Mistletoes Play Different Roles in a Modular Host-Parasite Network

Antagonistic interactions between host plants and mistletoes often form complex networks of interacting species. Adequate characterization of network organization requires a combination of qualitative and quantitative data. Therefore, we assessed the distribution of interactions between mistletoes and hosts in the Brazilian Pantanal and characterized the network structure in relation to nestedness and modularity. Interactions were highly asymmetric, with mistletoes presenting low host specificity (i.e., weak dependence) and with hosts being highly susceptible to mistletoe-specific infections. We found a non-nested and modular pattern of interactions, wherein each mistletoe species interacted with a particular set of host species. Psittacanthus spp. infected more species and individuals and also caused a high number of infections per individual, whereas the other mistletoes showed a more specialized pattern of infection. For this reason, Psittacanthus spp. were regarded as module hubs while the other mistletoe species showed a peripheral role. We hypothesize that this pattern is primarily the result of different seed dispersal systems. Although all mistletoe species in our study are bird dispersed, the frugivorous assemblage of Psittacanthus spp. is composed of a larger suite of birds, whereas Phoradendron are mainly dispersed by Euphonia species. The larger assemblage of bird species dispersing Psittacanthus seeds may also increase the number of hosts colonized and, consequently, its dominance in the study area. Nevertheless, other restrictions on the interactions among species, such as the differential capacity of mistletoe infections, defense strategies of hosts and habitat types, can also generate or enhance the observed pattern.

Parasites in the neighbourhood: Interactions of the mistletoe Phoradendron affine (Viscaceae) with its dispersers and hosts in urban areas of Brazil

Mistletoes constitute an important food resource for animals in many ecosystems. However, these plants are considered pests in urban areas because of deleterious effects they have on the host trees. Studies in urban areas were mostly focused on listing host species or procedures to control the "pest". In this sense, broader studies including several aspects of mistletoes ecology in urban ecosystems are still missing. We studied the interaction of the mistletoe, Phoradendron affine, with its dispersers and hosts in two urban sites in Uberlandia, Brazil. Phoradendron affine fruits were consumed almost exclusively by Euphonia chlorotica, which was crucial for seed germination. Parasitism was recorded in five hosts, two native (Handroanthus chrysotrichus and Tabebuia roseoalba) and three exotic species (Spathodea campanulata, Ligustrum lucidum and Melia azedarach). Mistletoes were found parasitizing larger host trees, a trend commonly reported for mistletoe-host interaction. Mistletoe seed germination was not affected by the trees species, whether host or non-host, but the radicle of germinated seeds could not penetrate the bark and seedlings invariably died in non-host species. We found a high prevalence of parasitism in our study, in comparison to what previous studies reported for natural areas. The spatial distribution of the hosts and high light incidence on isolated host trees may lead to this high prevalence in urban areas. Rather than eradicated, mistletoes in urban areas should be ecologically managed and their importance for bird species conservation must be considered. More studies to determine which bird species are favoured by mistletoe presence in urban areas will be essential for, this purpose. (C) 2012 Elsevier GmbH. All rights reserved.

FRUGIVORY OF NEOSILBA SPECIES (DIPTERA: LONCHAEIDAE) AND THEPYTUS ECHELTA (LEPIDOPTERA: LYCAENIDAE) ON PSITTACANTHUS (SANTALALES: LORANTHACEAE) IN ECOTONAL CERRADO-SOUTH PANTANAL, BRAZIL

This paper presents a survey of the insects that feed on fruits of Psittacanthus Martius (Santalales: Loranthaceae), a hemiparasitic mistletoe genus that infects trees in Brazil and other neotropical countries. The aim of the study was to identify candidate insects for biological control of Psittacanthus mistletoes. Unripe and mature fruits were collected in several localities of Cerrado, bordering South Pantanal, Southwestern Brazil, from 29 Apr 1998 to 30 Jul 2000. A total of 24,710 fruits (54 samples) of Psittacanthus acinarius infecting 15 species from 10 plant families were evaluated. Psittacanthus acinarius (Mart.) was the most abundant and frequent species of mistletoe parasitizing trees in the ecotonal Cerrado-Pantanal. From 24,710 fruits of Psittacanthus acinarius were obtained 1,812 insect larvae including 1,806 Neosilba McAlpine (Diptera: Lonchaeidae) species and 6 Thepytus echelta (Hewitson) (Lepidoptera: Lycaenidae). From these emerged 1,550 Neosilba spp. adults and 6 T. echelta. Neosilba pantanense Strikis was described from this research. Larvae of T. echelta occurred in fruits of P. acinarius parasitizing Cecropia pachystachya Trecul (Urticaceae) and Anadenanthera colubrina (Vellozo) Brenan (Fabaceae). Larvae of Neosilba caused no adverse effects on the germination of infected fruits of Psittacanthus, because they do not eat the embryo or viscin tissues. This differs from the larvae of T. echelta that interrupted the germination of seeds by feeding on those tissues. Thepytus echelta may be a promising insect for the biological control of P. acinarius in the ecotonal Cerrado-Pantanal, although its abundance and frequency were low throughout the sampling period.