High Levels Of Parasitism Research Articles

Fundamental limits of parasitoid-driven host population suppression: Implications for biological control.

Parasitoid wasps are increasingly being used to control insect pest populations, where the pest is the host species parasitized by the wasp. Here we use the discrete-time formalism of the Nicholson-Bailey model to investigate a fundamental question-are there limits to parasitoid-driven suppression of the host population density while still ensuring a stable coexistence of both species? Our model formulation imposes an intrinsic self-limitation in the host's growth resulting in a carrying capacity in the absence of the parasitoid. Different versions of the model are considered with parasitism occurring at a developmental stage that is before, during, or after the growth-limiting stage. For example, the host's growth limitation may occur at its larval stage due to intraspecific competition, while the wasps attack either the host egg, larval or pupal stage. For slow-growing hosts, models with parasitism occurring at different life stages are identical in terms of their host suppression dynamics but have contrasting differences for fast-growing hosts. In the latter case, our analysis reveals that wasp parasitism occurring after host growth limitation yields the lowest pest population density conditioned on stable host-parasitoid coexistence. For ecologically relevant parameter regimes we estimate this host suppression to be roughly 10-20% of the parasitoid-free carrying capacity. We further expand the models to consider a fraction of hosts protected from parasitism (i.e., a host refuge). Our results show that for a given host reproduction rate there exists a critical value of protected host fraction beyond which, the system dynamics are stable even for high levels of parasitism that drive the host to arbitrary low population densities. In summary, our systematic analysis sheds key insights into the combined effects of density-dependence in host growth and parasitism refuge in stabilizing the host-parasitoid population dynamics with important implications for biological control.

Role of Mermithid Nematodes in the Management of Agricultural and Household Insect Pests: A review

The increasing challenges associated with using chemicals in managing agricultural and household insect pests has prompted a re-evaluation of previous approaches and the search for new ones as alternatives or supplements to the present management programmes. The introduction and release of bio-agents, like fungi, bacteria, viruses, nematodes, and insects for the control of pests is a novel biological control strategy. Among bio-agents, the role of mermithid nematodes in insect-pest management has been considered. Mermithids are prime candidates for biocontrol of insects due to their adaptability to the life cycle of the host, a high degree of host specificity often limited to one or more species of insects, high reproductive potential, free swimming behavior making dissemination of pre-parasitic stage easy, pathogenic ability and high levels of parasitism. Another useful trait favoring their employability is their non-feeding habit soon after emerging from the host body, making their handling simple. The morphological, physiological, and behavioral responses of host insects are significantly disrupted by mermithid infective juveniles often the J2 stage. Many mermithid infections cause abdominal distortion, discolored cuticle/integument, and a decrease in total fat body content of the host. The parasitism by these nematodes can lead to formation of intersexual conditions in the host insects which also create distortion to endocrine system. Owing to such mechanism of parasitism of mermithids, these nematodes are one the best considerations as bio-control agents.

Natural Control of Sugarcane Top Borer Scirpophaga excerptalis Walker (Crambidae: Lepidoptera) by Its Egg Parasitoids

The sugarcane shoot borer (Scirpophaga excerptalis) is an herbivorous insect that primarily infests sugarcane plants, leading to the development of dead heart symptoms. This study aimed to investigate the contribution of egg parasitoids in mitigating the occurrence of dead heart caused by S. excerptalis infestation. The research was conducted in Asembagus and Malang, East Java, Indonesia. The samples collection of shoot borer eggs were done twice in Asembagus, and three times in Malang. The collected eggs were examined to determine the percentage of parasitism, and the emerged parasitoids were identified. The infestation level of shoot borers was evaluated by counting the dead heart symptoms within 5 m2 observation units, comprising 18 and 15 units in Asembagus and Karangploso, respectively. Three species of parasitoids, namely Telenomus sp., Trichogramma chilonis, and Tetrastichus sp., were found to parasitize S. excerptalis eggs. The average parasitism levels by Telenomus sp., T. chilonis, and Tetrastichus sp. were 74% (ranged: 50-100%), 0.6% (ranged: 0-4.4%), and 14.3% (ranged: 0-100%), respectively. Telenomus sp. was the predominant egg parasitoid observed in all observations at both sites. There was an inverse relationship between the mortality of shoot borer eggs by parasitoids and the occurrence of dead heart symptoms. Higher levels of parasitism were associated with reduced dead shoot symptoms. The natural control of S. excerptalis through the complex of egg parasitoids holds a promise for effective management of sugarcane shoot borers and promoting sustainable agriculture.

Haematological alterations of mullet Planiliza abu (Heckel, 1843) naturally infected by Ergasilus mosulensis Rahemo, 1982 (Copepoda: Ergaslidae) in a private fish farm from Basrah Province, Iraq

Generally, there is no previous information about haematological parameters of parasitized fish maintained in fish farms in Al- Mashab area, Basrah, Iraq. In this study, the effects of parasitism by the copepod Ergasilus mosulensis. on haemoglobin (Hb), haematocrit (HCT), red blood cells (RBCS), mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH), mean corpuscular haemoglobin concentration (MCHC), and leucocytes were analysed in infected Planiliza abu. The high level of parasitism found in infected fishes was responsible for alterations in blood picture Hb, HCT, RBCS, MCV, MCH, MCHC, and leucocytes (P > 0.05). This is the first report regarding hematology of cultivated freshwater fish which are infected with parasitic copepods in Basrah Province.

Biological Control Options for the Golden Twin-Spot Moth, Chrysodeixis chalcites (Esper) (Lepidoptera: Noctuidae) in Banana Crops of the Canary Islands.

Simple SummaryThe golden twin-spot moth, Chrysodeixis chalcites, is a pest whose larvae cause serious skin injuries to banana fruits in the Canary Islands, reducing their commercial value. The use of Integrated Pest Management (IPM) strategies (cultural, biological, and chemical control) is recommended for the effective and sustainable management of this pest. The identification of its parasitoids and the quantification of their effects on pest populations are essential for the development of biological controls. In this study, we conducted an extensive survey to identify the most important parasitoid species of Ch. chalcites and evaluated the efficacy of the egg parasitoid Trichogramma achaeae as a biological control agent in banana plantations in the Canary Islands. Our findings indicate that populations of native parasitoids can exert a certain degree of natural control over Ch. chalcites. However, their naturally occurring populations are insufficient to minimize the damage caused by this pest. Thus, the development of IPM programs based on the use of selective insecticides, the conservation of natural enemies and inundative releases of mass-reared wasps is also necessary. The parasitoid T. achaeae has been identified as a promising biological control agent of Ch. chalcites in greenhouse banana crops, but it is necessary to carry out further studies to establish the most appropriate release strategies.Chrysodeixis chalcites (Esper) (Lepidoptera: Noctuidae) is a significant pest in banana plantations in the Canary Islands. Field surveys were carried out to identify its naturally occurring parasitoids and estimate their parasitism rates between September 2007 and October 2010. Ch. chalcites was parasitized by six different larval/pupal parasitoid species: Cotesia sp., C. glomerata L. (Hym.: Braconidae), Aplomyia confinis Fallén (Dip.: Tachinidae), Hyposoter rufiventris Perez, Ctenochares bicolorus L. (Hym.: Ichneumonidae) and Aleiodes sp. (Hym.: Braconidae). Among them, Cotesia sp. was the most frequent species, accounting for 8.18% of parasitized larvae. High levels of egg parasitism were detected, with Trichogramma achaeae Nagaraja and Nagarkatti (Hym.: Trichogrammatidae) being the most widely distributed egg parasitoid. A greenhouse assay was also carried out on a commercial banana crop with the aim of evaluating the potential of T. achaeae as a biological control agent and compared with a chemical control. Five periodic inundative releases of 35 adults/m2 every 21 days were necessary to achieve an adequate parasitism level (56.25 ± 1.61%). Moreover, there was 15.75% less foliar damage in the biological control plot compared to the chemical control plot. These results indicate that T. achaeae could be a promising biocontrol agent of Ch. chalcites in greenhouse banana crops.

Relative risk scores generated from laboratory specificity tests predict non-target impacts of Microctonus spp. parasitoids in the field

A ‘relative risk score’ approach to help determine the potential impact of biological control agents on non-target species, previously proposed for weed biocontrol agents and aphid parasitoids, was examined in a retrospective study for Microctonus spp. parasitoids introduced to control pest weevils in New Zealand. ‘Relative risk scores’ (% parasitism for non-target weevil species/% parasitism for target weevil species) were calculated for 20 weevil (New Zealand adventive and indigenous) species and 3 introduced (New Zealand) Microctonus biocontrol taxa (Microctonus aethiopoides Moroccan biotype, Microctonus aethiopoides Irish biotype,and Microctonus hyperodae), based on previously published no-choice host range laboratory testing. Field hosts for each parasitoid and host combination were also examined through an extensive literature review and targeted field surveys. Strong correlations between ‘relative risk scores’ for no-choice laboratory assays and field host binary values (host: yes or no) were obtained for each Microctonus/weevil dataset, but there was no threshold score indicating that the approach cannot be relied upon to predict parasitoid field host ranges with a high degree of certainty. A second analysis that categorized weevil hosts as ‘major field hosts’, if literature records indicated high (≥10%) levels of parasitism in the field, showed a clearer relationship between relative risk score and the probability of a weevil being a major field host. There were no observations of a weevil being a major field host when the relative risk score value was <0.26. There was only one observation of a weevil not being a major field host where the relative risk score was >0.33. This nevertheless, indicates that the approach can mistakenly exclude some acceptable agents that would be host specific in the field. We conclude that this approach could potentially be used to assist risk assessment when introducing Microctonus spp. biocontrol agents, but other factors need to be assessed concurrently to reliably assess risk.

Change in beak overhangs of cliff swallows over 40 years: Partly a response to parasites?

Some birds exhibit a maxillary overhang, in which the tip of the upper beak projects beyond the lower mandible and may curve downward. The overhang is thought to help control ectoparasites on the feathers. Little is known about the extent to which the maxillary overhang varies spatially or temporally within populations of the same species. The colonial cliff swallow (Petrochelidon pyrrhonota) has relatively recently shifted to almost exclusive use of artificial structures such as bridges and highway culverts for nesting and consequently has been exposed to higher levels of parasitism than on its ancestral cliff nesting sites. We examined whether increased ectoparasitism may have favored recent changes in the extent of the maxillary overhang. Using a specimen collection of cliff swallows from western Nebraska, USA, spanning 40 years and field data on live birds, we found that the extent of the maxillary overhang increased across years in a nonlinear way, peaking in the late 2000’s, and varied inversely with cliff swallow colony size for unknown reasons. The number of fleas on nestling cliff swallows declined in general over this period. Those birds with perceptible overhangs had fewer swallow bugs on the outside of their nest, but they did not have higher nesting success than birds with no overhangs. The intraspecific variation in the maxillary overhang in cliff swallows was partly consistent with it having a functional role in combatting ectoparasites. The temporal increase in the extent of the overhang may be a response by cliff swallows to their relatively recent increased exposure to parasitism. Our results demonstrate that this avian morphological trait can change rapidly over time.

Seasonal activity of oil palm leaf webworm, Acria meyricki Shashank and Ramamurthy and its natural enemies in oil palm-cocoa intercropping system and their management in oil palm

The pest was active during October to March. The population density ranged from 0.31 to 2.31 larvae/frond and 0.05 to 9.35 larvae/frond during first and second study periods respectively. The larval parasitoid, Dolichogenidea hyposidrae Wilkinson (Hymenoptera: Braconidae) was recorded to the tune of 7.14 to 98.21% and 2.66 to 95.0% during the first and second study periods respectively. Level of parasitism by pupal parasitoid, Brachymeria albotibialis (Ashmead) (Hymenoptera: Chalcididae) was 8.62 to 64.0%. In oil palm-cocoa intercropping system, lower pest density, lower pest damage and high level of parasitism by natural enemies were recorded. Insecticides viz., deltamethrin, lambda cyhalothrin, chlorantraniliprole, thiodicarb and fipronil were found effective in managing this pest under severe conditions in oil palm gardens.

Climate change affects the parasitism rate and impairs the regulation of genes related to oxidative stress and ionoregulation of Colossoma macropomum

Global climate change represents a critical threat to the environment since it influences organismic interactions, such as the host-parasite systems, mainly in ectotherms including fishes. Rising temperature and CO2 are predicted to affect this interaction other and critical physiological processes in fish. Herein, we investigated the effects of different periods of exposure to climate change scenarios and to two degrees of parasitism by monogeneans in the host-parasite interaction, as well as the antioxidant and ionoregulatory responses of tambaqui (Colossoma macropomum), an important species in South American fishing and aquaculture. We hypothesized that temperature and CO2 changes in combination with parasite infection would interfere with the host’s physiological processes that are related to oxidative stress and ionoregulation. We experimentally exposed C. macropomum to low and high levels of parasitism in the current and extreme climate scenarios (4.5 °C and 900 ppm CO2 above current levels) for periods of seven and thirty days and we use as analyzed factors; the exposure time, the climate scenario and parasitism level in a 2 × 2 × 2 factorial through a three-way ANOVA as being fish the experimental unit (n = 8). An analysis of gill enzymatic and gene expression profile was performed to assess physiological (SOD, GPx and Na+/K+-ATPase enzymes) and molecular (Nrf2, SOD1, HIF-1α and NKA α1a genes) responses. A clear difference in the parasitism levels of individuals exposed to the extreme climate scenario was observed with a rapid and aggressive increase that was higher after 7 days of exposure though showed a decrease after 30 days. The combination of exposure to the extreme climate change scenario and parasitism caused oxidative stress and osmoregulatory disturbance, which was observed through the analysis of gene expression (Nrf2, SOD1, HIF-1α and NKA α1a) and antioxidant and ionoregulatory enzymes (SOD, GPx and Na+/K+-ATPase) on the host, possibly linked to inflammatory processes caused by the high degree of parasitism. In the coming years, these conditions may result in losses of performance for this species, and as such will represent ecological damage and economical losses, and result in a possible vulnerability in relation to food security.

Unexpected parasitism of Douglas-fir seed chalcid limits biocontrol options for invasive Douglas-fir in New Zealand

Douglas-fir seed chalcid (DFSC) Megastigmus spermotrophus, a small (3 mm long) host-specific seed-predatory wasp, was accidentally introduced into New Zealand in the 1920s. Concern over DFSC reducing Douglas-fir seed production in New Zealand led to an attempt at biocontrol in 1955 with the release, but failed establishment, of the small (2.5 mm long) parasitoid wasp, Mesopolobus spermotrophus. We investigated why DFSC causes little destruction of Douglas-fir seed in New Zealand (usually &lt;20%) despite the apparent absence of major natural enemies. Douglas-fir seed collections from 13 New Zealand sites yielded the seed predator (DFSC) but also potential parasitoids, which were identified using morphology and partial COI DNA sequencing. DFSC destroyed only 0.15% of Douglas-fir seed. All parasitoids were identified as the pteromalid wasp, Mes. spermotrophus, the host-specific biocontrol agent released in 1955. Total parasitism was 48.5%, but levels at some sites approached 90%, with some evidence of density-dependence. The discovery of the parasitoid Mes. spermotrophus could indicate that the biocontrol agent released in 1955 did establish after all. Alternatively, Mes. spermotrophus could have arrived accidentally in more recent importations of Douglas-fir seed. The high level of parasitism of DFSC by Mes. spermotrophus is consistent with DFSC being under successful biological control in New Zealand. Suppression of DFSC populations will benefit commercial Douglas-fir seed production in New Zealand, but it also represents the likely loss of a potential biological control agent for wilding Douglas-fir.

Pre‐emptive host‐specificity testing of Trissolcus japonicus (Ashmead) (Hymenoptera: Scelionidae) reveals high parasitism levels against the endemic New Zealand alpine shield bug in laboratory no‐choice tests

AbstractBrown marmorated stink bug (BMSB), Halyomorpha halys (Hemiptera: Pentatomidae), is a serious horticultural pest causing considerable damage to local production and international supply chains as it spreads around the world. The samurai wasp, Trissolcus japonicus (Hymenoptera: Scelionidae), is well recognised as the most promising classical biological control against BMSB. The wasp has been conditionally approved for release in New Zealand in the event the stink bug establishes here. Previous host range testing showed that all available non‐target New Zealand pentatomids except a single exotic species were accepted for oviposition and that the parasitoid was capable of parasitising the eggs of two native pentatomids at proportions similar to BMSB. Only one New Zealand species of pentatomid, the endemic alpine shield bug Hypsithocus hudsonae, was not previously tested owing to the difficulty of collecting it from the field. Here we report the results of no‐choice oviposition tests between H. hudsonae and T. japonicus, conducted in containment, to complement previous physiological host range testing of this parasitoid in New Zealand. Parasitoids emerged from 14 out of 15 egg masses, and in total, from 78 out of 83 eggs (94%). The mean sex ratio was 89% female, and no males emerged from six egg masses. H. hudsonae is confirmed as a physiological host for T. japonicus, and this finding is discussed in relation to the strengths and limitations of physiological host range studies.

Vector-Borne Blood Parasites of the Great-Tailed Grackle (Quiscalus mexicanus) in East-Central Texas, USA.

Great-tailed grackles (Quiscalus mexicanus) have dramatically expanded into North America over the past century. However, little is known about the blood that parasites they support. Here, for the first time, we document an assemblage of trypanosome, haemosporida, and filarial nematodes co-circulating in invasive great-tailed grackles. Between February and July, 2015, 61 individuals were captured in an urban environment of College Station, Texas. Field microscopy and molecular diagnostics indicate that 52% (24/46) were visually infected with filarioid nematodes, 24% (11/46) with avian trypanosomes, and 73% (n = 44/60) with haemosporida parasites, such as Haemoproteus (Parahaemoproteus) and Plasmodium cathemerium. Overall, 87% of great-tailed grackles were infected with blood parasites. Although 50% of individuals hosted parasites from multiple phylum, no patterns of parasite assembly were observed. Results indicate that great-tailed grackles can support a relatively high level of blood parasitism. However, the consequences for avian health remain to be determined.

Epidemiological transitions in human evolution and the richness of viruses, helminths, and protozoa.

Background and objectivesIn absolute terms, humans are extremely highly parasitized compared to other primates. This may reflect that humans are outliers in traits correlated with parasite richness: population density, geographic range area, and study effort. The high degree of parasitism could also reflect amplified disease risk associated with agriculture and urbanization. Alternatively, controlling for other variables, cultural and psychological adaptations could have reduced parasitism in humans over evolutionary time.MethodologyWe predicted the number of parasites that would infect a nonhuman primate with human phenotypic characteristics and phylogenetic position, and then compared observed parasitism of humans in eight geopolitical countries to the predicted distributions. The analyses incorporated study effort, phylogeny, and drivers of parasitism in 33 primate species.ResultsAnalyses of individual countries were not supportive of either hypothesis. When analyzed collectively, however, human populations showed consistently lower than expected richness of protozoa and helminths, but higher richness of viruses. Thus, human evolutionary innovations and new parasite exposures may have impacted groups of parasites in different ways, with support for both hypotheses in the overall analysis.Conclusions and implicationsThe high level of parasitism observed in humans only applies to viruses, and was not extreme in any of our tests of individual countries. In contrast, we find consistent reductions in protozoa and helminths across countries, suggesting reduced parasitism by these groups during human evolution. We propose that hygienic and technological advances might have extinguished fecal-orally or indirectly transmitted parasites like helminths, whereas higher human densities and host-shifting potential of viruses have supported increased virus richness.Lay SummaryVastly more parasite species infect humans than any other primate host. Controlling for factors that influence parasite richness, such as the intensity of study effort and body mass, we find that humans may have more viruses, but fewer helminths and protozoa, than expected based on evolutionary analyses of parasitism in other primates.

Phenology, parasitism and density dependence of Psyllaephagus bliteus on Eucalyptus camaldulensis

Glycaspis brimblecombei is an invasive insect species that specifically feeds on Eucalyptus leaves. Native from Australia, this species has spread to several countries becoming a major Eucalyptus pest. Even though its specific endoparasitoid Psyllaephagus bliteus has been present in Argentina since 2005, little is known about its ecology in the region. In this work we assess P. bliteus population development on Eucalypus camaldulensis and identify the meteorological variables associated with changes in its abundance. Furthermore, we study the level of natural parasitism in the field, and the density dependence relationship between P. bliteus and G. brimblecombei. We find that P. bliteus is present throughout the year with a maximum abundance at the end of spring-beginning of summer. Changes in its abundance are associated with temperature and relative humidity although it cannot be ruled out that this is due to an effect of climate on the density of its host. The highest levels of parasitism were registered when psyllid population was minimal, while density dependence analysis detected an inverse relationship between P. bliteus and its host.

The cost of ectoparasitism in Cliff Swallows declines over 35 years

AbstractHost–parasite dynamics often vary over time, brought about by changes in the parasite’s virulence or the host’s ability to resist or tolerate the parasite. Although virulence evolution in microparasites is well studied, we know little about temporal change in the pathogenicity of macroparasites such as blood‐feeding insects. Using data collected over 35 yr, we report a reduction in pathogenicity of the hematophagous swallow bug (Cimex vicarius) on its Cliff Swallow (Petrochelidon pyrrhonota) host. Relative to experimentally fumigated, parasite‐free nests, the negative effects of bugs on nestling swallow body mass and survival were less in the later years of the study than in the earlier years, and the negative relationship between nestling body mass and bug abundance became weaker over time. The survival of adult birds exposed to swallow bugs increased throughout the study, while survival of birds from parasite‐free nests decreased over time. Swallow bug abundance per nest, bug body size, and bug age ratios did not change during the study. Between‐colony transmission of bugs showed less immigration into larger colonies than in earlier studies, but there was no net change in transmission. Cliff Swallows did not reduce their exposure to bugs over time by being more likely to avoid infested nest or colony sites. Parents increased the number of food deliveries to their offspring over time in the presence of parasites, but the total amount of food delivered was unchanged. The reduced cost of swallow bug ectoparasitism does not seem related to changes in parasite narrow‐sense virulence, the host’s avoidance of parasites, the presence of alternative hosts for bugs, or climate‐driven phenological mismatches. The results probably reflect the Cliff Swallow’s evolving of greater tolerance to swallow bugs, brought about by the bird’s shift from natural cliff nesting sites to artificial structures that may harbor more bugs than natural cliffs. This study shows that hosts can respond relatively rapidly to high levels of parasitism, and provides support for models that suggest the evolution of tolerance should be expected in some host–parasite systems.

The Biology of &amp;lt;i&amp;gt;Szelenyiopria talitae&amp;lt;/i&amp;gt; (Hymenoptera: Diapriidae): Larval Parasitoid of the Leaf-Cutting Ant &amp;lt;i&amp;gt;Acromyrmex subterraneus&amp;lt;/i&amp;gt; (Hymenoptera: Formicidae)

The biology of a koinobiont parasitoid of leaf-cutting ant larvae, Szelenyiopria talitae (Hymenoptera: Diapriidae), was studied from naturally infested Acromyrmex subterraneus (Hymenoptera: Formicidae) nests. Nests were collected in the field from the Atlantic rainforest biome in the state of Rio de Janeiro. A total of fifty-three nests were collected from 2015 to 2018. Parasitized nests were only found during the months of September and October. Approximately 22% of the nests collected over a four-year period were found to have been parasitized by S. talitae. The mean within-nest parasitism rate was 66.3%. This diapriid displayed both solitary (14%) and gregarious parasitism (86%), with up to a maximum of 12 parasitoids developing within a single host. Gregarious parasitism with two (29%) or three (21%) S. talitae per host was most frequently observed. There was a positive correlation between the number of parasitoids per host and host size (dry weight), indicating that S. talitae females oviposited a higher number of eggs in larger hosts. There was also a negative correlation between S. talitae pharate adult size and the number of parasitoids per host, which could have been caused by sibling competition for limited host resources. The high levels of parasitism seen here had a debilitating effect on the colonies. Acromyrmex subterraneus is a serious pest in Brazil, and these studies lay the foundation for understanding the impact of S. talitae on ant populations.

Influence of the site of oviposition on the level of egg parasitism in the corn leafhopper, Dalbulus maidis (Hemiptera: Cicadellidae).

The corn leafhopper Dalbulus maidis (DeLong) (Hemiptera: Cicadellidae), transmits three important plant pathogens that adversely affect corn crop and ranges from the USA to Argentina. The vector has a rich natural enemy complex that generates high levels of parasitism, but its populations are persistent and prevalent. We characterized the oviposition sites of D. maidis on young corn plants in order to verify the hypothesis that the vector has an oviposition strategy for mitigating parasitism. Oviposition locations on plants were assessed in the laboratory and eggs within corn plants were exposed to natural parasitism in a cornfield. Eggs were located mostly laid in the unfolded leaves and were attacked by five parasitoid species. Parasitism was significantly affected by the class of leaf and the position of the egg in the leaf. Anagrus virlai Triapitsyn was the most abundant parasitoid species, which emerged significantly higher in the basal blade than other species. Our results suggest that leafhoppers minimize egg parasitism by laying their eggs within concealed locations on the plant.

Parasitism of Placobdelloides siamensis (Oka, 1917) (Glossiphoniidae: Hirudinea) in Snail-eating Turtles, Malayemys spp., and the effects of host and aquatic environmental factors.

The Siam Shield Leech, Placobdelloides siamensis, is a common leech found on Malayemys turtles in Thailand. Sixty Snail-eating Turtles (29 Malayemys macrocephala and 31 M. subtrijuga) were caught over twelve months (February 2017 – January 2018) to determine host characteristics (body size, weight and sex), parasitism (prevalence, intensity and density) and seasonal aquatic environmental factors (conductivity, nitrate nitrogen, dissolved oxygen, pH, salinity and total dissolved solids). There was no significant difference of infection rate between species and sex in both turtle species. Leech prevalence indicated that all turtle individuals were infected throughout year, while the infection rate was significantly higher in larger and heavier turtles mainly on the carapace with an average number of leech approximately 474.80 ± 331.38 individuals for individual host infection and 76.53 ± 20.27 individuals for infection per 100 g body weight. The high level of leech parasitism also caused a rot wound and shell hole which caused the host to die. Aquatic environmental factors did not influence the infection of leeches in both turtle species. Therefore, the factors that influenced the infection rate of P. siamensis were based on only host body size and weight without effect from season. In addition, this study also showed two new hosts, including Cyclemys oldhamii and Heosemys grandis and the widespread distribution from northern, north-eastern, western, central and southern Thailand were reported.

Phylogenetically conserved host traits and local abiotic conditions jointly drive the geography of parasite intensity

Abstract The role of biotic interactions in shaping species distributions is a cornerstone of biogeographic theory; yet, it remains elusive. Such interactions are more likely to have an influence on organisms with obligate associations, such as hosts and their parasites. Whereas abiotic conditions may affect the abundance and distribution of parasites in ways similar to free‐living species, attributes of the host could also play a part. Here, we focus on parasitic water mites and their dragonfly and damselfly hosts, and use a hierarchical Bayesian model to examine the relative influence of the abiotic environment and biotic factors such as local host community structure and individual host characteristics on parasite intensity along a broad‐scale environmental gradient. Specifically, we assessed how climate, surrounding vegetation, water chemistry, host community structure as well as the relative abundance and body mass of host species affected the intensity of parasitism on individual hosts along a latitudinal gradient. We found that water chemistry and body mass of the host were the best predictors of variation in parasite intensity among hosts. High parasite intensity was observed in hosts sampled from lakes with high pH, dissolved oxygen and conductivity. Additionally, we found that the intensity of parasitism was strongly influenced by host species identity. In particular, body mass, which shows strong phylogenetic signal, was negatively related to parasite intensity. It may be that larger species, or individuals within species, are more immune to high level of parasitism and/or body mass is correlated with other traits of the host which relate to immunity. Considering both the abiotic environment and attributes of host species is necessary to understand why certain host individuals and locations exhibit more intense parasitism. Amid widespread decline of insect populations world‐wide, some of which are attributed to pathogens and parasites, models predicting rates of parasitism in space and time could become an essential tool for guiding management and conservation efforts. A free Plain Language Summary can be found within the Supporting Information of this article.

Host sex and age typically explain variation in parasitism of rock ptarmigan: implications for identifying determinants of exposure and susceptibility

Measures of parasitism often differ between hosts. This variation is thought due in part to age or sex differences in exposure to parasites and/or susceptibility to parasitism. We assessed how often age or sex biases in parasitism were found using a large, multi‐year (2006–2017) dataset of 12 parasite species of Icelandic rock ptarmigan (Lagopus muta). We found host traits (i.e. age and/or sex) accounted for significant variation in abundance of 11 of the 12 parasite species. We often found increased abundance among juvenile hosts, although significant adult biases were observed for three parasite species. Additionally, higher levels of parasitism by many species were observed for female hosts, contrary to frequent male biases in parasitism reported for other vertebrates. Abundance of six parasite species was best explained by interactions between host age and sex; some degree of decrease in abundance with host age was present for both male and female hosts for four of those parasite species. We consider various host and parasite traits that could account for observed singular and repeated patterns of age and/or sex biases in parasitism (e.g. age‐ and sex‐related grouping behaviours, age‐specific mortality in relation to parasitism, acquisition of greater immunity with age). This work provides a foundation for future studies investigating age‐related differences in acquired immunity and age‐specific parasite‐mediated mortality for males and females, as well as studies on interactions between co‐infecting parasite species.