Marcílio Fagundes

Direct and indirect interactions involving ants, insect herbivores, parasitoids, and the host plant Baccharis dracunculifolia (Asteraceae)

Abstract.  1. The relative importance of direct and indirect interactions in controlling organism abundance is still an unresolved question. This study investigated the role of the direct and indirect interactions involving ants, aphids, parasitoids, and the host plant Baccharis dracunculifolia(Asteraceae) on a galling herbivore Baccharopelma dracunculifoliae(Homoptera: Psyllidae).

Ant effects on three-trophic level interactions: plant, galls, and parasitoids

1. Ants have evolved mutualistic relationships with a diverse array of plant and animal species. Usually, the predatory/aggressive behaviour of ants near food sources can limit herbivore damage.

Ants and their effects on an insect herbivore community associated with the inflorescences of Byrsonima crassifolia (Linnaeus) H.B.K. (Malpighiaceae)

The effects of ants on the insect community on inflorescences of Byrsonima crassifolia (Malpighiaceae) were tested in an ant exclusion experiment in a cerrado vegetation in southeastern Brazil. Forty-four species of insects (23 families) and nine species of ants (6 genera and 3 subfamilies) were found on the inflorescences of B. crassifolia. The exclusion of ants, primarily Camponotus sericeiventris and Camponotus spp., reduced the treehopper population to 20% of the original abundance. Ant exclusion and time influenced the abundance of chewing (Exclusion, P<0.001; Time, P<0.002), and sucking insects (Exclusion, P<0.02; Time, P<0.01). Twice as many chewing and sucking insects were found on ant-excluded inflorescences as compared to control inflorescences (P<0.001). One and half more sucking insects were found on ant-excluded than on control inflorescences. Only time significantly influenced the richness of chewing and sucking insects associated with B. crassifolia inflorescences. Inflorescences on control branches were significantly less attacked by herbivores than inflorescences on ant-excluded branches (P<0.001). Therefore, these results suggest that the presence of ants alters the structure of insect herbivore community associated with B. crassifolia.

A qualidade do solo afeta a germinação das sementes e o desenvolvimento das plântulas de Dimorphandra mollis Benth. (Leguminosae: Mimosoideae)

Os frutos de Dimorphandra mollis sao coletados de forma indiscriminada para fins comerciais, comprometendo a viabilidade das populacoes naturais. Este estudo teve como objetivo avaliar o efeito da qualidade do solo na germinacao das sementes e no desenvolvimento de plântulas de D. mollis. Solos de tres procedencias (cerrado arenoso, cerrado argiloso e mata seca) foram usados como substratos nos testes de germinacao e desenvolvimento das plântulas. As sementes de D. mollis apresentaram maior germinabilidade em solo de cerrado arenoso (60,5%), seguido por solo de cerrado argiloso (29,7%) e solo de mata seca (13,6%). Alem disto, o indice de velocidade de germinacao (IVG) das sementes de D. mollis foi maior no solo de cerrado arenoso. As raizes das plântulas cultivadas em solo de cerrado arenoso apresentaram maior comprimento do que as cultivadas nos solos de mata seca e cerrado argiloso. Contudo, a massa seca das raizes nao variou entre os tres tratamentos. As plântulas de D. mollis apresentaram maior crescimento e producao de biomassa da parte aerea quando cultivadas em solo de mata seca. Os solos das matas secas normalmente apresentam melhor qualidade nutricional que os solos do cerrado, justificando os resultados observados. Assim, para melhor sucesso da producao de mudas de D. mollis, as sementes devem ser germinadas em substratos que retem pouca agua e as plântulas devem ser cultivadas em solos de melhor qualidade nutricional.

Tri-trophic level interactions affect host plant development and abundance of insect herbivores

Understanding the interactions among plants, hemipterans, and ants has provided numerous insights into a range of ecological and evolutionary processes. In these systems, however, studies concerning the isolated direct and indirect effects of aphid colonies on host plant and other herbivores remain rare at best. The aphid Uroleucon erigeronensis forms dense colonies on the apical shoots of the host plant Baccharis dracunculilfolia (Asteraceae). The honeydew produced by these aphids attracts several species of ants that might interfere with other herbivores. Four hypotheses were tested in this system: (1) ants tending aphids reduce the abundance of other herbivores; (2) the effects of ants and aphids upon herbivores differ between chewing and fluid-sucking herbivores; (3) aphids alone reduce the abundance of other herbivores; and (4), the aphid presence negatively affects B. dracunculifolia shoot growth. The hypotheses were evaluated with ant and aphid exclusion experiments, on isolated plant shoots, along six consecutive months. We adjusted linear mixed-effects models for longitudinal data (repeated measures), with nested spatial random effect. The results showed that: (1) herbivore abundance was lower on shoots with aphids than on shoots without aphids, and even lower on shoots with aphids and ants; (2) both chewing and fluid-sucking insects responded similarly to the treatment, and (3) aphid presence affected negatively B. dracunculifolia shoot growth. Thus, since aphids alone changed plant growth and the abundance of insect herbivores, we suggest that the ant–aphid association is important to the organization of the system B. dracunculifolia-herbivorous insects.

Riqueza e abundância de herbívoros em flores de Vellozia nivea (Velloziaceae)

Vellozia nivea (Velloziaceae) e planta de porte herbaceo que ocorre em solos rochosos, nos campos rupestres da Serra do Cipo, MG. Suas flores hermafroditas sao extremamente macias, representando fonte tenra de alimento para os insetos que predam suas tepalas e estruturas reprodutivas. Este trabalho teve como objetivo observar a influencia da altura e do numero de flores da planta hospedeira na abundância e riqueza de insetos herbivoros. Foram encontradas o total de 21 morfoespecies de insetos (nove familias e tres ordens) associadas as flores de V. nivea. A altura e o numero de flores da planta nao apresentaram correlacoes significativas com a riqueza de herbivoros por planta (r2 = 0,17; P > 0,05). Entretanto, estes dois fatores juntos explicaram 39% da variacao observada na abundância dos insetos herbivoros por planta (P < 0,05). Portanto, o numero de flores e a altura das plantas hospedeiras influenciaram apenas a abundância dos herbivoros.

Ecological Interactions Shape the Dynamics of Seed Predation in Acrocomia aculeata (Arecaceae)

Background The complex network of direct and indirect relationships determines not only the species abundances but also the community characteristics such as diversity and stability. In this context, seed predation is a direct interaction that affects the reproductive success of the plant. For Acrocomia aculeata, the seed predation by Pachymerus cardo and Speciomerus revoili in post-dispersal may destroy more than 70% of the propagules and is influenced by the herbivory of the fruits during pre-dispersal. Fruits of plants with a higher level of herbivory during pre-dispersal are less attacked by predators in post-dispersal. We proposed a hypothesis that describes this interaction as an indirect defense mediated by fungi in a multitrophic interaction. As explanations, we proposed the predictions: i) injuries caused by herbivores in the fruits of A. aculeata favor fungal colonization and ii) the colonization of A. acuelata fruit by decomposing fungi reduces the selection of the egg-laying site by predator. Methodology/Principal Findings For prediction (i), differences in the fungal colonization in fruits with an intact or damaged epicarp were evaluated in fruits exposed in the field. For prediction (ii), we performed fruit observations in the field to determine the number of eggs of P. cardo and/or S. revoili per fruit and the amount of fungal colonization in the fruits. In another experiment, in the laboratory, we use P. cardo females in a triple-choice protocol. Each insect to choose one of the three options: healthy fruits, fruits with fungus, or an empty pot. The proposed hypothesis was corroborated. Fruits with injuries in the epicarp had a higher fungal colonization, and fruits colonized by fungi were less attractive for egg-laying by seed predators. Conclusion/Significance This study emphasizes the importance of exploring the networks of interactions between multitrophic systems to understand the dynamics and maintenance of natural populations.

Differential Female Attack and Larval Performance of a Galling Cecidomyiid on the Host, Astronium fraxinifolium (Anacardiaceae), in Contrasting Habitats

ABSTRACT: We tested two hypotheses that investigated the pattern of attack by a gall-inducing insect on its host plant Astronium fraxinifolium (Anacardiaceae) in two contrasting habitats: cerrado (a savannic formation that indicates harsh conditions) and gallery forest (indicating moist conditions): (i) that galling female preference and larval performance are higher in xeric than mesic habitats; (ii) that vigorous modules are more attacked by the galling female insects where their larvae achieve higher performance independent of the habitat. The attack preference by the female galling did not differ between habitats. However, the larval performance was higher in the xeric habitat (cerrado) (76%) compared to the mesic habitat (gallery forest) (24%), partially supporting the first hypothesis. In general, bottom-up and top-down forces controlling the gall-inducing insect were higher in the mesic habitat. Shoot size of A. fraxinifolium did not influence the selection by the females for oviposition in any of the habitats. But, larger shoots provided better larval performance only in xeric habitats. In this way, galling performance is strongly habitat dependent and long-term differences in mortality rates between mesic and xeric habitats may have led to greater performance and success in dry environments.

Reproductive strategy of Copaifera langsdorffii (Fabaceae): more seeds or better seeds?

The trade-off seed size/number is a recognized phenomenon capable of shaping ecological processes of colonization and establishment of plant species. Studies that describe trade-offs size/number of seeds in supraannual fruiting species are still rare. In this study, two predictions for trade-off size/number hypothesis were tested: (i) on a population scale, seeds produced during years of greater reproductive investment showed reduced size, and (ii) on individual scale there is an inverse relationship between size and number of seeds produced by individual plant. To test these predictions, 102 Copaifera langsdorffii adult plants were monitored monthly from January to September during four consecutive years (2008 to 2011) in order to study the reproductive investment of plants. C. langsdorffii plants exhibited reproductive activity only during years 2008 and 2011. The mean number of seeds per branch was 26.4 % greater in 2008 comparatively to 2011. It was also observed that seed size was greater in the year of 2008, when plants produced greater number of fruits. Thus, the data did not support the first prediction of seed size/number hypothesis. In both reproductive years, there was a negative relationship between seed size and number of seeds, supporting the second prediction of the seed size/number hypothesis. The interaction term with the reproductive year suggests that the trade-off size/number of seeds was indeed stronger in 2011, when the plants produced lower seed number. Finally, this study calls the attention to supra-annual fruiting pattern in C. langsdoffii, and suggests that the phenological patterns contribute to explain the wide variation in their seed size and geographical distribution. Rev. Biol. Trop. 63 (4): 1161-1167. Epub 2015 December 01.

Baccharis: A Neotropical Model System to Study Insect Plant Interactions

The genus Baccharis is composed of ca. 500 species which are distributed primarily in tropical America. It is dioecious and highly diverse in chemistry, architecture, phenology and occupy many different niches across several gradients of light, temperature, humidity, altitude and succession. It is host to the most speciose galling fauna, with more than 121 galling species on 40 host plant. This system provides an ideal scenario to test several ecological hypotheses, including the long standing plant sexual differences on timing and intensity of energy allocation, vigor, architecture and herbivore attack. Moreover its wide distribution enables to test latitudinal and altitudinal gradients on gall attack. We review the studies performed on these Neotropical shrubs related to galling insects. These studies have been crucial for the establishment of generalities and testing of ecological and evolutionary theories across the Americas, as well as to generate new ideas and hypotheses. For these reasons and power of the field and experimental observations we suggest that the galling insects on their Baccharis hosts may represent a Neotropical model system for studies on insect plant interactions.