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Evaluation of Two Parasitoids in Dairy Calf Greenhouses 2007

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Project Leaders: D. Rutz, Department of Entomology, Cornell University, Ithaca, NY; J.K. Waldron, NYS IPM

Abstract: Parasitoids are a critical component of a successful dairy fly IPM program.  In the first year of this three-year study we compared individual species parasitoid releases.  During year 2, we compared the best individual parasitoid from Year 1 (M. raptorellus) to a 50:50 ratio of M. raptor and M. raptorellus.  Due to record breaking rainfall in 2006, we felt it was critical to have another year of testing to fully compare and understand the differences between the two types of parasitoid releases observed in the 2006 study.  In 2007 (year 3), we again compared M. raptorellus to a 50:50 ratio of M. raptor and M. raptorellus.

Although spot cards have traditionally been used to evaluate house fly populations over time, we observed in this study that they fell well short of meeting our expectations in greenhouses.  In 2007, spot card counts rose throughout the study but in no time period did spot numbers exceed the action threshold level of 100 spots per card.  Interestingly, the average spots per card in 2007 were the lowest of all three years of the study, with the highest average being 57 spots per card.  In 2007, stable fly numbers on the no-release farms were higher than the parasitoid release farms during both the release and post-release periods. 

On no-release farms in 2007, M. raptor, a native NY parasitoid, accounted for 92% successful parasitism and M. raptorellus accounted for 9%.  On M. raptorellus-release farms, the released parasitoid accounted for 77% successful parasitism, while M. raptor accounted for 23%.  On M. raptor/M. raptorellus-release farms, M. raptor accounted for 54% successful parasitism, while M. raptorellus accounted for 46%.  None to very low parasitism was identified during the pre-release period and the first week of releases.  Successful parasitism immediately increased on the six release farms but remained low on the no-release farms for the duration of the study.  Successful parasitism averaged 3% on the no-release farms, 54% on M.raptorellus farms and 44% on M. raptor/M. raptorellus farms during the release period.  Total parasitism averaged 15% on no-release farms, 67% on M. raptorellus-release farms and 53% on M. raptor/M. raptorellus-release farms. 

Based on the results from the past three years of this study, the release of M. raptorellus alone resulted in generally higher overall fly mortality.  When releasing M. raptorellus alone, not only does it costs less than half of what it would to release the 50:50 mix of M. raptor and M. raptorellus,  it also results in the highest level of fly mortality of the three different parasitoid releases tested.