A positive coefficient of association (affinity) betweenThe study of association between species of mosquitoes can provide clues to an understanding of their biology and role in the transmission of pathogens. Associations can be due to the sharing of the same breeding places or to the flying and feeding behaviour of adults. For example, the coefficients and indices of association between Culex pipiens and Culex torrentium in containers and in ground pools were studied, with somewhat different values for each habitat 5 . Methods for the study of association were revised 6 , citing several studies on mosquitoes, though none done in South America.Mosquitoes were collected weekly from September to December 2001 in a trail at a secondary forest at Unidade de Conservação Ambiental Desterro (27 o 31'51" S 48 o 30'44" W, 50-150m a.s.l., Florianópolis, Santa Catarina, southern Brazil). Mosquitoes landing on two collectors in the morning, in ten points in the trail, were collected.Three hundred fifty eight mosquitoes, belonging to 22 species, 14 of them new for the fauna of the state, were obtained 4 . Runchomyia reversa Lane & Cerqueira,Ochlerotatus scapularis Rondani, Wyeomyia incaudata (Root) and Anopheles cruzii Dyar & Knab were the predominant species, constituting 62.9% of the total. Samples from below and from above the waist were separated, and 136 samples were analyzed.Coefficients of interspecific association 1 and indices of association 7 8 were calculated to clarify the relationship between pairs of the four species above. The coefficient (C AB ) considers only the numbers of occurrences in which both species are together or separated, while the index of association (I) considers also the numbers of mosquitoes in the collections in which they occur together. The values of the coefficients of association and of the indices of association can vary from +1 (complete association) to -1 (complete dissociation).The coefficients of association, shown in the Table 1, between the species indicate at a first glance some association between Runchomyia reversa and Wyeomyia incaudata (0.22±0.12) and between that species and Anopheles cruzii (0.83±0.04). However, except for the high value of X 2 (15.02) for the coefficient
76Marcondes CB et al of association 1 6 7 between R. reversa and A. cruzii, all the others were lower than the X 2 for the 2 x 2 analysis (3.84). Therefore, most coefficients of association were not significant. In the association between R. reversa and A. cruzii, the product of the number of samples in which both species are absent and that in which both are present is greater than the product of the numbers of samples in which one of them is absent; therefore, this association is positive (affinity) 7 .The indices of association for two pairs (O. scapularis vs W. incaudata and R. reversa vs A. cruzii) were respectively 0.92 and 0.38. This result should be added to the high coefficient of association for R. reversa vs An. cruzii. The habitats of immature insects of the first pair are quite diffe...