fragments on a 2.5% agarose gel. The two primers used were C2-J-3400 (COII-specific) and TK-N-3785 (tRNAZY~-specific); for primer details see [14]. 1 Drosophila melanogaster (Diptera: Drosophilidae), 2 Grylloblatta rothi (Grylloblattoidea: Grylloblattidae), 3 Ruspolia nitidula (Orthoptera, Ensifera: Tettigonioidea), 4 Cyphoderis monstrosus (Orthoptera, Ensifera: Haglidae), 5 Locusta migratoria (Orthoptera, Caelifera: Acrididae), 60edipoda coerulescens (Orthoptera, Caelifera: Acrididae), 7 Prosphena scudderi (Orthoptera, Caelifera: Pyromorphidae) es that the rearrangement has occurred within Orthoptera, unquestionably a monophyletic group with respect to the other taxa in our sample. These two sets of observations indicate that the KD~DK rearrangement has occurred at least twice during insect evolution; once in the lineage leading to Hymenoptera, and once in the lineage leading to the orthopteran suborder Caelifera. However, the overall divergence of the Apis genome, including the apparently high number of tRNA rearrangements (11 with respect to Drosophila), indicates that the observed gene orders are probably the result of quite separate rearrangement events in the different lineages. Therefore, the observations support a previous study of mtDNA gene order evolution which stressed the importance of considering rearrangements of groups of tRNA genes rather than of individual genes [13]. This has important consequences for any future studies of insect evolution using tRNA gene orders and is, to our knowledge, the first reported case of an apparently homoplastic mtDNA gene rearrangement in metazoans. The result emphasizes the need to sample both a representative number of insects, and a large enough sample of tRNA genes in order to make a correct interpretation of the data. Received March 1 and May 8, 1995