Ecology of mistletoe parasitism in rural landscapes

This study examined the distribution of native mistletoes in agricultural landscapes. Mistletoes occur in all types of wooded habitat, and provide resources for many species. Landscape structure, particularly the overall extent of tree cover, is vital for conserving mistletoes. Their future status depends on effective management across different land tenures.

Non-linear effects of landscape properties on mistletoe parasitism in fragmented agricultural landscapes

Ecological processes such as plant–animal interactions have a critical role in shaping the structure and function of ecosystems, but little is known of how such processes are modified by changes in landscape structure. We investigated the effect of landscape change on mistletoe parasitism in fragmented agricultural environments by surveying mistletoes on eucalypt host trees in 24 landscapes, each 100 km² in size, in south-eastern Australia. Landscapes were selected to represent a gradient in extent (from 60% to 2% cover) and spatial pattern of remnant wooded vegetation. Mistletoes were surveyed at 15 sites in each landscape, stratified to sample five types of wooded elements in proportion to their relative cover. The incidence per landscape of box mistletoe (Amyema miquelii), the most common species, was best explained by the extent of wooded cover (non-linear relationship) and mean annual rainfall. Higher incidence occurred in landscapes with intermediate levels of cover (15–30%) and higher rainfall (>500 mm). Importantly, a marked non-linear decline in the incidence of A. miquelii in low-cover landscapes implies a disproportionate loss of this species in remaining wooded vegetation, greater than that attributable to decreasing forest cover. The most likely mechanism is the effect of landscape change on the mistletoebird (Dicaeum hirundinaceum), the primary seed-dispersal vector for A. miquelii. Our results are consistent with observations that habitat fragmentation initially enhances mistletoe occurrence in agricultural environments; but in this region, when wooded vegetation fell below a threshold of ~15% landscape cover, the incidence of A. miquelii declined precipitously. Conservation management will benefit from greater understanding of the components of landscape structure that most influence ecological processes, such as mistletoe parasitism and other plant–animal mutualisms, and the critical stages in such relationships. This will facilitate action before critical thresholds are crossed and cascading effects extend to other aspects of ecosystem function.

Energetic cost of bot fly parasitism in free-ranging eastern chipmunks

The energy and nutrient demands of parasites on their hosts are frequently invoked as an explanation for negative impacts of parasitism on host survival and reproductive success. Although cuterebrid bot flies are among the physically largest and most-studied insect parasites of mammals, the only study conducted on metabolic consequences of bot fly parasitism revealed a surprisingly small effect of bot flies on host metabolism. Here we test the prediction that bot fly parasitism increases the resting metabolic rate (RMR) of free-ranging eastern chipmunks (Tamias striatus), particularly in juveniles who have not previously encountered parasites and have to allocate energy to growth. We found no effect of bot fly parasitism on adults. In juveniles, however, we found that RMR strongly increased with the number of bot fly larvae hosted. For a subset of 12 juveniles during a year where parasite prevalence was particularly high, we also compared the RMR before versus during the peak of bot fly prevalence, allowing each individual to act as its own control. Each bot fly larva resulted in a ~7.6% increase in the RMR of its host while reducing juvenile growth rates. Finally, bot fly parasitism at the juvenile stage was positively correlated with adult stage RMR, suggesting persistent effects of bot flies on RMR. This study is the first to show an important effect of bot fly parasitism on the metabolism and growth of a wild mammal. Our work highlights the importance of studying cost of parasitism over multiple years in natural settings, as negative effects on hosts are more likely to emerge in periods of high energetic demand (e.g. growing juveniles) and/or in harsh environmental conditions (e.g. low food availability).

The influence of stocking rate and mixed grazing of Angora goats and Merino sheep on animal and pasture production in southern Australia. 4. Gastrointestinal parasitism

Gastrointestinal nematodes limit the growth, production and welfare of goats but there are few reliable sources of information for recommending management practices across flocks. The effects of animal species (Angora goat, Merino sheep, mixed-grazed goats and mixed-grazed sheep at the ratio of 1:1) and stocking rate (SR: 7.5, 10, 12.5 animals/ha) on gastrointestinal parasitism were determined in a replicated experiment on improved annual temperate pastures in southern Australia, from 1981 to 1984. Detailed monitoring of gastrointestinal nematodes was undertaken on animals before, during (five times per year) and at the conclusion of studies using faecal strongyle egg counts (WEC) and total worm counts. Sheep had a greater proportion of nematodes as Teladorsagia spp. and goats a greater incidence of Trichostrongylus spp. Both goats and sheep developed resistance to Nematodirus spp. during the experiment. WEC was similar in goats and sheep at the start of the experimental period but, thereafter, was consistently greater in goats than in sheep. While WEC was highly related to total worm count, the regressions for sheep and goats were different. Increasing the SR increased the WEC of goats and mixed-grazed goats but not of sheep. During the experiment, WEC declined at 7 and 10 animals/ha but increased at 12.5/ha. Mixed grazing with goats provided beneficial effects for sheep at all stocking rates, but the effects for goats were dependent on the stocking rate, being beneficial at 7.5 and 10/ha but harmful at 12.5/ha. The WEC of separately grazed goats were generally higher than the WEC of mixed grazed goats. The WEC of mixed sheep were lower than those of separately grazed sheep. During the experiment, the WEC of mixed grazed sheep declined faster than the WEC of separately grazed sheep but the WEC of separately grazed goats at 12.5/ha and of mixed grazed goats at 10 and 12.5/ha increased. Under the environmental and pastoral conditions examined, Angora wether goats should not be grazed at SR above those recommended for wether sheep. In the present study, the impact of gastrointestinal-nematode infections in goats was reduced at lower SR. Further, mixed grazing of Angora wether goats with wether sheep at or below the recommended SR resulted in reduced gastrointestinal parasitism for both sheep and goats, compared with monospecific grazing conditions. Goats did not represent a gastrointestinal-nematode hazard to sheep. © 2014 CSIRO.

Adherence and intracellular parasitism of Paracoccidioides brasiliensis in Vero cells

Paracoccidioides brasiliensis is a dimorphic fungus known to produce invasive systemic disease in humans. The 43-kDa glycoprotein of P, brasiliensis is the major diagnostic antigen of paracoccidioidomycosis and may act as a virulence factor, since it is a receptor for laminin. Very little is known about early interact-ions between this fungus and the host cells, so we developed in vitro a model system employing cultured mammalian cells (Vero cells), in order to investigate the factors and virulence mechanisms of P. brasiliensis related to the adhesion and invasion process. We found that there is a permanent interaction after 30 min of contact between the fungus and the cells. The yeasts multiply in the cells for between 5 and 24 h. Different strains of P, brasiliensis were compared, and strain 18 thigh virulence) was the most strongly adherent, followed by strain 113 (virulent), 265 (considered of low virulence) and 113M(mutant obtained by ultraviolet radiation, deficient in gp43). P. brasiliensis adhered to the epithelial cells by a narrow tube, while depressions were noticed in the cell surface, suggesting an active cavitation process. An inhibition assay was performed and it was verified that anti-gp43 serum and a pool of sera from individuals with paracoccidioidomycosis were able to inhibit the adhesion of P. brasiliensis to the Vero cells. Glycoprotein 43 (gp43) antiserum abolished 85 % of the binding activity of P. brasiliensis. This fungus can also invade the Vero cells, and intraepithelial parasitism could be an escape mechanism in paracoccidioidomycosis. (C) 2000 Editions scientifiques et medicales Elsevier SAS.

Comparison of the susceptibility of Santa Ines and Ile de France ewes to nematode parasitism around parturition and during lactation

Breeds of sheep with resistance to nematode infection often display a reduced periparturient rise (PPR) in faecal egg counts (FEC) when compared with susceptible sheep. This trial was carried out to compare the resistance of Santa Ines, an indigenous Brazilian breed of sheep, and Ile de France ewes to natural infections by gastrointestinal nematodes, especially in the periparturient period. Twelve Santa lnes and 10 Ile de France ewes were estrus synchronized and then mated (December 2001). Lambing occurred from 30 April to 19 June 2002 and the lambs were weaned at 60 days of age. Faecal egg counts, packed cell volume (PCV), total plasma protein levels and peripheral eosinophils counts were determined from November 2001 to September 2002. To prevent deaths, individual treatment with anthelmintics was provided to ewes with FEC higher than 4000 eggs per gram (EPG) or with PCV lower than 21%. The percentage of Santa Ines ewes treated with anthelmintics was lower than that of Ile de France sheep. Eight of the 10 Ile de France ewes were treated, with one of them requiring four treatments, one requiring three treatments, and two requiring two treatments. The remaining four received a single treatment. In contrast, only 5 of the 12 Santa lnes ewes required treatment and for each this was done only once. The mean values of PCV were in the normal range in the Santa Ines ewes. In contrast, mean PCVs of Ile de France ewes reached a low of 24.5% in the second month after lambing and were significantly lower than Santa Ines 1 month before lambing (P < 0.05) and 2 months after lambing (P < 0.07). The mean plasma protein level was significantly lower in the Ile de France ewes in the second month after lambing (P < 0.01) coinciding with a reduction in PCV. The ewes of both breeds had high mean numbers of eosinophils in blood, which increased even further post-weaning when a marked reduction in FEC occurred. Haemonchus larvae were the most numerous genus in faecal cultures for both breeds followed by Trichostrongylus, Oesophagostomum and Cooperia. A periparturient rise in FEC was observed in both breeds. However, Santa Ines ewes showed a higher capacity to support the infection in an environment contaminated with large number of infective larvae of gastrointestinal nematodes. (C) 2004 Elsevier B.V. All rights reserved.

Parasitism by Oestrus ovis: Influence of sheep breed and nematode infections

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

New reports on parasitism by Haplometroides buccicola (Digenea, Plagiorchiidae) in Brazilian snakes

The occurrence of Haplometroides buccicola (Digenea, Plagiorchiidae) in the esophagus of two Brazilian snakes is reported in the present study. The trematodes were collected from one Micrurus corallinus (Elapidae) and one Phalotris lativittatus (Colubridae); both snakes were found in Botucatu city, São Paulo State, Brazil. Morphological and morphometric analyses of the trematodes are presented. For the first time Micrurus corallinus has been recorded as a host for H. buccicola and this is the second time that P. lativittatus has been reported as a host for this trematode species.

A new workerless inquiline in the Lower Attini (Hymenoptera: Formicidae), with a discussion of social parasitism in fungus-growing ants

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Temporal patterns of parasitism in Diatraea saccharalis Fabr. (Lep., Crambidae) populations at different spatial scales in sugarcane fields in Brazil

Biological control of Diatraea saccharalis is regarded as one of the best examples of successful classical biological control in Brazil. Since the introduction of the exotic parasitoid, Cotesia flavipes, from Pakistan at the beginning of the 1970s, decrease in D. saccharalis infestation in sugarcane fields has been attributed to the effectiveness of this agent. Recently, the native Tachinidae fly parasitoids (Lydella minense and Paratheresia claripalpis) have also been implicated in this success. However, quantitative data confirming the actual contribution of these agents to the control of D. saccharalis are rather limited. The purpose of this study was to investigate the dynamics of the interactions between D. saccharalis and its parasitoids, emphasizing the temporal patterns of parasitism. To investigate this question, a large data set comprising information collected from two sugarcane mills located in the state of São Paulo, Brazil (Barra and Sao Joao sugarcane mills), was analysed. Basically, the data set contained monthly information about the number of D. saccharalis larvae and their parasitoids in each sample (man-hour per sample), the sugarcane varieties cultivated, the age of the sugarcane plants (only at the Sao Joao sugarcane mill) as well as the sugarcane cut at sampling time. The data were collected from March 1984 to March 1997 and from May 1982 to December 1996 for the Barra and Sao Joao sugarcane mills, respectively. Temporal inverse density-dependent parasitism was predominant for both parasitoid species with respect to all spatial scales. Although the temporal pattern of parasitism was not directly density dependent, it was evident that the tachinids and C. flavipes presented positive numerical responses according to variations in D. saccharalis densities through time.

Parasitism capacity of Telenomus remus Nixon (Hymenoptera: Scelionidae) on Spodoptera frugiperda (Smith) (Lepidoptera: Noctuidae) eggs

Este trabalho estudou a capacidade de parasitismo de Telenomus remus Nixon (Hymenoptera: Scelionidae) em ovos de Spodoptera frugiperda (Smith) (Hymenoptera: Scelionidae) nas temperaturas de 15, 20, 25, 28, 31 e 35ºC objetivando usar esse inimigo natural em programas de controle biológico em culturas onde S. frugiperda é considerada praga. O parasitismo ocorrido nas primeiras 24 h foi de 60,90; 81,65; 121,05; 117,55 e 108,55 ovos parasitados por fêmea em massas ovos com aproximadamente 150 ovos, nas temperaturas de 15, 20, 25, 28 e 31ºC. Fêmeas de T. remus causaram mais de 80% do parasitismo dos ovos nas temperaturas de 15, 20, 25, 28 e 31ºC aos 5, 27, 8, 2 e 2 dias, respectivamente. Na temperatura de 35ºC não houve parasitismo. As maiores taxas de parasitismo ocorreram nas temperaturas de 20, 25, 28 e 31ºC. A longevidade média de fêmeas de T. remus nas temperaturas compreendidas entre 15 e 31ºC variou de 15,5 a 7,7 dias. A temperatura máxima testada (35ºC) foi inadequada ao desenvolvimento de T. remus, sendo que nessa temperatura as fêmeas apresentaram longevidade bastante reduzida (1,7±0,02 dia) e não houve emergência de adultos. Todas as curvas de sobrevivência para T. remus foram do tipo I o que mostram que para todas as temperaturas há um aumento da taxa de mortalidade com o tempo.

Parasitism of Greenbugs (Homoptera: Aphididae) by Lysiphlebus testaceipes (Hymenoptera: Braconidae) in Grain Sorghum: Implications for Augmentative Biological Control

Field cage studies were conducted to describe the relationship between the percentage of Lysiphlebus testaceipes (Cresson) parasitism (as measured by aphid mummies) and densities of greenbug, Schizaphis graminum Rondani, on grain sorghum, Sorghum bicolor L. In 1993 and 1994, a biotype E-susceptible grain sorghum hybrid was grown in field cages and L. testaceipes adults were released after each plant was infested with 20 biotype E greenbugs. The release rates were 0, 0.5, 1.0, and 2.0 wasps per plant in 1993, and 0, 0.16, 0.33, and 0.5 wasps per plant in 1994. Greenbugs and mummies were counted 1-2 times a week on all leaves of 2-4 randomly selected plants per cage. A release rate of 0.33-0.5 wasps per plant infested with 20 greenbugs maximized the number of mummies produced and prevented the greenbugs from reaching an economic threshold of 1,000 greenbugs per plant. Peak numbers of mummies occurred ≈400-500 DD (10°C base) after the initial wasp release. Regression analyses showed that the greenbug population started decreasing when the percentage of parasitism (as measured by mummies) reached 20-30 %. Greenbugs in the absence of wasps significantly reduced yield in 1994, but not in 1993.

Spatial pattern of parasitism in Diatraea saccharalis Fab. (Lep., Crambidae) populations at two different spatial scales in sugarcane fields in Brazil

The biological control of Diatraea saccharalis is regarded as one of the best examples of successful classical biological control in Brazil. Since the introduction of the exotic parasitoid, Cotesia flavipes, the decrease in D. saccharalis infestation in sugarcane fields has been attributed to the effectiveness of this agent. Native Tachinidae fly parasitoids (Lydella minense and Paratheresia claripalpis) have also been implicated in the success. Quantitative data confirming the actual contribution of these agents to the control of D. saccharalis are, however, rather scant. The purpose of this study was to investigate the spatial pattern of parasitism of these parasitoids in D. saccharalis populations at two large spatial scales (fields and zones). To investigate this subject, a large data set comprising information collected from a sugarcane mill located in the state of São Paulo, Brazil (São João sugarcane mill) was analysed. When regressions between the proportion parasitism against host density were computed, the percentage of significant regressions with either a positive or a negative slope was very small at both spatial scales for both parasitoid species. Regressing the densities of tachinid-parasitized hosts against host densities per field showed that these parasitoids presented a 'moderate aggregative' response to host densities, as 53.33% of the regressions were positively significant. Cotesia flavipes was 'weakly aggregated' on host densities at the field level, because only 33.33% of the regressions were positively significant. At the zone level, neither aggregative nor spatial proportion parasitism responses were evident for either parasitoid species due to the small percentage of significant regressions computed.