Abstract.  1. The study of phenotypic plasticity in host utilisation is crucial for predicting evolutionary patterns of insect – plant interactions. The presence of sufficient variation in plasticity may facilitate host race formation and sympatric speciation. 2. Aphis fabae genotypes showed high levels of phenotypic plasticity in the intrinsic rate of natural increase (rm), relative growth rate (RGR), birth weight (BW), adult weight (AW), fecundity (F), and development time (1/d). 3. Thirteen A. fabae genotypes reared both on broad bean and nasturtium exhibited statistically significant genotypic variability in phenotypic plasticity. 4. Some genotypes displayed fitness improvement on novel host plants. 5. Differences in genotypic correlation among fitness components between the two hosts and increased variance on nasturtium indicated different genomic expression on nasturtium. 6. The results indicated that phenotypic plasticity in a novel environment may be a major determinant of the evolutionary trajectory of a parasitic species and might support the idea that speciation starts with phenotypic plasticity.

-(Phenotypic variation and plastic potential of Eugenia calycina Cambess. (Myrtaceae) in a savanna/palm swamp transitional area). The aims of this work were to verify the incidence of phenotypic variation and the plastic potential of Eugenia calycina in a transitional savanna/palm swamp area. Subpopulations were characterized by seed weight, number of seeds per fruit and number of flowers per plant. Moreover, density of occurrence and the rate of parasitism on fruits by larvae of flies (Diptera: Tephritidae) in each area were significantly different. Asynchronism of the flowering period, being late for the savanna area, was also observed. A genetic quantitative model was used to measure phenotypic plasticity based on a reciprocal transplantation experiment of sibling-seeds into soils collected from each area. Three aspects of plastic potential were evaluated: height of steam and number and length of the seedlings leaves. Observed differences in these characters were attributed not only to genetic divergences but also to phenotypic plasticity. The individuals showed different plastic responses, diverging in their ability to respond to environmental influences. The data confirm the role of phenotypic plasticity in the adaptive and evolutionary process involved with ecotype formation in savanna/palm swamp transitional vegetation.Key words -Eugenia calycina, phenotypic plasticity, quantitative genetics RESUMO -(Variações fenotípicas e potencial plástico de Eugenia calycina Cambess. (Myrtaceae) em uma área de transição cerrado-vereda). Este estudo teve como objetivo verificar a ocorrência de variações fenotípicas e o potencial plástico de Eugenia calycina em uma área com gradiente de transição entre vereda e cerrado propriamente dito (ppd). As subpopulações foram caracterizadas quanto ao peso de sementes, número de sementes por fruto e número de flores por planta. Além disto, foram detectadas diferenças nas densidades de ocorrência e taxas de parasitismo por larvas de moscas (Diptera: Tephritidae) em cada área. Houve também assincronia temporal na floração, iniciada tardiamente nas áreas de cerrado ppd. Utilizando-se um modelo de genética quantitativa, a partir de um experimento de replicação recíproca de "sementes irmãs" em solos provenientes de cada área, avaliou-se o potencial para plasticidade em três caracteres: altura da parte aérea, número e comprimento de folhas das plântulas. Diferenças nestes caracteres foram geradas não somente por divergências genéticas entre plantas, mas também por plasticidade fenotípica. Os genótipos apresentaram diferentes respostas plásticas, diferindo em sua habilidade de responder às influências ambientais. Os dados obtidos confirmam o papel da plasticidade fenotípica como mecanismo gerador de variabilidade fenotípica e apontam sua importância nos processos adaptativos e evolutivos envolvidos na formação de ecótipos nas áreas de cerrado recortadas por veredas.Palavras-chave -Eugenia calycina, genética quantitativa, plasticidade fenotípica IntroduçãoPlasticidade fenotípica ...

The study of phenotypic plasticity in host choice behavior is crucial to predict evolutionary patterns of insect-plant interactions. The presence of sufficient variation in plasticity may facilitate host race formation and sympatric speciation. In this study, 13 Aphis fabae Scopoli genotypes reared both on broad bean and nasturtium exhibited statistically significant genotypic variability in host selection behavior. Some genotypes displayed increase in preference and acceptance in a novel host plant through generations. There are also strong conditioning effects of nasturtium as nasturtium reared genotypes are more willing to choose nasturtium over broad bean while broad bean reared genotypes do not show differences in choosing between the two host plants. There are also positive relationships between fitness and host choice behavior particularly for nasturtium. Results of the study supported the hypothesis that phenotypic plasticity in host choice behavior may be one of the major determinants of the evolutionary trajectory of a parasitic species, such as aphids.

ABSTRACT. We examined the influence of climate and man on size and fluctuating asymmetry in two species of Euglossine bees collected from a semideciduous forest reserve. Sixty males of each species were collected; four measurements were made of their wings to obtain a multivariable size index and a fluctuating asymmetry index. No significant differences in the size of Eulaema nigrita Lepeletier were found between the areas and seasons. Larger males of Euglossa pleosticta Dressler were collected during the hot and wet season; however, male size did not vary with location. Higher rainfall and a consequent increase in food availability could have influenced the increase in size of E. pleosticta. Bees collected during the hot and wet season at the forest border were more asymmetric than bees collected during the cold and dry season; the latter were found inside the forest. This indicates that climate and anthropic interferences influence the stability of development of E. pleosticta. Consequently, this species could be used as a bioindicator of stress. Apparently, E. nigrita is more resistant to environmental interference.

-The objective of this work was to record the diversity of parasitoid of two aphid species, Brevicoryne brassicae L. and Aphis nerii Boyer de Fonscolombe in a site at Uberlândia, MG, and the relationship between parasitoid size and their mummies size, with reference to the host species. B. brassicae were collected on kale (Brassica oleracea L. var. acephala D.C.) and A nerii on milkweed (Asclepias curassavica L.). Samplings were made monthly from May, 1999 to May, 2000 in two experimental gardens. Morphometric measurements for both aphids and parasitoids were simplified by PCA analysis to achieve a multivariate size index. The parasitic Hymenoptera species associated with A. nerii were also found as parasitoids of B. brassicae, but with distinctive relative frequencies. Diaeretiella rapae (M'Intoch) (93.2%), Aphidius colemani Viereck (4.5%) and Lysiphlebus testaceipes (Cresson) (2.3%) were the parasitoids obtained from B. brassicae. Hyperparasitoids associated with these parasitoids were Alloxysta fuscicornis (Ashmead) (57.8%), Syrphophagus aphidivorus (Mayr) (25.1%) and Pachyneuron sp. (17.1%). The parasitoids found in A. nerii were: L. testaceipes (96.1%), A. colemani (3.9%) and the hyperparasitoids Pachyneuron sp. (85.2%) and S. aphidivorus (14.8%). Parasitoid size was correlated with mummy size for both A. nerii and B. brassicae. S. aphidivorus from A. nerii were significantly larger than those from B. brassicae. However, such differences were not detected for L. testaceipes, A. colemani or for Pachyneuron. Mummies of A. nerii were significantly larger than those of B. brassicae. No sexual dimorphism for size was detected.