Host specialization in habitat specialists and generalists

Generalists and specialists use different cues to find their habitat and essential resources. While generalists have the advantage of exploiting a wider range of resources, they are predicted to be less efficient in using one particular resource compared to specialists. The level of specialization of parasitoids can be either at the habitat or at the host level; strategies used by either type are expected to differ. We examined interactions between three aphid parasitoid species that are a habitat specialist Aphidius rhopalosiphi, a habitat generalist Aphidius ervi, and a host generalist Praon volucre on three cereal aphids, Sitobion avenae, Metopolophium dirhodum and Rhopalosiphum padi. We compared total parasitism rate across behavioral and physiological variation in a non-choice test. Next, we addressed total parasitism in two phases to examine: (1) the response of parasitoids to different hosts through the behavioral sequence from antennation through oviposition, and (2) the physiological suitability of different hosts for oviposition and larval development. Parasitization typically involved the following behavioral steps: (1) antennal contact, (2) abdominal bending, and (3) ovipositor insertion (acceptance). A. rhopalosiphi had the same number of antennal contacts with the three aphids but showed fewer instances of abdominal bending towards R. padi. Pre-contact host preference was found for A. ervi but it did not correspond to the level of acceptance. The number of antennal contacts by P. volucre corresponded to the parasitization level of the aphid species but more mummies were produced on M. dirhodum than on R. padi. These results suggest that parasitoid species that are habitat specialists react similarly to the different host species present in the same habitat, whereas generalist species exhibit clear preferences during host selection. Preferences were, however, not always related to host suitability.     

Acceptability and suitability of the European Ostrinia nubilalis Hübner for Macrocentrus cingulum Brischke from Asia and Europe

We examined whether Macrocentrus cingulum (Hymenoptera: Braconidae) of Asian origin could serve as a biological control agent of the maize pest Ostrinia nubilalis (Lepidoptera: Crambidae) in Europe. M. cingulum is already present in Europe, where it does not parasitize O. nubilalis but Ostrinia scapulalis, a related species feeding on wild dicotyledons. In contrast, M. cingulum have been imported from Europe and Asia into North America (where O. nubilalis had been accidentally introduced from Europe), and does parasitize O. nubilalis there. We conducted laboratory infestations to assess host acceptability (parasitoid’s propensity to oviposit) and suitability (parasitoid’s ability to develop) of European O. nubilalis for M. cingulum of European and Asian origin, and of Ostrinia furnacalis (their original host) for Asian M. cingulum. Asian M. cingulum parasitized European O. nubilalis as readily as O. furnacalis, and developed equally well in terms of: % female cocoons, time to first emergence from the cocoon, total number of adult offspring, % female offspring and adult longevity. Adult female parasitoids were significantly larger when emerging from O. nubilalis, mixed-sex and male cocoons were significantly more and less frequent, respectively. The acceptability of O. nubilalis was significantly lower for European than for Asian M. cingulum, and its suitability was zero. Asian M. cingulum appears a potential candidate for introduction as a biological control agent of a major maize pest, European O. nubilalis, provided environmental impact studies, economic analyses, and foreseeable interactions with other biological control agents such as the egg parasitoid Trichogramma brassicae (Hymenoptera: Trichogrammatidae) are satisfying.     

Comparison of the suitability of Liriomyza chinensis and L. trifolii (Diptera: Agromyzidae) as hosts for Neochrysocharis okazakii (Hymenoptera: Eulophidae)

Effective parasitoid production or mass-rearing is one of the key components in practicing biological control with parasitoids. Selection of host species for rearing parasitoids is a major approach to improve the production efficiency. The stone leek leafminer Liriomyza chinensis (Kato) is a destructive pest of onion crops in many Asian countries, which is difficult to control with chemicals. The present study examined whether the production of Neochrysocharis okazakii Kamijo, a promising native biological agent of L. chinensis, could be effective if kidney bean-Liriomyza trifolii (Burgess) system was used as an alternative rearing procedure. The suitability of L. chinensis and L. trifolii as hosts of N. okazakii was investigated in the laboratory. Neochrysocharis okazakii completed its development on both two host species, and the total development time was similar on these hosts. Longevity of N. okazakii females provided with L. chinensis was longer than those on L. trifolii. There were no significant differences in fecundity and offspring sex ratio when females had been provided with these two host species. The adult parasitoids emerged from L. chinensis were significantly larger than those from L. trifolii. However, the intrinsic rate of increase was higher, and mean generation time was lower, for L. trifolii than L. chinensis. Thus, mean net reproductive rate (Ro) was higher when L. trifolii was used as host. Although the two host species were equally suitable as host for N. okazakii, our findings suggested that L. trifolii and kidney bean is an ideal system for N. okazakii production.     

Behavioral interference and facilitation in the foraging cycle shape the functional response

Individual forager behaviors should affect per capita intakerates and thereby population and consumer-resource properties.We consider and incorporate conspecific facilitation and interferenceduring the separate foraging-cycle stages in a functional responsemodel that links individual behavioral interactions with consumer-resourceprocesses. Our analyses suggest that failing to properly considerand include all effects of behavioral interactions on foraging-cyclestage performances may either over- or underestimate effectsof interactions on the shape of both functional responses andpredator zero-growth isoclines. Incorporation of prey- and predator-dependentinteractions among foragers in the model produces predator isoclineswith potentials for highly complex consumer-resource dynamics.Facilitation and interference during the foraging cycle aretherefore suggested as potent behavioral mechanisms to causepatterns of community dynamics. We emphasize that correct estimationsof interaction-mediated foraging-cycle efficiencies should beconsidered in empirical and theoretical attempts to furtherour understanding of the mechanistic link between social behaviorsand higher order processes.     

Evaluation of cold-stored eggs of Dolycoris baccarum (Hemiptera: Pentatomidae) for parasitization by Trissolcus nigripedius (Hymenoptera: Scelionidae)

Trissolcus nigripedius Nakagawa (Hymenoptera: Scelionidae) is an egg parasitoid of Dolycoris baccarum L. (Hemiptera: Pentatomidae), a polyphagous insect pest of many crops including soybean. As a method for mass-rearing to augment the parasitoid, cold storage of host eggs were evaluated in the laboratory. After 0 (control), 8, 20, 60, 90, and 120 days of refrigeration, host eggs were given to adult female T. nigripedius. Host acceptance behaviors of the parasitoid, categorized as drumming, oviposition, and marking, on the refrigerated eggs and biological attributes of offspring were assessed. Most of the attributes examined were affected by the refrigeration of host eggs. But host eggs could be refrigerated for up to two months without significant change in emergence rate and sex ratio and with 90% of parasitism. In addition, the second generation of the parasitoid was not negatively affected at all. However, frozen eggs of D. baccarum can not be used for rearing the parasitoid since parasitism rate decreased to 44% on host eggs frozen for 8 days. Refrigeration of D. baccarum eggs could be useful for mass-rearing and augmentation of T. nigripedius to control D. baccarum without reduction in the quality of parasitoid’s progeny. Furthermore, refrigerated eggs could be supplemented in the field to boost the population of T. nigripedius since immature D. baccarum can not hatch after 20 days of refrigeration.     

捕食风险及其对动物觅食行为的影响

对捕食风险的涵义及其对猎物动物觅食行为的影响、猎物动物面对捕食风险时的反应进行了论述。捕食风险可以简单地理解为一定时间内猎物动物被杀死的概率。当捕食风险存在时 ,动物会选择相对安全但觅食效益较低的地点觅食 ;由于死亡率和消化方面的限制 ,一般都会产生食谱收缩 ;觅食活动方式的时间格局也会因捕食风险而发生改变 ,如水生动物的昼夜垂直迁移、某些陆生动物昼行性与夜行性活动的转换、月光回避等。在与捕食者发生遭遇时 ,猎物动物的主要反应是 :①发出某些信号以阻止捕食者的追捕 ;②靠近并注视捕食者 ;③逃逸 ;④在一定的时间恢复觅食活动。在以往的研究中 ,对捕食者种类已经有了较多的了解 ,而对猎物如何判断捕食者丰富度信息、估计风险程度等方面则知之甚少 ;同时 ,对捕食风险水平的调控、对多种因素的综合分析也较少涉及。在今后的研究中 ,还应该考虑研究的尺度问题 ,因为在不同尺度的环境条件下 ,猎物动物对于捕食风险的反应可能大相径庭。     

Herbivore population suppression by an intermediate predator, <Emphasis Type="Italic">Phytoseiulus macropilis</Emphasis>, is insensitive to the presence of an intraguild predator: an advantage of small body size?

Recent work in terrestrial communities has highlighted a new question: what makes a predator act as a consumer of herbivores versus acting as a consumer of other predators? Here we test three predictions from a model (Rosenheim and Corbett in Ecology 84:2538–2548) that links predator foraging behavior with predator ecology: (1) widely foraging predators have the potential to suppress populations of sedentary herbivores; (2) sit and wait predators are unlikely to suppress populations of sedentary herbivores; and (3) sit and wait predators may act as top predators, suppressing populations of widely foraging intermediate predators and thereby releasing sedentary herbivore populations from control. Manipulative field experiments conducted with the arthropod community found on papaya, Carica papaya, provided support for the first two predictions: (1) the widely foraging predatory mite Phytoseiulus macropilis strongly suppressed populations of a sedentary herbivore, the spider mite Tetranychus cinnabarinus, whereas (2) the tangle-web spider Nesticodes rufipes, a classic sit and wait predator, failed to suppress Tetranychus population growth rates. However, our experiments provided no support for the third hypothesis; the sit and wait predator Nesticodes did not disrupt the suppression of Tetranychus populations by Phytoseiulus. This contrasts with an earlier study that demonstrated that Nesticodes can disrupt control of Tetranychus generated by another widely foraging predator, Stethorus siphonulus. Behavioral observations suggested a simple explanation for the differing sensitivity of Phytoseiulus and Stethorus to Nesticodes predation. Phytoseiulus is a much smaller predator than Stethorus, has a lower rate of prey consumption, and thus has a much smaller requirement to forage across the leaf surface for prey, thereby reducing its probability of encountering Nesticodes webs. Small body size may be a general means by which widely foraging intermediate predators can ameliorate their risk of predation by sit and wait top predators. This effect may partially or fully offset the general expectation from size-structured trophic interactions that smaller predators are subject to more intense intraguild predation.     

Predation on nests: a case of apparent competition

We describe a field experiment designed to evaluate indirect effects in a prey community sharing common predators. A simple prey community was mimicked with two types of artificial nests. Firstly, it was shown that predation rate increased with nest density when only a single prey was present. Secondly, it was shown that an increase in the density of one nest type increased the predation rate on another type. This is the first experimental evidence for indirect effects in vertebrate communities, which also may help to explain the strong interspecific aggression observed in some communities. In a previous treatment we had shown that there is no observer effect on nest predation in the form of density-dependent scent marking while laying out the artificial nests.     

Optimal traits when there are several costs: the interaction of mortality and energy costs in determining foraging behavior

I analyzed the interaction of different types of costs in determiningoptimal behavior using mathematical models. The analysis concentrateson foraging behavior and asks (1) whether the cost factor thathas the greatest effect on fitness generally has the greatesteffect on optimal trait values and (2) whether increasing thesize of one type of cost makes the optimal behavior absolutelyor relatively more sensitive to that cost. The foraging costsconsidered are energy expenditure, predation risk, and othermortality factors. It is shown that increasing the magnitudeof one cost often decreases the relative and absolute sensitivityof the optimal foraging strategy to that cost. The relativefitness effects of different costs generally differ from therelative sensitivities of the optimal strategies to the costfactors. Researchers should therefore measure the shapes ofcost curves rather than their average magnitudes to determinewhich of several costs can be ignored in cost-benefit analyses.     

Does avian predation risk depress reproduction of voles?

Reproductive output and the growth of captive voles were quantified under high and low avian predation risk in a semi-natural experiment. Voles were exposed to Eurasian kestrels (Falco tinnunculus), the main avian predator of vole species studied (Clethrionomys glareolus, Microtus agrestis and M. rossiaemeridionalis). Vole pairs were housed in cages settled under nest-boxes occupied by breeding kestrels or in control cages settled under empty nest-boxes for 2 weeks. The experiment was conducted in mid-summer when kestrels had half-grown nestlings, because in that time hunting adults and begging nestlings produce noise and scats which may indicate significant predation threat to voles housed underneath the nest-boxes. The risk of kestrel predation did not have any obvious impact on pregnancy rates, mean litter sizes, or growth rates of kestrel-exposed voles compared with control voles studied. These results indicate that the risk of avian predation does not depress the reproductive investment of voles. Received: 3 November 1997 / Accepted: 16 February 1998     

Unhealthy herds: Some epidemiological consequences of host heterogeneity in predator-host-parasite systems

Models in which all hosts respond in the same fashion to challenge by disease make a number of clear predictions regarding the ameliorating effect of predation on disease burden in prey populations. However, natural populations are typically exposed to a broad spectrum of stressors, some of which can induce changes in an individual's susceptibility to infection and transmission, as well as vulnerability to mortality once infected. When only a subset of the population is exposed to these other factors, host populations will express some heterogeneity in resistance to disease. Here I investigate the influence that such heterogeneity can have on the predicted beneficial epidemiological effect of predators on certain homogeneous prey populations. Results show that, under some conditions, predation can exacerbate disease burden in the heterogeneous prey population. I conclude that such a possibility might have implications for wild and domesticated animal management programs.     

The parasitoidOoencyrtus nezarae (Hymenoptera: Encyrtidae) prefers hosts parasitized by conspecifics over unparasitized hosts

Summary Two laboratory experiments were conducted to examine the ovipositional preferences of the egg parasitoidOoencyrtus nezarae Ishii (Hymenoptera: Encyrtidae) for parasitized and unparasitizedMegacopta punctatissimum Montandon (Hemiptera: Plataspidae). Females that had never oviposited or that had not oviposite for 3 days preferred recently parasitized hosts more than unparasitized hosts. The preference for recently parasitized hosts appeared to be mediated by the punctures in already parasitized hosts made by the ovipositor of the first female. Survival of the parasitoid progeny was lower in recently parasitized hosts than in unparasitized hosts. However, handling time of parasitized hosts was extremely short relative to that of unparasitized hosts, because the superparasitizing female could use the punctures made by the previous females. It is concluded that the females preferred the parasitized hosts over unparasitized hosts because the benefit of saving time and energy for drilling was more than the cost of progeny survival.     

The effect of learning and search images on predator–prey interactions

In dealing with the spatial and temporal variability of prey species, predators may be able to forage optimally if they have flexible and rapid behavioral plasticity rather than predetermined responses. For predators that learn to focus attention on the cryptic prey type most frequently encountered during recent searching (termed a “search image”), rare prey types may be overlooked because of a focus on more common prey. Search imaging reflects biased searching for one of a number of available prey types, and has been studied widely in birds and mammals. Here we discuss the significant implications of this phenomenon for insect predator–prey systems, particularly with respect to parasitic wasps searching for host species using learned olfactory cues. We (1) review studies about perceptual development through individual ontogeny, (2) define the term “search image” and discuss the cognitive mechanisms involved in search-image formation, (3) discuss the role of search images and frequency-dependent predation as a proximate mechanism in the maintenance of prey diversity, (4) examine data on host–parasitoid olfactory search imaging, and (5) conclude by identifying important research areas for future studies in the field of olfactory search images.     

Encounters with aphid predators or their residues impede searching and oviposition by the aphid parasitoid Aphidius ervi （Hymenoptera： Aphidiinae）

Intraguild predation （IGP） can be an important factor influencing the effective- ness of aphid natural enemies in biological control. In particular, aphid parasitoid foraging could be influenced by the presence of predators. This study investigated the effect of larvae of the predatory hoverfly Episyrphus balteatus DeGeer （Diptera： Syrphidae） and the multicolored Asian ladybird Harmonia axyridis Pallas （Coleoptera： Coccinellidae） on the foraging behavior of the aphid parasitoid, Aphidius ervi Haliday （Hymenoptera： Aphidiidae） in choice experiments using a leaf disc bioassay. Wasp response to chemical tracks left by those predator larvae was also tested. Parasitoid behavior was recorded using the Observer （Noldus Information Technology, version 5.0, Wageningen, the Netherlands）. The experiments were conducted under controlled environmental conditions using leaves of the broad bean plant, Viciafaba L. （Fabaceae） with Myzus persicae Sulzer （Homoptera： Aphididae） as the host complex. A. ervi females avoided aphid patches when larvae of either predator were present. A similar avoidance response was shown by A. ervi to aphid patches with E. balteatus larval tracks, whereas no significant response was observed to tracks left by H. axyridis larvae. It was concluded that IG predator avoidance shown by the aphid parasitoid A. ervi may be a factor affecting their distribution among host patches.     

黄猄蚁对大蜜蜂的捕食行为及其潜在影响

捕食作用会对访花昆虫的种群、行为以及植物适合度产生影响,是植物与传粉者相互关系研究中常被忽视的因素.本文报道了黄猄蚁对大蜜蜂的捕食行为,并模拟捕食的关键环节研究了捕食过程对重要访花昆虫行为的影响.结果表明,黄猄蚁能够利用局部环境主动攻击猎物,利用群体合作捕获采集过程中的体型较大的大蜜蜂,捕食威胁是其影响植物-访花者关系的重要机制.大蜜蜂具有感知花上危险的能力,模拟处理的个体会逃离危险的花或植株并在花上留下标记,将危险信息传递给其它个体.其它拜访者对具有危险信号花的采集频次明显减少,采集时间缩短;模拟处理的影响会随时间推移而较快地消失.此外,该实验没有发现大蜜蜂在花上停留采集过程中具有明显的防御行为.     

Reappraisal of the role of big,fierce predators!

The suggestion in the early 20th century that top predators were a necessary component of ecosystems because they hold herbivore populations in check and promote biodiversity was at first accepted and then largely rejected. With the advent of Evolutionary Ecology and a more full appreciation of direct and indirect effects of top predators, this role of top predators is again gaining acceptance. The previous views were predicated upon lethal effects of predators but largely overlooked their non-lethal effects. We suggest that conceptual advances coupled with an increased use of experiments have convincingly demonstrated that prey experience costs that transcend the obvious cost of death. Prey species use adaptive behaviours to avoid predators, and these behaviours are not cost-free. With predation risk, prey species greatly restrict their use of available habitats and consumption of available food resources. Effects of top predators consequently cascade down to the trophic levels below them. Top predators, the biggies, are thus both the targets of and the means for conservation at the landscape scale.