Host Stage Research Articles

Induced Resistance in Fruit and Vegetables: A Host Physiological Response Limiting Postharvest Disease Development.

Harvested fruit and vegetables are perishable, subject to desiccation, show increased respiration during ripening, and are colonized by postharvest fungal pathogens. Induced resistance is a strategy to control diseases by eliciting biochemical processes in fruits and vegetables. This is accomplished by modulating the progress of ripening and senescence, which maintains the produce in a state of heightened resistance to decay-causing fungi. Utilization of induced resistance to protect produce has been improved by scientific tools that better characterize physiological changes in plants. Induced resistance slows the decline of innate immunity after harvest and increases the production of defensive responses that directly inhibit plant pathogens. This increase in defense response in fruits and vegetables contributes to higher amounts of phenols and antioxidant compounds, improving both the quality and appearance of the produce. This review summarizes mechanisms and treatments that induce resistance in harvested fruits and vegetables to suppress fungal colonization. Moreover, it highlights the importance of host maturity and stage of ripening as limiting conditions for the improved expression of induced-resistance processes.

Defining the filarial N-glycoproteome by glycosite mapping in the human parasitic nematode Brugia malayi

N-linked glycosylation is a critical post translational modification of eukaryotic proteins. N-linked glycans are present on surface and secreted filarial proteins that play a role in host parasite interactions. Examples of glycosylated Brugia malayi proteins have been previously identified but there has not been a systematic study of the N-linked glycoproteome of this or any other filarial parasite. In this study, we applied an enhanced N-glyco FASP protocol using an engineered carbohydrate-binding protein, Fbs1, to enrich N-glycosylated peptides for analysis by LC-MS/MS. We then mapped the N-glycosites on proteins from three host stages of the parasite: adult female, adult male and microfilariae. Fbs1 enrichment of N-glycosylated peptides enhanced the identification of N-glycosites. Our data identified 582 N-linked glycoproteins with 1273 N-glycosites. Gene ontology and cell localization prediction of the identified N-glycoproteins indicated that they were mostly membrane and extracellular proteins. Comparing results from adult female worms, adult male worms, and microfilariae, we find variability in N-glycosylation at the protein level as well as at the individual N-glycosite level. These variations are highlighted in cuticle N-glycoproteins and adult worm restricted N-glycoproteins as examples of proteins at the host parasite interface that are well positioned as potential therapeutic targets or biomarkers.

Strong effects of food quality on host life history do not scale to impact parasitoid efficacy or life history

Parasitoids are small insects, (e.g., small wasps or flies) that reproduce by laying eggs on or within host arthropods. Parasitoids make up a large proportion of the world’s biodiversity and are popular agents of biological control. Idiobiont parasitoids paralyze their hosts upon attack and thus are expected to only target hosts large enough to support offspring development. Host resources generally impact host attributes and life histories including size, development, and life span. Some argue slow host development in response to resource quality increases parasitoid efficacy (i.e., a parasitoid’s ability to successfully reproduce on or within a host) due to longer host exposure to parasitoids. However, this hypothesis is not always supported and does not consider variation in other host traits in response to resources that may be important for parasitoids (e.g., variation in host size is known to impact parasitoid efficacy). In this study we test whether trait variation within host developmental stages in response to host resources is more important for parasitoid efficacy and life histories than trait variation across host developmental stages. We exposed seed beetle hosts raised on a food quality gradient to mated female parasitoids and measured the number of hosts parasitized and parasitoid life history traits at the scale of host stage- and age-structure. Our results suggest host food quality does not cascade to impact idiobiont parasitoid life histories despite large food quality effects on host life history. Instead, variation in host life histories across host developmental stages better predicts parasitoid efficacy and life histories, suggesting finding a host in a specific instar is more important for idiobiont parasitoids than finding hosts on or within higher quality resources.

Selection on an extreme-yet-conserved larval life-history strategy in a tapeworm.

Evolutionary stasis characterizes many phenotypes, even ones that seem suboptimal. Among tapeworms, Schistocephalus solidus and its relatives have some of the shortest developmental times in their first intermediate hosts, yet their development still seems excessively long considering they can grow faster, larger, and safer in the next hosts in their complex life cycles. I conducted 4 generations of selection on the developmental rate of S. solidus in its copepod first host, pushing a conserved-but-counterintuitive phenotype toward the limit of known tapeworm life-history strategies. Faster parasite development evolved and enabled earlier infectivity to the stickleback next host, but low heritability for infectivity moderated fitness gains. Fitness losses were more pronounced for slow-developing parasite families, irrespective of selection line, because directional selection released linked genetic variation for reduced infectivity to copepods, developmental stability, and fecundity. This deleterious variation is normally suppressed, implying development is canalized and thus under stabilizing selection. Nevertheless, faster development was not costly; fast-developing genotypes did not decrease copepod survival, even under host starvation, nor did they underperform in the next hosts, suggesting parasite stages in successive hosts are genetically decoupled. I speculate that, on longer time scales, the ultimate cost of abbreviated development is reduced size-dependent infectivity.

Comparative demography, population projection, functional response and host age preference behavior of the parasitoid Goniozus legneri on two lepidopterous insect hosts

BackgroundThis study was conducted to investigate life table characteristics of the parasitoid species, Goniozus legneri Gordh (Hymenoptera: Bethylidae), a major gregarious larval ecto-parasitoids of the carob moth, Ectomyelois ceratoniae Zeller (Lep.: Pyralidae). Demographic parameters of G. legneri reared on two hosts, the carob moth and the flour moth, Ephestia kuehniella (Zeller) (Lepidoptera: Pyralidae), were studied under laboratory conditions using age-stage, two-sex life table. Host stage preference and the functional response of this parasitoid were also determined.ResultsThe duration of the immature period, adult pre-ovipositional period and total pre-ovipositional period of G. legneri reared on E. kuehniella was significantly longer than that of those reared on E. ceratoniae, while fecundity and ovipositional days of the wasp were greater/longer in females reared on E. ceratoniae. There were also significant differences in intrinsic and finite rates of increase and mean generation time between wasp parasitoid reared on two hosts. Moreover, population projection indicated that the G. legneri population can grow swifter when reared on E. ceratoniae than on E. kuehniella. Based on the experiments conducted to determine the larval stage preferences of G. legneri, for both hosts, larger larvae were more preferred stages compared to smaller ones, thereby fulfilling the optimal oviposition theory. The functional responses of G. legneri to different population densities of E. kuehniella two last instar larvae were determined as type III at 25 °C and 60% RH.ConclusionThe results offer valuable information on some life history attributes of G. legneri. Although G. legneri performed better on E. ceratoniae larvae than on E. kuehniella, as the use of E. ceratoniae larvae as the main host in rearing of G. legneri might be a laborious process and can increase the production costs, E. kuehniella can be used as an alternative host. Further studies are required under greenhouse and field conditions for effective use of this biocontrol agent against the carob moth.

Human ectoparasitosis by mites of the genus Pyemotes Amerling 1861 (Acarina: Pyemotidae).

The mites of the family Pyemotidae Berlese (1897) are a large family of ectoparasitoids arthropods, known as pathogen for humans since the 18th century and responsible for the so-called "straw itch" or "grain itch" in granary and dock workers. The identified species of the genus Pyemotes are divided into two groups: the scolyti group (P. scolyti, P. parviscolyti and P. dimorphus) and the ventricosus group (P. tritici and P. ventricosus). The first group is characterized by nonvenomous mites usually parasitizing bark beetles; the ventricosus group includes species associated with a large number of hosts (Coleoptera, Lepidoptera, Hymenoptera, Diptera and Rhynchota), parasitizing all host stages, often highly poisonous and responsible for itchy skin lesions for humans. Several species of Pyemotes mites can be pathogenic to humans, especially in spring and summer and in indoor environments, where worm-eaten wood or infested foodstuffs are present. The most frequent clinical feature is the "strophulus," characterized by small erythematous, edematous, and papular lesions centered by a tiny vescicle evolving into a small erosion covered by crust, or by a central hemorrhagic punctum. Other less frequently observed clinical features are urticaria-like lesions, erythematous excoriated papular and pustular lesions, and rarely scabies-like eruptions. The parasitological diagnosis together with the environmental disinfestation and removing of each substrate infested by insects parasitized by Pyemotidae is mandatory to definitely solve Pyemotes dermatitis.

Pathogens stabilize or destabilize depending on host stage structure.

A common assumption is that pathogens more readily destabilize their host populations, leading to an elevated risk of driving both the host and pathogen to extinction. This logic underlies many strategies in conservation biology and pest and disease management. Yet, the interplay between pathogens and population stability likely varies across contexts, depending on the environment and traits of both the hosts and pathogens. This context-dependence may be particularly important in natural consumer-host populations where size- and stage-structured competition for resources strongly modulates population stability. Few studies, however, have examined how the interplay between size and stage structure and infectious disease shapes the stability of host populations. Here, we extend previously developed size-dependent theory for consumer-resource interactions to examine how pathogens influence the stability of host populations across a range of contexts. Specifically, we integrate a size- and stage-structured consumer-resource model and a standard epidemiological model of a directly transmitted pathogen. The model reveals surprisingly rich dynamics, including sustained oscillations, multiple steady states, biomass overcompensation, and hydra effects. Moreover, these results highlight how the stage structure and density of host populations interact to either enhance or constrain disease outbreaks. Our results suggest that accounting for these cross-scale and bidirectional feedbacks can provide key insight into the structuring role of pathogens in natural ecosystems while also improving our ability to understand how interventions targeting one may impact the other.

New geographical records for tick-borne pathogens in ticks collected from cattle in Benin and Togo.

Ticks are obligate hematophagous arthropods capable of transmitting a great variety of endemic and emerging pathogens causing diseases in animals and humans. The aim of this study was to investigate the presence of Bartonella spp., Rickettsia spp., Borrelia burgdorferi sensu lato (s.l.) and Anaplasma phagocytophilum in ticks collected from cattle in Benin and Togo. Overall, 396 (148 males, 205 females and 43 nymphs) ticks were collected from cattle in 17 districts (Benin and Togo) between 2019 and 2020. Ticks were pooled into groups of 2-6 ticks per pool according to individual host, location, species and developmental stage. The DNA of each pool was extracted for molecular screening. PCR results revealed that 20 tick pools were positive for Bartonella spp. (Benin and Togo) and 23 tick pools positive for Rickettsia spp. (Benin), while all pools were negative for A. phagocytophilum and B. burgdorferi s.l. Sequence analysis of positive Rickettsia samples revealed the presence of Rickettsia aeschlimannii. The present study highlights the presence of zoonotic agents in ticks collected from cattle in Benin and Togo. This information will raise awareness of tick-borne diseases among physicians and veterinarians, stimulate further studies to monitor these pathogens, and advise on necessary measures to control the spread of these zoonoses.

Life table parameters of the predatory mite, Blattisocius mali Oudemans (Mesostigmata: Blattisociidae), fed on eggs and larvae of the stored product mite, Tyrophagus putrescentiae (Schrank)

BackgroundThe predatory mite, Blattisocius mali Oudemans (Mesostigmata: Blattisociidae), feeds on various species of storage mites such as Tyrophagous putresentiae (Schrank). In this study, life table parameters and consumption rates of B. mali were determined when fed on the eggs and larvae of T. putrescentiae as the prey under laboratory conditions.ResultsBased on the age-stage two-sex life table analysis, the total pre-ovipositional period (TPOP) of the predator was considerably lower by feeding on host larvae than that on eggs. Also, mean fecundity (eggs/female) of the B. mali was 2.60-fold higher on host larvae than its eggs. Moreover, the intrinsic rate of increase (r), as the most important parameter was 0.272 and 0.357 day−1, respectively, by host mite eggs and larvae as food. This showed the significantly greater influence of T. putrescentiae larvae than eggs on mass production of the predatory mite. The same trend was observed in finite rate of increase (λ), net reproductive rate (R0), gross reproductive rate. But mean generation times (T) were statistically the same by feeding both host stages. Maximum longevity of male and female individuals was, respectively, 21 and 22 days when eggs were fed. By feeding on larvae as prey, maximum longevity was lowered to 20 days in both predator sexes. However, the net predation rate (C0) and transformation rate from prey population to predator offspring (QP) were significantly higher by feeding on host eggs (97.420 and 3.049) than its larvae (41.3936 and 0.5575), respectively.ConclusionFrom practical biocontrol view, both eggs and larvae of T. putrescentiae can be consumed and therefore controlled by the predatory mite, B. mali. From mass production view, larvae of T. putrescentiae produced a better fitness in the predatory mite than its eggs and can be used in augmentation programs of B. mali.

Fungal and bacterial oxylipins are signals for intra- and inter-cellular communication within plant disease.

Lipids are central at various stages of host–pathogen interactions in determining virulence and modulating plant defense. Free fatty acids may act as substrates for oxidizing enzymes [e.g., lipoxygenases (LOXs) and dioxygenases (DOXs)] that synthesize oxylipins. Fatty acids and oxylipins function as modulators of several pathways in cell-to-cell communication; their structural similarity among plant, fungal, and bacterial taxa suggests potential in cross-kingdom communication. We provide a prospect of the known role of fatty acids and oxylipins in fungi and bacteria during plant–pathogen interactions. In the pathogens, oxylipin-mediated signaling pathways are crucial both in development and host infection. Here, we report on case studies suggesting that oxylipins derived from oleic, linoleic, and linolenic acids are crucial in modulating the pathogenic lifestyle in the host plant. Intriguingly, overlapping (fungi-plant/bacteria-plant) results suggest that different inter-kingdom pathosystems use similar lipid signals to reshape the lifestyle of the contenders and occasionally determine the outcome of the challenge.

Parasitic behavior of Pyemotes zhonghuajia (Trombidiformes: Pyemotidae) on fall armyworm Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae)

Fall armyworm Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) is a destructive, migratory pest that seriously damages corn, sorghum, and other crops. The “insect killer” Pyemotes zhonghuajia (Trombidiformes: Pyemotidae) is an ectoparasitic mite of agricultural and forestry pests in China. To explore the biological control efficiency of P. zhonghuajia on S. frugiperda, we evaluated the parasitic selectivity of P. zhonghuajia on S. frugiperda of different life stages, and distribution of P. zhonghuajia on different body parts of S. frugiperda larvae and pupae, food intake of S. frugiperda larvae affected by P. zhonghuajia density, and field population dynamics of S. frugiperda in relation to the releasing population density of P. zhonghuajia. We found that P. zhonghuajia preferred 4th- to sixth-instar larvae and pupae of S. frugiperda for parasitism, and the ventral part of abdominal segments of fourth-instar larvae and the ventral part of pupal thorax for feeding. Freezing of S. frugiperda 4th instar larvae and pupae had little effect on the distribution of P. zhonghuajia on the surface of these two host stages. The parasitism of P. zhonghuajia regardless of mite population size (i.e., 5, 10, or 20 mites) could significantly decrease the cumulative food intake of fifth-instar larvae of S. frugiperda. Releasing two and three boxes (50,000 mites/box) of P. zhonghuajia significantly suppressed the field population of S. frugiperda on sorghum plants/25 m2 within 7 days. Our results show that P. zhonghuajia may be a potential biological control agent and can be used for biological control of S. frugiperda in the field.

Evolution of parasitoid host preference and performance in response to an invasive host acting as evolutionary trap.

The invasion of a novel host species can create a mismatch in host choice and offspring survival (performance) when native parasitoids attempt to exploit the invasive host without being able to circumvent its resistance mechanisms. Invasive hosts can therefore act as evolutionary trap reducing parasitoids' fitness and this may eventually lead to their extinction. Yet, escape from the trap can occur when parasitoids evolve behavioral avoidance or a physiological strategy compatible with the trap host, resulting in either host‐range expansion or a complete host‐shift. We developed an individual based model to investigate which conditions promote parasitoids to evolve behavioral preference that matches their performance, including host‐trap avoidance, and which conditions lead to adaptations to the unsuitable hosts. The model was inspired by solitary endo‐parasitoids attacking larval host stages. One important aspect of these conditions was reduced host survival during incompatible interaction, where a failed parasitization attempt by a parasitoid resulted not only in death of her offspring but also in host killing. This non‐reproductive host mortality had a strong influence on the likelihood of establishment of novel host–parasitoid relationship, in some cases constraining adaptation to the trap host species. Moreover, our model revealed that host‐search efficiency and genetic variation in host‐preference play a key role in the likelihood that parasitoids will include the suboptimal host in their host range, or will evolve behavioral avoidance resulting in specialization and host‐range conservation, respectively. Hence, invasive species might change the evolutionary trajectory of native parasitoid species, which is important for predicting biocontrol ability of native parasitoids towards novel hosts.

Host stage preference and demographic parameters of Leptomastix dactylopii (Hymenoptera: Encyrtidae) on vine mealybug Planococcus ficus (Hemiptera: Pseudococcidae)

BackgroundThis study was conducted to investigate host stage preference and demographic parameters of the parasitoid species, Leptomastix dactylopii Howard (Hymenoptera: Encyrtidae), the parasitoid of vine mealybug Planococcus ficus (Signoret) (Hemiptera: Pseudococcidae), an important pest in vineyards in many countries.ResultsThe results revealed that L. dactylopii was not able to develop on the 1st and 2nd nymphal instars of P. ficus and preferred female mealybugs as the host to the 3rd nymphal instar. Hind tibia length and head capsule width of both female and male parasitoids emerged from the mummies of mealybugs parasitized in the female stage were greater than the values of the parasitoids emerged from the mummies of mealybugs parasitized in the 3rd nymphal instar. Demographic parameters of the parasitoid were calculated with the use of development and reproduction data obtained from life table of L. dactylopii. The intrinsic rate of increase was determined as (r = 0.1527 d−1), finite rate of increase as (λ = 1.1650 d−1), net reproductive rate as (R0 = 46.0667 offspring), and mean generation time as (T0 = 25.0830 d).ConclusionsIt was concluded that L. dactylopii was able to develop, especially in the female and in the 3rd nymphal instar of P. ficus and could be used for biological control of the vine mealybug.

Interspecific interaction between Anagyrus fusciventris and Tetracnemoidea brevicornis for controlling Pseudococcus calceolariae

ABSTRACT Anagyrus fusciventris and Tetracnemoidea brevicornis (Hymenoptera: Encyrtidae) are solitary endoparasitoids of Pseudococcus calceolariae and P. longispinus (Hemiptera: Pseudococcidae), major pests of many horticultural crops. The interspecific interaction relate to host-parasitoid association between these two parasitoid species was tested in the laboratory. To test the hypothesis that both species prefer the same life stages of P. calceolariae, first instar to adult mealybugs were exposed to female parasitoids of both species for either 24 h or 10 days. The parasitism by each parasitoid species of eggs and newly emerged or late first instar P. calceolariae was individually tested. A sequential test was also carried out, where mealybugs were exposed to either of the two parasitoid species with 24-h intervals between the exposure to the first and second parasitoid species. Regardless of the time or order of exposure, T. brevicornis females produced a larger proportion of parasitoid progeny within their short adult lifespan (< 10 days). The maximum daily reproductive output of T. brevicornis (32) was higher than A. fusciventris (8). Egg to adult development period of A. fusciventris was shorter (20 ± 1.6 (SD) days) than T. brevicornis (36.6 ± 4.6 (SD) days). A complementary effect of the two species on mealybug suppression was highlighted in our findings, due to their species-specific host stage preference, A. fusciventris prefer older life stages while T. brevicornis prefer younger life stages. Therefore both species together could provide stable control of the pest population more effectively than one species alone.

Phenology‐regulated defence mechanisms as drivers for Fusarium basal rot in onion (Allium cepa)

AbstractFusarium basal rot (FBR), caused by Fusarium spp., is a serious impediment for onion production. In the present study, the interaction of onion (Allium cepa) var. Takstar F1 with Allium‐derived isolates of the toxigenic species F. oxysporum and F. proliferatum was investigated at seedling and bulb stage. Using a set of isolates with distinct virulence profiles, we provide evidence that the outcome of FBR is driven by the phenology of onion. Reverse transcription‐quantitative PCR analysis revealed distinct expression of reliable marker genes for phenylalanine ammonia‐lyase (PAL1, PAL2), lipoxygenase (LOX2), chalcone synthase (CHS), anthocyanidin synthase (ANS) and pectin methylesterases (PME) during the infection of seedlings and bulbs. These defence‐related genes in seedlings were differentially expressed depending on the aggressiveness of Fusarium isolates. Despite these differential kinetics, the activated plant defence did not seem to be effective in protecting the seedlings from Fusarium infection and proliferation. Meanwhile, gene expression in the bulb organs correlated positively with FBR severity, indicating an ineffective defence response. Among the major metabolites of these Fusarium species, beauvericin was not toxic to either the seedlings or the bulbs, while fumonisin B1 appeared to be a virulence factor specific for the seedling stage. This points to differential roles of fumonisin B1 during an infection of F. proliferatum depending on the infected organ and the phenological stage of the onion host. We hypothesize that this variation, along with the differences within and between Fusarium species in terms of virulence and metabolism, contributes to the determination of disease outcome.

A chromosome-level genome of the human blood fluke Schistosoma japonicum identifies the genomic basis of host-switching.

The evolution and adaptation of S.japonicum, a zoonotic parasite that causes human schistosomiasis, remain unclear because of the lack of whole-genome data. We construct a chromosome-level S.japonicum genome and analyze it together with 72 samples representing six populations of the entire endemic region. We observe a Taiwan zoophilic lineage splitting from zoonotic populations ∼45,000 years ago, consistent with the divergent history of their intermediate hosts. Interestingly, we detect a severe population bottleneck in S.japonicum, largely coinciding with human history in Asia during the last glacial maximum. We identify several genomic regions underlying natural selection, including GATAD2A and Lmln, both showing remarkable differentiation among different areas. RNAi knockdown suggests association of GATAD2A with parasite development and infection in definitive hosts, while Lmln relates to the specificity of the intermediate hosts. Our study provides insights into the evolution of S.japonicum and serves as a resource for further studies.

Differences in Transporters Rather than Drug Targets Are the Principal Determinants of the Different Innate Sensitivities of Trypanosoma congolense and Trypanozoon Subgenus Trypanosomes to Diamidines and Melaminophenyl Arsenicals

The animal trypanosomiases are infections in a wide range of (domesticated) animals with any species of African trypanosome, such as Trypanosoma brucei, T. evansi, T. congolense, T. equiperdum and T. vivax. Symptoms differ between host and infective species and stage of infection and are treated with a small set of decades-old trypanocides. A complication is that not all trypanosome species are equally sensitive to all drugs and the reasons are at best partially understood. Here, we investigate whether drug transporters, mostly identified in T. b. brucei, determine the different drug sensitivities. We report that homologues of the aminopurine transporter TbAT1 and the aquaporin TbAQP2 are absent in T. congolense, while their introduction greatly sensitises this species to diamidine (pentamidine, diminazene) and melaminophenyl (melarsomine) drugs. Accumulation of these drugs in the transgenic lines was much more rapid. T. congolense is also inherently less sensitive to suramin than T. brucei, despite accumulating it faster. Expression of a proposed suramin transporter, located in T. brucei lysosomes, in T. congolense, did not alter its suramin sensitivity. We conclude that for several of the most important classes of trypanocides the presence of specific transporters, rather than drug targets, is the determining factor of drug efficacy.

Virulence and sex-dependent invasion efficiency of entomopathogenic nematodes on developmental stages of Phthorimaea operculella (Lep., Gelechidae)

• By IJs concentration established Steinernema in PTM increased. • Sex ratio of S. carpocapsae in pre-pupa was affected by IJ concentration. • An inverse relationship was recorded between penetration rate and IJs concentration. • No correlation was observed between the invasion efficiencies (IE) and LC50 values of EPNs. • Despite higher Steinernema IE into pupae, mortality was lower compared to pre-pupa. Virulence and invasion efficiency of the three entomopathogenic nematodes, Heterorhabditis bacteriophora , Steinernema carpocapsae and S. feltiae against the potato tuber moth (PTM), Phthorimaea operculella was evaluated. Also evaluated were the sex ratio of Steinernema spp. and host stages to determine if 1) the developmental stage of the host affects sex ratio of nematodes; 2) infective juveniles (IJs) concentration affects sex ratio in host developmental stages and 3) the establishment of IJs is affected by developmental stages of host. The PTM pre-pupa and pupa were exposed to IJs in filter substrate petri dish bioassays. By increasing the IJs concentrations, the number of established Steinernema spp. in both PTM stages increased and only decreased at the highest concentration. No reduction in established nematode numbers at the highest concentration was observed for H. bacteriophora . Sex ratio of S. carpocapsae in pre-pupa was affected by IJ concentration. PTM was more susceptible to Steinernema spp. than H. bacteriophora . Pre-pupa were more susceptible to S. feltiae but S. carpocapsae recorded as the most virulent EPN on pupa. Invasion efficiencies were similar for Steinernema and considerably higher than for H. bacteriophora . Despite a higher invasion efficiency of Steinernema into pupae, mortality was lower compared to pre-pupa No correlation was recorded between the invasion efficiencies of the EPNs and mortalities of PTM. The results showed that the invasion efficiency is not appropriate criterion to reflect the virulence of studied EPNs. Compared to H. bacteriophora both tested Steinernema spp. were good candidates for further studies as biocontrol agents of PTM.

Parasitism efficiency and progeny fitness of Peristenus spretus Chen et van Achterberg vary with nymphal instar of host, Apolygus lucorum (Meyer-Dür)

Peristenus spretus Chen et van Achterberg (Hymenoptera: Braconidae) is the dominant parasitoid of Apolygus lucorum (Meyer-Dür) nymphs (Hemiptera: Miridae) and exerts considerable control of the mirid’s populations in China. To understand developmental fitness of P. spretus in response to host stage selection, the development duration, parasitism efficiency, host handling time, survival rate, offspring size, and sex ratio of the parasitoid were determined when parasitoids were presented with five different instars of A. lucorum. The results showed that the developmental time of P. spretus individuals that parasitized 1st instar nymphs of A. lucorum was significantly longer than that of parasitoids developing in 2nd through 5th instars in no-choice parasitism tests. The sex ratio (as percent female) of P. spretus progeny was not significantly difference among host instars, and the regression between sex ratio (as percent female) and host instar was y = 9.80 ln (x) + 38.12. The best overall performance of P. spretus was observed when wasps parasitized 2nd, 3rd, or 4th instar hosts, because of shorter developmental duration, a higher parasitism rate, more offspring, a higher percent of female offspring, and a larger progeny size (measured as the length of the hind tibia). In choice parasitism test, fitness of P. spretus varied when it was reared in host stages ranging from 1st to 5th instars, and the parasitoid preferred to parasitize 2nd-4th instars. In addition, when parasitizing 3rd−5th instar hosts, parasitoids did not complete their development until their host had molted to an adult. Host body size significantly affected the time required for host capture and parasitization by P. spretus, and the parasitoid required the least time to parasitize medium-sized hosts. The longest handling times of P. spretus were observed for 1st and 5th instar nymphs, with values of 19.8 and 18.3 s, respectively, while the shortest handling time was 13.1 s, for 3rd instars. Our study has provided useful information for the mass rearing of this parasitoid in support of field releases of P. spretus.

Microbiomes associated with cultures of Gambierdiscus australes and Ostreopsis cf. ovata, two epibenthic dinoflagellates from the NE Atlantic Ocean (Las Palmas, Gran Canaria)

AbstractOur study focuses on bacterial communities associated with two benthic, epiphytic dinoflagellates, Gambierdiscus australes and Ostreopsis cf. ovata, isolated from coastal waters of Las Palmas, Gran Canaria, and grown in clonal cultures. The goal was to characterize the stable bacterial consortia found within the phycosphere of each dinoflagellate species and establish into which functional group they fell. High‐throughput sequencing (HTS) results highlighted a higher bacterial diversity in O. ovata compared with G. australes. Alphaproteobacteria dominated in both dinoflagellates with Marivita and Labrenzia as the most represented OTUs in Ostreopsis and Gambierdiscus, respectively, and Thalassospira and Oceanicaulis well represented in both species. Based on SIMPER analyses, Labrenzia and the Phycispherales SM1A02, dominant in Gambierdiscus and Ostreopsis, respectively, accounted for the most significant difference between the two microbiomes. The microbiomes described here differed from those described for the same dinoflagellate species in other studies, which could depend on differences in environmental conditions, macroalgal substrate, and/or growth stage or bloom phase of the microalgal hosts. The distinct bacterial communities associated with the two potentially toxic dinoflagellates, isolated from the same site and sampling event and cultivated under the same conditions, suggest different modalities of interaction and interexchange between bacteria and their hosts.