Host-parasitoid System Research Articles

Parasitoid Competition and the Dynamics of Host-Parasitoid Models

The standard host-parasitoid models assume that each parasitized host yields the same number of parasitoid progeny; but in many parasitoid species, the number of progeny per host depends on the number of times that host was encountered. I present a family of new host-parasitoid models incorporating this encounter-density-dependent variability in parasitoid reproduction per host. Such within-host competition (which could be between ovipositing females, between larvae, or both) interacts with the distribution of encounters (i.e., aggregation) to determine the net parasitoid density dependence. Greater density dependence increases host equilibrium abundances while generally increasing the stability of the interaction. Overcompensating scramble-like parasitoid competition can be more stabilizing than contest-like competition, especially when the host has a moderate to high intrinsic rate of increase and encounters are moderately aggregated; overcompensation is destabilizing only at very high host reproductive rates. These results suggest that we must study parasitoid density dependence directly, both within a host and between generations within a population, in order to understand the dynamics of any actual host-parasitoid system. The most practical method appears to be to (1) describe the mean yield (parasitoid recruitment) per parasitized host as a function of the density of either parasitoids or parasitized hosts; and (2) relate the number (not the percentage) of parasitized hosts to parasitoid (and perhaps host) densities.

Effects of patch scale on density-dependence and species-dependence in two host-parasitoid systems.

Data from two host-parasitoid communities were analyzed to ascertain whether patch scale affected the kinds of correlations existing between 1) spatial differences in host density and the intensity of parasitism (density-dependence) and 2) number of species of parasitoids and the intensity of parasitism (species-dependence). We concluded that parasitization rates are usually independent of both host density and number of parasitoid species present regardless of patch scale. Therefore, the responses of parasitoids to host density and the addition of parasitoid species to a community are equally unpredictable in outcome.

The Frequency of Density Dependence in Insect Host‐Parasitoid Systems

I examined case studies of density—related parasitism in insect host—parasitoid systems reported in the literature. For 171 examples, the frequency of density dependence was 25% (n = 43), of inverse density dependence 23% (n = 39), and of independence 52% (n = 89). This is a considerably lower frequency of density dependence than previously reported in other reviews (Lawton and McNeill 1979, Lessells 1985, but see Dempster 1983). Biological features of case histories gave few clues as to the expected frequency of density dependence. Such features included host order, life stage attacked, parasite group, native vs. introduced status of hosts or parasites, number of attacking parasitoid species, mobile vs. sedentary hosts, and monophagous vs. polyphagous hosts or parasitoids. Biotic and abiotic factors may, however, provide good reasons for a low overall frequency of density dependence.

On Assessing the Role of Spatially-Heterogeneous Density-Independent Host Mortality on the Stability of Host-Parasitoid Systems

In an already classical work, Beddington et al. (1978) analysed several cases of successful biological control and suggested that their common feature was a displacement to a new equilibrium with a strong depression of the host population (low q values, q = N*/K, where K is the equilibrium density before the introduction of the parasitoid and N* the one afterwards). Since then, one of the aims of theoretical studies on hostparasitoid dynamics was considered to be the identification of processes that lead to the stability of these systems at low q values (for a review see Hassell 1978). Spatial heterogeneity in the distribution of hosts and parasitoids has been singled out as the most important process leading to the stability of host-parasitoid systems at low values of q, either when it results in spatial density-dependent (Hassell and May 1973, 1974, Murdoch and Oaten 1975, Murdoch 1977) or inverse density-dependent mortality of the host (Hassell 1984). Parasitoid aggregation, which leads to spatially-heterogeneous but density-independent mortality, has also been identified as an important stabilizing mechanism (May 1978, Murdoch et al. 1984). This view has been challenged by Murdoch et al. (1984, 1985, Reeve and Murdoch 1985) on the grounds that neither stability nor sufficiently strong spatial differences in host mortality are common features of successful biological control. Murdoch et al. (1984, and Reeve and Murdoch 1985) devised two methods (one graphical, the other statistical) to measure the strength of spatially-heterogeneous, density-independent host mortality based on May's (1978) model. In this model, host and parasitoid survival rates are considered as density-independent and f, the fraction of hosts evading parasitism (see Appendix), is given by the zero term of the negative binomial distribution (f = (1 + a P,/k)-k, where a is the search efficiency, k determines the degree of clumping in parasitoid attacks and P, is the mean predator density at generation t). This model is stable if and only if k < 1. A similar conclusion is attained for realistically low values of q with models in which density dependent survival is represented by a logistic function (May et al. 1981). The methods proposed by Murdoch et al. allow determination of whether k is lower than 1 in natural host-parasitoid systems. They used these methods in two studies of systems formed by scale insects and introduced parasitoids. In the system formed by the olive scale (Parlatoria oleae Culvee) and two introduced parasitoids (Murdoch et al. 1984), the host density was reduced from over 200 cales per twig to one or two per 50 twigs, (q = 0.0001). Whilst Murdoch et al. (1984) suggested that the system is unstable, Huffaker et al. (1986), on the basis of a long-term study, argued in the opposite sense. The second system (the California red scale, Aonidiella aurantii, and its parasitoid Aphytis melinus) is said to be stable (Reeve and Murdoch 1985), and the data provided by the authors suggest a q value between 0.1 and 0.01. No clear evidence of density-dependent or inverse density-dependent mortality was found in either system. In both host-parasitoid interactions k is greater than 1, and so Murdoch et al. (1984, Reeve and Murdoch 1985) concluded that spatial heterogeneity does not play a key role in the stability of either system. Their conclusions are discussed in the following paragraphs. May (1978) proposed the negative binomial distribution to describe parasitoid aggregation on phenomenological grounds (it fits many data sets), but pointed out that it could be derived by supposing that the parasitoids are gamma distributed among spatially discrete patches and the searching of parasitoids within patches is totally random. The same conclusion was reached by Murdoch et al. (1984; Chesson and Murdoch 1986): If ut is the number of parasitoids in the vicinity of each host and s(u) the probability density function of ut, then the average or expected proportion of unparasitized hosts (f) is given by

Density Dependence and the Stability of Host-Parasitoid Systems

I present a host-parasitoid model including: a) a flexible representation of the host density dependence (i.e.: whether contest, scramble or intermediate) and b) the possible differences in susceptibility to competition between non parasitized and parasitized hosts (and the parasitoids inside the latter). Neighbourhood stability analysis points out that these factors can have a marked influence on the system, contracting or expanding its boundaries of stability. Contest-like density dependence and similar susceptibility to competition between parasitized and non parasitized hosts lead to ranges of stability that other models produce only if they include the aggregation of the attacks by parasitoids.

"Searching time aggregation" and density dependent parasitism in a laboratory host-parasitoid interaction.

Assuming random search by parasitoids within host-containing patches, and a constant search rate, current host-parasitoid models suggest that "searching time aggregation" by parasitoids in patches of high host density should tend to produce spatially density dependent parasitism at the patch level. It is not clear, however, that statistically significant "searching time aggregation" necessarily implies that significant density dependent parasitism will occur. In actual host-parasitoid systems the amounts of searching time allocated to patches of equal host density may vary a great deal from patch to patch. Such behavioral variability may be capable of obscuring an underlying density dependent trend, producing density independent parasitism at the patch level despite significant searching time aggregation in patches of high host density. This possibility is tested using data from an earlier laboratory study (Morrison and Lewis; Ent. exp. et appl. 30:31-39 [1981]) of the foraging behavior of Trichogramma pretiosum Riley, a generalist parasitoid of lepidopteran eggs. Searching time allocation is found to be highly variable among patches of equal host density, and significant density dependent parasitism does not occur despite significant searching time aggregation in patches of high host density. This suggests that in cases in which density independent or "density vague" patterns of parasitism are observed in field samples, direct field measurements of searching time allocation in patches of different host density may be necessary to demonstrate the presence or absence of significant searching time aggregation by foraging parasitoids.

Competition Among Parasitoids of Endophytic Hosts

Previous articleNext article No AccessNotes and CommentsCompetition Among Parasitoids of Endophytic HostsDon C. ForceDon C. Force Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by The American Naturalist Volume 126, Number 3Sep., 1985 Published for The American Society of Naturalists Article DOIhttps://doi.org/10.1086/284430 Views: 2Total views on this site Citations: 13Citations are reported from Crossref Copyright 1985 The University of ChicagoPDF download Crossref reports the following articles citing this article:Y. Feng, S. Wratten, H. Sandhu, M. Keller Interspecific competition between two generalist parasitoids that attack the leafroller Epiphyas postvittana (Lepidoptera: Tortricidae), Bulletin of Entomological Research 105, no.44 (Jan 2015): 426–433.https://doi.org/10.1017/S0007485314000923Hai-Yun Xu, Nian-Wan Yang, Fang-Hao Wan, Erik V. Thuesen Competitive Interactions between Parasitoids Provide New Insight into Host Suppression, PLoS ONE 8, no.1111 (Nov 2013): e82003.https://doi.org/10.1371/journal.pone.0082003PETER M. MAGDARAOG, JEFFREY A. HARVEY, TOSHIHARU TANAKA, RIETA GOLS Intrinsic competition among solitary and gregarious endoparasitoid wasps and the phenomenon of ‘resource sharing’, Ecological Entomology 37, no.11 (Jan 2012): 65–74.https://doi.org/10.1111/j.1365-2311.2011.01338.x 10.1007/BF02380670, CrossRef Listing of Deleted DOIs 56 (Jan 2011).https://doi.org/10.1007/BF02380670MIGUEL R. PANIAGUA, ENRIQUE MEDIANERO, OWEN T. LEWIS Structure and vertical stratification of plant galler-parasitoid food webs in two tropical forests, Ecological Entomology 34, no.33 (Jun 2009): 310–320.https://doi.org/10.1111/j.1365-2311.2008.01079.xJeffrey A. Harvey, Rieta Gols, Michael R. Strand Intrinsic competition and its effects on the survival and development of three species of endoparasitoid wasps, Entomologia Experimentalis et Applicata 130, no.33 (Mar 2009): 238–248.https://doi.org/10.1111/j.1570-7458.2008.00816.xH. Gibb, J. Hilszczański, J. Hjältén, K. Danell, J. P. Ball, R. B. Pettersson, O. Alinvi Responses of parasitoids to saproxylic hosts and habitat: a multi-scale study using experimental logs, Oecologia 155, no.11 (Oct 2007): 63–74.https://doi.org/10.1007/s00442-007-0887-8Consuelo M. De Moraes, Mark C. Mescher Intrinsic competition between larval parasitoids with different degrees of host specificity, Ecological Entomology 30, no.55 (Oct 2005): 564–570.https://doi.org/10.1111/j.0307-6946.2005.00723.xTania Zaviezo, Nick Mills The response of Hyssopus pallidus to hosts previously parasitised by Ascogaster quadridentata : heterospecific discrimination and host quality, Ecological Entomology 26, no.11 (Oct 2008): 91–99.https://doi.org/10.1046/j.1365-2311.2001.00289.xConsuelo M. De Moraes, A. M. Cortesero, J. O. Stapel, W. J. Lewis Intrinsic and extrinsic competitive interactions between two larval parasitoids of Heliothis virescens, Ecological Entomology 24, no.44 (Dec 2001): 402–410.https://doi.org/10.1046/j.1365-2311.1999.00212.xF. A. N. Alebeek, D. Rojas-Rousse, L. Leveque Interspecific competition between Eupelmus vuilleti and Dinarmus basalis, two solitary ectoparasitoids of Bruchidae larvae and pupae, Entomologia Experimentalis et Applicata 69, no.11 (Apr 2011): 21–31.https://doi.org/10.1111/j.1570-7458.1993.tb01724.xBRADFORD A. HAWKINS Do galls protect endophytic herbivores from parasitoids? A comparison of galling and non-galling Diptera, Ecological Entomology 13, no.44 (Nov 1988): 473–477.https://doi.org/10.1111/j.1365-2311.1988.tb00381.xD. C. Force, D. J. Moriarty Effects of patch scale on density-dependence and species-dependence in two host-parasitoid systems, Oecologia 76, no.33 (Aug 1988): 439–444.https://doi.org/10.1007/BF00377040

Host-age Structure and Parasitism in a Laboratory System of Two Hymenopterous Parasitoids and Larvae of Zabrotes subfasciatus (Coleoptera: Bruchidae)

Host-age structure of Zabrotes subfasciatus (Boheman) on larval parasitism by two hymenopterous parasitoids, Heterospilus prosopidis Viereck (Braconidae) and Anisopteromalus calandrae (Howard) (Pteromalidae), were examined in a series of laboratory experiments. Ages of the hosts offered to the parasitoids were varied and the number of host larvae successfully parasitized was monitored. The sex ratio of the resulting parasitoids was also monitored. A life-history refuge from parasitism by both parasitoids was found, consisting of the egg stage and the small, young larvae. The refuge length differed for both parasitoids. Host individuals were not parasitized efficiently by A. calandrae for the first 14-16 days, whereas they were not parasitized at all by H. prosopidis for the first 12 days. Host individuals were protected from attack during these refuge periods for up to 60% of their larval period. Host-age refuges were important in the stability of these two host–parasitoid systems. Stability increased with increasing length of the refuge period. The shorter refuge period in the H. prosopidis –host system may lead to further instability by creating asynchrony between the host and parasitoid life cycles. The age of the larval host also determined the sex ratio of the parasitoid populations. This factor may further destabilize the H. prosopidis populations, while having a lesser effect on A. calandrae .

Erratum: Niche Overlap of Parasitoids in Host-Parasitoid Systems: Its Consequence to Single Versus Multiple Introduction Controversy in Biological Control

Erratum: Niche Overlap of Parasitoids in Host-Parasitoid Systems: Its Consequence to Single Versus Multiple Introduction Controversy in Biological Control

Host Susceptibility as a Component in Host-Parasitoid Systems

Utilisation du modele de simulation de Monte Carlo dans lequel les hotes sont soit tous egalement sensibles au parasitisme ou presentent un degre de sensibilite qui varie au hasard (dans le cadre d'etudes sur la dynamique des populations d'hotes et de parasites)

Niche Overlap of Parasitoids in Host-Parasitoid Systems: Its Consequence to Single Versus Multiple Introduction Controversy in Biological Control

Four kinds of organic-inorganic cementing and coating materials were prepared by a coating method using water as the solvent, and the corresponding cemented and coated fertilizers (B2, PS, F2, and F2F) were produced by disc pelletizer. The tests on the properties of these fertilizers showed that the granulation rate, compression strength, and film-forming rate were B2 > PS > F2 > F2F. Soil column leaching experiment showed that the curve of accumulated nitrogen-dissolving rate was the gentlest for B2. In 48 days, the accumulated nitrogen-dissolving rate was in the order of B2, 54.65% < PS, 56.16% < F2, 59.47%, < F2F, 63.12%. Field experiment showed that compared with the same application amount of NPK, all the test fertilizers had better effects on corn yield, among which, B2 was the best, with the corn yield and fertilizer use efficiency increased by 19.72% and 20.30%, respectively. The yield-increasing effect of other test fertilizers was in the order of PS > F2 > F2F.

Behavior of Parasitized Aposematic Caterpillars: Advantageous to the Parasitoid or the Host?

Smith Trail (1980) suggested that this system (Euphydryas phaeton caterpillars and their parasitoids) is appropriate for testing the hypothesis of host suicide, and that parasitized hosts advertise themselves to predators and, thus, contribute to increased survivorship of their nonparasitized siblings. However, it appears from this study, other life-history information cited on this system, and data cited on the E. editha-parasitoid system that host suicide is unlikely in such nymphalid butterflies. Rather, these observations support the hypothesis that the behavior of parasitized larvae prior to parasitoid emergence may increase the parasitoids' chances of escaping predation and parasitism. Consequently, behavior of parasitized hosts in host-parasitoid systems may contribute to higher survivorship of parasitoids just as the behavior of hosts parasitized by true parasites promotes acquisition by definitive hosts and, thus, parasite survival.

A Simulation Model of Spatial Heterogeneity and Non-Random Search in an Insect Host-Parasitoid System

SUMMARY (1) A population model of the interactions between insect parasitoids and hosts in a patchy environment is proposed. It describes the searching behaviour of an individual parasitoid as being simple innate responses to host and parasitoid associated stimuli. However, the probability of a given response being elicited by a given stimulus is assumed to vary with an individual's current rate of oviposition. (2) The model includes the following behavioural responses of the parasitoid: (a) a functional response to the host density of a patch; (b) a response to other parasitoids encountered on a patch; (c) an aggregative response caused by the individual parasitoid being attracted more often to the favourable patches and spending more time on them than on less attractive patches; (d) a response to previously attacked hosts. (3) The model predicts the number of parasitoids and parasitized hosts to be found on the different host patches as well as the number of parasitoids in transit between the patches. (4) The model is used to simulate the dynamics of a laboratory host-parasitoid system consisting of the ichneumonid Nemeritis canescens Grav. and larvae of the moth Ephestia cautella. The simulations show that the model accounts very well for the observed adaptive behaviour of Nemeritis.

Some Consequences of Habitat Heterogeneity for Population Dynamics

The dynamic effects of spatial heterogeneity are discussed in relation to three systems: (1) a single-species system, (2) a parasitoid-host system, and (3) a disease-host system. In each case, a heterogeneous environment of discrete patches is specified, between which the animals are distributed. The central conclusion is the same irrespective of the system: the more contagious the distribution of the animals per patch, the greater is the population stability. In the single-species and disease-host systems, this arises because increased clumping accentuates the density dependent mortality within a patch, while in the parasitoid-host system it results from differential susceptibility of host individuals to parasitism.

Properties of Food Webs

On the assumption that systems of interacting species, when perturbed from equilibrium, should return to equilibrium quickly, one can predict four properties of foods web; (1) food chains should be short, (2) species feeding on more then one trophic level (omnivores) should be rare, (3) those species that do feed on more than one trophic level should do so by feeding on species in adjacent trophic levels, and (4) host—parasitoid systems are likely to be exceptions to (1)—(3) when interaction coefficients permit greater trophic complexity. By generating random, model food webs (with many features identical to webs described from a variety of marine, freshwater, and terrestrial systems), it is possible to generate expected values for the number of trophic levels and the degree of omnivory within webs. When compared with these random webs, real world webs are shown to have fewer trophic levels, less omnivory, and very few omnivores feeding on nonadjacent trophic levels. Insect webs are shown to have a greater degree of omnivory than other webs. The confirmation of all these predictions from stability analyses suggests that system stability places necessary, though not sufficient, limitations on the possible shapes of food webs.

Host-Parasitoid Systems in Patchy Environments: A Phenomenological Model

SUMMARY (1) A host-parasitoid model is presented which is intermediate in complexity between the Nicholson-Bailey model (in which the parasitoids search independently randomly in a homogenous environment) and complicated models for incorporating environmental patchiness (in which the overall distribution of parasitoid attacks is derived from detailed assumptions about their searching behaviour and about the spatial distribution of the hosts). The model assumes the overall distribution of parasitoid attacks per host to be of negative binomal form. There are consequently three biological parameters: two are the usual parasitoid 'area of discovery', a, and the host 'rate of increase', F; the third is the negative binomial clumping parameter, k. Such intermediate-level models have proved useful in sorting out ideas in the related disciplines of epidemiology and parasitology. (2) Empirical and theoretical arguments for using the negative binomial to give a phenomenological description of the essential consequences of spatial patchiness in models are surveyed. (3) A biological interpretation of the parameter k in host parasitoid models is offered. If the parasitoids be distributed among patches according to some arbitrary distribution which has a coefficient of variation CVp, and if the parasitoid attack distribution within a patch be Poisson, then the ensuing compound distribution can be approximated by a negative binomial which will have the same variance as the exact distribution provided k is identified as k = (I I/CVp)2. (4) Expressions are obtained for the equilibrium values of host and parasitoid popula- tions. These equilibria are stable if, and only if, k < 1; that is, provided there is sufficient clumping. (5) The dynamical effects of parasitoid aggregation in some respects mimic those introduced by mutual interference among parasitoids; the appropriate coefficient of 'psuedo-interference' is calculated.