Non-parasitized Hosts Research Articles

Ecology of Myrmecofauna (Genus: Crematogaster) Associated to Helixanthera mannii (Oliv.) Danser (Loranthaceae) to Cocoa Trees in Oboa: Center Region of Cameroon, Africa

In order to find an effective control method against Helixanthera mannii (Oliv) Danser, parasite of agroecosystems in the northern part of the city of Yaoundé, a study of the myrmecofauna associated with this plant was carried out in an orchard of Oboa in Soa district. The total parasitism rate by Helixanthera mannii Danser was 20.43% for the entire orchard. 168 ants belonging to 12 species including ten genera and four subfamilies were collected from unparasitized and parasitized host individuals of Theobroma cacao. 86 ants belonging to two subfamilies were collected from selected branches of Helixanthera mannii from parasitized cocoa trees, namely Formicinae (Camponotus flavomarginatus) and Myrmicinae (Crematogaster (oxygyne) sp., Crematogaster (decacrema) sp. and Cataulacus sp. ) or 58.14% of the myrmecofauna during the flowering of this Loranthaceae and 41.86% during its fruiting. The ants of the genus Crematogaster proved to be the most active and abundant, i.e., 76.83% on non-parasitized hosts and 93.03% on hosts parasitized by Theobroma cacao by Helixanthera mannii. Crematogaster (oxygyne) sp. had an occupancy rate of 69.77% followed by Crematogaster (decacrema) sp. with 23.26% or 93.03% of the myrmecofauna recorded during the flowering and fruiting of Helixanthera mannii. Crematogaster (oxygyne) sp. proved to be the most active ant on these hosts. Note that the dominant ant status recognized for ants of the genus Crematogaster and their foraging activity on the flowers and fruits of Helixanthera mannii can contribute to the reduction of these parasitisms.

Metabolomics Provides New Insights into Host Manipulation Strategies by Asobara japonica (Hymenoptera: Braconidae), a Fruit Fly Parasitoid

Asobara japonica (Hymenoptera: Braconidae) is an endoparasitoid wasp that can successfully parasitize a wide range of host species across the Drosophila genus, including the invasive crop pest Drosophila suzukii. Parasitoids are capable of regulating the host metabolism to produce the nutritional metabolites for the survival of their offspring. Here, we intend to investigate the metabolic changes in D. melanogaster hosts after parasitization by A. japonica, using the non-targeted LC-MS (liquid chromatography-mass spectrometry) metabolomics analysis. In total, 3043 metabolites were identified, most of which were not affected by A. japonica parasitization. About 205 metabolites were significantly affected in parasitized hosts in comparison to non-parasitized hosts. The changed metabolites were divided into 10 distinct biochemical groups. Among them, most of the lipid metabolic substances were significantly decreased in parasitized hosts. On the contrary, most of metabolites associated with the metabolism of amino acids and sugars showed a higher abundance of parasitized hosts, and were enriched for a wide range of pathways. In addition, eight neuromodulatory-related substances were upregulated in hosts post A. japonica parasitization. Our results reveal that the metabolites are greatly changed in parasitized hosts, which might help uncover the underlying mechanisms of host manipulation that will advance our understanding of host-parasitoid coevolution.

A new model formulation for host depletion in parasitoids

A new model of host depletion in the functional response of parasitoids is presented. Most existing models describe the dynamics of prey consumption as a sequential-memoryless/Markovian process of searching for, handling, and consuming prey, but the feeding interaction between a parasitoid and its host is different. One of the most important characteristics is that the host is not consumed, and remains in the arena. On the other hand, functional response models of solitary parasitoids assume that each host can accommodate an infinite number of oviposition events without being killed or becoming unsuitable as a host without the parasitoid noticing it. As a consequence, host depletion is never considered in parasitoid functional response models. To solve that issue, we extended the traditional random predator and random parasitoid functional response models of Rogers into a compartmental model formulated with ordinary differential equations, to group hosts with a different number of attacks to simulate how the parasitoid spreads the attacks between already parasitized and non-parasitized hosts. This model was further modified to simulate non-sequential memoryless search, handling and oviposition. We studied the behaviour of these models to understand how a variation of their parameters led to different shapes of functional response curves and statistical distributions of the number of parasitoid eggs laid per host. The results showed that the expected curves differ from those predicted by the simpler Holling's disk equation (type II functional response), random parasitoid models (no depletion), and the random predator model (proportional depletion). Finally, the non-sequential-memoryless models predict straight curves resembling a type I functional response at low host densities.

Resetting our expectations for parasites and their effects on species interactions: a meta-analysis.

Despite the ubiquitous nature of parasitism, how parasitism alters the outcome of host-species interactions such as competition, mutualism and predation remains unknown. Using a phylogenetically informed meta-analysis of 154 studies, we examined how the mean and variance in the outcomes of species interactions differed between parasitized and non-parasitized hosts. Overall, parasitism did not significantly affect the mean or variance of host-species interaction outcomes, nor did the shared evolutionary histories of hosts and parasites have an effect. Instead, there was considerable variation in outcomes, ranging from strongly detrimental to strongly beneficial for infected hosts. Trophically-transmitted parasites increased the negative effects of predation, parasites increased and decreased the negative effects of interspecific competition for parasitized and non-parasitized heterospecifics, respectively, and parasites had particularly strong negative effects on host species interactions in freshwater and marine habitats, yet were beneficial in terrestrial environments. Our results illuminate the diverse ways in which parasites modify critical linkages in ecological networks, implying that whether the cumulative effects of parasitism are considered detrimental depends not only on the interactions between hosts and their parasites but also on the many other interactions that hosts experience.

Parasitism shapes selection by drastically reducing host fitness and increasing host fitness variation.

Determining the effects of parasites on host reproduction is key to understanding how parasites affect the underpinnings of selection on hosts. Although infection is expected to be costly, reducing mean fitness, infection could also increase variation in fitness costs among hosts, both of which determine the potential for selection on hosts. To test these ideas, we used a phylogenetically informed meta-analysis of 118 studies to examine how changes in the mean and variance in the outcome of reproduction differed between parasitized and non-parasitized hosts. We found that parasites had severe negative effects on mean fitness, with parasitized hosts suffering reductions in fecundity, viability and mating success. Parasite infection also increased variance in reproduction, particularly fecundity and offspring viability. Surprisingly, parasites had similar effects on viability when either the male or female was parasitized. These results not only provide the first synthetic, comparative, and quantitative summary of the strong deleterious effects of parasites on host reproductive fitness, but also reveal a consistent role for parasites in shaping the opportunity for selection.

Changes in the Host Gut Microbiota during Parasitization by Parasitic Wasp Cotesia vestalis.

Simple SummaryCotesia vestalis is a larval endo-parasitoid of the diamondback moth (Plutella xylostella), which is a severe pest of cruciferous crops. The function of the gut microbiota of insects has been widely studied. However, it was unclear whether, and how, the gut microbiota of P. xylostella responds to its natural enemy, C. vestalis. In this study, a time-course experiment was performed to examine changes in the host–microbial community from the start of parasitization to the mature stage of the parasitoid larvae. Our results will provide a framework for studies of host-gut microbiota and parasitic wasp interactions.Parasites attack the host insects and possibly impact the host-gut microbiota, which leads to provision of a suitable host environment for parasites’ development. However, little is known about whether and how the parasitic wasp Cotesia vestalis alters the gut microbiota of the host Plutella xylostella. In this study, 16S rDNA microbial profiling, combined with a traditional isolation and culture method, were used to assess changes in the bacterial microbiome of parasitized and non-parasitized hosts at different developmental stages of C. vestalis larvae. Parasitization affected both the diversity and structure of the host-gut microbiota, with a significant reduction in richness on the sixth day post parasitization (6 DPP) and significant differences in bacterial structure between parasitized and non-parasitized hosts on the third day. The bacterial abundance of host-gut microbiota changed significantly as the parasitization progressed, resulting in alteration of potential functional contribution. Notably, the relative abundance of the predominant family Enterobacteriaceae was significantly decreased on the third day post-parasitization. In addition, the results of traditional isolation and culture of bacteria indicated differences in the bacterial composition between the three DPP and CK3 groups, as with 16S microbial profiling. These findings shed light on the interaction between a parasitic wasp and gut bacteria in the host insect during parasitization.

The natural interaction between Myotis nigricans (Schinz, 1821) and its trematodes: A histopathological analysis.

Bats have a wide diversity of digeneans; however, even with the recent increased interest in studies of parasites on these hosts, there are no data on the microscopic alterations of this host-parasite interaction. The present work characterizes and compares the histological aspects of the liver, gallbladder, and intestine of non-parasitized and parasitized Myotis nigricans by digeneans. Ten specimens of Myotis nigricans collected in an urban area of Western Amazonia were analyzed for parasites. The digeneans were removed from the hosts and identified. Tissue samples of the liver, gallbladder, and intestines of parasitized and non-parasitized hosts were collected for histological studies. The gallbladder was observed in repletion and presents mucosa formed by simple epithelium that varies from cubic to cylindrical. The hepatic lobes do not have a classic polyhedral-hexagonal aspect. Variations in basophilia, acidophile, and cytoplasmatic granulations were observed in hepatocytes. The parasitism of the intestinal digeneans was restricted to space delimited by the extensions of villi in high association with the intestinal epithelium, not invading the region of the intestinal glands at the base of the villi. Trematodes maintained attached to the villus by the oral sucker and acetabulum, connected by a “pleat” composed of epithelium and lamina propria layers. We observed no signs of inflammatory processes and cellular defense infiltrates in host tissues. Cytochemistry alterations, size variation, and granular deposits in hepatocytes, enterocytes, and goblet cells were observed. Thus, this report is the first study of the natural parasite-host interaction in the liver, gallbladder, and intestine in M. nigricans in the neotropical region.

Comparison of the Parasitization of Chelonus inanitus L. (Hymenoptera: Braconidae) in Two Spodoptera Pests and Evaluation of the Procedure for Its Production.

Simple SummarySuccessful integrated pest management of horticultural crops requires the evaluation of natural enemies used in biological control. To improve the mass rearing of Chelonus inanitus (L.) in the factitious host Ephestia kuehniella Zeller, we investigated the influence of host age and number of females parasitizing simultaneously on quality parameters evaluated in the commercial production of biological control agents, such as overall rearing success, duration of life cycle and body size. Under semi-field conditions, we investigated how the competition among females impacted the parasitism success on important pests Spodoptera exigua (Hübner) and S. littoralis (Boisduval). For the parasitoid mass rearing optimization, mature eggs seem to be more convenient because they increased the female percentage in the offspring and shortened the parasitoid life cycle. Furthermore, a high number of females parasitizing simultaneously reduced the emergence of non-parasitized hosts. Under more realistic conditions, the parasitoid effectively controlled both pests, but S. exigua may be a more convenient host because the parasitoid offspring was much larger. With this research, we provide a foundation that aims to better manage these cosmopolitan, highly polyphagous pests that exhibit long-distance migratory potential, alongside the potential use of this natural enemy.Chelonus inanitus (L.) is an egg-larval parasitoid of noctuids Spodoptera exigua (Hübner) and S. littoralis (Boisduval), whose mass rearing or real potential has not been targeted yet. To improve the rearing in the factitious host Ephestia kuehniella Zeller, we investigated the influence of host age and number of females parasitizing simultaneously on the overall rearing success, the influence of host age on the life cycle, and the influence of host species on the parasitoid body size. The proportion of emerging C. inanitus was higher from young host eggs, but more females emerged from mature eggs. Under high parasitoid competition, we observed a reduction in non-parasitized hosts without reducing parasitoid emergence. The parasitoid life cycle was longer in females, but the mismatch between sexes was smaller in mature eggs. The parasitoid size was smaller in the factitious host than in the natural hosts. Under semi-field conditions, we investigated the competition among parasitoid females on the overall parasitism success. The reproductive parasitism was more successful in S. exigua than in S. littoralis, and the maximum emergence was reached with three and four females, respectively. The control of S. littoralis may be attributed to the high developmental mortality, a non-reproductive parasitism that is often underestimated.

Parasitic plant, from inside out: endophytic development in Lathrophytum peckoltii (Balanophoraceae) in host liana roots from tribe Paullineae (Sapindaceae).

Balanophoraceae is one of the most bizarre and biologically interesting plant clades. It groups species with peculiar features that offers an opportunity for investigating several aspects of parasite plant development and morphogenesis. We analysed the development and the mature vegetative body of Lathrophytum peckoltii Eichler, focusing on the formation of the host-parasite interface. Additionally, we analysed how this parasitic interaction causes modifications to the anatomy of Paullinia uloptera Radlk and Serjania clematidifolia Cambess host roots. Vegetative bodies of the parasite at different developmental stages were collected while infesting the roots of Sapindaceae vines. Non-parasitized host roots were also collected for comparison. Light, epifluorescence, confocal and scanning electron microscopy were used for the analysis. The initial cells of the vegetative axis divide repeatedly, originating a parenchymatous matrix, which occupies the space from the cortex to the vascular cylinder of the host's root. In the peripheral layers of the matrix, located near the xylem of the host's roots, a few cells initiate the process of wall lignification, originating the parasitic bundle. The vascular cambium of the host's root changes the division plane and becomes composed of fusiform initials, forming the vascular bundle. The vegetative axis presents a dermal tissue similar to a phellem, a parenchymatous matrix and a vascular system with different origins. The parasite reproduces by endophytic development, in a manner similar to that observed for endoparasites. The strategy of late cell differentiation could aid the parasite in avoiding early detection and triggering of defence responses by the host. This development causes changes to the host root cambial activity, leading to the establishment of direct, vessel to vessel connection between host and parasite. We associate these changes with the cambium modularity and an influx of parasite-derived hormones into the host cambium.

Comparative transcriptome analysis reveals a potential mechanism for host nutritional manipulation after parasitization by Leptopilina boulardi

Parasitoids have been extensively found to manipulate nutrient amounts of their hosts to benefit their own development and survival, but the underlying mechanisms are largely unknown. Leptopilina boulardi (Hymenoptera: Figitidae) is a larval-pupal endoparasitoid wasp of Drosophila melanogaster whose survival relies on the nutrients provided by its Drosophila host. Here, we used RNA-seq to compare the gene expression levels of the host midgut at 24 h and 48 h post L. boulardi parasitization. We obtained 95 and 191 differentially expressed genes (DEGs) in the parasitized host midgut at 24 h and 48 h post L. boulardi parasitization, respectively. A KEGG analysis revealed that several metabolic pathways were significantly enriched in the upregulated DEGs, and these pathways included “starch and sucrose metabolism” and “galactose metabolism”. A functional annotation analysis showed that four classes of genes involved in carbohydrate digestion process had increased expression levels in the midgut post L.boulardi parasitization than nonparasitized groups: glucosidase, mannosidase, chitinase and amylase. Genes involved in protein digestion process were also found among the DEGs, and most of these genes, which belonged to the metallopeptidase and serine-type endopeptidase families, were found at higher expression levels in the parasitized host midgut comparing with nonparasitized hosts. Moreover, some immune genes, particularly those involved in the Toll and Imd pathways, also exhibited high expression levels after L.boulardi parasitization. Our study provides large-scale transcriptome data and identifies sets of DEGs between parasitized and nonparasitized host midgut tissues at 24 h and 48 h post L. boulardi parasitization. These resources help improve our understanding of how parasitoid infection affects the nutrient components in the hosts.

Characterization and comparison of the bacterial microbiota of Lysiphlebia japonica parasitioid wasps and their aphid host Aphis gosypii.

Endosymbiotic bacteria have been reported to mediate interactions between parasitoids and their insect hosts. How parasitic wasps influence changes in host microbial communities and the relationship between them are of great importance to the study of host-parasitoid co-evolutionary and ecological interactions. However, these interactions remain largely unreported for interactions between Aphis gossypii and Lysiphlebia japonica. In this study, we characterize the bacterial microbiota of L. japonica wasps at different developmental stages and monitor changes over time in the bacterial microbiota of their parasitized and nonparasitized aphid hosts, using metagenomic analysis of 16S rDNA sequencing data. Proteobacteria, Firmicutes, and Actinobacteria were the three most abundant bacterial phyla identified in L. japonica. We found that parasitism was associated with an increased abundance of Buchnera nutritional endosymbionts, but decreased abundance of Acinetobacter, Arsenophonus, Candidatus_Hamiltonella, and Pseudomonas facultative symbionts in aphid hosts. Functional analysis of enriched pathways of parasitized aphids showed significant differences in the 'transport and metabolism of carbohydrates' and 'amino acid, lipid, and coenzyme biosynthesis' pathways. Notably, the composition of symbiotic bacteria in wasp larvae was highly similar to that of their aphid hosts, especially the high abundance of Buchnera. The results provide a conceptual framework for L. japonica interactions with A. gossypii in which the exchange of symbiotic microbes provides a means by which microbiota can potentially serve as evolutionary drivers of complex, multilevel interactions underlying the ecology and co-evolution of these hosts and parasites. © 2021 Society of Chemical Industry.

Host discrimination in the fruit fly parasitoid Diachasmimorpha longicaudata: evidence from virgin female behaviour and egg distribution patterns.

Many parasitoid species discriminate already parasitized hosts, thus avoiding larval competition. However, females incur in superparasitism under certain circumstances. Superparasitism is commonly observed in the artificial rearing of the parasitoid Diachasmimorpha longicaudata, yet host discrimination has been previously suggested in this species. Here, we addressed host discrimination in virgin D. longicaudata females in a comprehensive way by means of direct and indirect methods, using Ceratitis capitata and Anastrepha fraterculus which are major fruit fly pests in South America. Direct methods relied on the description of the foraging behaviour of females in arenas with parasitized and non-parasitized host larvae. In the indirect methods, healthy larvae were offered to single females and the egg distributions were compared to a random distribution. We found that D. longicaudata was able to recognize parasitized host from both host species, taking 24 h since a first parasitization for A. fraterculus and 48 h for C. capitata. Indirect methods showed females with different behaviours for both host species: complete discrimination, non-random (with superparasitism), and random distributions. A larger percentage of females reared and tested on A. fraterculus incurred in superparasitism, probably associated with higher fecundity. In sum, we found strong evidence of host discrimination in D. longicaudata, detecting behavioural variability associated with the host species, the time since the first parasitization and the fecundity of the females.

Fitting different visual models to behavioral patterns of parasitic egg rejection along a natural egg color gradient in a cavity-nesting host species

Avian brood parasites lay their eggs in other birds’ nests, and hosts can mitigate the fitness cost of raising unrelated offspring by rejecting parasitic eggs. A visually-based cognitive mechanism often thought to be used by hosts to discriminate the foreign egg is to compare it against the hosts’ own eggshell by size, shape, maculation, and/or ground coloration (i.e., absolute chromatic contrast). However, hosts may instead discriminate eggs based on their colors along a scale of natural avian eggshell coloration (i.e., directional chromatic contrast). In support of this latter visual process, recent research has found that directional chromatic contrasts can explain some host species’ rejection behavior better than absolute chromatic or achromatic contrasts. Here, for the first time, we conducted an experiment in a cavity-nesting host species to test the predictions of these different visual mechanisms. We experimentally parasitized nests of the Common Redstart Phoenicurus phoenicurus, a regular host of a mimetic-egg laying Common Cuckoo Cuculus canorus host-race, using painted, immaculate 3D-printed model eggs in two geographically distant areas (Finland and Czech Republic). We found that directional chromatic contrasts better explained rejection behaviors in both parasitized (Finland) and non-parasitized (Czech Republic) host populations, as hosts rejected eggs that were noticeably browner, but not eggs that were noticeably bluer, than redstart eggs. These results support the paradigm of a single rejection threshold predicted by the directional chromatic contrast model and contribute to a growing generality of these patterns across diverse avian host-brood parasite systems.

Healing while parasitized: impact of a naturally‐occurring nematode during energy‐intensive wound‐healing in a beetle

AbstractThe rigours of the daily lives of insects sometimes lead to minor injuries and wounds, which must be healed to avoid entry of pathogens and to resume normal function. Such healing requires energy, which must be diverted from other bodily reserves. What happens if energy reserves are already low, as would occur in individuals coping with internal parasites? This question is addressed in the presemt study, using horned passalus beetles (Odontotaenius disjunctus) and their naturally‐occurring nematode Chondronema passali. Oxygen consumption rates are tested at rest, as well as after an experimental wound is applied, to evaluate energy requirements of wound‐healing in parasitized and nonparasitized hosts. Furthermore, wound‐healing rates are visually tracked with a numerical scoring system to directly measure the cost of parasitism on healing. At rest, parasitized beetles show no elevation in respiration (oxygen consumption). After wounding, the oxygen consumption of parasitized beetles is 10% higher than that in nonparasitized beetles. Beetles with moderate‐ to heavy worm burdens have slower healing than those with few or no nematodes. These results show that this parasite carries little cost to the host during day‐to‐day activities, whereas, during times of immediate energy demand, there is a cost; hosts require more energy to repair wounds, and the wounds take longer to close. This conclusion leads to the question of whether this parasite is truly benign, and how many other apparently benign parasites, in insects or other animals, have similar ‘hidden’ effects.

Mistletoe effects on the host tree Tapirira guianensis: insights from primary and secondary metabolites

Mistletoes are parasitic plants that are capable of penetrating the living tissue of another plant’s stems and branches and extracting the necessary resources for their survival. This study aimed to compare the leaves and branches of parasitized and non-parasitized Tapirira guianensis host trees to gain insights of reciprocal effects of Phoradendron perrottetii (mistletoe) infection and profiles of primary metabolites and phenolic compounds of T. guianensis. Our hypothesis was that either the host’s chemical profile determines mistletoe infestation, or that the mistletoe infestation leads to fundamental changes in the metabolite profile of the host. Plant material was collected from T. guianensis parasitized by P. perrottetii, yielding samples from infested and non-infested host branches and their respective leaves. Infested branches were divided into two regions, the proximal region and the host-parasite interface (gall) region. Leaves and branches of non-parasitized plants were also collected. Statistical analyses revealed negative effects of the parasite on infested branches regarding most of the analyzed primary metabolites, especially soluble carbohydrates. This suggests a flow of carbohydrates towards the mistletoe, indicating a partially heterotrophic nutrition. Additionally, we observed a positive effect on the tannin contents of non-infested host branches caused by the mistletoe, which might suggest that this parasitic relationship induces a systemic response in T. guianensis. Finally, high contents of flavonoids at the gall region could indicate a mechanism of ROS quenching.

Persistent expression of Cotesia plutellae bracovirus genes in parasitized host, Plutella xylostella.

Cotesia plutellae (= vestalis) bracovirus (CpBV) is symbiotic to an endoparasitoid wasp, C. plutellae, and plays crucial roles in parasitism against the diamondback moth, Plutella xylostella. CpBV virion genome consists of 35 circular DNAs encoding 157 putative open reading frames (ORFs). This study re-annotated 157 ORFs with update genome database and analyzed their gene expressions at early and late parasitic stages. Re-annotation has established 15 different viral gene families, to which 83 ORFs are assigned with remaining 74 hypothetical genes. Among 157 ORFs, 147 genes were expressed at early or late parasitic stages, among which 141 genes were expressed in both parasitic stages, indicating persistent nature of gene expression. Relative frequencies of different viral circles present in the ovarian lumen did not explain the expression variation of the viral ORFs. Furthermore, expression level of each viral gene was varied during parasitism along with host development. Highly up-regulated CpBV genes at early parasitic stage included BEN (BANP, E5R and NAC1), ELP (EP1-like protein), IkB (inhibitor kB), P494 (protein 494 kDa) family genes, while those at late stage were mostly hypothetical genes. Along with the viral gene expression, 362 host genes exhibited more than two fold changes in expression levels at early parasitic stage compared to nonparasitized host. At late stage, more number (1,858) of host genes was regulated. These results suggest that persistent expression of most CpBV genes may be necessary to regulate host physiological processes during C. plutellae parasitism.

Interspecific competition between Fopius arisanus and Psyttalia incisi (Hymenoptera: Braconidae), parasitoids of Bactrocera dorsalis (Diptera: Tephritidae)

Fopius arisanus (Sonan) and Psyttalia incisi (Silvestri) are two important solitary endoparasitoids of Bactrocera dorsalis (Hendel). This study investigated the interspecific competition between these two parasitoids in the oriental fruit fly and the parasitic effect of P. incisi on hosts that have previously been parasitized by F. arisanus. The results showed that P. incisi did not discriminate against hosts that had been parasitized by F. arisanus at the egg stage. The parasitism percentage by P. incisi was lower on hosts previously parasitized by F. arisanus (75.3%) than on non-parasitized hosts (83.3%). Successive parasitization by F. arisanus and P. incisi resulted in the mass mortality of host larvae and pupae, with the death of 50.8% of the host pupae. The dissection of multiparasitized hosts showed that F. arisanus was the dominant parasitoid of host larvae; the higher mortality in the supernumerary P. incisi was due to physiological inhibition by the pioneer. The results further indicated that F. arisanus won almost all competitions against P. incisi, as demonstrated by the finding that F. arisanus emerged more often than P. incisi from multiparasitized hosts. The total emergence of parasitoids (76.5%) from the treatment in which the hosts were successively exposed to the two parasitoids was slightly higher than the emergence from the treatments in which the hosts were exposed to only one species (F. arisanus: 62.9%, P. incisi: 71.8%), which suggests that the combined application of these two parasitoids is a promising approach for biological control.

Intra- and interspecific competition in two congeneric parasitoids of the diamondback moth

In solitary parasitoids, a host can only support the complete development of a single parasitoid. For this reason, intraspecific or interspecific competition takes place whenever two or more individuals of the same or different species parasitize the same host. The exotic Diadegma semiclausum (Hellen) (Hymenoptera: Ichneumonidae) was introduced into Kenya in 2002 for the control of the diamondback moth, Plutella xylostella L. (Lepidoptera: Plutellidae), and led to the competitive displacement of its indigenous congeneric species Diadegma mollipla (Holmgren) in some areas but not in others. In an attempt to understand this process, superparasitism in D. mollipla and multiparasitism involving both species were investigated in the laboratory through exposure of non-parasitized and parasitized host larvae to D. mollipla. Hosts were exposed to the two congeners both simultaneously and sequentially. The study revealed that D. mollipla minimizes parasitism and superparasitism in the presence of hosts containing a larva of a conspecific female. When the two parasitoid species competed for non-parasitized hosts simultaneously, there were no significant differences in the total progeny produced under intraspecific vs. interspecific competition. Under simultaneous interspecific competition, D. semiclausum produced 74% of total progeny. Under sequential exposure, the species that attacked first always dominated with 85–96% of the resultant progeny, irrespective of the exposure interval. Offspring sex ratio was significantly more female-biased when the larvae were exposed to D. mollipla first. Overall, our results indicate that D. semiclausum dominates under simultaneous competition and D. mollipla dominates in terms of female progeny, but under delayed exposure to the other species, the first attacker is always the winner. On the basis of our results, D. semiclausum may not completely displace D. mollipla from diamondback moth in the field.

Characterization of joining sites of a viral histone H4 on host insect chromosomes.

A viral histone H4 (CpBV-H4) is encoded in a polydnavirus, Cotesia plutellae bracovirus (CpBV). It plays a crucial role in parasitism of an endoparasitoid wasp, C. plutellae, against diamondback moth, Plutella xylostella, by altering host gene expression in an epigenetic mode by its N-terminal tail after joining host nucleosomes. Comparative transcriptomic analysis between parasitized and nonparasitized P. xylostella by RNA-Seq indicated that 1,858 genes were altered at more than two folds in expression levels at late parasitic stage, including 877 up-regulated genes and 981 down-regulated genes. Among parasitic factors altering host gene expression, CpBV-H4 alone explained 16.3% of these expressional changes. To characterize the joining sites of CpBV-H4 on host chromosomes, ChIP-Seq (chromatin immunoprecipitation followed by deep sequencing) was applied to chromatins extracted from parasitized larvae. It identified specific 538 ChIP targets. Joining sites were rich (60.2%) in AT sequence. Almost 40% of ChIP targets included short nucleotide repeat sequences presumably recognizable by transcriptional factors and chromatin remodeling factors. To further validate these CpBV-H4 targets, CpBV-H4 was transiently expressed in nonparasitized host at late larval stage and subjected to ChIP-Seq. Two kinds of ChIP-Seqs shared 51 core joining sites. Common targets were close (within 1 kb) to genes regulated at expression levels by CpBV-H4. However, other host genes not close to CpBV-H4 joining sites were also regulated by CpBV-H4. These results indicate that CpBV-H4 joins specific chromatin regions of P. xylostella and controls about one sixth of the total host genes that were regulated by C. plutellae parasitism in an epigenetic mode.

Brood parasites manipulate their hosts: experimental evidence for the farming hypothesis

Parasites show a wide variety of strategies to maximize the successful transmission of themselves and/or their offspring, by exploiting hosts. One such strategy occurs when parasites manipulate host behaviour in a way that increases their probability of transmission to an uninfected host. Here, we examine whether brood parasitic brown-headed cowbirds, Molothrus ater , attack and cause nest failure in late-stage, and hence, inappropriate host nests, which theory suggests they may do to parasitize the replacement nests at an opportune time, effectively manipulating their host's reproductive behaviour and improving their own transmission. Critical to this ‘farming’ hypothesis, cowbirds must be attuned to the reproductive stage of their host and act accordingly by destroying nonparasitized clutches they find late in the nesting cycle. We conducted a series of experimental manipulations in which we presented captive cowbirds with nests simulating early and late stages. We found that cowbirds caused significantly greater destruction in the late-stage nests. Moreover, our results suggest that cowbirds are capable of using both direct assessment and absolute egg number to assess which clutches to destroy. Corroborating our findings in the laboratory, 10 years of field data show that cowbirds significantly increase the intensity of their attacks (i.e. the proportion of the clutch destroyed) on nonparasitized host nests as the nesting cycle progresses; however, we found no such trend for parasitized host nests. These results indicate that cowbirds evaluate the reproductive stage of their hosts using multiple mechanisms and use this information to vary the intensity of their attacks.