Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 1, 1996
Publication Date: N/A
Interpretive Summary: At present there are no objective criteria for evaluating the potential of imported fly parasites as biological control agents under different climatic conditions within the US. In this project, temperature effects on host attacks (fly mortality) and reproductive performance of a Brazilan parasitoid, Spalangia gemina, were compared with the two other important native fly parasites. The tests were done under constant temperature conditions so that a computer model could be developed, and then repeated under fluctuating real world conditions for model validation. The Spalangia parasites produced proportionally more males at a high than at low temperatures. One species of parasites had a higher host attack rate and produced more progeny than either the other two species under the test conditions, and was less sensitive to temperature extremes. Models were developed for all species that were highly accurate in predicting host attacks and reproduction under variable temperatures. The models can be incorporated easily into existing fly management models. Based on the data obtained in this study, one species of parasites is predicted to perform well in enclosed poultry facilities throughout the year, and in outdoor situations such as feedlots in early summer and fall, or when mean daily temperatures rarely exceed 25oC.
Technical Abstract: In assays at constant temperatures, Spalangia gemina, S. cameroni and Muscidifurax raptor females killed more house fly pupae at 30oC than at 15, 20, 25 or 35oC, with attack rates for the three species of 11.2, 12.6, and 21.1 pupae killed per parasitoid per day, respectively. Progeny production followed a similar pattern, with maximum daily rates of progeny production of 6.8, 7.5, and 9.2 parasitoids per day at 30oC for S. gemina, S. cameroni, and M. raptor, respectively. Both Spalangia species produced proportionally fewer males at higher temperatures than at lower temperatures; sex allocation by M. raptor was relatively unaffected by temperature except for a trend to produce fewer females at 15oC (29.6% females) than at higher temperatures (43-47%). The four parameter thermodynamic model of Sharpe and DeMichele with high temperature inhibition fit the attack rate and progeny production rate data well. These models were very effective at predicting host attacks and parasitism at high, variable temperatures typical of outdoor mid- summer conditions in many regions, provided that one-hour time steps were used in rate summation algorithms. Assays for long-term net rates of fly destruction revealed that S. gemina and S. cameroni would be most effective for fly control at 25oC and substantially less effective at either low (15oC) or high (35oC) temperatures. M. raptor was equally effective at killing house fly pupae over the 15- 30oC range, but was significantly less effective at 35oC.