The 'Goldilocks Grub': reproductive responses to leafroller host development in Goniozus jacintae, a parasitoid of the light brown apple moth.

Many parasitoids alter their reproductive behaviour in response to the quality of encountered hosts. They make adaptive decisions concerning whether to parasitise a potential host, the number of eggs laid on an accepted host, and the allocation of sex to their offspring. Here we present evidence that Goniozus jacintae Farrugia (Hymenoptera: Bethylidae), a gregarious ectoparasitoid of larval tortricids, adjusts its reproductive response to the size and developmental stage of larvae of the light brown apple moth (LBAM), Epiphyas postvittana (Walker) (Lepidoptera: Tortricidae). Goniozus jacintae parasitises instars 3-6 of LBAM, but most readily parasitises the later, larger, instars. Brood sizes were bigger on larger hosts and brood sex ratios were female biased (proportion of males = 0.23) with extremely low variance (never >1 male in a brood at emergence), perhaps the most precise of all studied bethylids. Host size did not influence brood development time, which averaged 19.64 days, or the body size of male offspring. However, the size of females was positively correlated with host size and negatively correlated with brood size. The sizes of individual males and females were positively related to the average amount of host resource available to individuals within each brood, suggesting that adult body size is affected by scramble competition among feeding larvae. Average brood sizes were: 3rd instar host, 1.3 (SE ± 0.075); 4th instar, 2.8 (SE ± 0.18); 5th instar, 4.7 (SE ± 0.23); 6th instar, 5.4 (SE ± 0.28). The largest brood size observed was 8 individuals (7 females, 1 male) on the 6th instar of LBAM. These results suggest that later instars would give the highest yield to optimise mass-rearing of G. jacintae if used for augmentative biological pest control.

Effect of Host Size on Susceptibility of Melanotus Communis (Coleoptera: Elateridae) Wireworms to Entomopathogens.

Wireworms, the soil-borne larvae of click beetles (Coleoptera: Elateridae), are important crop pests throughout the world. In the eastern U.S., Melanotus communis larvae attack grain, root/ tuber, and vegetable crops. Our objectives were to characterize the pathogenicity and virulence of fungal and nematode entomopathogens on M. communis wireworms, and determine if wireworm size affected virulence. Pathogens tested included five entomopathogenic nematodes, Steinernema carpocapsae (All strain), S. feltiae (SN strain), S. riobrave (355 strain), Heterorhabditis bacteriophora (VS strain), and H. indica (HiHom1 strain); and two entomopathogenic fungi, Beauveria bassiana (GHA strain) and Cordyceps javanica (WF-GA17 strain). None of the pathogens tested caused >15% mortality at 7 or 14 days post-inoculation. Mortality was highest in S. carpocapsae (All strain); the other entomopathogens did not cause higher mortality than the untreated control. Overall, smaller wireworms were more susceptible than larger wireworms. Our results suggested that M. communis wireworms have defenses that limit the ability of the entomopathogens we tested to infect the wireworms. Conceivably, other entomopathogen strains or species may be more effective. Natural populations of entomopathogens may contribute to wireworm population reduction, but further studies are warranted before entomopathogens can be used for M. communis management.

Helminth communities in amphibians from Latvia, with an emphasis on their connection to host ecology.

Helminth infracommunities were studied at 174 sites of Latvia in seven hosts from six amphibian taxa of different taxonomical, ontogenic and ecological groups. They were described using a standard set of parasitological parameters, compared by ecological indices and linear discriminant analysis. Their species associations were identified by Kendall's rank correlation, but relationships with host size and waterbody area were analysed by zero-inflated Poisson and zero-inflated negative binomial regressions. The richest communities (25 species) were found in post-metamorphic semi-aquatic Pelophylax spp. frogs, which were dominated by trematode species of both adult and larval stages. Both larval and terrestrial hosts yielded depauperate trematode communities with accession of aquatic and soil-transmitted nematode species, respectively. Nematode loads peaked in terrestrial Bufo bufo. Helminth infracommunities suggested some differences in host microhabitat or food object selection not detected by their ecology studies. Associations were present in 96% of helminth species (on average, 7.3 associations per species) and dominated positive ones. Species richness and abundances, in most cases, were positively correlated with host size, which could be explained by increasing parasite intake rates over host ontogeny (trematode adult stages) or parasite accumulation (larval Alaria alata). Two larval diplostomid species (Strigea strigis, Tylodelphys excavata) had a negative relationship with host size, which could be caused by parasite-induced host mortality. The adult trematode abundances were higher in larger waterbodies, most likely due to their ecosystem richness, while higher larval abundances in smaller waterbodies could be caused by elevated infection rates under high host densities.

Reproductive Traits of Ontsira mellipes (Hymenoptera: Braconidae), a North American Parasitoid, as a Novel Biological Control Agent for Exotic Anoplophora glabripennis (Coleoptera: Cerambycidae).

Ontsira mellipes Ashmead is a gregarious larval ectoparasitoid of woodboring cerambycids that is native to North America but can readily attack the exotic Asian longhorned beetle, Anoplophora glabripennis (Motschulsky). To evaluate the potential of the parasitoid as a novel association control agent for the pest beetle, this study investigated some key reproductive traits of the parasitoid, including egg maturation dynamics, and host size preference and suitability in association with the beetle. Results showed that female wasps emerged with a substantial portion (38%) of their lifetime complement of mature eggs and matured eggs rapidly, reaching a peak 4-6 d post-eclosion. The number of mature eggs was positively related to the female wasp's body size. Oviposition prompted production of more mature eggs by young female wasps. The parasitoid did not show a significant preference for large over small hosts in a choice test. Host size did not affect the parasitoid's offspring survival, developmental time, or sex ratio. However, clutch size increased with increasing host size. Female wasps that developed from large hosts had larger body size and consequently a higher mature egg load than those reared from small hosts. Neither longevity nor the total number of parasitized hosts over a female's lifetime was affected by the female's size, but the total number of offspring produced per female increased with the female's size. These results have important implications for improving rearing and field-release strategies as well as understanding the ecological mechanisms underlying host size selection in gregarious parasitoids.

Species Identity and Size are Associated with Rat Lungworm Infection in Gastropods.

Angiostrongylus cantonensis, the rat lungworm, is an emerging zoonotic pathogen that cycles between definitive rat and intermediate gastropod hosts. Zoonotic infection occurs when humans intentionally or accidentally consume infectious larvae in a gastropod host, and may manifest as neuroangiostrongyliasis, characterized by eosinophilic meningitis, severe neurological impairment, and even death. Thus, the risk of A. cantonensis zoonoses may be related to the distribution of A. cantonensis larvae across gastropod hosts. We screened 16 gastropod species from 14 communities on the island of O'ahu, Hawai'i, USA, to characterize the distribution of A. cantonensis among species and across host size. Prevalence (proportion of the population infected) and infection intensity (density of worms in host tissue) varied among gastropod species. Prevalence also varied with gastropod host size, but this relationship differed among host species. Most host species showed a positive increase in the probability of infection with host size, suggesting that within species relatively larger hosts had higher prevalence. The density of worms in an infected snail was unrelated to host size. These results suggest that variation in A. cantonensis infection is associated with demographic structure and composition of gastropod communities, which could underlie heterogeneity in the risk of human angiostrongyliasis across landscapes.

Prevalence and Intensity of Cornudiscoides Agarwali (Monogenoidea) on the Gills of Day's Mystus (Mystus Bleekeri) in Relation to Some Ecological and Biological Factors from Arunachal Pradesh, India.

This work investigated the relationship of host size, seasons, and water quality parameters with the prevalence and intensity of Cornudiscoides agarwali on Mystus bleekeri collected from the Dikrong River in Arunachal Pradesh, India from February 2016 to January 2017. A total of 2760 specimens of C. agarwali were recovered from 114 individuals of M. bleekeri. The levels of mean intensity, but not the prevalence, of infection of C. agarwali were positively correlated with fish host size, peaking in the largest size class (45.20 ± 5.69 parasites/fi sh). The prevalence values had a statistically significant seasonal trend, reaching highest (100 %) during the pre-monsoon season, followed by 91.8% during the post-monsoon period and 87.5 % during the monsoon season. The levels of mean intensity of infection were also dependent on the seasons, reaching significantly higher levels during the pre-monsoon season (42.75 ± 4.18 parasites/fi sh). All water quality parameters measured were within the safety value recommended for freshwater aquaculture. Cornudiscoides agarwali maintained its prevalence above 87.5 % throughout the annual cycle, which means it was able to reproduce year-round in a non-polluted river. This could be an indication of monogenoidean community and population dynamics thriving best under optimum water quality parameters. Also, this article draws the attention of parasitologists and ichthyologists to a taxonomic problem of the misidentification of Mystus spp., and therefore, possibly of their parasitic monogenoids.

Major determinants of the occurrence of a globally invasive parasite in riverine fish over large-scale environmental gradients.

The increased rate of outbreaks of infectious diseases in ecosystems is a dramatic consequence of global change, particularly when outbreaks affect important resources such as freshwater fish. However, the links between disease-inducing epizootics and widespread human impacts, including nutrient pollution and high water conductivity, in freshwater organisms are largely unexplored. We used data from extensive surveys in northeastern Spain (99,700 km2, 15 river catchments, n = 530 sites) to explore the environmental factors that singly, or in combination, are likely to influence the occurrence of the invasive parasite, Lernaea cyprinacea, after accounting for host fish characteristics. Smaller fish, lower altitudes, higher water conductivity and nutrient pollution were associated with higher probabilities of infection in 19 endemic and widely distributed fish species. We found no evidence that interactive effects among riverine stressors related to water and physical habitat quality better explained the probability of occurrence of L. cyprinacea in fish than did additive-stressor combinations. Nutrient pollution and high water conductivity were two of the major factors contributing to the increased occurrence of L. cyprinacea. Therefore, the improvement of wastewater treatment processes and agricultural practices probably would help to reduce the occurrence of this parasite among native fish.

Population dynamics and development of the rhizocephalan Sacculina carcini, parasitic on the shore crab Carcinus maenas.

The ecologically important shore crab Carcinus maenas is commonly infected in its native range by the rhizocephalan Sacculina carcini. However, several aspects of this host-parasite interaction are poorly understood. Here, we analyse data from approximately 60000 Danish crabs to unravel factors governing infection patterns in time and space, and according to host sex and size. Female crabs were more frequently infected (12.6%) than males (7.9%). Sites with high salinity supported the highest infection prevalence. Infection prevalence peaked in summer (10 to 15%) and winter (20 to 35%) due in part to emergence of virginal externae in summer (main outbreak) and autumn (minor outbreak) preceded by peaks in crabs with lost externa (scars). Younger externae and scars dominated among males, whereas adult externae were most frequent among females. Infection prevalence increased with size in females but decreased in males, and modified (feminized) males showed lower scar frequency than unmodified ones. Modified males occurred frequently among the smaller size classes, whereas unmodified males dominated the larger size classes. Externa size was positively related to host size in both genders (same linear relationship). Molecular analyses suggested that hosts below 16 mm in carapace width do not become infected. Dissections of infected hosts revealed marked reduction of ovaries, whereas testes were unaffected by sacculinization. Our study demonstrates great spatio-temporal variation in infection prevalence mainly related to the parasite's life history. S. carcini appears capable of infecting all host sizes except the smallest. Owing to incomplete feminization of males, infections are rapidly lost from the larger and highly profitable male hosts.

Host size influences the effects of four isolates of an amphibian chytrid fungus.

Understanding factors that influence host-pathogen interactions is key to predicting outbreaks in natural systems experiencing environmental change. Many amphibian population declines have been attributed to an amphibian chytrid fungus, Batrachochytrium dendrobatidis (Bd). While this fungus is widespread, not all Bd-positive populations have been associated with declines, which could be attributed to differences in pathogen virulence or host susceptibility. In a laboratory experiment, we examined the effects of Bd isolate origin, two from areas with Bd-associated amphibian population declines (El Copé, Panama, and California, USA) and two from areas without Bd-related population declines (Ohio and Maine, USA), on the terrestrial growth and survival of American toad (Anaxyrus americanus) metamorphs reared in larval environments with low or high intraspecific density. We predicted that (1) Bd isolates from areas experiencing declines would have greater negative effects than Bd isolates from areas without declines, and (2) across all isolates, growth and survival of smaller toads from high-density larval conditions would be reduced by Bd exposure compared to larger toads from low-density larval conditions. Our results showed that terrestrial survival was reduced for smaller toads exposed to Bd with variation in the response to different isolates, suggesting that smaller size increased susceptibility to Bd. Toads exposed to Bd gained less mass, which varied by isolate. Bd isolates from areas with population declines, however, did not have more negative effects than isolates from areas without recorded declines. Most strikingly, our study supports that host condition, measured by size, can be indicative of the negative effects of Bd exposure. Further, Bd isolates' impact may vary in ways not predictable from place of origin or occurrence of disease-related population declines. This research suggests that amphibian populations outside of areas experiencing Bd-associated declines could be impacted by this pathogen and that the size of individuals could influence the magnitude of Bd's impact.

Effects of Size and Age of the Host Musca domestica (Diptera: Muscidae) on Production of the Parasitoid Wasp Spalangia endius (Hymenoptera: Pteromalidae).

One method of control of house flies, Musca domestica L. (Diptera: Muscidae), and other filth flies is by repeated release of large numbers of pupal parasitoids such as Spalangia endius Walker. Rearing these parasitoids may be facilitated by understanding how host factors affect their production. Previous studies have examined the effects of host size and host age on parasitoid production, but have not examined the interaction between host size and host age or the effects with older females, which may be less capable of drilling tough hosts. Females were given hosts of a single size-age category (small young, small old, large young, or large old) for 2 wk. The effect of host size and of host age on parasitoid production depended on female age. On their first day of oviposition, females produced more offspring from large than from small hosts, but host age had no significant effect. The cumulative number of parasitoids produced in the first week was not significantly affected by host size or host age. However, the cumulative number of parasitoids produced over 2 wk was affected by both host size and host age, with the greatest number of parasitoids produced from small young hosts. Thus, not only are smaller hosts cheaper to produce, but these results suggest that their use may have no effect or a positive effect on the number of parasitoids that can be produced when females are ovipositing for a week or two.

Drilling-in and Chewing-out of Hosts by the Parasitoid Wasp Spalangia endius (Hymenoptera: Pteromalidae) When Parasitizing Musca domestica (Diptera: Muscidae).

Many organisms are protected from natural enemies by a tough exterior. Such protection is particularly important for immobile stages, such as pupae. The pupa of some insects is protected by a puparium, which is a shell formed from the exoskeleton of the last larval instar. However, the puparium of certain fly species is drilled through by adult females of the wasp Spalangia endius Walker. The female wasp then deposits an egg on the fly pupa within the puparium. After the wasp offspring finishes feeding on the fly pupa, it chews through the puparium to complete emergence. Despite the apparent toughness of the puparium, there was no detectable wear on the ovipositor of S. endius females even when females had been encountering fly pupae (Musca domestica L.) for weeks, and regardless of whether the pupae were large or old or both. Energy dispersive spectroscopy did not reveal any metal ions in the ovipositor's cuticle to account for this resistance against wear. Offspring of S. endius that chewed their way out of pupae also showed no detectable wear on their mandibles. Tests with a penetrometer showed that the force required to penetrate the center of a puparium was greater for larger and for older pupae; and an index of overall thickness was greater for large old pupae than for small old pupae. The lack of an effect of pupal size or age on wear may result from wasps choosing locations on the puparium that are easier to get through.

Flea (Siphonaptera) species richness in the Great Basin Desert and island biogeography theory.

Numbers of flea (Siphonaptera) species (flea species richness) on individual mammals should be higher on large mammals, mammals with dense populations, and mammals with large geographic ranges, if mammals are islands for fleas. I tested the first two predictions with regressions of H. J. Egoscue's trapping data on flea species richness collected from individual mammals against mammal size and population density from the literature. Mammal size and population density did not correlate with flea species richness. Mammal geographic range did, in earlier studies. The intermediate-sized (31 g), moderately dense (0.004 individuals/m(2)) Peromyscus truei (Shufeldt) had the highest richness with eight flea species on one individual. Overall, island biogeography theory does not describe the distribution of flea species on mammals in the Great Basin Desert, based on H. J. Egoscue's collections. Alternatively, epidemiological or metapopulation theories may explain flea species richness.

Subjective and objective components of resource value additively increase aggression in parasitoid contests.

Two major categories of factors are predicted to influence behaviour in dyadic contests; differences in the abilities of the contestants to acquire and retain resources (resource holding potential), and the value of the contested resource (resource value, RV; which comprises objective and subjective components). Recent studies indicate that subjective components affect contest behaviour in several animal taxa but few have simultaneously investigated objective RV components. We find that both an objective (host size) and a subjective (contestant age) component of RV affect contest intensity in the parasitoid wasp Goniozus legneri. These additively influence aggressiveness, with a larger effect from the subjective component than the objective component. The greater influence of subjective RV adds weight to the recent surge of recognition of this RV component's importance in contest behaviour.

Qualidade de diferentes espécies de pulgões como hospedeiros do parasitóide Lysiphlebus testaceipes (Cresson) (Hymenoptera: Braconidae, Aphidiinae) / Quality of different aphids as hosts of the parasitoid Lysiphlebus testaceipes (Cresson) (Hymenoptera: Braconidae, Aphidiinae)

O endoparasitóide solitário Lysiphlebus testaceipes (Cresson) tem uma ampla faixa de afídeos hospedeiros e a qualidade desses afídeos pode interferir nos parâmetros biológicos do mesmo. Este trabalho teve como objetivo avaliar a qualidade de três Macrosiphini, Brevicoryne brassicae (L.), Lipaphis erysimi (Kaltenbach) e Myzus persicae (Sulzer), e três Aphidini, Schizaphis graminum (Rondani), Rhopalosiphum maidis (Fitch) e Aphis gossypii Glover, como hospedeiros de L. testaceipes e determinar a possível relação da preferência do parasitóide com o tamanho e a qualidade do hospedeiro. Os testes foram conduzidos em câmara climática a 25 ± 1°C, 70 ± 10 por cento UR e 12h fotofase. O parasitóide não ovipositou em B. brassicae e L. erysimi e as demais espécies foram adequadas nutricionalmente ao parasitóide. L. testaceipes apresentou preferência por pulgões da tribo Aphidini e esses hospedeiros apresentaram maior qualidade para o parasitóide quando comparados aos Macrosiphini. Foi encontrada relação entre tamanho, preferência e qualidade entre os Aphidini. O parasitóide apresentou preferência (76,7 por cento de parasitismo) por R. maidis, o maior hospedeiro (tíbia posterior de 0,281 mm), e este proporcionou maior tamanho (tíbia posterior de 0,49 mm) e emergência (95,6 por cento) ao parasitóide quando comparado a A. gossypii (55,7 por cento de parasitismo), hospedeiro menor (0,266 mm) e que proporcionou menor tamanho (0,45 mm) e maior mortalidade ao parasitóide (72,1 por cento de emergência). Contudo, o desenvolvimento de ovo a múmia foi menor e a longevidade foi maior em A. gossypii (6,3 e 5,4 dias respectivamente) do que em R. maidis (6,7 e 3,8 dias respectivamente), não estando relacionados ao tamanho do hospedeiro.

Lysiphlebus testaceipes (Cresson) has a broad aphid host range; however the quality of these preys may interfere in its biological feature. This study aimed to evaluate the quality of three Macrosiphini, Brevicoryne brassicae (L.), Lipaphis erysimi (Kaltenbach) and Myzus persicae (Sulzer), and three Aphidini Schizaphis graminum (Rondani) Rhopalosiphum maidis (Fitch) and Aphis gossypii Glover as hosts to L. testaceipes and to determine the relation possible of host preference, of size and quality of the host. The tests were carried out in climatic chamber at 25 ± 1°C, RH 70 ± 10 percent and 12h photophase. The parasitoid did not oviposite in B. brassicae and L. erysimi, while the other species were nutritionally suitable to the parasitoid. L. testaceipes showed preference for aphids from tribe Aphidini and these hosts presented better quality to the parasitoid when compared to Macrosiphini. Interactions among size, preference and quality between the Aphidini were found. L testaceipes showed preference (parasitism rate 76.7 percent) for R. maidis, the bigger host (hind tibia with 0.281 mm). This host provided bigger size (hind tibia with 0.49 mm) and higher emergence rate (95.6 percent) to the parasitoid when compared to A. gossypii (parasitism rate of 55.7 percent). Also the smaller host A. gossypii (0.266 mm) provided smaller size hind tibia (0.45 mm) and higher mortality of the parasitoid (emergence rate 72.1 percent). However, the development time was shorter and the longevity was higher in A. gossypii (6.3 and 5.4 days, respectively) when compared to the host R. maidis (6.7 and 3.8 days, respectively), and not been related to host size.

Host choice and fitness correlates for conopid flies parasitising bumblebees.

Two parasitoid flies,Physocephala rufipes andSicus ferrugineus (Diptera, Conopidae), and their hosts,Bombus spp., coexist at various locations in northwestern Switzerland. A detailed field study showed that both conopid species use the hostB. pascuorum to a similar degree, while the hostB. terr-luc (a pooled category ofB. terrestris andB. lucorum) is more frequently parasitised than expected byS. ferrugineus. The hostB. lapidarius in turn is exclusively used byP. rufipes. Furthermore, hosts ofB. terr-luc andB. pascuorum parasitised byS. ferrugineus were larger than hosts parasitised byP. rufipes, or than those not parasitised. The findings suggest thatS. ferrugineus selects larger hosts and may displaceP. rufipes. Pupal weight, a predictor of adult body size and parasitoid fecundity, is positively correlated with host size and larger pupae are more likely to emerge, while host species had no effect on the probability of emergence in either conopid species. Host species affected pupal weight inS. ferrugineus, but not inP. rufipes, althoughP. rufipes grew larger in hosts of a given size. Daughters emerged from larger pupae than males, but this did not correlate with larger host sizes. These observations add to the scarce knowledge of dipteran parasitoids.

Host size and sex allocation of parasitoids in a gall forming community.

The sex ratios of three Mesopolobus species were found to vary in different hosts in a gall-forming community in Berkshire. These relationships were consistent with Charnov's host size-sex ratio hypothesis (Charnov 1979). Due to the segregation of host species on different species of Quercus, it was possible to conduct a geographical variation experiment proposed by Charnov et al. (1981). The results of this experiment suggest that the parasitoids have a fixed 'rule of thumb' and are not flexible in their sex allocation in response to changes in host size distribution. The data, therefore, do not support the prediction of Charnov's hypothesis. Problems associated with this kind of field experiment are discussed.

Host-size-dependent sex ratios among parasitoid wasps: does host growth matter?

Waage's (1982) hypothesis that host-size-dependent sex ratios will occur in parasitoids of nongrowing hosts and not in parasitoids of growing hosts is examined using published data on parasitoid wasps. Waage's hypothesis is supported as a general, but not absolute, rule: among solitary parasitoid wasps, a significantly greater proportion of parasitoids of nongrowing than of growing hosts show some evidence of host-size-dependent sex ratios (85% versus 42%, G=6.54, P< 0.05). The premise of Waage's hypothesis-that for parasitoids which develop in a growing stage, host size at oviposition is not a good predictor of the amount of resources available to the developing parasitoid-is also examined. It is suggested that across host species Waage's premise will hold for some, but not all, parasitoids of growing hosts. Likely exceptions to Waage's premise, and thus his prediction, are discussed. Parasitoids of growing hosts which are expected to have evolved hostsize-dependent sex ratios include parasitoids which utilize a narrow size range of host species, parasitoids which can distinguish among host species by some criterion other than size, and parasitoids which utilize host species whose susceptible instars do not overlap in size.

The reproductive strategy of the gregarious parasitoid, Pteromalus puparum (Hymenoptera: Pteromalidae) : 2. Host size discrimination and regulation of the number and sex ratio of progeny in a single host.

Host size of Pteromalus puparum, a gregarious pupal parasitoid, shows a wide inter- and intraspecific variation. Experiments were made to study the regulation of the number and sex ratio of progeny per host by the parasitoid. The parasitoid could discriminate inter- and intraspecific size differences of the host and regulate the number of eggs according to the host size when a single female attacked the host. The sex ratio of progeny (proportion males) was about 0.1. The number of progeny laid by the female agreed with the energetically most efficient number og eggs in order to maximize total weight of progeny per host but not with the reproductively most efficient number of eggs to maximize the total fecundity of the progeny. The parasitoid laid smaller number of eggs in a half buried host, but the number was much larger than a half of those in a fully exposed host. When more than one female attacked a single host, the number and sex ratio of progeny per host increased with the number of females attacking the host, but the number of progeny per female decreased. The change of the sex ratio agreed with the prediction of the local mate competition model.