Host Larvae Research Articles

Genome-wide survey of open chromatin regions in two swallowtail butterflies Papilio machaonand P. bianor.

Papilio machaon was assigned as the type species for all butterflies by Linnaeus and P. bianor is a congener but exhibits a great difference in morphology (especially larva and adult color pattern) and larval host plants from P. machaon. Thus, they are the ideal models to investigate genetic mechanisms underlying morphology and plasticity between congeners. The reference genomes of both species were dissected in our previous studies, but little is known about their regulatory genome and the epigenetic regulation of gene expression throughout developmental stages. Here, we profiled the chromatin accessibility and gene expression of three developmental stages (the 4th instar larva [L4], the 5th instar larva [L5], and pupa [P]) using transposase accessible chromatin sequencing (ATAC-seq) and RNA-seq. Results showed that many accessible chromatin peakswere identified at three developmental stages (peak number, P. machaon: 44,977 [L4], 36,919 [L5], 47,147 [P]; P. bianor: 20,341 [L4], 44,668 [L5], 62,249 [P]). Moreover, the number of differentially accessiblepeaks and differentially expressed genesbetween larval stages of each butterfly species are significantly fewer than that between larval and pupal stages, suggesting a higher similarity within larvae and a significant difference between larvae and pupae. This study added the annotated information of chromatin accessibility genome-wide of the two papilionid species and will promote the investigation of gene regulation in butterfly evolution.

The Spatial and Temporal Variations in the Superparasitism ofDiachasmimorpha longicaudataPopulation Lines on Different Hosts After Field Release.

Evaluating the behavior of the parasitoid Diachasmimorpha longicaudata (Ashmead) (Hymenoptera: Braconidae) in the field allows improving strategies for its release. Thus, the aim of this study was to evaluate spatial and temporal variations in the superparasitism of two populations of D. longicaudata on two fruit fly hosts after releasing them in a guava (Psidium guajava L.; cultivar 'Paluma') orchard. The two parasitoid populations used were CS and AS, which were reared on Ceratitis capitata (Wiedemann) and Anastrepha fraterculus (Wiedemann), respectively. Four releases were carried out without host choice. Host larvae were offered to the parasitoids in sentinel traps attached at varying heights on the plant, and in plants located at eight different directions and seven distances (7.0, 21.0, 35.0, 49.0, 59.4, 63.0, and 69.3m) from the center of the parasitoid release point. The traps remained in the orchard for 24, 48, and 168h after release. After removing the traps, they were taken to the laboratory for scar counting. The percentages of parasitism, superparasitism, mortality, and emergence of parasitoids were determined. Data were analyzed using the generalized linear mixed-effect model (GLMM). The AS females were more active, as they exerted higher parasitism and superparasitism at the first distance and 48h after release, leaving a higher number of oviposition scars on the host A. fraterculus. Additionally, higher host mortality was observed in A. fraterculus at the closest points and the first 48h. The highest percentage of parasitoid emergence was observed in C. capitata parasitized by AS females.

The effects of a naturalized weed, Lepidium virginicum, on the development and behaviors of the diamondback moth and its natural enemies in Hawaii

Weeds can play numerous important roles in pest suppression in agroecosystems. These include influencing the host searching behaviors of herbivorous pests and their natural enemies and providing shelter and alternative food sources for predators and parasitoids. Virginia pepperweed, Lepidium virginicum, is a widespread naturalized weed in Hawaii and can often be found in and around agricultural fields. It is a member of the Brassicaceae family and is a known host plant of the diamondback moth (DBM), Plutella xylostella. In this study, we found that DBM preferentially oviposit on L. virginicum (vegetative stage) when presented with a choice of cabbage. Using laboratory and semi-field trials, we investigated the responses of the natural enemies of DBM to the vegetative stage of L. virginicum and cabbage infested with DBM larvae. When DBM-infested plants were placed in the field for 48 h, more spiders and parasitized DBM larvae were recovered from the L. virginicum than from cabbage. In laboratory choice experiments, we demonstrated that the dominant DBM parasitoid species in Hawaii (Cotesia vestalis) oviposited in more host larvae on L. virginicum compared to cabbage, though this had no particular benefit for parasitoid development (adult size and sex ratio). Our findings suggest that the presence of L. virginicum in cabbage agroecosystems could be beneficial by serving to divert DBM oviposition away from cabbage and promoting predator and parasitoid populations.

Recruitment varies among milkweed seed sources for habitat specialist but not generalist

If sufficient seedling establishment can be achieved, seed‐based restoration provides an affordable, active restoration approach that can be implemented quickly at scale. However, establishment has served as a major restoration bottleneck, highlighting the need for improved understanding of seed germination niche and interactions with site conditions. Germination niche breadth (NB) is expected to increase with gene flow, resulting in broader environmental tolerance range, reduced sensitivity to site conditions, and less variation among seed sources. To investigate how germination NB relates to inter‐ and intraspecific variation in establishment from seed, we compared field recruitment for two milkweeds (Asclepias), the larval host plant of the monarch butterfly and thus a high priority group for habitat creation. Consistent with species‐level NB derived from laboratory trials, there was strong evidence that early life stages of the habitat specialist (Asclepias incarnata) varied among seed collection regions (separated by 423–572 km) but no evidence that the generalist (A. syriaca) varied among seed sources collected across an approximately 750‐km transect. Regeneration trends demonstrate that A. incarnata is significantly more sensitive to seed source and therefore requires more restricted seed zones. However, climate change may necessitate that we separate seed collection zones from seed application zones, upending the traditional framework of seed transfer zones. Until taxon‐specific studies have identified the scale of adaptive, phenotypic variance, restoration practitioners should continue to adjust the scale of seed collection zones for milkweeds and other taxa based on species traits known to influence gene flow, such as abundance and habitat specificity.

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.

Increasing radiation doses in Anastrepha obliqua (Diptera: Tephritidae) larvae improve parasitoid mass-rearing attributes.

Doses of 40, 80, 120, and 160 Gy were applied to 5-, 6-, 7-, and 8-day-old Anastrepha obliqua larvae, which were exposed to the Neotropical-native braconids Doryctobracon crawfordi and Utetes anastrephae and the Asian braconid Diachasmimorpha longicaudata. These tests were performed to know the effect of the increase in host radiation on the emergence of the aforementioned parasitoids and the related consequences of oviposition on the host. The study was based on the fact that higher radiation doses may cause a decrease in the host immune activity. There was a direct relationship between the increase in radiation dose and the parasitoid emergence. Both, the weight and the mortality of the host larvae were not affected by radiation. Although the larval weight of the larvae was lower and the mortality was higher in the younger larvae. Both, the number of scars and immature stages per host puparium originated from the younger larvae were lower than those from older larvae. Only U. anastrephae superparasitized more at lower radiation. Superparasitism by D. longicaudata was more frequent at 160 Gy. Qualitative measurements of melanin in the larvae parasitized showed that the levels were lower with increasing radiation. As radiation doses increased, the antagonistic response of the A. obliqua larva was reduced. Host larvae aged 5- and 6-day-old irradiated at 120-160 Gy significantly improve parasitoid emergence. This evidence is relevant for the mass production of the three tested parasitoid species.

Suitability of Turkey Oak, European Beech, and Hornbeam to Gypsy Moth Feeding

Pest resistance of trees should be taken into account in future forest strategy planning and predicting risks of defoliation. The gypsy moth (GM) (Lymantria dispar L.) is a serious forest pest with outbreaking population dynamics. To estimate defoliation risk of the most widely distributed tree species in Balkan Peninsula and Europe (Turkey oak Quercus cerris L., European beech Fagus sylvatica L. and hornbeam Carpinus betulus L.), we carried out laboratory feeding trials and investigated their acceptability and suitability for GM development. We determined morphological and chemical attributes of these hosts as well as larval host preference, growth and nutritional indices. Preference, growth, and efficiency of food conversion into biomass were ranked in the order: Turkey oak ˃ European beech ˃ hornbeam. Hornbeam was the most avoided and showed the lowest conversion efficiency although, comparing to optimal oak host, its leaves were less tough, contained more water and exhibited similar values of nitrogen (index of protein content) and C/N ratio (index of investment into carbon based plant defense). We suggest that hornbeam and beech leaf chemical profiles should be further studied to reveal specific compounds that impose high metabolic cost to GM larvae. Moreover, additional research are needed to understand how intermediate hosts in natural populations affect GM outbreaks.

Butterfly fauna (insecta: Lepidoptera: Papilionoidea) and larval host plant in Bongaon town, West Bengal, India

An appraisal of butterfly species diversity was carried out in the suburban town of Bongaon, southern West Bengal, India whose butterfly faunal diversity remained undocumented. A total of 76 species of butterflies were recorded from October 2018 to October 2019. The highest number of butterflies were recorded belonging to the family Nymphalidae (27 species), followed by Lycaenidae (21 species), Hesperiidae (13 species), Pieridae (8 species) and Papilionidae (7 species). Among the 76 butterfly species that have been recorded, nine species come under the protection category as per the Indian Wildlife (Protection) Act, 1972. Over the study period, 54 species of larval host plants were also documented. This communication will be the first comprehensive work on butterflies of Bongaon town and serve as baseline data for future research on the butterfly.

Host plant specificity of the monarch butterfly Danaus plexippus: A systematic review and meta-analysis.

The preference-performance hypothesis explains host specificity in phytophagous insects, positing that host plants chosen by adults confer the greatest larval fitness. However, adults sometimes oviposit on plants supporting low larval success because the components of host specificity (adult preference, plant palatability, and larval survival) are non-binary and not necessarily correlated. Palatability (willingness to eat) is governed by chemical cues and physical barriers such as trichomes, while survival (ability to complete development) depends upon nutrition and toxicity. Absence of a correlation between the components of host specificity results in low-performance hosts supporting limited larval development. Most studies of specificity focus on oviposition behavior leaving the importance and basis of palatability and survival under-explored. We conducted a comprehensive review of 127 plant species that have been claimed or tested to be hosts for the monarch butterfly Danaus plexippus to classify them as non-hosts, low performance, or high performance. We performed a meta-analysis to test if performance status could be explained by properties of neurotoxic cardenolides or trichome density. We also conducted a no-choice larval feeding experiment to identify causes of low performance. We identified 34 high performance, 42 low performance, 33 non-hosts, and 18 species with unsubstantiated claims. Mean cardenolide concentration was greater in high- than low-performance hosts and a significant predictor of host status, suggesting possible evolutionary trade-offs in monarch specialization. Other cardenolide properties and trichome density were not significant predictors of host status. In the experiment, we found, of the 62% of larvae that attempted to eat low-performance hosts, only 3.5% survived to adult compared to 85% of those on the high-performance host, demonstrating that multiple factors affect larval host plant specificity. Our study is the first to classify all known host plants for monarchs and has conservation implications for this threatened species.

Larval Exposure to Parasitic Varroa destructor Mites Triggers Specific Immune Responses in Different Honey Bee Castes and Species.

Innate immune systems are key defenses of animals and particularly important in species that lack the sophisticated adaptive immune systems as found in vertebrates. Here, we were interested to quantify variation in innate immune responses of insects in hosts that differ in their parasite susceptibility. To do this, we studied immune responses in honey bees, which can host a remarkable number of different parasites, which are major contributors of declining bee health and colony losses. The most significant parasite of honey bees is the mite Varroa destructor, which has infested the majority of global honey bee populations, and its control remains a major challenge for beekeepers. However, a number of nonmanaged honey bees seem able to control Varroa infections, for example, the Eastern honey bee Apis ceranacerana or the African honey bee Apis mellifera scutellata. These bees therefore make interesting study subjects to identify underlaying resistance traits, for example, by comparing them to more susceptible bee genotypes such as Western honey bees (A. melliferaligustica). We conducted a series of interlinked experiments and started with behavioral assays to compare the attractiveness of bee larvae to mites using different honey bee genotypes and castes. We found that 6-day-old larvae are always most attractive to mites, independently of genotype or castes. In a next step, we compared volatile profiles of the most attractive larvae to test whether they could be used by mites for host selection. We found that the abundance of volatile compounds differed between larval ages, but we also found significant differences between genotypes and castes. To further study the expected underlaying physiological differences between potentially resistant and susceptible host larvae, we compared the larval hemolymph proteomes of the three honey bee genotypes and two castes in response to mite exposure. We identified consistent upregulation of immune and stress-related genes in Varroa-exposed larvae, which differed between genotypes and castes. Tolerant honey bee castes and genotypes were characterized by stronger or more distinct immune esponses. In summary, we provide first insights into the complex involvement of the innate immune system of tolerant honey bees against mite infestations, which could be used for future breeding purposes.

Whole-genome sequencing analysis and protocol for RNA interference of the endoparasitoid wasp Asobara japonica.

Asobara japonica is an endoparasitic wasp that parasitizes Drosophila flies. It synthesizes various toxic components in the venom gland and injects them into host larvae during oviposition. To identify and characterize these toxic components for enabling parasitism, we performed the whole-genome sequencing (WGS) and devised a protocol for RNA interference (RNAi) with A. japonica. Because it has a parthenogenetic lineage due to Wolbachia infection, we generated a clonal strain from a single wasp to obtain highly homogenous genomic DNA. The WGS analysis revealed that the estimated genome size was 322 Mb with a heterozygosity of 0.132%. We also performed RNA-seq analyses for gene annotation. Based on the qualified WGS platform, we cloned ebony-Aj, which encodes the enzyme N-β-alanyl dopamine synthetase, which is involved in melanin production. The microinjection of double-stranded RNA (dsRNA) targeting ebony-Aj led to body colour changes in adult wasps, phenocopying ebony-Dm mutants. Furthermore, we identified putative venom genes as a target of RNAi, confirming that dsRNA injection-based RNAi specifically suppressed the expression of the target gene in wasp adults. Taken together, our results provide a powerful genetic toolkit for studying the molecular mechanisms of parasitism.

Parasitism of Corn Earworm, Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae), by Tachinid Flies in Cultivated Hemp.

Simple SummaryHemp has become a rapidly growing industry in the United States in recent years. However, due to many decades of prohibition, there has been relatively little research on insect pests and their interactions with natural enemies in hemp production systems. Here, we provide the first quantitative assessment of corn earworm (CEW) Helicoverpa zea parasitism in a hemp system. Corn earworm larvae exhibited high parasitism rates by tachinid flies resulting in elevated mortality. Host mortality increased with the number of tachinid eggs per larva even though typically only one parasitoid successfully developed per host. Larger CEW larvae were more likely to survive parasitism, but frequently, neither parasitoid nor host larvae successfully developed. Our results suggest that tachinid flies hold promise as biological control agents for populations of this important pest attacking hemp.In a survey on hemp grown in western Kentucky we found an average of 27.8 CEW larvae per plant. We recorded 45% parasitism of CEW in these fields by two species of tachinid flies, Winthemia rufopicta and Lespesia aletiae. Most parasitized larvae were third to sixth instars at the time of collection. We found up to 22 tachinid eggs per host larva, 89% of which typically bore between 1 and 5 eggs on the thorax. 45.9% of CEW bearing eggs died. The number of tachinid eggs per host was unrelated to host body mass, but both the number of tachinid eggs and caterpillar body mass influenced CEW survival. Larger CEW often survived parasitism and the number of fly eggs was negatively related to survival rate. The emergence of adult flies was positively correlated with the number of eggs, but no influence of the host size was found. High mortality of CEW larvae and the parasitoids developing within them in this system suggests that secondary chemicals (or poor nutrition) of the hemp diet may be negatively affecting host and parasitoid development and influencing their interactions.

Unique neural coding of crucial versus irrelevant plant odors in a hawkmoth.

The sense of smell is pivotal for nocturnal moths to locate feeding and oviposition sites. However, these crucial resources are often rare and their bouquets are intermingled with volatiles emanating from surrounding 'background' plants. Here, we asked if the olfactory system of female hawkmoths, Manduca sexta, could differentiate between crucial and background cues. To answer this question, we collected nocturnal headspaces of numerous plants in a natural habitat of M. sexta. We analyzed the chemical composition of these headspaces and used them as stimuli in physiological experiments at the antenna and in the brain. The intense odors of floral nectar sources evoked strong responses in virgin and mated female moths, most likely enabling the localization of profitable flowers at a distance. Bouquets of larval host plants and most background plants, in contrast, were subtle, thus potentially complicating host identification. However, despite being subtle, antennal responses and brain activation patterns evoked by the smell of larval host plants were clearly different from those evoked by other plants. Interestingly, this difference was even more pronounced in the antennal lobe of mated females, revealing a status-dependent tuning of their olfactory system towards oviposition sites. Our study suggests that female moths possess unique neural coding strategies to find not only conspicuous floral cues but also inconspicuous bouquets of larval host plants within a complex olfactory landscape.

In the Pursuit of Synchrony: Northward Shifts in Western Spruce Budworm Outbreaks in a Warming Environment

Outbreaks of western spruce budworm (Choristoneura freemani Freeman) in Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] forests of western Canada have shifted northward in recent decades. Using forest health survey data collected during the previous century (1909 to 2011) to assess the pattern of range shifts, we found that outbreaks have rapidly shifted to higher latitudes and elevations while gradually retracting from the southern and western portions of its range. Given that the survival of western spruce budworm is affected by access to developing buds, we tested the prediction that this shift was associated with climate change-induced alterations in synchrony between budworm larval emergence and Douglas-fir bud development. We simulated the dates of larval emergence and host budburst annually from 1901 to 2011 using existing phenology models and long-term weather data. Over the last century, the timing of larval emergence in relation to budburst has converged toward optimal synchrony at higher latitudes and elevations, while diverging at lower latitudes and elevations. Shifting synchrony arises from differential responses to temperature by the insect and its host tree; both are reliant upon degree day accumulation, but Douglas-fir bud development is putatively dependent upon an additional photoperiodic threshold. Thus, the potential for warming to cause directional shifts in phenological matching between early season folivores and their host trees may be contingent upon the degree to which each depends on different components of their environments for their development.

Distribution and phenology of monarch butterfly larvae and their milkweed hosts in the South Central US

South Central US milkweeds (Asclepias) are critical adult nectar and larval food resources for producing the first spring and last summer/fall generations of declining eastern migratory monarch butterflies (Danaus plexippus). This study addresses multiple gaps in assessment of monarch conservation priorities for the South Central US through analyses of monarch larval host selectivity, phenology, and spatial density, as well as the phenology, niche modeled distribution, and land cover selectivity of important milkweed hosts. Results are synthesized to estimate seasonal milkweed resource areas. About 70% of monarch larval activity occurred from mid-March to mid-July (early season) and 30% from mid-August to late November (late season). Twenty-six wild milkweed (Apocynaceae) hosts were mapped, including four new records for North America. Important hosts included Asclepias a. ssp. capricornu, A. viridis, and A. oenotheroides, that were utilized more frequently during early season, and Asclepias latifolia, utilized more frequently during late season. Landscape host selectivity was positive for A. viridis and A. a. ssp. capricornu in late and early seasons, respectively, and negative for A. oenotheroides in late season. Milkweed land cover selectivity was positive for Developed-Open Space and Grassland Herbaceous, and negative for Cultivated Crops and Shrub/Scrub. Seasonal milkweed resource areas and larval spatial densities resolved interior and coastal corridors providing functional connectivity for monarch spring and fall migrations. A potential gap in milkweed resource areas was identified in South Texas. The novel merging of milkweed niche models with larval phenology, host selectivity, milkweed phenology, and land cover selectivity informs conservation assessment.

Effects of Different Pesticides on the Biological Control Agent, Habrobracon hebetor Say (Hymenoptera: Braconidae): A Review

I reviewed effects of different pesticides used against target insect of Habrobracon hebetor Say (an idiobiont and gregarious ectoparasitoid wasp), on the demography and functional response of this important biocontrol agent in Iran. For demographic studies, the young wasps of H. hebetor (under 24h old) were exposed to LC30 of each pesticide for 24h and then their desired features are investigated. About the functional response, sixty mated females of H. hebetor were treated by LC30 of selected pesticides for 24h. Then, among them six wasps were selected and introduced to different densities of host larvae for 24h. In conclusion, result of review confirmed that botanical and insect growth regulator (IGRs) pesticide due to the lowest negative effects on H. hebetor were compatible compared with the other pesticides for their successful combination in integrated pest management (IPM) designs.

Impacts of larval host plant species on dispersal traits and free-flight energetics of adult butterflies

Animals derive resources from their diet and allocate them to organismal functions such as growth, maintenance, reproduction, and dispersal. How variation in diet quality can affect resource allocation to life-history traits, in particular those important to locomotion and dispersal, is poorly understood. We hypothesize that, particularly for specialist herbivore insects that are in co-evolutionary arms races with host plants, changes in host plant will impact performance. From their coevolutionary arms-race with plants, to a complex migratory life history, Monarch butterflies are among the most iconic insect species worldwide. Population declines initiated international conservation efforts involving the replanting of a variety of milkweed species. However, this practice was implemented with little regard for how diverse defensive chemistry of milkweeds experienced by monarch larvae may affect adult fitness traits. We report that adult flight muscle investment, flight energetics, and maintenance costs depend on the host plant species of larvae, and correlate with concentration of milkweed-derived cardenolides sequestered by adults. Our findings indicate host plant species can impact monarchs by affecting fuel requirements for flight.

Effect of Pupal Cold Storage on Reproductive Performance of Microplitis manilae (Hymenoptera: Braconidae), a Larval Parasitoid of Spodoptera frugiperda (Lepidoptera: Noctuidae).

Simple SummaryParasitoids are one of the most important biological control agents, and there are increasing requirements for long-term breeding. It is critical to figure out the parasitoid biological properties and disclose the effects of cold storage on them to extend their longevity. In this study, we investigated the field parasitism rate and clarified the biological parameters of Microplitis manilae, a dominant larval parasitoid of Spodoptera frugiperda. Further analysis revealed that the pupal cold storage, including different storage temperatures, storage period and storage time, significantly affected the emergence rate, parasitism rate and longevity of wasp adults, and the optimal storage condition was middle-aged pupae stored at 10 °C for 5–10 d. These results provide a novel insight into the mass-rearing of M. manilae and contribute to the biological control using M. manilae against S. frugiperda.As a major invasive pest in China, Spodoptera frugiperda (Smith) (Lepidoptera: Noctuidae) has caused great damage to crops. Hymenopteran parasitoids, especially the braconid wasps, play crucial roles in depressing pest populations. However, there was little information about the ideal storage of parasitoids to achieve their mass-rearing. Here, we identified a dominant parasitoid of S. frugiperda, Microplitis manilae (Ashmead) (Hymenoptera: Braconidae), in the Hainan province of China with a field parasitism rate of 5.66–19.10%. The investigation of biological parameters revealed that the parasitism rate of M. manilae significantly decreased with an increase in both wasp adult longevity and host age, and the wasp of 1–3 d post eclosion performed best on the first instar of host larvae, showing the highest parasitism rate. We also discovered that the decreased temperature from 30 to 20 °C greatly extended the longevity of wasp adults, and a similar result was observed after feeding on 10% sucrose water compared with sterile water. Then, the effects of different pupal cold storage temperatures (4 and 10 °C), storage period (prepupa, middle-aged pupa, late-aged pupa) and storage time (5, 10 or 20 d) on the emergence rate, parasitism rate, female proportion and longevity of M. manilae were investigated. The results demonstrated that the middle-aged wasp pupae stored at 10 °C for 5–10 d possessed a stronger parasitic ability and longer longevity. These findings may promote the flexibility and efficacy of large-scale production of M. manilae, thus contributing to its biological field control against S. frugiperda.

Mutualism has its limits: consequences of asymmetric interactions between a well-defended plant and its herbivorous pollinator.

Concern for pollinator health often focuses on social bees and their agricultural importance at the expense of other pollinators and their ecosystem services. When pollinating herbivores use the same plants as nectar sources and larval hosts, ecological conflicts emerge for both parties, as the pollinator's services are mitigated by herbivory and its larvae are harmed by plant defences. We tracked individual-level metrics of pollinator health-growth, survivorship, fecundity-across the life cycle of a pollinating herbivore, the common hawkmoth, Hyles lineata, interacting with a rare plant, Oenothera harringtonii, that is polymorphic for the common floral volatile (R)-(-)-linalool. Linalool had no impact on floral attraction, but its experimental addition suppressed oviposition on plants lacking linalool. Plants showed robust resistance against herbivory from leaf-disc to whole-plant scales, through poor larval growth and survivorship. Higher larval performance on other Oenothera species indicates that constitutive herbivore resistance by O. harringtonii is not a genus-wide trait. Leaf volatiles differed among populations of O. harringtonii but were not induced by larval herbivory. Similarly, elagitannins and other phenolics varied among plant tissues but were not herbivore-induced. Our findings highlight asymmetric plant-pollinator interactions and the importance of third parties, including alternative larval host plants, in maintaining pollinator health. This article is part of the theme issue 'Natural processes influencing pollinator health: from chemistry to landscapes'.

Anti‐oxidants reverse DNA damage caused by fluconazole in the pathogenic fungus Cryptococcus neoformans

Understanding development of resistance to anti‐fungal drugs in the pathogenic fungus, Cryptococcus neoformans, is crucial for improving anticryptococcal therapy. We have previously determined that presence of anti‐oxidants in growth medium can reverse the fungal inhibition caused by the azole drug, fluconazole. However, the host/pathogen response to co‐treatment with fluconazole and anti‐oxidants remains poorly characterized. In our study, we have used growth assays, infection assays using a heterologous host model, Minimum Inhibitory Concentration (MIC) assays, and flow cytometry to determine how anti‐oxidants influence susceptibility and resistance of C. neoformans to fluconazole. The larval host, Galleria mellonella, was susceptible to C. neoformans and showed higher survival rate when co‐treated with fluconazole and the pathogen. Co‐treatment with select anti‐oxidants, including Pyrrolidine Dithio Carbamate (PDTC), reversed the therapeutic effect of fluconazole. Fluconazole alone causes an increase in DNA content in C. neoformans, detected as additional DNA peaks using flow cytometry, while co‐treatment with fluconazole and select anti‐oxidants reversed the presence of extra stained DNA. Finally, preliminary evidence suggested that C. neoformans lacking the cell cycle regulator, a homologue of Wee1, exhibit higher resistance to fluconazole. Defects in cell division partly account for inhibition of growth of C. neoformans by fluconazole and the ability of anti‐oxidants to reverse an increase in DNA content caused by fluconazole. Our studies suggest that the cell cycle regulator, Wee1 may be important for C. neoformans susceptibility to fluconazole.