Habitats and parasitoid abundance influence spatial density dependence patterns, rendering an asilid fly as a potential biological controller of white grubs (original) (raw)
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Austral Ecology, 2010
The density-dependence in parasitism by the robber fly Mallophora ruficauda (Diptera: Asilidae) on scarab beetle larvae (Coleoptera: Scarabaeidae) populations was studied in the present research. Mallophora ruficauda is a pestiferous species common in the open grasslands of the Pampas region of South America. Adults are predators of insects and larvae are solitary parasitoids of third instar larvae of several species of scarab beetle (Coleoptera: Scarabaeidae). In contrast with most studied host-parasitoid interactions, host searching by M. ruficauda is carried out by both larvae and adults. Typically, robber fly females lay eggs on tall grasses from where larvae drop to the ground, and attack hosts which are buried in the soil. We carried out our study at two spatial scales close to 14 apiaries located in the provinces of Buenos Aires and Entre Ríos (Argentina). We found that parasitism is density-independent at the larger spatial scale and inversely density-dependent at the smaller one. We also found that M. ruficauda selects Cyclocephala signaticollis among several scarab beetle species. Specificity is observed both at large and small spatial scales. We discuss the implications of both host specificity and host searching behaviour on the observed parasitism patterns.
Biological Control, 2016
The ability of parasitoids to maintain a high rate of parasitism under varying conditions is 16 considered crucial to their ability to control the populations of their hosts. Here, I tested 17 parasitism rate by Anagrus parasitoids and its dependency on the density of Erythroneura leafhopper eggs at two spatial scales (leaf and field) and two habitat types (natural vs. agricultural). The rate of parasitism differed among field sites, increased across the season, and was similar in natural and agricultural sites. At the leaf scale, the rate of parasitism was density-independent or inversely density-dependent, consistent with a weak aggregation of parasitoids on leaves with high host densities and with limited oviposition-rate or egg supply. At the field scale, in contrast, parasitism rate was positively dependent on host density, which may be explained by demographic processes, such as higher recruitment and higher fecundities of females in host-rich field sites. Overall, the results demonstrate that parasitism patterns are highly dynamic in time and space and depend on the scale of observation.
Latania Scale Insect Parasitoid Interactions under Field Conditions
Current Trends in Entomology and Zoological Studies, 2018
Studying the natural relationship between the insects and their natural enemies under field condition is useful for determining their response to the density of their hosts. This study was carried out to evaluate the density-dependent response for insect parasitoids associated with the latania scale, Hemiberlesia lataniae (Signoret) (Diaspididae: Hemiptera) on fig, guava, and loquat plants. The density dependent response was affected by several factors i.e season, plant and parasitoid species. Two parasitoid species, Aphytis diaspidis Howard (Aphelinidae: Hymenoptera) and Signiphora sp. (Signiphoridae: Hymenoptera) were found associated with H. lataniae on all host plants. The parasitoid A. diaspidis showed a positive density-dependent response to density of its host during winter, spring, and summer generations on loquat tree; inverse-density response on guava tree during winter and summer, and both responses to latania scale densities on fig tree. The parasitoid, Signiphora sp. showed differences in its response on the tested host plant species. On guava, it showed a positive-density dependent response to H. lataniae populations during winter and spring, but negatively during summer. On the other hand, fig tree, this response was negative during winter and positive during summer, whereas it is disappeared during spring season. On loquat, Signiphora sp. exhibited positive responses to its host during winter and spring seasons, whereas this response was negative during summer season. This variation in parasitoid responses could be attributed to several reasons, among them the effects of interspecific competition and host plant. Almost, both parasitoid species showed a tendency to aggregate where host density is highest on loquat.
Bulletin of Insectology, 2009
The present work contributes to an accurate quantification method of the parameters of the biotic potential of Encarsia formosa Gahan (Hymenoptera Aphelinidae), applicable to other species of whitefly parasitoids. The oviposition devices are easy to make and they allow standardisation of a whitefly parasitoid study by daily observations of the main parameters such as fecundity, longevity and host-feeding by adult parasitoids, which are important for the parasitoids mass-production and biological control of whiteflies. Results show that two physical parameters determine the expression of biotic potential: the confinement induces an important decrease of the fecundity and longevity of E. formosa; the position of plant leaf with nymphs of Trialeurodes vaporariorum (Westwood) (Homoptera Aleyrodidae) that the parasitoid female can explore for oviposition and host-feeding influences on the biotic potential. The heterogeneity observed in the replicates suggests that during their mass-proce...
Functional Ecology, 2013
1. Theory predicts that organisms should invest more heavily in overcoming factors that more frequently emerge as the primary constraints to fitness, and especially, those factors that constrain the fitness of the most highly reproductive members of the population. 2. We tested the hypothesis that the fecundity of a pro-ovigenic parasitoid (where females emerge with their full egg load) should be positively correlated with the mean expectation for oviposition opportunities in the environment. More specifically, we tested whether females from agricultural systems, where hosts are often relatively abundant, emerge with more eggs than those from natural habitats. 3. We studied the pro-ovigenic parasitoid wasp Anagrus daanei, which parasitizes eggs of leafhoppers of the genus Erythroneura. Erythroneura spp. leafhoppers feed on Vitis spp. (grapes) and are major pests of commercial vineyards as well as common herbivores of wild Vitis californica, which grows in riparian habitats. We sampled leafhoppers and parasitoids from eight vineyards and eight riparian habitats in central California. 4. We found that leafhopper density was higher at vineyards than in riparian habitats, whereas leafhopper egg volume and parasitoid body size did not differ among these habitat types. Parasitoids from vineyards had higher egg loads than parasitoids from wild grapes, and fecundity was positively related to host density across field sites. Parasitoid egg volume was larger in natural sites; however, this variation was not significantly correlated with host density across field sites. Within a single population of parasitoids collected from a vineyard, parasitoid egg load was negatively correlated with longevity, suggesting a trade-off between reproduction and life span. 5. The results may be explained by a rapid evolution of reproductive traits in response to oviposition opportunities; or alternatively, by the occurrence of maternal effects on the fecundity of daughters based on the foraging experience of their mothers. 6. The ability of parasitoid fecundity to track mean host availability is likely to modulate the likelihood that parasitoid fitness will be constrained by a shortage of eggs and strengthen the ability of parasitoids to suppress the population densities of their hosts.
2001
1. A simple, intuitive argument and the tenets of the biological control literature both suggest that, in general, parasitoids with a greater fecundity will provide better control of their hosts, and will thus be better biological control agents. 2. A model of host-parasitoid dynamics, based on the standard Thompson± Nicholson±Bailey approach and incorporating the effects of parasitoid fecunditylimitation and host density-dependence, also indicates that as parasitoid fecundity decreases so does local stability and the degree of host suppression. 3. A taxonomically diverse data set obtained from the biological control record failed to support this theoretical prediction, but at the same time indicated a strong effect of host taxon on the outcome of biological control. 4. The hypothesis that the fecundity of parasitoids is correlated positively with their ability to suppress host populations is supported by data exclusively from the host order Lepidoptera. 5. Possible explanations for the divergence between the fecundity-limitation hypothesis and the complete data set include: the ability of parasitoids to provide long-term control of pests without the presence of a stable host±parasitoid equilibrium; differences between the concepts of successful control in theory and practice; evolutionary trade-offs between fecundity and other parasitoid life-history features, such as search ef®ciency, leading to better pest control by parasitoids with low fecundity; and differing windows of vulnerability to parasitoid attack between host taxa.
Behavioral Ecology and Sociobiology, 2006
For parasitoids, host finding is a central problem that has been solved through a variety of behavioural mechanisms. Among species in which females do not make direct contact with hosts, as is the case for many dipteran parasitoids, eggs must be laid in an appropriate part of the host habitat. The asilid fly Mallophora ruficauda lays eggs in clusters on tall vegetation. Upon eclosion, pollen-sized larvae fall and parasitize soil-dwelling scarab beetle larvae. We hypothesized that wind dissemination of M. ruficauda larvae is important in the host-finding process and that females lay eggs at heights that maximize parasitism of its concealed host. Through numerical and analytical models resembling those used to describe seed and pollen wind dispersal, we estimated an optimal oviposition height in the 1.25-to 1.50-m range above the ground. Our models take into account host distribution, plant availability and the range over which parasitic larvae search for hosts. Supporting our findings, we found that the results of the models match heights at which egg clusters of M. ruficauda are found in the field. Generally, work on facilitation of host finding using plants focuses on plants as indicators of host presence. We present a case where plants are used in a different way, as a means of offspring dispersal. For parasitoids that carry out host searching at immature stages rather than as adults, plants are part of a dissemination mechanism of larvae that, as with minute seeds, uses wind and a set of simple rules of physics to increase offspring success.
Journal of Animal Ecology, 2005
Habitat complexity may stabilize interactions among species of different trophic levels by providing refuges to organisms of lower trophic levels. 2. Searching behaviour of the parasitoid, Diadegma semiclausum , was followed in different semifield set-ups, a low and high-density monoculture of Brassica oleracea and two intercrops, B. oleracea with Sinapis alba (also a member of the Brassicaceae) and B. oleracea with Hordeum vulgare (Poaceae). 3. When a low-density monocrop of B. oleracea was compared with a high-density monocrop, no differences were found in the ability of the female wasps to locate a hostinfested plant, B. oleracea , infested with Plutella xylostella that was placed in the centre of the set-up. 4. The efficiency of the parasitoid to locate the host-infested plant was differentially affected by the species composition of the vegetation. Wasps entered the Sinapis-Brassica set-up faster, but took more time to find the host-infested plant than in the Hordeum-Brassica set-up. 5. The horizontal arrangement, i.e. by mixing S. alba or H. vulgare with, or placing them as rows between B. oleracea , did not affect host-finding efficiency. 6. Plant height did influence host finding. Wasps found the host-infested plants earlier in the set-up with short Sinapis plants compared with tall Sinapis plants. 7. Once the wasps had landed on the host-infested plant, the surrounding vegetation did not affect time needed to parasitize five consecutive hosts on the same infested plant, regardless of the composition or horizontal/vertical arrangement of the set-up. 8. Chemical and structural refuges in complex landscapes may play an important role in the persistence of this system through dampening oscillations of parasitoid and host populations.
Cascading effects of host size and host plant species on parasitoid resource allocation
Ecological Entomology, 2011
1. The bottom-up factors that determine parasitoid host use are an important area of research in insect ecology. Host size is likely to be a primary cue for foraging parasitoids due to its potential influence on offspring development time, the risk of multiparasitism, and host immunocompetence. Host size is mediated in part by host-plant traits that influence herbivore growth and potentially affect a herbivore's quality as a host for parasitoids.
Temporal/spatial structure and the dynamical property of laboratory host-parasitoid systems
Researches on Population Ecology, 1996
The effects of spatial structure in terms of local capacity, or the maximum number of larvae surviving competition at resource patches, and temporal structure in terms of the period vulnerable to parasitoid attack in host populations on the persistence of host-parasitoid systems were quantitatively evaluated by laboratory experiments and well-parameterized model analyses. One of two bruchid beetles, Callosobruchus maculatus and C. phaseoli, were used as a host with Heterospilus prosopidis used as the parasitoid. C. maculatus, in which few larvae survive competition to become adults in each bean, and C. phaseoli, in which many larvae become adults in each bean, along with two kinds of beans, the mung and the azuki, were combined to construct four (2 • 2) resourceherbivorous host-parasitoid systems that differed in local capacity and vulnerable period. The mung-C, maculatus system with the parasitoid was the most persistent, i.e., took the longest time for extinction of either the host or parasitoid to occur. Since this resource-herbivorous host combination exhibited the lowest local capacity and the shortest vulnerable period, these two conditions possibly promoted the persistence of the system. A model incorporating the host population structure supported the observed persistence. Furthermore, the possible contribution of the timing of densitydependent competition of the host on the host-parasitoid persistence is predicted.