasitization in the untreated control plot were observed in Maryland as well as one of the Virginia locations. Overall results show results show ambiguity in the data and high levels of natural parasitism occurring on Ephestia eggs sentinels.
In 2005 and 2006, several insecticides were evaluated for controlling O. nubilalis and impacting arthropod natural enemies in bell pepper. In addition, we compared the effectiveness of an integrated pest management program based around inundative releases of T. ostriniae to a conventional insecticide-based program for O. nubilalis control in multiple locations in the Mid- Atlantic US. To evaluate the insecticides, small plots of bell pepper were established at four locations in Virginia, Maryland, Delaware, and Pennsylvania. Insecticides were applied weekly from first fruit until final harvest (5 to 7 applications). Results indicated that the biorational insecticides, spinosad, indoxacarb, and methoxyfenozide provided comparable control of O. nubilalis as the broadspectrum conventional insecticides, acephate, and lambda-cyhalothrin. At most locations, multiple sprays of lambda-cyhalothrin resulted in flares (outbreaks) of green peach aphids most likely from destruction of arthropod natural enemies. Indoxacarb also caused a similar aphid flare at one of the locations. For the IPM demonstration experiment, pepper plots were established at 5 locations in the Mid-Atlantic U.S. in 2005 and 2006. Treatments included: "conventional", which involved weekly applications of acephate or lambda-cyhalothrin from first fruit until final harvest; 2) "IPM", which included three or four inundative releases of T. ostriniae and a judicial application of methoxyfenozide only if lepidopteran pests exceeded action thresholds; and 3) an untreated control. No significant treatment effect was found in either year on cumulative number of marketable fruit or percentage of fruit damaged by lepidopteran pests. A significant treatment effect was found on peak numbers of green peach aphids, with the conventional insecticide approach causing aphid flares and the untreated control or IPM approach not having aphid pest problems. Inundative releases of T. ostriniae may be a more environmentally-sound approach to managing O. nubilalis in peppers, although a comparison with conventional insecticides under greater lepidopteran pest pressure is still needed.