João Vasconcellos-Neto

NATURAL HISTORY OF MISUMENOPS ARGENTEUS (THOMISIDAE): SEASONALITY AND DIET ON TRICHOGONIOPSIS ADENANTHA (ASTERACEAE)

Abstract Seasonal fluctuations, phenology and diet of Misumenops argenteus (Araneae, Thomisidae) on Trichogoniopsis adenantha (Asteraceae) were investigated in the Serra do Japi, southeastern Brazil, over a 2 year period. This spider population increased at the beginning of the rainy season, reaching a peak in March, and decreased in May, reaching its lowest density in the cold/dry season. In the rainy season (December–May), most of the individuals were in the young or juvenile phase (3rd–6th instars). The spiders reached adulthood between the end of the cold/dry season and the beginning of the hot/rainy season. Analysis of temporal displacement (with up to a 3 month delay) detected a one month delay between the blooming period of T. adenantha and the beginning of the rainy season. The number of arthropods (potential prey of M. argenteus) on the plants increased concomitantly with the increase in the number of reproductive branches. The M. argenteus population also increased numerically 2 months after the rise in arthropod density. These results indicate that the spiders require time to respond to changes in environmental conditions. Of the 595 spiders examined, 76 (12.8%) had prey. Prey items included arthropods belonging to several guilds, but spiders showed a preference for wingless prey or prey that remained on the branches for longer periods of time.

ANTI‐HERBIVORE PROTECTION BY MUTUALISTIC SPIDERS AND THE ROLE OF PLANT GLANDULAR TRICHOMES

Although specific associations between spiders and particular types of plants have been reported for several taxonomic groups, their consequences for spiders and plants are still poorly understood. The most common South American lynx spiders, Peucetia flava and P. rubrolineata, live strictly associated with various plant species that have glandular trichomes. To understand more about these spider-plant relationships, we investigated the influence of the spiders on the fitness of a neotropical glandular shrub (Trichogoniopsis adenantha) and on the arthropod community structure on the plant. We also tested whether glandular hairs provided any benefit to the spiders. Spiders reduced the abundance of several species and guilds of herbivores on the leaves and inflorescences. Consequently, damage to the leaves, capitula, ovaries, corollas, and stigmas caused by leaf-mining and chewing insects, as well as endophagous insects, were strongly reduced in the presence of Peucetia spp. Although the spiders fed on flower visitors, their negative influence on ovary fertilization was only marginally nonsignificant (P = 0.065). Spiders on plants of Trichogoniopsis adenantha that fed on common fruit flies that had died before adhering to the glandular trichomes did not lose body mass. However, those living on plants without stalked glandular trichomes (Melissa officinalis) did not feed on dead flies and lost 13-20% of their biomass. These results indicate that Peucetia spiders are effective plant bodyguards and that when there is limited live prey they may feed on insect carcasses adhered to glandular trichomes. Since several spider species of the genus Peucetia live strictly associated with glandular trichome-bearing plants in neotropical, Neartic, Paleartic, and Afrotropical regions, this type of facultative mutualism involving Peucetia and glandular plants may be common worldwide.

Discrimination and release of unpalatable butterflies by Nephila clavipes, a neotropical orb‐weaving spider

Abstract. 1. Nephila clavipes (L.), a common spider in neotropical forests, discriminates some unpalatable prey and releases them unharmed from its web. Release is not accidental but results from a specific behavioural sequence.

Inspection and evaluation of host plant by the butterfly Mechanitis lysimnia (Nymph., Ithomiinae) before laying eggs: a mechanism to reduce intraspecific competition

Females of Mechanitis lysimnia (Lepidoptera: Nymphalidae) show a characteristic searching, inspecting and evaluating behavior on their Solanum host plants. The average egg-clutch size for this butterfly varied with the host species of Solanum. There was a positive relationship between the egg-clutch size of M. lysimnia and the number of leaves, indicating an adjustment between the reproductive effort of the insect and the amount of food available to its offspring. Field experiments showed that butterflies were able to recognize conspecific egg-clusters by visual cues and preferred to lay eggs on egg-free host plants. On large plants that received two or more egg-clusters, later clutches contained fewer eggs than the first one. The butterflies seem to evaluate the amount of food by inspecting the quantity of leaves and by checking for presence or absence of eggs and, possibly, caterpillars before deciding if and how many eggs to lay. These behavioral mechanisms should be important in reducing direct intraspecific competition for the five rare, small and ephemeral host plant species used by this insect.

Microhabitats Occupied by Loxosceles intermedia and Loxosceles laeta (Araneae: Sicariidae) in Curitiba, Paraná, Brazil

Abstract A survey was done of the environments and substrata occupied by Loxosceles intermedia Mello-Leitão, 1934 and Loxosceles laeta (Nicolet, 1849) (Araneae: Sicariidae) in urban woods and anthropic constructions in Curitiba. In total, 2,099 trees, 364 decaying logs as well as stones and roots, built-up areas, and wasteland in six urban parks and 60 residences were inspected. In total, 1,775 m2 of vegetation was inspected, but spiders and their vestiges were collected only in and around buildings in urban parks and residences. L. intermedia was more common than L. laeta and occurred both indoors and outdoors, whereas L. laeta was more common indoors in wooden houses. The two species did not occur in the same microhabitats, although both preferred paper, wood, and construction materials. Spiders collected in urban parks were heavier than those collected in residences, although only males collected in urban parks were larger than those from residences. The lack of vestiges indicative of a previous occupation in the urban parks suggested that both species occupied primarily the anthropic environment where they found numerous substrata that offered thermal isolation and suitable conditions for web fixation, ecdysis, and reproduction.

SPATIAL DISTRIBUTION AND MICROHABITAT PREFERENCE OF PSECAS CHAPODA (PECKHAM & PECKHAM) (ARANEAE, SALTICIDAE)

Abstract Although spiders generally do not have a strong association with the plants on which they live, the jumping spider Psecas chapoda inhabits and breeds on Bromelia balansae (Bromeliaceae). To understand the relationship between Psecas chapoda and Bromelia balansae, we investigated whether the type of habitat (forest or grassland), the size of the bromeliad and the inflorescence of the host plants affected the preference and/or density of P. chapoda. We also examined how spiders of different ages and their eggsacs were distributed on the leaf layers of the rosette of host plants and whether P. chapoda used other plants in addition to B. balanasae. Psecas chapoda occurred with higher frequency on bromeliads in grasslands to those in forest. In grassland, larger bromeliads had more spiders, but this was not true of bromeliads in the forest. This spider avoided bromeliads with inflorescence. Most of the spiderlings (70%) occurred in the central layer of the rosette leaves, and their distribution pattern suggested that they sought shelter to protect themselves from desiccation or cannibalism, both of which are commonly observed in this species. Older spiders, as well as females without eggsacs, occurred in the external layers whereas 90% of the females with eggsacs occurred close to the central layers. Deposition of the eggsacs near the center of the rosette can allow the spiderlings to reach their shelter rapidly and to be less exposed to desiccation and cannibalism. The non-detection of P. chapoda on non-bromeliad plants, and the stereotyped behaviors on the host-plant suggest that this jumping spider was strongly associated with B. balansae.

THE PREY AND PREDATORS OF LOXOSCELES INTERMEDIA MELLO-LEITÃO 1934 (ARANEAE, SICARIIDAE)

Abstract We examined the prey caught in L. intermedia webs in one fragment of forest and in the garage of an urban house in Curitiba, Brazil. A total of 693 prey items was recorded in 131 webs. The prey richness was greater in the forest. The results show that L. intermedia is a dietary generalist. We found remains of L. intermedia in the feces of a frog and a bat in the forest.

Orb‐web spiders (Araneae: Araneomorphae; Orbiculariae) captured by hunting‐wasps (Hymenoptera: Sphecidae) in an area of Atlantic Forest in south‐eastern Brazil

Members of two hunting‐wasp families, Pompilidae and Sphecidae, are among the major predators of orb‐web spiders. In this study, we collected paralysed spiders from natural nests and trap‐nests provisioned by sphecids in an area of Brazilian Atlantic Forest, and compared these data with the composition of species collected by visual searching during one year. Prey preferences were analysed based on the relative abundance of spider species, their size and web characteristics. We also compiled a list of orb‐weavers captured by four sphecid genera reported in 40 other studies. A large number of prey was obtained from natural nests of Trypoxylon (Trypargilum) albonigrum in Parque Estadual Intervales, especially species of Eustala, Parawixia, and Araneus (Araneidae). Other prey, stored in trap‐nests by T. lactitarse and unidentified hunting‐wasp species, included Nephila (Tetragnathidae), Parawixia, Ocrepeira, Mecynogea, Acacesia (Araneidae), and other spider species that were less abundant. All the species that were heavily preyed upon had a relatively lower abundance in our samples of prey availability. The range of body sizes of spiders captured by Trypoxylon in our study area include the size of some abundant orb‐weavers always absent in their nests. These results indicate that factors other than abundance in the field and the spiders size influence prey selection or susceptibility to attack.

Foraging by the flower-dwelling spider, Misumenops argenteus (Thomisidae), at high prey density sites

In this study, the foraging sites of the crab spider Misumenops argenteus on Trichogoniopsis adenantha (Asteraceae) were investigated over a 2-year period. The choice of sites was examined in relation to prey density in rainy and dry seasons, in leaves versus stems, reproductive branches versus vegetative branches, and in flowerheads in different phenophases. Misumenops argenteus generally occupied sites where the prey frequency was high, indicating that this species was able to evaluate the quality of the foraging sites, as predicted by optimal foraging theory. One exception to the rule was that adult males occurred at all sites, independently of prey density, as also observed in other spider species in which males search for females and not for prey. In addition, young (third and fourth instar) spiders occupied flowerheads with few prey, but which provided shelter.

Population dynamics, age structure and sex ratio of the bromeliad-dwelling jumping spider, Psecas chapoda (Salticidae)

In this study, the population fluctuations, phenology and sex ratio of the bromeliad-dwelling jumping spider Psecas chapoda were investigated in an area of semi-deciduous forest in south-eastern Brazil. Psecas chapoda occurred and reproduced on Bromelia balansae (Bromeliaceae) throughout the year. The number of egg sacs increased at the beginning of the rainy season (September to December), but the population size and phenology were stable over time and correlated weakly with rainfall and temperature. The principal factor affecting the dynamics of P. chapoda was the blooming of B. balansae, which expelled spiders because of the drastic change in plant architecture. Male spiders were more frequent than females during the juvenile phase, whereas females were more frequent than males during the subadult and adult phases, suggesting a sex ratio that favoured males. The biotic and abiotic factors that influence the population dynamics and sex-dependent vulnerability determination are discussed.