Conspecific Avoidance During Foraging in Venturia canescens (Hymenoptera: Ichneumonidae): The Roles of Host Presence and Conspecific Densities

We explored the effects of the presence of conspecifics on host patch choice decisions made by the parasitoid Venturia canescens. Different odor sources were located in plastic boxes at the end of each arm of a glass Y-tube olfactometer. In a set of experiments, odor sources were either (a) host kairomone patches with or without conspecifics (5 or 20) or (b) two odor sources located in successive boxes (a host kairomone patch and a patch with 20 conspecifics in one arm versus a host patch and an empty patch in the other). Our results indicate that V. canescens avoids competition only at high conspecific densities. Avoidance occurs only when foraging wasps perceive the combined odors from host kairomones and conspecific females. Separating the host patch from conspecific parasitoids does not perturb avoidance behavior.     

Ecological interactions of Pseudacteon parasitoids and Solenopsis ant hosts: environmental correlates of activity and effects on competitive hierarchies

1. Solenopsis (Hymenoptera: Formicidae) fire ants are host to Pseudacteon (Diptera: Phoridae) parasitoids. The activity of S. geminata (F.) hosts and relative abundance of Pseudacteon phorids, along with five environmental variables, were measured at weekly intervals over an 8‐month period at two sites. 2. Pseudacteon relative abundances often varied greatly from week to week, and were only weakly positively correlated with S. geminata activity. 3. A quadratic function of soil temperature was the single best predictor of ant activity at both sites, explaining 32 and 73% of the variation in ant activity. A linear function of soil moisture was the single best predictor of phorid relative abundance at one site (r² = 0.23) whereas no measured variables were significant predictors of phorid relative abundance at the other site. 4. Interspecific interactions at 600 baits were monitored at a third site to document dominance hierarchies and determine whether the presence of Pseudacteon phorids mediated interspecific interactions in their host, S. geminata. 5. Solenopsis geminata was near the top of dominance hierarchies, which did not diverge greatly from a linear pattern. Three species (S. geminata, S. invicta Buren, and Crematogaster laeviuscula Mayr) won the majority of their interspecific interactions and appear to be co‐dominants at this microhabitat‐rich site. 6. Overall, the presence of phorids had no significant effect on the outcome of interspecific contests involving S. geminata and all other ant species grouped together. Phorids may have contributed to some of the S. geminata losses against other co‐dominant species.     

Oviposition behavior of an ant-parasitizing fly,Neodohrniphora curvinervis (Diptera: Phoridae), and defense behavior by its leaf-cutting ant hostAtta cephalotes (Hymenoptera: Formicidae)

This study examines the oviposition behavior of the phorid parasitoid Neodohrniphora curvinervisand the antiparasitoid defense behavior of its leafcutting ant host Atta cephalotes. N. curvinervisfemales are diurnal sit- and- wait parasitoids that attack only outbound foragers of head width 1.6 mm or greater. Females deposit a single egg through the foramen magnum of each host successfully parasitized. Pursuit of hosts is usually initiated when an outbound forager of acceptable size passes by a parasitoid perch site. Individual foragers defend themselves against pursuing parasitoids by outrunning them along the foraging trail or by standing their ground and fending them off with their legs,antennae, and mandibles. At the colony level, susceptible foragers are protected against parasitism by a shift in the forager size distribution toward smaller unsusceptible sizes during the day when parasitoids are active and toward larger sizes at night when parasitoids are inactive. The frequency of parasitism of susceptible foragers was 15%, which is more than five times the frequency found in another system involving the phorid parasitoid Apocephalus attophilusand the leafcutting ant host Atta colombica.We offer several possible explanations for such differences in the frequency of parasitism and also examine reasons for the high incidence of superparasitism (19%) observed in the system studied.     

The blood parasite Haemoproteus reduces survival in a wild bird: a medication experiment

While avian chronic haemoparasite infections induce reproductive costs, infection has not previously been shown to affect survival. Here, we experimentally reduced, through medication, the intensity of infection by Haemoproteus parasites in wild-breeding female blue tits Cyanistes caeruleus. However, this treatment did not reduce the intensity of infection in males or the intensity of infection by Leucocytozoon. Medicated females, but not males, showed increased local survival until the next breeding season compared with control birds. To our knowledge, this is the first empirical evidence showing long-term direct survival costs of chronic Haemoproteus infections in wild birds.     

Odonates,gregarines and water mites: why are the same host species infected by both parasites?

1. Damselflies and dragonflies are widely parasitised insects and numerous studies have tried to understand this host–parasite relationship. However, most of these studies have concentrated on a single host species, neglecting the larger pattern within the Odonata order. 2. The aim of this paper was to examine different damselfly and dragonfly species for common endo‐ and ectoparasites and whether a general infection pattern can be found. Additionally, the goal was to investigate whether the phylogeny of the host species could explain these possible infection patterns. To this end, a dataset from the existing literature was compiled and the prevalence of endoparasitic gregarines and ectoparasitic water mites was analysed for 46 different odonate species. 3. Three distinct patterns were found: (i) most of the odonate host species had both gregarines and water mites, rather than only either one or neither; (ii) there appears to be a positive association between gregarine and water mite prevalences across host species; (iii) a weak phylogenetic signal was detected in gregarine prevalence and a strong one in water mite prevalence. 4. It is hypothesised that, due to the infection and transmission mechanisms by which water mites and gregarines infect different odonate host species, parasitism is aggregated to common, high‐density species. However, much research is needed in order to fully understand this relationship between odonates and their parasites, especially within the same host populations and host species assemblages.     

Does structural parasitism by epiphytes exist? A case study between Tillandsia recurvata and Parkinsonia praecox

The effects that epiphytes have on their hosts have been poorly explored in an experimentally. Correlational evidence suggests that epiphytes may be either mutualists or structural parasites, as has been proposed for Tillandsia recurvata on Parkinsonia praecox. To test the effect of T. recurvata upon P. praecox, the epiphyte load on branches of P. praecox was measured and two 1‐year experiments were performed to detect the effect of transplantation/removal of epiphytes and shade (0%, 35%. 50% and 80%) on shoot dynamics. If T. recurvata represents a selective pressure for P. praecox, then the frequency of branches carrying large epiphyte loads will be high, and host shoot survival will decrease in the presence of T. recurvata and with increased shade. A weak inverse relationship between epiphyte load and percentage of dead shoots in the host was detected. Shoot survival was independent of epiphyte presence. Shade decreased shoot survival by 35–72%. Results suggest that at the study site, T. recurvata is a commensalist of P. praecox. An alternative hypothesis to explain the correlation between high epiphyte load and branch/tree decay is that older branches carry more epiphytes, receive more shade from neighbouring branches and could be undergoing a natural decline process.     

When trade-offs interact: balance of terror enforces dominance discovery trade-off in a local ant assemblage

1. Trade-offs underpin local species coexistence. Trade-offs between interference and exploitative competitive ability provie a mechanism for explaining species coexistence within guilds that exploit overlapping resources. 2. Omnivorous, leaf litter ants exploit a shared food base and occur in species-rich assemblages. In these assemblages, species that excel at usurping food items from other species are poor at finding food items first. In assemblages where some members are attacked by phorid fly parasitoids, host species face an additional trade-off between defending themselves against parasitic attack and maximizing their competitive abilities. Host species thus face two trade-offs that interact via the trait-mediated indirect interaction generated by phorid defence behaviour. 3. In this study we test for the existence of these trade-offs and evaluate the predictions of a model for how they interact in an assemblage of woodland ants in which two behaviourally dominant members are attacked by phorid fly parasitoids as they attempt to harvest food resources. 4. The major findings are that unparasitized species in the assemblage follow a dominance-discovery trade-off curve. When not subject to attack by phorid flies, host species violate that trade-off by finding resources too quickly for their level of behavioural dominance. In contrast, when attacked by their phorid parasitoids, the host species dominance drops such that they fall into the assemblage trade-off. 5. These results match the predictions of the balance of terror model, which derives the optimal host response to parasitism, indicating that the host species balance the competing fitness costs of reduced competitive dominance and loss of workers to parasitism. This result supports the view that understanding the structure of ecological communities requires incorporating the indirect effects created by trait plasticity.