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 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 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.