A reliable method for rearing the subterranean summer morph of the sugarbeet root aphid, Pemphigus betae Doane, is described. Field-collected aphids were reared using hydroponic growth pouches that allowed exposed root tissue to be fed on by P. betae. The aphid has been maintained in continuous culture for over 3 years. Open pouches were subsequently modified with cages to provide more successful mass rearing. Cages placed on the pouch were devised to provide an arena that concentrated aphids on one area of the pouch, minimized wandering behavior, and ensured a more vigorous colony. During a 10-week mass rearing experiment, caged pouches consistently averaged 120.8± 9.6(SE) aphids per cage (fourth instars and adults) following 2-week incubation periods. Caged pouches also were used to isolate individual aphids for development and fecundity studies. Age-specific life tables were developed for P betae using both open pouches at 20°C, and caged pouches at 24°C. Although the intrinsic rate of increase (rm) was lower at 20 °C on a daily time scale (rm = 0.2314 versus 0.2591), rmwas significantly greater at 20°C on a degree-day (DD 7.6°C) time scale (rm =0.0187 versus 0.0158). The difference on a DD basis resulted primarily from a longer time interval from birth to first reproduction (TFR) at 24°C (TFR = 158.5 versus 147.1 DD at 20°C). These results corroborate previous experience with P. betae, indicating that 20°C appeared to be an optimum temperature for mass rearing. Stable age distributions for P. betae cohorts were only slightly affected by temperature; on average approximately 55, 22, 11, 7, and 5% of the aphids were first, second, third, and fourth instars, and adults, respectively. Though similar studies have not been reported for other Pemphigus spp., all demographic statistics were characteristic of many foliar-feeding aphids held under similar constant temperature conditions.
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We thank Jay Miller (Betaseed Inc., Shakopee, MN) and Bill Neihaus (American Crystal Sugar Co., Moorhead, MN) for providing seed for the project. We also acknowledge Jim Widner, Mark Law, Mark Bredehoeft, Ken Dahl, Mark Bloomquist, and Peter Caspers (Southern Minnesota Sugarbeet Cooperative, Renville, MN) for assistance with locating P. betae infestations in southwestern Minnesota. Appreciation is extended to Roger Moon (University of Minnesota) for reviewing a previous draft of the manuscript. This research was funded in large part by a grant from the Sugarbeet Research and Education Board of Minnesota and North Dakota, and by the University of Minnesota. This is publication 21,421 of the Minnesota Agricultural Experiment Station.
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