Field experiments were conducted to investigate the mechanism of the underlying patterns (abundance, species richness, diversity and similarity) of rove beetles in transgenic Bt (MON810) and in near isogenic maize stands in Hungary. During the three-year (2001-2003) survey, 1538 individuals and 21 species were sampled with pitfall traps. The Cry1Ab protein expressed by the MON810 maize hybrid did not influence the overall community structure. After grouping staphylinids into guilds we found no significant differences for non-aphidophagous predators and parasitoids, whereas there were significantly and marginally significantly higher abundances for predators with aphids in their diet in isogenic maize stands in 2002 and 2003 respectively. The abundance of the prey Rhopalosiphum padi (L.) showed a high fluctuation between stands and years and was numerically higher only in isogenic stands in the second half of the maize-growing season. The abundance of predatory guilds including aphids in their diet did not correlate with the total annual number of R. padi in the same year, but there was a linear correlation in successive years.