REARING METHODS AND DEMOGRAPHIC-STATISTICS FOR A SUBTERRANEAN MORPH OF THE SUGAR-BEET ROOT APHID (HOMOPTERA, APHIDIDAE)

A reliable method for rearing the subterranean summer morph of the sug arbeet root aphid, Pemphigus betae Doane, is described. Field-collecte d aphids were reared using hydroponic growth pouches that allowed expo sed root tissue to be fed on by P. betae. The aphid has been maintaine d in continuous culture for over 3 years. Open pouches were subsequent ly 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 en sured 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. Cage d 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 degrees C, and caged pouches at 24 degrees C. Although the intrinsic rate of increase (r(m)) was lower a t 20 degrees C on a daily time scale (r(m) = 0.2314 versus 0.2591), r( m) was significantly greater at 20 degrees C on a degree-day (DD > 7.6 degrees C) time scale (r(m) = 0.0187 versus 0.0158). The difference o n a DD basis resulted primarily from a longer One interval from birth to first reproduction (TFR) at 24 degrees C (TFR = 158.5 versus 147.1 DD at 20 degrees C). These results corroborate previous experience wit h P. betae, indicating that 20 degrees C appeared to be an optimum tem perature for mass rearing. Stable age distributions for P. betae cohor ts were only slightly affected by temperature; on average approximatel y 55, 22, 11, 7, and 5% of the aphids were first, second, third, and f ourth instars, and adults, respectively. Though similar studies have n ot been reported for other Pemphigus spp., all demographic statistics were characteristic of many foliar-feeding aphids held under similar c onstant temperature conditions.