POPULATION TRENDS AND COMPARISON OF SAMPLING METHODS FOR DIURAPHIS-NOXIA AND OTHER CEREAL APHIDS (HOMOPTERA, APHIDIDAE) IN NORTHERN IDAHO

Weekly sampling of Diuraphis noxia ia (Kurdjumov) infesting wheat and barley at four sites in northern Idaho was conducted during the growing seasons from 1989 to 1992. Infestations were higher in the spring-planted than in the fall-planted cereals. Populations of D. noxia began increasing during inflorescence emergence, Zadoks growth stage (ZCS) 50, and reached peak numbers during dough development and caryopsis ripening, ZGS 80-90. D. noxia infestations were highest during 1990 and lowest during 1992. Three survey methods were compared. These included collection of 100 seedlings or tillers per sample for Berlese extraction, an in-field examination of 500 tillers per sample, and an area wide suction trap sample. Results of the comparisons revealed higher mean numbers of D. noxia per tiller from the Berlese method than from the field count method. Comparison of field results with the suction trap collections revealed a definite temporal relationship, suggesting that suction trap counts reflect emigration following local field build up of cereal aphids infesting grain in northern Idaho rather than long distance immigration. Data collected over time from suction trap catches may be useful in predicting future field infestation rates, but will not eliminate the need for field surveys.