Laboratory rearing conditions select for differences in gene expression between laboratory and wild type horn flies

Poly(A) RNA was purified from newly emerged, 3-5-day-old horn flies, Haemat obia irritans (L.), reared under standardized laboratory conditions, a samp le of the laboratory strain flies reared on a steer for 3-5 days following emergence, and a mixed-age sample of horn flies collected from cattle at th e Camp Cooley ranch in Robertson County, Texas. Differences in gene express ion between these four samples were identified by Northern blot analysis of the RNA, probing with gene-specific probes from eight cDNA clones each enc oding a unique open reading frame (ORF). One cDNA clone, CCMP41, possessed high sequence homology to a gene encoding an alpha E7 carboxylesterase asso ciated with organophosphate (OP) resistance in Lucilia cuprina (Wiedemann). The CCMP41 blot revealed the Camp Cooley field population, which is resist ant to OP insecticides, expressed higher levels of the specific alpha E7-li ke mRNA than the laboratory strain which is susceptible to OPs. Various pat terns of gene expression were detected with the other seven cDNA probes. Th e expression of five mRNAs was much higher in the 3-5-day-old laboratory st rain flies fed on an animal compared to flies from the same strain and of t he same age but reared in cages on citrated bovine blood. These results ind icate that population rearing conditions and history must be considered car efully when conducting comparative studies of gene expression between labor atory-reared and field populations.