Differences In Parasitism Rates Research Articles

Optimizing the Release Pattern of Telenomus podisi for Effective Biological Control of Euschistus heros in Soybean.

An augmentative biological control program using the egg parasitoid Telenomus podisi Ashmead (Hymenoptera: Platygastridae) is a promising tool for the management of the brown stink bug, Euschistus heros (Fabricius) (Hemiptera: Pentatomidae) in soybeans. The T. podisi are released as adults or pupae within lab-reared E. heros eggs. Because of the small size of the parasitoid and potentially limited dispersal ability, determining the optimal release pattern is critical for biological control of the target pest. This study used sentinel E. heros eggs to investigate T. podisi dispersal within soybean crops during two distinct phenological stages: the beginning of flowering (Vn-R1) and the grain-filling phase (R5-R6). Data were analyzed using semi-variograms and kriging maps. The results indicate significant differences in parasitism rates between the two plant growth stages and among different matrices. The maximum dispersal range for T. podisi was calculated at 39.0 m in the Vn-R1 stage with a maximum parasitism rate of 42%, while in the R5-R6 stage, the maximum dispersal range was calculated to be 30.9 m with a maximum parasitism of 73%. Therefore, it is recommended that release points for T. podisi be spaced no further than 30 m apart. These results provide valuable insights for future research and applications in biological control strategies, including adjustment of the logistics and release technique depending upon the crop phenological stage.

Helminths of freshwater turtles in Northeastern Brazil: parasite–host–environment relationships

ABSTRACT The parasitic fauna of reptiles is considered understudied compared to that of other vertebrates and is even less well known than the parasitic fauna of chelonians. Yet parasites are considered one of the main controllers of host populations because they can strongly impact population structure and species diversity. The objective of the present study was to identify the helminth fauna infecting freshwater turtles Phrynops geoffroanus and Mesoclemmys tuberculata, to evaluate the effects of host features (body mass and sex) and seasonality (dry and rainy seasons) on the abundance of parasites, and to compare infection rates in each host species between different biomes (Caatinga and Atlantic Forest) in an area of Northeastern Brazil. We found seven species of helminths that belong to Nematoda (Physaloptera sp., Serpinema amazonicus, Serpinema monospiculatus and Spiroxys figueiredoi), Cestoda (unidentified specimen), Digenea (Echinostomatidae) and Monogenea (Polystomoides brasiliensis). For both freshwater turtle species, we did not find a significant difference in the abundance of helminths related to the maximum carapace length, body mass or host sex; however, males had higher prevalence than females, while females presented greater abundance when infected. We observed significant differences in the infection levels between biomes and between seasons (dry and rainy), where the Atlantic Forest specimens showed higher infection rates compared to the Caatinga and the highest rates occurred in the dry season. The main parasitological parameters observed in P. geoffroanus and M. tuberculata showed that the studied biomes directly influenced the levels of parasitic infection. Variations in habitat characteristics can directly influence patterns of helminth diversity and abundance, and interactions between these characteristics can generate differences in parasitism rates of the same host species in different environments.

Early damage enhances compensatory responses to herbivory in wild lima bean.

Damage by herbivores can induce various defensive responses. Induced resistance comprises traits that can reduced the damage, while compensatory responses reduce the negative effects of damage on plant fitness. Timing of damage may be essential in determining the patterns of induced defenses. Here, we tested how timing and frequency of leaf damage affect compensatory responses in wild lima bean plants in terms of growth and seed output, as well as their effects on induced resistance to seed beetles. To this end, we applied mechanical damage to plants at different ontogenetical stages, at one time point (juvenile stage only) or two time points (seedling and juvenile stage or juvenile and reproductive stage). We found that plants damaged at the seedling/juvenile stage showed higher compensatory growth, and seed output compared to plants damaged only at the juvenile stage or juvenile/reproductive stage. Seeds from plants damaged at the juvenile and juvenile/reproductive stages had fewer beetles than seeds from undamaged plants, however this was driven by a density dependent effect of seed abundance rather than a direct effect of damage treatments. We did not find differences in parasitism rate by parasitoid wasps on seed beetles among plant treatments. Our results show that damage at the seedling stage triggers compensatory responses which implies that tolerance to herbivory is enhanced or primed by early damage. Herbivory often occurs at several time points throughout plant development and this study illustrates that, for a full understanding of the factors associated with plant induced responses in a dynamic biotic environment, it is important to determine the multitrophic consequences of damage at more than one ontogenetical stage.

Annual and Seasonal Changes in Parasitism Rates by Hadronotus Pennsylvanicus (Hymenoptera: Scelionidae) on the Squash Bug Anasa Tristis (Hemiptera: Coreidae) in Squash Fields: Implications for Augmentative Releases.

This study evaluated parasitism rates by Hadronotus pennsylvanicus (Ashmead) (Hymenoptera: Scelionidae) on the squash bug Anasa tristis DeGeer (Hemiptera: Coreidae) over a six-year period in squash fields in Maryland. From 2016-2021, 2226 wild squash bug egg masses were collected, 2180 (98.0%) A. tristis egg masses and 46 (2.0%) A. armigera egg masses. The mean (±SE) parasitism rate was 10.9 ± 0.16%. Yearly parasitism rates were significantly different with rates in 2017 and 2018 that were significantly lower than in 2019, 2020, and 2021. The significant difference in parasitism rates based on planting date was primarily due to the high parasitism rate observed in 2021. These results suggest that the use of augmentative releases early in the season could result in effective control by increasing parasitism earlier in the season and by causing the parasitism rate in the field to peak at a higher number late in the season.

Female Cuckoo Calls Deceive Their Hosts by Evoking Nest-Leaving Behavior: Variation under Different Levels of Parasitism.

The common cuckoo (Cuculus canorus) is an obligate brood parasite that has evolved a series of strategies to trick its hosts. The female cuckoo has been hypothesized to mimic the appearance and sounds of several raptors to deceive the hosts into exhibiting anti-predator behavior. Such behavior would relax the protection of the host nest and thus allow the female cuckoo to approach the host nest unopposed. Many anti-parasite strategies have been found to vary among geographical populations due to different parasitic pressures from cuckoos. However, the effect of female cuckoo calls related to different levels of parasitic pressure has not been examined. Here, we studied the effect of female cuckoo calls on the oriental reed warbler (Acrocephalus orientalis), one of the major hosts of the common cuckoo, in two geographical populations experiencing different levels of parasite pressure. Four kinds of sounds were played back to the hosts: the calls from female common cuckoos, male common cuckoos, sparrowhawks (Accipiter nisus), and oriental turtle doves (Streptopelia orientalis). The results showed that the female cuckoo calls induced the hosts to leave their nests more frequently than the male cuckoo or dove calls in both populations, and two populations of the hosts reacted similarly to the female cuckoo calls, implying that the function of female cuckoo calls would not be affected by the difference in parasitism rate. This study indicates that female cuckoo calls function to distract the hosts' attention from protecting their nests. However, we propose that such a deception by the female cuckoo call may not be due to the mimicry of sparrowhawk calls, but rather that the rapid cadence of the call that causes a sense of anxiety in the hosts.

Larval parasitism in a specialist herbivore is explained by phenological synchrony and host plant availability.

Parasitism is a key factor in the population dynamics of many herbivorous insects, although its impact on host populations varies widely, for instance, along latitudinal and altitudinal gradients. Understanding the sources of geographical variation in host-parasitoid interactions is crucial for reliably predicting the future success of the interacting species under a context of global change. Here, we examine larval parasitism in the butterfly Aglais urticae in south-west Europe, where it is a mountain specialist. Larval nests were sampled over 2years along altitudinal gradients in three Iberian mountain ranges, including the Sierra Nevada, home to its southernmost European population. Additional data on nettle condition and adult butterflies were obtained in the study areas. These data sources were used to investigate whether or not differences in parasitism rates are related to the geographical position and phenology of the host, and to the availability of the host plants. Phenological differences in the host populations between regions were related to the severity of summer drought and the corresponding differences in host plant availability. At the trailing-edge of its distribution, the butterfly's breeding season was restricted to the end of winter and spring, while in its northern Iberian range the season was prolonged until mid-summer. Although parasitism was an important source of mortality in all regions, parasitism rates and parasitoid richness were highest in the north and lowest in the south. Moreover, within a region, there was a notable increase in parasitism rates over time, which probably led to selection against an additional late summer host generation in northern regions. Conversely, the shorter breeding season in Sierra Nevada resulted in a loss of synchrony between the host and one important late season parasitoid, Sturmia bella, which may partly explain the high density of this butterfly species at the trailing-edge of its range. Our results support the key role of host phenology in accounting for differences in parasitism rates between populations. They also provide insights into how climate through host plant availability affects host phenology and, ultimately, the impact of parasitism on host populations.

Variation of dipteran ectoparasites (Streblidae) on Anoura geoffroyi Gray, 1838 (Phyllostomidae) in two caves in southeastern Brazil.

Bats are parasitized by many different arthropods, among which the dipteran families Nycteribiidae and Streblidae are exclusive to bats. Researches that relate the ecology of ectoparasites with their hosts are fundamental for understanding issues related to the interactions between these two groups, in addition to epidemiological aspects of pathogen transmission. The present study evaluated the rate of infestation by dipteran (Streblidae) ectoparasites in two colonies of Anoura geoffroyi associated with caves in the southeastern Brazil. It also evaluated whether parasitological indices differ significantly with regard to host sex and reproductive condition. A total of 1377 bats were captured, of which 84% were parasitized. From these, a total of 5047 streblid bat flies belonging to three species of three genera were collected and identified. The most abundant was Exastinion clovisi (57%), followed by Anastrebla modestini (30%) and Trichobius propinquus (13%). In general, the populations of ectoparasites fluctuated throughout the year, with peaks of abundance during the rainy season. The sex ratios for the species of ectoparasites were close to one, which differs from what is reported in the literature. In addition, there were significant differences in parasitism rates in relation to host sex and reproductive condition. In both populations, ectoparasite infestation of pregnant or lactating females was significantly higher than for non-reproductive females. New studies aimed at assessing whether these higher rates of infestation have any effect on female bat reproduction are needed.

Responses of two introduced larval parasitoids to the invasive emerald ash borer (Coleoptera: Buprestidae) infesting a novel host plant, white fringe tree: Implication for biological control

Emerald ash borer (EAB), Agrilus planipennis is a buprestid species native to Asia, where it is a pest of ash trees, Fraxinus spp. Since it was accidentally introduced to the United States in the 1990s, this beetle has become one of the most destructive invasive pests of North American ash trees. In 2015 it was found attacking the white fringe tree, Chionanthus virginicus, indicating the potential for host range expansion. This study evaluates the responses of two introduced larval parasitoids, Spathius agrili and S. galinae, to EAB larvae infesting this novel host plant. Third to fourth instar EAB larvae reared with tropical ash in the laboratory were inserted into green ash and white fringe tree bolts. Infested bolts were exposed to gravid females of both Spathius spp. under no-choice and S. galinae under choice testing conditions. No-choice testing indicated no difference in parasitism rate on EAB larvae between white fringe and green ash for either parasitoid species. Two-choice testing with S. galinae also indicated no difference in parasitism rate when green ash was an option. Sex ratio and brood size were unaffected by host substrate for EAB, but both species emerged sooner on EAB in white fringe tree under no-choice conditions. EAB larvae can be successfully parasitized in white fringe tree under laboratory conditions. These results indicate that S. agrili and S. galinae have potential to attack EAB larvae infesting white fringe tree.

Parasitism potential of Dirhinus giffardii (Silvestri) (Hymenoptera: Chalcididae) on pupae of the fruit fly species, Zeugodacus cucurbitae (Coquillett) and Bactrocera dorsalis (Hendel) (Diptera: Tephritidae), during variable exposure durations

BackgroundFruit flies are important insect pests of horticultural crops. Pesticides used to control them which cause environmental and health hazards; therefore, other alternative sustainable management measures are required.Main bodySuccessful implementation of an integrated pest management program, using biological control agents, needs synchronization of parasitoids with hosts selection and exposure time. The present study was conducted to assess the biological activity of the parasitoid species, Dirhinus giffardii (Silvestri) (Hymenoptera: Chalcididae), against the melon fruit fly, Zeugodacus cucurbitae (Coquillett), and the oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae), at different exposure durations (24, 48, and 72 h). The experiments were conducted under standard laboratory conditions. Significant differences in the parasitism rate of D. giffardii were observed for both species at different exposure durations. The maximum parasitism rate of D. giffardii (52.60 ± 2.84%) and (42.73 ± 2.74%) was observed at 48-h exposure period for Z. cucurbitae and B. dorsalis, respectively. Also, a comparison between both species showed a difference in parasitism rate at 24 and 48 h and a positive correlation between percent parasitism and exposure duration. Adult emergence of D. giffardii showed a maximum emergence rate from pupae of Z. cucurbitae (63.55 ± 4.02%) and B. dorsalis (51.61 ± 2.33%) at 10 days interval, respectively. However, the daily emergence of the parasitoid was not correlated to exposure duration in both species. The results of the present study may serve in the mass rearing of D. giffardii.ConclusionThe biological activity of D. giffardii was maximum at 48 h of exposure for both fruit fly species, and this important information may improve the mass rearing technology of D. giffardii.

Oviposition behavior of Telenomus busseolae, Telenomus isis and Trichogramma bournieri on eggs of east African cereal stemborers

The oviposition behavior of the scelionids Telenomus busseolae, Telenomus isis and the trichogrammatid Trichogramma bournieri was studied on eggs of lepidopteran cereal stemborers, which included the noctuid Busseola fusca, Sesamia calamistis, Sesamia nonagrioides, the crambid Chilo partellus, and the pyralid Eldana saccharina. Unlike Tr. bournieri, Telenomus spp. did not attack eggs of C. partellus and E. saccharina. Five distinct behavioral steps were observed, which included foraging, drumming with the antennae on the eggs, ovipositor insertion, egg marking, and walking and resting. Foraging, walking and resting were observed less frequently than the other behaviors. There was a clear hierarchy of behavioral steps leading to successful parasitism, which culminated in marking of eggs. Self-superparasitism (i.e., oviposition in an egg previously parasitized by the same female) was between 2.7–5.9% indicating that the three parasitoids were able to discern eggs that were already parasitized. Earlier studies on the bionomics and host finding ability together with the present findings on the oviposition behavior of the different parasitoids cannot explain differences in parasitism rates by the parasitoids in the field. It is suggested that the plant species and alternative hosts occurring in crop and natural habitats may play an important role in the population dynamics of the parasitoids and affect their importance in controlling key pests of maize.

Elevational contrast in predation and parasitism risk to caterpillars in a tropical rainforest

AbstractInvertebrate predators and parasitoids are among the most important natural enemies of insect herbivores. Yet, the strength of natural enemy pressure along an altitudinal gradient and interactions between the groups of natural enemies (such as predation on parasitized prey) are not well known. Various methods are used to reveal the mortality factors of herbivores. Predation pressure is usually assessed through exposure of artificial prey. However, this method cannot provide information about the attacks of parasitoids, or their eventual interactions with predators. Furthermore, artificial or dead prey might not attract predators because they do not show expected host behavior, and this method mostly cannot distinguish between predation and scavenging. For the first time in a tropical rainforest, we quantified elevational contrast in mortality factors using exposure of live caterpillars. We exposed a total of 800 live caterpillars of Talanga excelsalis moresbyensis Strand (Lepidoptera: Crambidae) on saplings of Ficus copiosa Steud. (Moraceae) at two elevations in primary tropical rain forest in Papua New Guinea (200 and 1 200 m a.s.l.). We exposed the caterpillars in two treatments: exposed to and protected from invertebrate predators and parasitoids. Disappearance of caterpillars was significantly higher in the exposed treatment. Furthermore, caterpillar disappearance was significantly higher in lowlands than in highlands (43 vs. 12%). We consider the vast majority of the disappearance to be due to predation, as migration of the caterpillars from the focal trees was not observed (except one caterpillar). This estimate of invertebrate predation rate corresponds with studies which used artificial caterpillar models. No significant difference in parasitism rate between the two elevations was observed (12 vs. 13%). The combination of the disappearance and parasitism rate patterns means that larval parasitoids face stronger pressure from invertebrate predators through higher predation of their hosts in the lowlands than in the highlands.

Deciphering host-parasitoid interactions and parasitism rates of crop pests using DNA metabarcoding

An accurate estimation of parasitism rates and diversity of parasitoids of crop insect pests is a prerequisite for exploring processes leading to efficient natural biocontrol. Traditional methods such as rearing have been often limited by taxonomic identification, insect mortality and intensive work, but the advent of high-throughput sequencing (HTS) techniques, such as DNA metabarcoding, is increasingly seen as a reliable and powerful alternative approach. Little has been done to explore the benefits of such an approach for estimating parasitism rates and parasitoid diversity in an agricultural context. In this study, we compared the composition of parasitoid species and parasitism rates between rearing and DNA metabarcoding of host eggs and larvae of the millet head miner, Heliocheilus albipunctella De Joannis (Lepidoptera, Noctuidae), collected from millet fields in Senegal. We first assessed the detection threshold for the main ten endoparasitoids, by sequencing PCR products obtained from artificial dilution gradients of the parasitoid DNAs in the host moth. We then assessed the potential of DNA metabarcoding for diagnosing parasitism rates in samples collected from the field. Under controlled conditions, our results showed that relatively small quantities of parasitoid DNA (0.07 ng) were successfully detected within an eight-fold larger quantity of host DNA. Parasitoid diversity and parasitism rate estimates were always higher for DNA metabarcoding than for host rearing. Furthermore, metabarcoding detected multi-parasitism, cryptic parasitoid species and differences in parasitism rates between two different sampling sites. Metabarcoding shows promise for gaining a clearer understanding of the importance and complexity of host-parasitoid interactions in agro-ecosystems, with a view to improving pest biocontrol strategies.

Population study of the B chromosome frequency in the grasshopper Abracris flavolineata

Additional parasitic elements known as B chromosomes have been described in approximatey 15% of eukaryotic species. They have primary characteristics that define their origin, composition, ways of accumulation and evolution, such as irregular modes of inheritance, pairing incapacity with standard A chromosomes during meiosis and accumulation of distinct repetitive DNAs. The grasshopper Abracris flavolineata presents diploid number 2n = 23, X0 (male) and 2n = 24, XX (female) and presence of one or two B submetacentric chromosomes were reported exclusively in Rio Claro/SP population, varying in frequency temporally from 13.5% to 31.5% in males. In this work aiming to understand the spatial variation of B chromosome we investigated presence and frequency of B chromosomes in males belonging to three populations, Santa Bárbara do Pará/PA, Cabo/PE and Posadas/Misiones/Argentina using 61, 19 and 14 individuals, respectively. For Argentina population the frequency estimated was only 7,14% (one individual), while for Pernambuco it was higher with about 21,05% (four individuals), and for Pará none of the individuals presented B chromosomes. None of the populations presented individuals with 2B chromosome as reported in Rio Claro/SP, suggesting differential drive and accumulation. The fluctuation of B chromosome frequency and accumulation in these natural populations could be explained by several factors, like differences in parasitism rate, genetic drift or else by negative effects for host development. Moreover local environment characteristics, associated to possible reproductive isolation, caused by vicariance processes, could also influence B chromosome frequency variation. Here we expanded the knowledge of B chromosome geographic distribution in A. flavolineata and the next step is to check if the B chromosome is the same variant in distinct populations, using for example the U2 snDNA as probe, wich is present in the B chromosome from Rio Claro/SP population.

Effects of host larval stage preferences and diet on life history traits of Diadegma mollipla, an African parasitoid of the Diamondback Moth

ABSTRACTKnowledge of the biological attributes of parasitoids plays a fundamental role in improved management of their pest hosts. Diadegma mollipla is a major indigenous parasitoid of the Diamondback Moth (DBM), Plutella xylostella (Linnaeus), in Eastern Africa. Two laboratory experiments were conducted to determine the DBM larval stage preferences of D. mollipla and their influence on life history traits and the effect of different diets (20% honey, 20% sugar solution, water or nothing) on adult parasitoid longevity. In the first study, 60 DBM larvae (15 each of larval stages L1–L4) were exposed to either one adult parasitoid female or four competing females in choice experiments. When DBM larvae were exposed to one parasitoid, in terms of parasitism, L1 and L2 were found to be the most preferred stages, followed by L3 and then L4. Sex ratio (females/males) increased with host larval stage from 1.3 to 3.1. Pre-imaginal development time was longer in L1 than in the other three stages. When exposed to four parasitoids, no significant differences in parasitism rates and progeny production were obtained between DBM larval stages. However, sex ratio increased from 0.8 in L1 to 4.1 in L4. Developmental time was longest in L4, intermediate in L1 and L3, and shortest in L2. In the diet experiment, honey and sugar were found to significantly increase longevity for D. mollipla adults of both sexes. Overall, combined adult male and female longevity was 24.5, 9.9, 2.2 and 1.9 days when fed on honey, sugar, water or nothing, respectively.

Spatial Distribution of Megacopta cribraria (Hemiptera: Plataspidae) Adults, Eggs and Parasitism by Paratelenomus saccharalis (Hymenoptera: Platygastridae) in Soybean.

Since 2014, populations of the kudzu bug, Megacopta cribraria (F.) (Hemiptera: Plataspidae), have declined in the southeastern United States and seldom require treatment. This decline follows the discovery of Paratelenomus saccharalis (Dodd; Hymenoptera: Platygastridae), a non-native egg parasitoid. The objective of this project was to observe the temporal and spatial dynamics of P. saccharalis parasitism of kudzu bug egg masses in commercial soybean fields. Four fields were sampled weekly for kudzu bugs and egg masses at a density of one sample per 0.6 ha. Sampling commenced when soybean reached the R2 maturity stage and continued until no more egg masses were present. Responses including kudzu bugs, egg masses, and parasitism rates were analyzed using ANOVA, Spatial Analysis by Distance Indices (SADIE), and SaTScan spatial analysis software. Egg masses were collected from the field, held in the lab and monitored for emergence of kudzu bug nymphs or P. saccharalis. Kudzu bug populations were generally lower than previously reported in the literature and spatial aggregation was not consistently observed. Egg parasitism was first detected in early July and increased to nearly 40% in mid-August. Significant spatial patterns in parasitism were observed with spatio-temporal clusters being loosely associated with clusters of egg masses. There were no significant differences in parasitism rates between field margins and interiors, suggesting that P. saccharalis is an effective parasitoid of kudzu bug egg masses on a whole-field scale.

Ploidy in <i>Lolium</i> spp. cultivars affects Argentine stem weevil parasitism by <i>Microctonus hyperodae</i>


 
 
 A laboratory study was conducted to: (1) advance earlier work to determine the susceptibility of Listronotus bonariensis (Argentine stem weevil) to its parasitoid biological control agent, Microctonus hyperodae, in the presence of diploid ryegrasses such as Lolium multiflorum or Lolium perenne; and (2) determine whether or not plant orientation (i.e. horizontal vs. vertical) had any effect on parasitism rates. No significant differences in parasitism rates were found in the Listronotus bonariensis populations in the two grasses. However, combining and analysing these data with those from an earlier experiment conducted in the same way showed that parasitism rates were significantly lower in diploid Lolium multiflorum cultivars than in tetraploid Lolium multiflorum. This is the first clear evidence of a ploidy effect on parasitism rates in the presence of Lolium multiflorum. Tetraploid Lolium multiflorum has fewer, more robust and larger tillers than the diploid Lolium spp. so higher parasitism rates may be related to the lack of hiding places for an evasive genetically-driven behaviourally-based resistance by Listronotus bonariensis.
 
 

Landscape diversity and crop vigor outweigh influence of local diversification on biological control of a vineyard pest

AbstractThe influence of local and landscape habitat diversification on biological control of the Western grape leafhopper (Erythroneura elegantula Osborn) by its key parasitoids Anagrus erythroneurae S. Trjapitzin & Chiappini and Anagrus daanei Triapitsyn was studied in wine grape vineyards. At the landscape scale, Anagrus rely on alternative host species in non‐crop habitats outside of the vineyard to successfully overwinter, while at the local scale vineyard diversification can provide resources, such as shelter and floral nectar, which improve parasitoid performance. In a two‐year experiment, plots with and without flowering cover crops were compared in vineyards representing a gradient of landscape diversity. While the cover crops did attract natural enemies, their populations were unchanged in the crop canopy and there was no difference in parasitism rate, leafhopper density, crop quality, or yield. Vineyards in diverse landscapes had higher early‐season abundance of Anagrus spp., which was linked to increased parasitism and decreased late‐season populations of E. elegantula. Leafhopper densities were also positively associated with crop vigor, regardless of landscape or cover crops. Flowering cover crops did increase abundance of some natural enemy species as well as parasitism rate in vineyard landscapes with intermediate levels of diversity, indicating a local × landscape interaction, although this did not lead to reductions in E. elegantula densities. These findings indicate that, in this agroecosystem, landscape diversity mediates and in many ways outweighs the influence of local diversification and that E. elegantula densities were regulated by a combination of biological control and crop vigor.

Bat Flies (Diptera: Nycteribiidae, Streblidae) Parasitising Rousettus madagascariensis (Chiroptera: Pteropodidae) in the Parc National d'Ankarana, Madagascar: Species Diversity, Rates of Parasitism and Sex Ratios

We present details on bat flies of the families Nycteribiidae and Streblidae parasitising an endemic Malagasy fruit bat, Rousettus madagascariensis, including aspects of species diversity, rates of parasitism and sex ratios. Data were collected from 639 bats occupying the same cave day roost site in the Parc National d'Ankarana, extreme northern Madagascar, and visited on three occasions: end of dry season (September 2014 and September 2015) and during the rainy season (January 2015). From a collection of over 3500 bat flies, two species were identified — Eucampsipoda madagascarensis (n = 3227) of the family Nycteribiidae and Megastrebla wenzeli (n = 350) of the family Streblidae. The number of E. madagascarensis per bat host showed seasonal variation with a notable reduction during the rainy season. The sex ratio of E. madagascarensis was significantly biased towards males, and this pattern was more pronounced during the dry season. In comparison, M. wenzeli, which were distinctly less common, showed statistical differences between the three site visits in prevalence, but not for the number of parasites per host. For E. madagascarensis parasitism rates varied with age and sex, with adult male R. madagascariensis having more ectoparasites than females, subadults and neonates, while no difference in parasitism rate was found for M. wenzeli based on host age and sex.

Geographic variation and trade-offs in parasitoid virulence.

Host-parasitoid systems are characterized by a continuous development of new defence strategies in hosts and counter-defence mechanisms in parasitoids. This co-evolutionary arms race makes host-parasitoid systems excellent for understanding trade-offs in host use caused by evolutionary changes in host immune responses and parasitoid virulence. However, knowledge obtained from natural host-parasitoid systems on such trade-offs is still limited. In this study, the aim was to examine trade-offs in parasitoid virulence in Asecodes parviclava (Hymenoptera: Eulophidae) when attacking three closely related beetles: Galerucella pusilla, Galerucella calmariensis and Galerucella tenella (Coleoptera: Chrysomelidae). A second aim was to examine whether geographic variation in parasitoid infectivity or host immune response could explain differences in parasitism rate between northern and southern sites. More specifically, we wanted to examine whether the capacity to infect host larvae differed depending on the previous host species of the parasitoids and if such differences were connected to differences in the induction of host immune systems. This was achieved by combining controlled parasitism experiments with cytological studies of infected larvae. Our results reveal that parasitism success in A.parviclava differs both depending on previous and current host species, with a higher virulence when attacking larvae of the same species as the previous host. Virulence was in general high for parasitoids from G.pusilla and low for parasitoids from G.calmariensis. At the same time, G.pusilla larvae had the strongest immune response and G.calmariensis the weakest. These observations were linked to changes in the larval hemocyte composition, showing changes in cell types important for the encapsulation process in individuals infected by more or less virulent parasitoids. These findings suggest ongoing evolution in parasitoid virulence and host immune response, making the system a strong candidate for further studies on host race formation and speciation.

Differential Parasitism Between Two Suitable Cowbird Hosts

Host choice by the brood parasitic Brown-headed Cowbird (Molothrus ater) is an evolved response to host suitability, resulting in patterns of differential parasitism rates among species within a community. In the ponderosa pine (Pinus ponderosa) forests of the Colorado Front Range, we recorded that Western Wood-pewee (Contopus sordidulus) is infrequently parasitized (1%, n = 259 nests) by the Brown-headed Cowbird, whereas the Plumbeous Vireo (Vireo plumbeus) is heavily parasitized (51%, n = 292). To account for differences in parasitism rates on these species we experimentally parasitized pewee nests with cowbird eggs, and we compared host aggression towards cowbird models, host nest attentiveness, nest placement, and egg-laying dates in these species. Pewees accepted cowbirds eggs and reacted more aggressively towards the cowbird model than the control model, were more attentive at their nest sites than vireos, and placed their nests higher and closer to the trunk than vireos. Egg-laying dates for vireos and cowbirds overlapped more than the egg-laying dates for pewees and cowbirds. We suggest that temporal asynchrony in host availability, coupled with differences in nest placement and behavior at the nest, help to account for the observed differences in parasitism rates between these two species.