We investigated the distributional pattern of galling insects along an altitudinal gradient in southeastern Brazil. We sampled insects on 33,000 herbs, 3,520 shrubs, and 1,760 trees, at 44 sites across an elevational gradient of 700 m, in order to test four hypotheses: (a) harsh environment hypothesis that predicts higher galling species richness (GSR) in xeric than in mesic habitats; (b) altitudinal gradient hypothesis that predicts a negative correlation between GSR and altitude; (c) plant richness hypothesis that predicts a positive correlation between GSR and plant species richness (PSR); and (d) plant architecture hypothesis that predicts a positive correlation between GRS and the structural complexity of plants. Only hypothesis (a) was completely confirmed by our study; galling species richness was higher in xeric than in mesic habitats (Wilcoxon test = 5.5816, P < 0.0001). The altitudinal gradient negatively influenced galling richness in xeric habitats (for all plant categories, r 2 = 0.83, F 1,22 = 107.585, P < 0.0001), but there was no significant correlation between galling richness and altitude in mesic habitats (for all plant categories, F 1,18 = 2.251, P > 0.05). The mean number of galling insects was higher on woody than on herbaceous plants, but did not differ between shrubs and trees, refuting the plant architecture hypothesis. The plant richness hypothesis was rejected because the correlation between GSR and PSR could have been influenced by the distribution of plant species along the altitudinal gradient.

ABSTRACT. Galling insect (Insecta) communities in different "cerrado" physiognomies in Minas Gerais, Brazil. Studies on the communities ofgalli ng insects and their host plants were performed in three "cerrado" physiognomies that occ ur in Minas Gerais: "campo suj o", "ce'Tado" sensu slriclu, and "ce'Tadão". Galls and host plants were collected along transects in a total of3,OOO herbs, 300 shrubs and 135 trees in each physiognomy. Ninety two species 01' galling insects (morphotypes) on 62 host plant species of 28 families were found. The highest galling insect richness was observed in the "cen·ado". Approximate ly 75 .0% of galling insects belonged to the Cecidomy iidae (Diptera). The highest gall frequency was found on leaves (58.70%) ofthe host plants, and was glabrous (83.70%). Most gall shape were ellipti c (30.43%). A low similarity in galling insec t species was observed among the three sampled phys iognomies -the highest similarity index was observed between "cerrado" and "cam po sujo" (S~rense n index = 0.20), indicating that the presence of rare spec ies of ga lling insects might be common in these environments.

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Nutrient concentration in the soil had more influence, indirectly, on free-feeding insects than did composition of Q. parviflora leaves. However, gall-forming insects are affected more by leaf quality, attacking fewer sclerophyllous leaves, with larger nutrient but smaller tannin concentrations.

RESUMO -A hipótese do vigor de plantas (HVP) prediz que plantas ou módulos de plantas mais vigorosos são preferencialmente selecionados por fêmeas de insetos galhadores como sítios de oviposição, pois aumentam a chance de sobrevivência da prole. A HVP foi testada para Neopelma baccharidis Buckhardt (Homoptera: Psyllidae) e Rhoasphondylia friburgensis Tavares (Diptera: Cecidomyiidae) que causam galhas em Baccharis dracunculifolia D.C. (Asteraceae), e para duas espécies diferentes de Cecidomyiidae (Diptera) que provocam galhas em Maytenus salicifolia Reiss. (Celastraceae) e Vernonia polyanthes Less (Asteraceae). A abundância de galhas aumentou com o aumento do comprimento do ramo nas quatro espécies, como previsto pela HVP. Entretanto, ao considerarmos a taxa de ataque por unidade de ramo (cm), que inclui nas análises o efeito da disponibilidade de recursos por unidade de comprimento, o padrão de resposta dos quatro galhadores desapareceu. R. friburgensis e o cecidomiídeo que induz galhas em M. salicifolia não responderam ao vigor do ramo (P > 0,05), enquanto as outras espécies responderam diferencialmente. A abundância de galhas de N. baccharidis correlacionou-se negativamente com o aumento do comprimento do ramo (y = 0,185 -0,007x; r² = 0,21; F = 6,013, P < 0,05), enquanto o número de galhas provocadas pelo cecidomiídeo em V. polyanthes correlacionou-se positivamente com o vigor do ramo (y = 0,09 + 0,002x; r² = 0,34; F = 6,157; P < 0,05). Portanto, apenas o padrão de ataque do cecidomíideo galhador em V. polyanthes suportou a HVP. PALAVRAS-CHAVE: Insecta, Diptera, Homoptera, galhas, interações insetoplanta.ABSTRACT -The plant-vigor hypothesis (PVH) predicts that females of galling insects preferentially oviposit on the most vigorous plant or plant modules, where their offspring performance is highest. We tested the PVH on Neopelma baccharidis Buckhardt (Homoptera: Psyllidae) and Rhoasphondylia friburgensis Tavares (Diptera: Cecidomyiidae) which induce galls on Baccharis dracunculifolia D.C. (Asteraceae), and on two different Cecidomyiidae (Diptera)Received 25/II/98. Accepted 23/I/99.