Biotypes B and Q of Bemisia tabaci (Gennadius), collected from the islands of Tenerife and Majorca respectively, were exposed to competition conditions on tomato cv. Marmande in the laboratory. Both biotypes were established in single and mixed cultures at different densities. Increased mortality of biotype Q females and immature instars was observed together with a lower rate of fecundity and progeny size compared to biotype B, when reared in single or mixed cultures. The female:male sex ratio of F1 individuals of biotype Q was higher in single than in mixed cultures. However, the sex ratio of F1 individuals of biotype B was the same in single and mixed cultures, suggesting reproductive interference. Whitefly density did not affect interspecific interactions. It had a moderate effect on developmental rate of both biotypes, and on mortality of immature instars and progeny size of biotype B only. The results indicate that under laboratory conditions the studied biotype B should displace biotype Q.

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The contamination of cereals with mycotoxins produced by species ofFusarium is an important risk to human and animal health. The toxigenic profile is different depending on theFusarium species considered and, in some species, differences can also be observed at intraspecific level. Information about the distribution and variability of the mycotoxigenicFusarium species allow prediction of the toxins that may occur and to devise control strategies. In this work, the occurrence of mycotoxigenicFusarium species associated to cereals was analysed in a wide sample of durum wheat fields (Triticum durum Desf.) and maize from the South West of Spain (Andalucía).F. equiseti, F. graminearum andF. culmorum were the most frequentFusarium species detected in wheat fields followed byF. sambucinum andF. avenaceum, whereas in the case of maize,F. verticillioides andF. proliferatum were the onlyFusarium species present. The relationships of the Spanish isolates from theF. equiseti, F. avenaceum andF. sambucinum species were analysed by nucleotide sequence comparison of a partial region of the Elongation Factor 1 alpha (EF-1α) with other sequences available in data bases. The results indicated thatF. avenaceum andF. equiseti showed high variability and that the SpanishF. equiseti isolates seemed to belong toF. equiseti type II.

The RAPD-PCR technique was employed to identify three endemic Spanish species of Barbus: Barbus bocagei, B. graellsii and B. sclateri, that present very similar morphologies. Using seven primers, six diagnostic bands were found in B. bocagei, 11 in B. graellsii and nine in B. sclateri. Cluster analysis of the genetic similarity values obtained from RAPD data indicated that the species B. bocagei and B. graellsii are more related to each other than to B. sclateri. 1998 The Fisheries Society of the British Isles

The tephritid Bactrocera oleae (Gmelin) is a harmful pest of olive crops; its larvae are monophagous and feed exclusively on olive fruits. Despite the economic importance of this species, important issues remain to be clarified. In the present study, the genetic variability within and among 21 populations was assessed using random amplified polymorphic DNA–PCR (seven primers). A considerable level of intraspecific diversity was detected (at population level: P = 51–70%, Hpop = 4.61; at species level: P = 63%, Hsp = 5.38) but the genetic differentiation among the populations was low (Shannon’s diversity index 14%, amova 4–8%). However, the dendrogram and principal components analysis reflect some interesting points. The most southerly of the Mediterranean populations (Tunisia) differ significantly from the remaining populations. The general results might be explained by the length of time that has elapsed as B. oleae became established in the Mediterranean region, the large effective sizes expected of its populations and gene flow among these populations. The results strongly suggest the existence of a single, large Northern Mediterranean olive fly population rather than several small, isolated populations and have a significant value in terms of control practices.

Random amplified polymorphic DNA (RAPD) markers were used to estimate the population structure and phylogenetic relationships among the eight species of the genus Barbus that inhabit the Iberian Peninsula. Ten random oligodecamers were used to amplify DNA from 232 fish sampled from 15 populations. A total of 270 markers were detected that revealed low levels of genetic variability. The conclusions of cluster analysis indicate two main branches and three welldifferentiated groups: north-eastern, Mediterranean and

Fruit flies (Diptera: Tephritidae) are a species-rich and economically important group. The phylogenetic relationships among the many taxa are still to be fully resolved and the monophyly of several groups is still to be confirmed. This paper reports a study of the phylogenetic relationships among 23 economically important tephritid species (representing several major lineages of the family) which examines the sequence of a region of mitochondrial DNA encompassing the cytb, tRNA(Ser) and ND1 genes. Substitutions characteristic of particular taxa were found that could help classify members of the family at any developmental stage. The trees obtained by the maximum parsimony, neighbour joining and maximum likelihood methods were generally compatible with present morphological classification patterns. However, the data reveal some characteristics of the phylogenetic relationships of this family that do not agree with present classifications. The results support the probable non-monophyletic nature of the subfamily Trypetinae and suggest that Bactrocera cucurbitae (Coquillet) is more closely related to the genus Dacus than to other species of Bactrocera.