Fresh Hosts Research Articles

The dynamics of phage predation on a microcolony

Phage predation is an important factor for controlling the bacterial biomass. At face value, dense microbial habitats are expected to be vulnerable to phage epidemics due to the abundance of fresh hosts immediately next to any infected bacteria. Despite this, the bacterial microcolony is a common habitat for bacteria in nature. Here, we experimentally quantify the fate of microcolonies of Escherichia coli exposed to virulent phage T4. It has been proposed that the outer bacterial layers of the colony will shield the inner layers from the phage invasion and thereby constrain the phage to the colony’s surface. We develop a dynamical model that incorporates this shielding mechanism and fit the results with experimental measurements to extract important phage-bacteria interaction parameters. The analysis suggests that, while the shielding mechanism delays phage attack, T4 phage are able to diffuse so deep into the dense bacterial environment that colony-level survival of the bacterial community is challenged.

Development of a Method for Rearing Nezara viridula (Heteroptera: Pentatomidae) on a Semi-solid Artificial Diet.

A method for rearing the southern green stinkbug, (Nezara viridula L.) (Heteroptera: Pentatomidae), using a modified lygus semi-solid artificial diet was developed. First to second-instar nymph were reared in a density of 631.5 ± 125.05 eggs per Petri-dish (4 cm deep × 15 cm diam). Second instar to adult were reared in a density of 535.0 ± 112.46 s instar nymphs per rearing cage (43 × 28 × 9 cm). Mating and oviposition occurred in popup rearing cages (30 × 30 cm), each holding 60-90 mixed sex adults of similar age. Adults emerged 35.88 ± 2.13 d after oviposition and survived for an average of 43.09 ± 9.53 d. On average, adults laid 223.95 ± 69.88 eggs in their lifetime, for a total production of 8,099 ± 1,277 fertile eggs/oviposition cage. Egg fertility was 77.93% ± 16.28. Egg masses held in petri-dishes had a total hatchability of 79.38% ± 20.03. Mortality of early nymphs in petri-dishes was 0.64% ± 0.12 for the first instar and 1.37% ± 0.45 for second instar. Late nymphal mortality in rearing cages was 1.41% ± 0.10, 3.47% ± 1.27, and 4.72% ± 1.29 for the third, fourth, and fifth instars, respectively. Survivorship from nymphs to adults was 88.48% ± 2.76. Using artificial diet for rearing N. viridula could reduce cost by avoiding time-consuming issues with daily feeding fresh natural hosts and insect manipulation. It could increase reliability and simplicity of bug production, which should facilitate mass rearing of its biological control agents.

Plasticity in life features, parasitism and super-parasitism behavior of Bracon hebetor, an important natural enemy of Galleria mellonella and other lepidopteran host species.

The wasp, Bracon hebetor Say, is an important potential biocontrol agent of a wide range of lepidopteran insect species. The current study was subjected to compare these ectoparasitoid fitness traits on different host species belonging to the order Lepidoptera. Moreover, we determine the population dynamic with different host densities, sex ratio patterns, super-parasitism, longevity, paralysis success, and reproductive potential under laboratory conditions. Our results revealed that oviposition increased with an increase in host density, while the adult emergence and egg hatching were decreased due to the super-parasitism on host larvae. A higher male and female-biased population were observed when virgin and mated females offered fresh hosts. Adults' longevity was recorded more in females than males when kept only with bee honey + royal jelly + host larvae. The mean duration of egg-adult development was recorded higher on Galleria mellonella and lowest on Busseola fusca. The parasitization rate, super-parasitism, and cumulative fecundity of mated and virgin female wasps with different host species were observed higher on specific host Galleria mellonella while it was lower on Phthorimaea operculella. Furthermore, the parasitoids having mating experience preferred fresh, while the parasitoids' lack of mating experiences preferred paralyzed host under olfactometer test. Besides, this research has produced novel facts on the biology of parasitic wasp, B. hebetor that may guide the advancement of sustainable biological control programs to control lepidopteran pests.

Pest categorisation of Liriomyza sativae.

The EFSA Panel on Plant Health performed a pest categorisation of Liriomyza sativae (Diptera: Agromyzidae) for the EU. L. sativae (the cabbage or vegetable leaf miner; EPPO code: LIRISA) is a polyphagous pest native to the Americas which has spread to Africa, Asia and Oceania. L. sativae can have multiple overlapping generations per year. Eggs are inserted in the leaves of host plants. Three larval instars, which feed internally on field vegetables (leaves and stems), follow. Then, the larva jumps into the soil where a fourth larval instar occurs immediately before pupation, which takes place in the soil. L. sativae is regulated in the EU by Commission Implementing Regulation (EU) 2019/2072 (Annex IIA). Within this Regulation, import of soil or growing medium as such or attached to plants for planting from third countries other than Switzerland is regulated. Therefore, entry of L. sativae pupae is prevented. However, immature stages on plants for planting (excluding seeds) and fresh leafy hosts for consumption, cut branches, flowers and fruit with foliage provide potential pathways for entry into the EU. L. sativae has been repeatedly intercepted in the EU, especially in basil (Ocimum spp.). Climatic conditions and the wide availability of host plants provide conditions to support establishment in the EU, both in open fields and greenhouses. Impacts on field vegetables and ornamentals as well as hosts in greenhouses would be possible. Phytosanitary measures are available to reduce the likelihood of entry. L. sativae satisfies the criteria that are within the remit of EFSA to assess for it to be regarded as a potential Union quarantine pest. Although human‐assisted movement of vegetables is considered the main spread way for L. sativae, this agromyzid does not meet the criterion of occurring in the EU for it to be regarded as a potential Union regulated non‐quarantine pest.

Pest categorisation of Nemorimyza maculosa.

The EFSA Panel on Plant Health performed a pest categorisation of Nemorimyza maculosa (Malloch) (Diptera: Agromyzidae) for the European Union (EU). N. maculosa is an oligophagous pest; cultivated hosts include Chrysanthemum, lettuce and other Asteraceae although there is little evidence of recent impacts. N. maculosa occurs widely in the Americas and is present on the island of Madeira (Portugal), where it is under official control. N. maculosa is not known to occur in mainland Portugal based on surveys. N. maculosa can have multiple overlapping generations per year. Eggs are inserted into the leaves of host plants. Developing larvae feed within leaves causing blotch mines. Pupation takes place in the soil or under debris on the ground. Immature stages on leafy host plant material such as Chrysanthemum cut flowers provide potential pathways for entry into the EU. Human‐assisted movement of cut flowers, fresh leafy hosts for consumption and plants for planting with foliage are considered the main pathways for entry. Climatic conditions and the wide availability of cultivated and wild host plants provide conditions to support establishment in the EU in the open and in greenhouse. The extent of potential impacts on hosts such as ornamental Asteraceae and lettuce in the EU is uncertain. N. maculosa is regulated in the EU by Commission Implementing Regulation 2019/2072 (Annex IIA) where it appears using a synonym, Amauromyza maculosa. Within the Regulation, the import of soil or growing medium, from third countries other than Switzerland is regulated and therefore prevents the entry of N. maculosa pupae. All criteria assessed by EFSA above for consideration either as a potential union quarantine pest or as a potential regulated non‐quarantine pest were met.

Population dynamics of fresh water snail intermediate hosts of <i>Schistosoma spp.,</i> in the Federal Capital Territory, Abuja, Nigeria

This study was carried out to provide information on the population dynamics of the snail intermediate host of Schistosoma spp., in Abuja. A cross-sectional study was carried out on water bodies with high human contact activities in all the six area councils in Federal Capital Territory including; Narachi, Rafir shawa, Shetiko, Ushafa, Yangoji and Basa Rivers in Abaji, Gwagwalada, Kuje, Bwari, Kwali and Abuja Municipal Area Council respectively. Sampling of snail was based on convenience and presence of snail in the selected areas. Each settlement in the sample population was visited once monthly between March and September, 2017 for snail sample collection. A total of 766 fresh water snails identified to be snail intermediate hosts of schistosomiasis were collected during the study. The prevalence of fresh water snail intermediate hosts of Schistosoma spp., in Abuja comprises 30.16% Bulinus globosus, 11.75% of Bulinus truncatus and 58.09% of Biomphilaria pfeifferi. These fresh water snails were found to be more prevalent in the month of March in all the Local Government Area Council sampled with Gwagwalada Area Council having the highest prevalence of fresh water snail while Bwari Area Council had the lowest. This study revealed that there was high prevalence of snail intermediate hosts of schistosomiasis in Abuja. Hence, there is need for appropriate intervention by the Federal Ministry of Health (FMOH), in collaboration with the National Schistosomiasis Control Program (NSCP) to control snail intermediate hosts of Schistosomes spp., in the study-area using chemical or biological molluscide.Keywords: Water bodies; human contact; Schistosoma spp

Evidence for trans-generational effects on egg maturation schedules in a syn-ovigenic parasitoid

The lifetime reproductive success of a female parasitoid is limited by (1) host (or time) limitation – the number of hosts available for oviposition during its lifetime; and (2) egg limitation – its egg supply. Host limitation is expected to select for increased longevity and/or foraging efficiency, while increased fecundity is predicted to evolve under egg limitation. If the limiting factor varies, phenotypic plasticity in egg maturation schedules may be advantageous, i.e. adjusting investment in egg production to host availability. In the polyembryonic parasitoid Copidosoma koehleri, environmental conditions experienced during development indeed influence resource allocation to egg maturation. However, whether parasitoids’ maternal environment also influences their daughters’ egg production has hardly been studied. To address this knowledge gap, we tested whether exposure of C. koehleri females to previously parasitized hosts (signaling intraspecific exploitation competition and risk of host limitation) reduces their daughters’ initial egg loads. We presented newly-emerged females with hosts that were either fresh or parasitized by conspecifics. The following day, we exposed both groups to additional fresh hosts, and reared out the daughters of these previously experienced, 24+ h old, individuals. The daughters’ egg loads and body sizes were similar under both experimental conditions. Nevertheless, their egg loads were ~30% higher, and body sizes were ~10% lower, than in daughters of just-emerged parasitoids. We suggest that female experience or age, but not conditions associated with host exploitation, trigger maternal effects on the reproductive and developmental physiology of their daughters.

Pathogenic modification of plants enhances long-distance dispersal of nonpersistently transmitted viruses to new hosts.

Aphids spread the majority of plant viruses through nonpersistent transmission (NPT), whereby virus particles attach transiently to these insects’ probing mouthparts. Virus acquisition from infected plants and inoculation to healthy host plants is favored when aphids briefly probe plant epidermal cells. It is well established that NPT virus infection can alter plant–vector interactions, and, moreover, such pathogen modifications are found in a range of plant and animal systems. In particular, viruses can make plants more attractive to aphids but inhibit aphid settling on infected plants. It is hypothesized that this viral “reprogramming” of plants promotes virus acquisition and encourages dispersal of virus‐bearing aphids to fresh hosts. In contrast, it is hypothesized that virus‐induced biochemical changes encouraging prolonged feeding on infected hosts inhibit NPT. To understand how these virus‐induced modifications affect epidemics, we developed a modeling framework accounting for important but often neglected factors, including feeding behaviors (probing or prolonged feeding) and distinct spatial scales of transmission (as conditioned by wingless or winged aphids). Analysis of our models confirmed that when viruses inhibit aphid settling on infected plants this initially promotes virus transmission. However, initially enhanced transmission is self‐limiting because it decreases vector density. Another important finding is that virus‐induced changes encouraging settling will stimulate birth of winged aphids, which promotes epidemics of NPT viruses over greater distances. Thus our results illustrate how plant virus modifications influence epidemics by altering vector distribution, density, and even vector form. Our insights are important for understanding how pathogens in general propagate through natural plant communities and crops.

Attraction of Spathius Agrili Yang (Hymenoptera: Eulophidae) to Male-Produced “Aggregation-sex Pheromone”: Differences Between the Sexes and Mating Status

Male and female Spathius agrili Yang were tested for attraction to the synthetic male pheromone. Lures consisting of a 3-component pheromone blend were placed in the center of a white filter paper target used to activate upwind flight in the wind tunnel. When virgin males and females were tested for attraction, both sexes were attracted to the lure prior to mating. However, only males were attracted to the pheromone lures after mating. In another experiment, of females that flew to the lure as virgins, half were subsequently mated and the other half were not, and mated females were no longer attracted. Then both mated and virgin females were provided with host material (emerald ash borer larvae in sticks of ash) to determine if oviposition affected attraction. They were supplied with fresh hosts ad libidum and subsequently tested for attraction for 55 days, and results showed that oviposition did not affect attraction to the pheromone. The key factor in attraction to the pheromone was mating. Because this pheromone is released by one sex and is attractive to both sexes for the purpose of mating, it qualifies as an “aggregation-sex pheromone”.

The Impact of Spatial Structure on Viral Genomic Diversity Generated during Adaptation to Thermal Stress

BackgroundMost clinical and natural microbial communities live and evolve in spatially structured environments. When changes in environmental conditions trigger evolutionary responses, spatial structure can impact the types of adaptive response and the extent to which they spread. In particular, localized competition in a spatial landscape can lead to the emergence of a larger number of different adaptive trajectories than would be found in well-mixed populations. Our goal was to determine how two levels of spatial structure affect genomic diversity in a population and how this diversity is manifested spatially.Methodology/Principal FindingsWe serially transferred bacteriophage populations growing at high temperatures (40°C) on agar plates for 550 generations at two levels of spatial structure. The level of spatial structure was determined by whether the physical locations of the phage subsamples were preserved or disrupted at each passage to fresh bacterial host populations. When spatial structure of the phage populations was preserved, there was significantly greater diversity on a global scale with restricted and patchy distribution. When spatial structure was disrupted with passaging to fresh hosts, beneficial mutants were spread across the entire plate. This resulted in reduced diversity, possibly due to clonal interference as the most fit mutants entered into competition on a global scale. Almost all substitutions present at the end of the adaptation in the populations with disrupted spatial structure were also present in the populations with structure preserved.Conclusions/SignificanceOur results are consistent with the patchy nature of the spread of adaptive mutants in a spatial landscape. Spatial structure enhances diversity and slows fixation of beneficial mutants. This added diversity could be beneficial in fluctuating environments. We also connect observed substitutions and their effects on fitness to aspects of phage biology, and we provide evidence that some substitutions exclude each other.

Co-existence of Paragonimus harinasutai and Paragonimus bangkokensis metacercariae in fresh water crab hosts in central Viet Nam with special emphasis on their close phylogenetic relationship

During our epidemiological surveys for Paragonimus species in central Viet Nam, we found four morphologically different Paragonimus metacercariae in mountainous crabs. They were identified as metacercariae of Paragonimus westermani, P. bangkokensis, P. proliferus, and P. harinasutai in the order of their prevalence in crab hosts. This is the first discovery of P. harinasutai in Viet Nam, co-inhabiting with P. bangkokensis and other species. Metacercariae of P. harinasutai were given orally to a cat to obtain adult worms. Then, ITS2 and CO1 sequences of metacercariae and adults of P. harinasutai, and metacercariae of P. bangkokensis collected from the same place were determined for analyses of phylogenetic relationships to other P. harinasutai and P. bangkokensis populations as well as related species. The results of molecular analyses showed that P. harinasutai from Quang Binh province of central Viet Nam was almost completely identical with those from Vientiane, Lao PDR; P. bangkokensis from Quang Binh, Viet Nam was also almost completely identical with those from Lao PDR and from Quang Ninh province, Viet Nam. Except for one P. harinasutai isolate from China, all populations of P. harinasutai and P. bangkokensis from Thailand, Lao and Viet Nam make a single clade in both ITS2 and CO1 trees. In ITS2 sequences, AT deletion and ATC insertion were observed in some isolates of both species, indicating recent gene flow between P. harinasutai and P. bangkokensis. Moreover, because of their extremely high genetic similarities and their co-inhabitation in the same crab hosts found in Thailand, Lao PDR and Viet Nam, they should be considered as the sister species at the early stage of divergence. In addition, P. microrchis previously described from Yunnan, China should be placed as the synonym of P. harinasutai, because of their morphological and molecular similarities.

‘Chickens, Crops, and Tractors’

This essay argues that machines filled a sacred purpose in the middle of the twentieth century that has gone unrecognized by scholars of religion. The Mennonites who hosted African-American children from urban environments for one- to two-week stays in the country used tractors to promote their religious Fresh Air programs. From 1950 through 1979, tractors also figured prominently in the children’s testimonies about their rural sojourns. Fresh Air hosts, promoters, and participants thus used a diesel-powered machine for religious ends and, in so doing, featured an industrialized product as a symbol of a natural retreat. Mennonite Fresh Air programs also reveal similarities between the city and country that religious and secular narratives of the period have obscured. Scholarship in the tradition of Leo Marx will be enriched by shifting attention from the chronology of machine-based industrialization to the uses of machines in natural settings for religious purposes.

Ectoparasites of the Occult Bat,Myotis occultus(Chiroptera: Vespertilionidae)

Only a single previous study has examined ectoparasites of the occult bat (Myotis occultus), from which only 2 species of fleas were identified. For our study, we examined 202 individuals, 52 fresh hosts and 150 museum specimens, from New Mexico and southern Colorado for ectoparasites. We recorded 2158 ectoparasites, 634 from fresh hosts and 1524 from museum specimens. Ectoparasites belonged to 10 families and 13 genera of insect or acari and represent new host and locality records. In general, ectoparasites collected from fresh hosts and museum specimens were represented by 4 major species of mite: Macronyssus crosbyi, Alabidocarpus calcaratus, Acanthophthirius lucifugus, and Alabidocarpus nr. eptesicus. From our study, we found fresh hosts to have significantly greater prevalence values for Myodopsylla gentilis (flea), Chiroptonyssus robustipes (mite), and Leptotrombidium myotis (chigger), whereas museum specimens had significantly greater prevalence values for A. calcaratus (mite) and A. nr. eptesicus (mite). There were no significant differences between prevalence values for 4 mites including M. crosbyi, A. lucifugus, Pteracarus nr. minutus, and Cryptonyssus sp. Our study represents the only extensive study of ectoparasites on M. occultus and provides evidence for the importance of examining fresh hosts and museum specimens in future ectoparasite studies.

Parasites and their Freshwater Fish Host

This study reviews the effects of parasites of fresh water fish hosts. Like other living organisms, fish harbour parasites either external or internal which cause a host of pathological debilities in them. The parasites live in close obligate association and derive benefits such as nutrition at the host\'s expense, usually without killing the host. They utililize energy otherwise available for the hosts growth, sustenance, development, establishment and reproduction and as such may harm their hosts in a number of ways and affect fish production. The common parasites of fishes include the unicellular microparasites (viruses, bacteria, fungi and protozoans). The protozoans i.e. microsporidians and mixozoans are considered in this review. The multicellular macroparasites mainly comprised of the helminthes and arthropods are also highlighted. The effects of parasites on their fish hosts maybe exacerbated by different pollutants including heavy metals and hydrocarbons, organic enrichment of sediments by domestic sewage and others such as parasite life cycles and fish population size. Keywords: Parasites, Helminths, Protozoans, Microparasites, Macroparasites, Debilities, Freshwater fishBio-Research Vol. 6 (1) 2008: pp. 328-338

Twisted winged endoparasitoids

Strepsiptera are parasitoids exhibiting a unique degree of sexual dimorphism. The males are free-living, whereas the females are typically maggot-like and neotenic, living within the body of the host insects. First instar larvae of both sexes, however, are free-living and motile, seeking fresh hosts to parasitize. Strepsipterans are known to affect hosts in thirty five families belonging to six orders of Class Insecta. Parasitization by strepsipterans is also known as stylopization, and can grossly affect morphological characters and physiological activities of the hosts, often even causing sterility in the host. So far 585 species of strepsipterans, in 41 genera, have been recorded from around the world, including 21 Indian species.

Desempenho reprodutivo de Nasonia vitripennis Walker (Hymenoptera: Pteromalidae) em pupas crioconservadas de Chrysomya megacephala Fabricius (Diptera: Calliphoridae): avaliação preliminar

Avaliou-se o desempenho reprodutivo de Nasonia vitripennis Walker (Hymenoptera: Pteromalidae) em pupas de Chrysomya megacephala Fabricius (Diptera: Calliphoridae) previamente armazenadas a - 20ºC de temperatura, durante 77 dias, com e sem passagem prévia em nitrogênio líquido (NL) por um, três e 15 minutos. O grupo controle foi caracterizado por pupas hospedeiras frescas. Os muscóides foram expostos aos parasitóides durante 72 horas. Utilizou-se a relação de uma pupa muscóide por fêmea parasitóide. A amostra de pupas frescas permitiu a emergência de 15 parasitóides/ pupa, em média, enquanto 10 parasitóides / pupa emergiram dos espécimens prévia e diretamente armazenados em freezer (-20ºC). Observou-se um acentuado decréscimo do desempenho reprodutivo dos microhimenópteros que exploraram os substratos previamente submetidos ao NL durante um, três e 15 minutos (<img border=0 id="_x0000_i1026" src="../../../../img/revistas/cr/v34n1/n1a32fr01.gif">: 6,1; 5,5 e 5,7, respectivamente). A dissecação das pupas hospedeiras revelou um expressivo número de pteromalídeos imaturos, nas amostras que foram expostas ao NL, e de adultos faratos, em todos os tratamentos

Host finding and host discrimination ability in Anaphes nitens Girault, an egg parasitoid of the Eucalyptus snout-beetle Gonipterus scutellatus Gyllenhal

We investigated host finding and host discrimination ability in Anaphes nitens, a solitary egg parasitoid that attacks a gregarious host, the egg capsules of the Eucalyptus snout-beetle, Gonipterus scutellatus. In a first experiment, females were assigned to three treatments: no experience, one experience on an unparasitized egg capsule or one experience on a parasitized egg capsule. We combined this variable with three types of hosts: unparasitized, previously parasitized by the experimental female, or parasitized by conspecifics. Females were observed in a no-choice test, and results indicate that: (1) naive females can discriminate but do not refrain from superparasitism, (2) previous experience and the type of egg capsule affect host acceptance and visit duration, and (3) there is no evidence of self-discrimination. The acceptance of parasitized hosts decreased from 90% for the inexperienced females at their first encounter with the host, to 45% for the experienced females, and visit duration from 17.2 to 9.2 min. In a second experiment, a choice test was performed to assess A. nitens preference towards hosts of different age. Females oviposited preferentially in very young hosts. A field experiment tested the ability to find new hosts within the window of vulnerability of the egg capsules, by manipulation of the time that hosts were exposed to parasitism. Results showed that parasitoids need one day to discover the hosts and that parasitism does not increase after three days. We conclude that A. nitens biocontrol success is due to its ability to find fresh hosts, and to its discrimination ability, even if the female is inexperienced. 2003 Elsevier Inc. All rights reserved.

Video analysis of aphid flight behaviour

Video techniques have been used to study the flight behaviour of aphids over a number of years. Experimental approaches include: (1) two-dimensional analysis of flight responses to visual stimuli in a video-computer automated vertical wind tunnel; (2) three-dimensional analysis of flight tracks in horizontal wind tunnels and in the field; and (3) assessment of behaviour after landing and factors affecting the probability of subsequent take-off. Studies in the laboratory have concentrated on the host-alternating black bean aphid, Aphis fabae. Both crowd-induced long-day winged females (summer alate virginoparae) which fly to fresh summer hosts and short-day induced, winged autumn forms (gynoparae) have been investigated. Individual A. fabae can be flown for many hours in a vertical wind tunnel when changes in the rate of climb are countered by corresponding changes in downward air flow. Such control may be automated by coupling the video signal of the flying aphid, via a teletracker and through a computer, to servo control air flow. The computer is also used to effect the presentation of visual stimuli. The two-dimensional flight track of the insect can be saved to computer disc for later analysis and responses to visual stimuli presented during flight can be detailed. Studies have revealed major differences in initial flight behaviour between summer and autumn winged forms, as well as a maximum response to a visual target illuminated with green, monochromatic light at wavelengths of ≈550 nm. To obtain a more accurate analysis of flight, a technique was developed to examine three-dimensional aspects of aphid flight tracks. By superimposing the signals from two video cameras placed side-by-side with overlapping fields of view, two images of the insect appear on the monitor and the distance between them is proportional to the distance from the cameras. The x y z co-ordinates during flight can then be calculated at up to 50 Hz and flight track parameters computed. This technique was used with aphids flying in a horizontal wind tunnel in the laboratory and, when coupled to an ultrasonic anemometer, in the field. Studies show that aphids tend to control ground speed and to land into the wind. When young adult winged aphids, which have flown from their natal plant in culture cabinets, are placed on host or non-host plant material, they may stay and settle or fly off. The use of close-up video showed that gynoparae of A. fabae can discriminate between a summer host (broad bean, Vicia faba) and the winter, relevant host (spindle tree, Euonymus europaeus) within a 5-min period. On the unsuitable plant, 75% initiate flight. Plant factors detected during brief stylet penetration of epidermal cells appear to be responsible for this discrimination.

Population fluctuation and persistence of one‐host–two‐parasitoid systems depending on resource distribution: from parasitizing behavior to population dynamics

AbstractPopulation dynamics and variability were examined in one‐host–two‐parasitoid experimental systems with different resource distributions: resource‐clumped and resource‐sparse conditions. The system consists of a seed beetle host, Callosobruchus chinensis, and two parasitoid wasps, Anisopteromalus calandrae (Pteromalidae) and Heterospilus prosopidis (Braconidae). In the resource‐clumped condition, suitable hosts for parasitism (the late fourth‐instar larvae and pupae) were clumped in 1 large resource patch, but they were scattered evenly among 16 small patches in the resource‐sparse condition. Population censuses were conducted at 10‐day intervals in long‐term cultures, renewing 10 g of azuki beans (Vigna angularis). In both resource conditions, the first period was a single‐species system of C. chinensis only, and A. calandrae was added in the second period. The one‐host–one‐parasitoid system with C. chinensis and A. calandrae showed stable population dynamics with small fluctuations. After addition of H. prosopidis in the third period, two of three replicates persisted to day 800 in each resource condition, although one replicate in each went to extinction at an immediate outbreak of the H. prosopidis population after the introduction. Population variabilities of C. chinensis and H. prosopidis were significantly higher and the mean population size of A. calandrae was significantly smaller in the resource‐sparse condition than that in the resource‐clumped one. A short‐term experiment on parasitism efficiencies revealed that H. prosopidis parasitized significantly more at a low host density in the resource‐sparse condition than in the resource‐clumped one. Mutual interference of H. prosopidis was weak enough at low parasitoid densities but became abruptly stronger with high densities. Providing fresh hosts in a mixture of already parasitized ones, host‐searching behaviors of a parasitoid were recorded by video for 3 h and were compared between the two wasp species. H. prosopidis could parasitize fresh hosts more efficiently than A. calandrae through frequent long‐distance walks (walking to distant beans at one bout or outside a clump of beans with hosts and back soon on a distant bean of the clump) after reencounters with parasitized hosts. Considering all the experimental results, populations were judged to be more fragile and more likely to go to extinction in the resource‐sparse condition than in the resource‐clumped one. A higher attacking efficiency of H. prosopidis destabilized population dynamics more in the resource‐sparse condition.

Patch Defence in the Parasitoid Wasp Trissolcus basalis (Insecta: Scelionidae): The Time Structure of Pairwise Contests, and the ‘Waiting Game’

AbstractAggressive defence of host patches has been reported in many parasitoid wasps, but rarely examined in quantitative detail. One aspect of interest is that foraging female parasitoids do not simply consume resource patches, they invest offspring in them. Therefore, patch defence in parasitoids can involve not only resource defence prior to oviposition, but also postoviposition defence of offspring (maternal care). In this paper, the time‐structure and sequence of pairwise agonistic contests between females of the parasitoid Trissolcus basalis (Wollaston) (Hymenoptera: Scelionidae) are analysed. Three main periods were evident in contests. In the first period, both females exploited the patch with no aggression. After the initiation of fighting, they entered a ‘contest period’, during which resident and intruder roles became clearly resolved. The resident then usually guarded the patch for up to several hours before leaving. This signalled the beginning of the third period, in which the intruder returned to superparasitise the patch. During the contest period, resident behaviour initially reflected the trade‐off between exploiting fresh hosts, and defending those it had already parasitised from the intruder, which persistently returned to the patch to try and oviposit, with some success. However, when the patch became fully parasitised, both resident and intruder switched to a ‘waiting game’, in which they sat motionless for extended periods, the resident on the patch and the intruder at a distance. These stand‐offs were punctuated by occasional aggressive patrolling by the resident, and cryptic returns to the palch by the intruder. This waiting game appears to be an informational war of attrition, suggesting a conceptual basis for modelling patch‐leaving decisions using evolutionary game theory.