Commercially reared parasitoids were released into three high-rise, caged-layer poultry houses; one house received only N. vitripennis Walker, the second house received only M. raptorellus Kogan & Legner, and the third house received an equal ratio of both species. Overall, house fly parasitism by M. raptorellus was never higher than 7% in any house. Most parasitism in the M. raptorellus release house was attributed to N. vitripennis. Parasitism of house fly pupae by M. raptorellus did not significantly increase during or after the 6-wk release period in the house that received both parasitoids. However, a depression in total parasitism was not detected when releases of the two species were made in this house.

No abstract

Potato leafhopper [PLH; Empoasca fabae (Harris)] is the most damaging pest of alfalfa (Medicago sativa L.) in midwestern and eastern states. Our objective was to compare alfalfa populations with glandular‐hairs (PLH‐resistant) and susceptible populations for forage yield and quality, PLH damage, and PLH nymph and adult populations. Potato leafhopper‐resistant and susceptible alfalfa populations were planted in New York (NY) plot trials in 1997, 1998, and 1999, and compared seeding year through second production year. When PLH populations exceeded the action threshold for NY, PLH‐resistant populations had lower PLH damage scores (2.3 vs. 3.7), fewer number of nymphs per 10 stems (3.5 vs. 6.2), and fewer adult PLHs per five sweeps (9.1 vs. 18.1) than susceptible populations. However, PLH‐resistant populations yielded more than susceptible populations only in one of four trials. Irrespective of PLH damage level, PLH‐resistant populations had higher crude protein (CP) concentration (203 vs. 194 g kg−1) and matured earlier than susceptible populations. Seeding year trials were severely damaged by PLH. The following year at first harvest, PLH‐resistant populations yielded more than susceptible populations (0.24 Mg ha−1 more in 1997 trial, and 0.61 Mg ha−1 more in 1999 trial), even though PLHs were not causing economic damage. Resistant populations that were not treated with insecticide averaged lower total season yields than insecticide‐treated, PLH‐susceptible populations (0.29 Mg ha−1 less in seeding year, 0.95 Mg ha−1 less in production yrs). Potato leafhopper‐resistant populations provide benefits to growers such as higher CP concentration and less hopperburn, but do not provide complete protection against yield loss from PLH damage.

The impact of commercially reared house fly parasitoids released into nine dairy calf coverall facilities were evaluated over 3 yr. Individual and equally mixed ratios of the pteromalid parasitoids Muscidifurax raptor Girault and Saunders and M. raptorellus Kogan and Legner were released at a rate of 500 parasitoids per calf per week for 8 wk. Prerelease, release, and postrelease parasitism was monitored using nearly 100,000 sentinel house fly, Musca domestica L., pupae during the 3 yr study. In general, very few adult parasitoids were recovered during the prerelease period and on the no-release farms during any period. However, considerable numbers of M. raptor and M. raptorellus were recovered from sentinel pupae on respective release farms. As expected, the greatest successful parasitism occurred during release periods, with a drop during postrelease periods. High successful parasitism and uneclosed pupae on M. raptorellus release farms suggests that this parasitoid was aggressive in attacking hosts with progeny production at approximately four wasps per pupa. Solitary releases of M. raptor provided sentinel mortality between 31 and 38%, whereas sentinel mortality on M. raptorellus-release farms was double, at 59-80%. Using mixed releases of the two species, overall fly mortality was slightly lower than that observed on M. raptorellus-only farms. This study documents the advantage of releasing M. raptorellus rather than M. raptor on New York dairy calf facilities, as supported by higher parasitism rates and lower costs (35-75%) for purchase of these gregarious wasps, as 75-80% fewer parasitized pupae are needed to achieve similar adult parasitoid levels.

supplemented by timely cultivations. Growers require more information, especially economic information, be-The USDA has a goal of implementing integrated pest management fore they will adopt these weed management practices. (IPM) practices on 75% of crop area by 2000. Growers require more economic information before adopting IPM practices. A field study of the rotary hoe supplemented by cultivation compared Plant Pathology, Cornell Univ., Ithaca, NY 14853; J.S. Singer, Dep.with broadcast herbicides resulted in similar weed conof Ext., Rutgers Univ., New Brunswick, NJ 08901-8520. Received 9 July 1998. *Corresponding author (wjc3@cornell.edu).Abbreviations: GDD, growing degree days; IPM, integrated pest management. Published in Agron.