COMPARATIVE EFFECTIVENESS OF 3 RELEASE RATES FOR A PTEROMALID PARASITOID (HYMENOPTERA) OF HOUSE-FLIES (DIPTERA) IN BEEF-CATTLE FEEDLOTS

Muscidifurax zaraptor Kogan and Legner (Hymenoptera: Pteromalidae) was released at three rates in nine beef cattle feedlots in eastern Nebra ska to measure dosage response. Dosage response was measured by the pe rcentage parasitism of sentinel house fly pupae. Releases were made fr om a single location near the center of the pen at three feedlots, fro m two locations within the pen at three feedlots, and from four corner s of the pen at three feedlots. One-time releases initiated held propa gation of M. zaraptor using freeze-killed house fly pupae as hosts. Th ree treatment rates, averaging 4480, 20,300, and 37,100 parasitoids, w ere released weekly over a 15-week period with each of the three relea se methods receiving a low, medium, or high treatment rate. All nine r elease sites produced significantly higher levels of parasitoid emerge nce and sentinel host mortality than sentinel hosts at two control fac ilities. The three sites receiving the high treatment rate averaged 38 % host mortality, compared with 26% for the medium treatment rate and 17% for the low treatment rate. The two control sites averaged 2% host mortality. No significant differences could be detected in the number of release stations except at the four-station method using the low t reatment rate. High temperatures during at least two of the weekly per iods were detrimental to the released parasitoids. (C) 1995 Academic P ress, Inc.