In order to estimate the sensitivity of the arthropod pathogen microarray (APM) two positive control samples were prepared in the presence and absence of pathogen-free honey bee RNA. A fulllength (9,264 nucleotide) Drosophila C virus (DCV) clone was in vitro transcribed, serially diluted into honey bee RNA, reversetranscribed, amplified, dye-labeled and hybridized to the APM as described above. Detection of at least 3 of the 8 unique DCV oligonucleotides and their reverse complements resulted in an estimated DCV detection level of 1.9610 5 genome copies (1 pg DCV genomic RNA) in an A. mellifera RNA (1 mg) background. Similarly, detection of a BQCV genome segment (452 nt), corresponding to one array oligo and its reverse complement, diluted into either pathogen-free honey bee RNA (0.5 mg) or water indicated detection limits of 1.2610 5 genome segment copies (30 fg BQCV RNA segment) and 1.2610 4 genome segment copies (3 fg BQCV RNA segment) respectively.