Differential thermal biology may explain the coexistence of Platygaster matsutama and Inostemma seoulis (Hymenoptera: Platygastridae) attacking Thecodiplosis japonensis (Diptera: Cecidomyiidae)

Two dominant parasitoids, Platygaster matsutama Yoshida and Inostemma seoulis Ko, often coexist in the host-parasitoid community of the pine needle gall midge, Thecodiplosis japonensis Uchida et Inouye. Subtle differences in parasitoid phenology appear to play a key role in reducing interspecific competition, but the specific thermal conditions for development of each species have not been defined. We examined the thermal biology of two sympatric parasitoids during postdiapause development at seven constant temperatures (12, 15, 18, 21, 24, 27, and 30 °C) to determine species-specific developmental parameters. The lower developmental threshold was estimated to be 4.2 °C and 8.4 °C, and the thermal constant was 741.2 and 946.1 degree days (DD) for P. matsutama and I. seoulis, respectively, using the linear model. The nonlinear model determined that the optimal temperature was 24.8 and 26.5 °C for P. matsutama and I. seoulis, respectively, but with an upper threshold temperature (30 °C) that was the same for both species. The development rate of P. matsutama was higher than that of I. seoulis over the entire thermal range, and the difference was highest at 21.5 °C. Despite the lower developmental rate, I. seoulis was more heat tolerant and its optimal temperature was closer to that of host insect than those of P. matsutama. The results showed clear differences in thermal biology between P. matsutama and I. seoulis. Potential implications are discussed with respect to coexistence of two parasitoids on a single host and biological control of T. japonensis.     

Effects of parasitoid community structure upon the population dynamics of the honeysuckle leafminer,Chromatomyia suikazurae (Diptera: Agromyzidae)

Population dynamics of a leafminer,Chromatomyia suikazurae (Agromyzidae, Diptera) and its parasitoid community were studied for ten years at seven natural populations along an altitudinal gradient in Japan. This species which mines leaves of a forest shrub,Lonicera gracilipes (Caprifoliaceae), was attacked by 25 hymenopterous parasitoid species. Annually, the parasitoid community structure varied less within a population than among populations. The seven parasitoid communities were clustered into three groups corresponding to the altitudinal gradient: (a) lowland communities dominated by late-attacking, generalist pupal idiobiont eulophids and with highest species diversity, (b) hillside communities dominated by an early-attacking, specialist larval-pupal koinobiont braconid and (c) highland communities dominated by an early-attacking, generalist larval idiobiont eulophid. Annual changes of the host larval densities among the local populations were largely synchronous rather than cyclic. Among these populations, host density levels and mortality patterns greatly varied. By analyzing these inter-populational differences of host mortality patterns, the following conclusions were drawn: (1) The host mortality patterns were determined by the host utilization patterns of the locally dominant species. (2) The host pupal mortality but not larval mortality was related to species diversity but not to species richness itself of each parasitoid community. (3) Density dependence was detected only in pupal mortality at a lowland population dominated by late-attacking pupal parasitoids. These results suggest that interspecific interactions of parasitoids add additive effects to host population dynamics dissimilarly among local populations with different parasitoid communities.     

Aggregation of parasitism risk in an aphid-parasitoid system: Effects of plant patch size and aphid density

Few studies have linked density dependence of parasitism and the tritrophic environment within which a parasitoid forages. In the non-crop plant-aphid, Centaurea nigra–Uroleucon jaceae system, mixed patterns of density-dependent parasitism by the parasitoids Aphidius funebris and Trioxys centaureae were observed in a survey of a natural population. Breakdown of density-dependent parasitism revealed that density dependence was inverse in smaller colonies but direct in larger colonies (>20 aphids), suggesting there is a threshold effect in parasitoid response to aphid density. The CV² of searching parasitoids was estimated from parasitism data using a hierarchical generalized linear model, and CV²>1 for A. funebris between plant patches, while for T. centaureae CV²>1 within plant patches. In both cases, density independent heterogeneity was more important than density-dependent heterogeneity in parasitism. Parasitism by T. centaureae increased with increasing plant patch size. Manipulation of aphid colony size and plant patch size revealed that parasitism by A. funebris was directly density dependent at the range of colony sizes tested (50–200 initial aphids), and had a strong positive relationship with plant patch size. The effects of plant patch size detected for both species indicate that the tritrophic environment provides a source of host density independent heterogeneity in parasitism, and can modify density-dependent responses.     

The role of parasitoids in regulation of Polistes wasp population (Hymenoptera, Vespidae: Polistinae)

The study conducted in 2005–2010 analyzes the behavioral response of the parasitoids Latibulus argiolus (Rossi) (Hymenoptera, Ichneumonidae) and Elasmus schmitti Ruschka (Hymenoptera, Eulophidae) to the distribution of their host, Polistes wasps (Hymenoptera, Vespidae). Various conditions of the parasitoid-host system and conditions of regulation of the host abundance are discussed. The parasitoid females are more active in wasp colony clusters and tend to infest larger nests. If the parasitoids are abundant, infestation of host colonies starts earlier, sometimes before the worker emergence; therefore, density-dependent behavioral response of parasitoids is caused primarily by the impact of the aggregation component. Thus, the host population density factor appears to be mediated not only by the non-uniform development rates of colonies and their spatial distribution, but also by the seasonal (temporal) aspect of their development. Low density of the host population, at which the parasitoids regulate the wasp abundance, corresponds to a certain phase of the seasonal colony development, namely to the period before the emergence of workers. On the whole, we are dealing with a host-parasitoid system in which the spatial and temporal factors are closely interrelated.     

Structure,organization, and response of a species-rich parasitoid community to host leafminer population dynamics

The parasitoid community dynamics of an agromyzid honeysuckle leafminer, Chromatomyia suikazurae (Agromyzidae, Diptera) were studied between 1981 and 1990 in a natural forest in Kyoto, Japan. The parasitoid fauna composed three koinobionts (all larval-pupal solitary parasitoids) and 22 idiodiont species (11 larval solitary, nine pupal solitary and one pupal gregarious). The parasitoid community was dominated by early-attacking oligophagous braconid koinobionts at early periods, but was gradually displaced by late-attacking polyphagous eulophid idiobionts. Accordingly, the diversity index of the parasitoid community peaked at an intermediate point in the intra-generational succession. The succeeding attack-in-waves by the late-attacking idiobionts greatly reduced not only the survival rates of early-attacking parasitoid larvae but also the survival rates of hosts. The density-dependence observed in the host pupal mortality was thought to result from density-dependent host-switching by a keystone polyphagous pupal idiobiont parasitoid, Chrysocharis pubens, whereas high host pupal mortality was potentially attained by an early-attacking koinobiont braconid. Supposed aggregation of polyphagous parasitoids at high host density resulted in intense within-host competition and in an increase of host-feeding attack, both of which contributed to low emergence rates of parasitoids at high host densities. Parasitoid emergence rates were also reduced at low host densities, probably by inter- and intra-specific hyperparasitism among oligophagous parasitoids for limited hosts. The regulation effects of the species-rich parasitoid community upon the host population dynamics are thought to derive from succeeding attack-in-waves by polyphagous late-attacking idiobionts, especially by the keystone species.     

Density dependence and environmental factors affect population stability of an agricultural pest and its specialist parasitoid

Host–parasitoid dynamics are intrinsically unstable unless the risk of parasitism is sufficiently heterogeneous among hosts. Spatial aggregation of parasitoids can contribute to this heterogeneity, stabilising host–parasitoid population dynamics and thereby reducing pest outbreaks. We examined the spatial distribution of mango gall fly (Procontarinia matteiana, Kiefer and Cecconi), a non-native pest of South African mango orchards, which is controlled by a single parasitoid (Chrysonotomyia pulcherrima, Kerrich). We assessed whether spatial aggregation of parasitoids is associated with proximity to natural vegetation and/or to host density-dependent and host density-independent factors at three spatial scales. We found evidence for higher parasitism rates near natural vegetation at the field scale, and inverse host-density dependent and density-independent parasitoid aggregation at both the leaf scale and field scale. Therefore, we conclude that natural vegetation plays a role in promoting stabilising aggregation of parasitoids, possibly through provision of non-host resources (nectar, pollen), in this system.     

Adaptive host preference and the dynamics of host-parasitoid interactions

Models of two independent host populations and a common parasitoid are investigated. The hosts have density-dependent population growth and only interact indirectly by their effects on parasitoid behavior and population dynamics. The parasitoid is assumed to experience a trade-off in its ability to exploit the two hosts. Three alternative types of parasitoid are investigated: (i) fixed generalists whose consumption rates are those that maximize fitness; (ii) "ideal free" parasitoids, which modify their behavior to maximize their rate of finding unparasitized hosts within a generation; and (iii) "evolving" parasitoids, whose capture rates change between generations based on quantitative genetic determination of the relative attack rates on the two hosts. The primary questions addressed are: (1) Do the different types of adaptive processes stabilize or destabilize the population dynamics? (2) Do the adaptive processes tend to equalize or to magnify differences in host densities? The models show that adaptive behavior and evolution frequently destabilize population dynamics and frequently increase the average difference between host densities.     

Convergence and Divergence in Direct and Indirect Life-History Traits of Closely Related Parasitoids (Braconidae: Microgastrinae)

Closely related species in nature often show similarities in suites of direct and indirect traits that reveal aspects of their phylogenetic history. Here we tested how common descent affects trait evolution in several closely related parasitoid species in the genera Cotesia and Microplitis (Hymenoptera: Braconidae: Microgastrinae) by comparing development, resource use and allocation into reproduction and maintenance. Parasitoids in these genera exhibit traits, like haemolymph feeding as larvae and external pupation that are rare in most parasitoid lineages. The growth of parasitized hosts was reduced by 90 % compared with healthy hosts, and maximum host size depended to a large extent on adult parasitoid size. Development time was longer in the more generalist parasitoids than in the specialists. Adult body mass was sexually dimorphic in all Cotesia species, with females being larger, but not in Microplitis spp. In contrast, in one of the Microplitis species males were found to be the larger sex. Egg load dynamics during the first 6 days after emergence were highly variable but egg number was typically higher in Cotesia spp. compared to Microplitis spp. Longevity in the various species was only greater in female than in male wasps in two Microplitis sp. There was a clear inverse relationship between resource use and allocation, e.g. maximum egg load and longevity, in these parasitoids. Our results reveal that adaptation to constraints imposed by host quality and availability has resulted in trait convergence and divergence at the species, genus and subfamily level.     

Adaptive Host Preference and the Dynamics of Host–Parasitoid Interactions

Models of two independent host populations and a common parasitoid are investigated. The hosts have density-dependent population growth and only interact indirectly by their effects on parasitoid behavior and population dynamics. The parasitoid is assumed to experience a trade-off in its ability to exploit the two hosts. Three alternative types of parasitoid are investigated: (i) fixed generalists whose consumption rates are those that maximize fitness; (ii) “ideal free” parasitoids, which modify their behavior to maximize their rate of finding unparasitized hosts within a generation; and (iii) “evolving” parasitoids, whose capture rates change between generations based on quantitative genetic determination of the relative attack rates on the two hosts. The primary questions addressed are: (1) Do the different types of adaptive processes stabilize or destabilize the population dynamics? (2) Do the adaptive processes tend to equalize or to magnify differences in host densities? The models show that adaptive behavior and evolution frequently destabilize population dynamics and frequently increase the average difference between host densities.     

The influence of the rearing host on the response of the parasitoid Venturia canescens (Gravenhorst) (Hymenoptera: Ichneumonidae) to odours from Ephestia kuehniella and Plodia interpunctella in a Y-tube olfactometer

Venturia canescens (Gravenhorst) is an ichneumonid generalist parasitoid that successfully attacks the larvae of different lepidopteran pests that infest stored products. These pest species include Plodia interpunctella and Ephestia kuehniella. In this study, we aimed to evaluate the influence of the rearing host on the parasitoid’s ability to detect and respond to a new host different from the rearing species. For this reason, the trials tested the preference of parasitoids reared on P. interpunctella or E. kuehniella for products that were or were not infested with larvae of these hosts. The trials were conducted in a Y-tube olfactometer. Regardless of the rearing host species, the parasitoids showed no preference for uninfested products. The parasitoids were attracted to products infested with larvae of their rearing host in preference to uninfested products. They also showed preferential attraction to products infested with the new host over uninfested products. E. kuehniella was the preferred host, irrespectively of the parasitoid host rearing species. The results are discussed to develop a better understanding of the ecology of V. canescens for its application in biological control.     

Autoparasitism, interference, and parasitoid-pest population dynamics

Autoparasitoids ("heteronomous hyperparasitoids") are parasitoids that lay female eggs on homopteran hosts and male eggs on juvenile parasitoids of either the same species or another species. Males develop as hyperparasitoids and eventually kill the juvenile parasitoid. We present a series of stage-structured models that investigate the effects of autoparasitism on population dynamics. Autoparasitism causes density-dependent mortality on juvenile parasitoids and therefore has a stabilizing effect. This also leads to an increase in host population abundance. In most cases an autoparasitoid leads to higher host equilibrium densities than a comparable primary parasitoid (except when the primary parasitoid is arrhenotokous (sexual) and the autoparasitoid has a low preference for attacking parasitized hosts or can attack the parasitized host for only a small portion of its development). When male autoparasitoids are followed explicitly in the models, mate limitation reduces the stabilizing effect of autoparasitism and leads to a further increase in host abundance. Coexistence of an autoparasitoid with a nonprimary parasitoid or second autoparasitoid is possible when the level of conspecific autoparasitism is greater than the level of heterospecific autoparasitism. When an autoparasitoid coexists with a primary parasitoid, the resulting host density is always greater than that with only the primary parasitoid. Therefore, autoparasitoids have the potential to disrupt control achieved by primary parasitoids. When two autoparasitoids coexist, the resulting host density is always lower than that attained by either autoparasitoid alone. The effects of autoparasitism are compared with those of other forms of interference competition.     

A simulation study of population interaction between the greenhouse whitefly,Trialeurodes vaporariorum Westwood (Homoptera: Aleyrodidae) and the parasitoidEncarsia formosa Gahan (Hymenoptera: Aphelinidae) II. Simulation analysis of population dynamics and strategy of biological control

Simulation studies were performed to analyze factors affecting the population dynamics of the system with the greenhouse whitefly (Trialeurodes vaporariorumWestwood ) and the parasitoid Encarsia formosaGahan and to develop strategies for the introduction of E. formosa. The reduction of parasitization efficiency with an increase in parasitoid density promotes the stability of the system, which coincides with the prediction from current theory. The stability of the system is also shown to be promoted by the effect of host feeding. The population levels of the system are remarkably suppressed with an increase in searching efficiency and a decrease in host oviposition. The control effect of the parasitoids is enhanced when the number of parasitoids is divided among many introductions. An optimal time, an optimal density ratio of parasitoids to hosts and optimal densities of hosts and parasitoids exist in the introduction programme of parasitoids.     

Sources of variation in larval parasitism of two sympatrically outbreaking birch forest defoliators

1. Studies of insect communities rarely support the parasitoid–host regulation hypothesis. Spatio‐temporal variation in parasitoid prevalence due to complex food web interactions or abiotic factors may prevent parasitoids from regulating hosts. 2. We examined the relative contribution of spatial (altitude) and temporal (years) sources to total variation in parasitoid prevalence rates in outbreaks of Epirrita autumnata Borkhausen and Operophtera brumata Linnaeus populations. We tested whether prevalence rates of generalist parasitoids were correlated between sympatric host populations and to what extent any of the parasitoids were host density dependent. 3. Four larval parasitoids (two specialists and two generalists) exhibited significantly structured spatio‐temporal dynamics over years and altitudes. The prevalence rates of one of the generalists were spatio‐temporally correlated between the two host species, while for the other they were not. 4. Three parasitoids showed tendencies for direct or delayed positive density dependence as expected from numerical and functional responses to their hosts. However, the effects were weak and minute compared to the variation attributed to year and altitude. 5. We conclude that unknown aspects of the larval parasitoid ecology that co‐vary with altitude and year in the study system dominate their prevalence dynamics and thus act to hinder density‐dependent responses that could potentially regulate host populations.     

Competitive Interactions between Parasitoids Provide New Insight into Host Suppression

Understanding the dynamics of potential inter- and intraspecific competition in parasitoid communities is crucial in the screening of efficient parasitoid species and for utilization of the best parasitoid species combinations. In this respect, the host-parasitoid systems, Bemisia tabaci and two parasitoids, Eretmocerus hayati (exotic) and Encarsia sophia (existing) were studied under laboratory conditions to investigate whether interference competition between the exotic and existing species occurs as well as the influence of potential interference competition on the suppression of the host B. tabaci. Studies on interspecific-, intraspecific- and self-interference competition in two parasitoid species were conducted under both rich and limited host resource conditions. Results showed that (1) both parasitoid species negatively affect the progeny production of the other under both rich and limited host resource conditions; (2) both parasitoid species interfered intraspecifically on conspecific parasitized hosts when the available hosts are scarce and; 3) the mortality of B. tabaci induced by parasitoids via parasitism, host-feeding or both parasitism and host-feeding together varied among treatments under different host resource conditions, but showed promise for optimizing control strategies. As a result of our current findings, we suggest a need to investigate the interactions between the two parasitoids on continuous generations.     

Host Plants Affect the Foraging Success of Two Parasitoids that Attack Light Brown Apple Moth Epiphyas postvittana (Walker) (Lepidoptera: Tortricidae)

The light brown apple moth, Epiphyas postvittana is a key pest of wine grapes in Australia. Two parasitoids, Dolichogenidea tasmanica and Therophilus unimaculatus, attack the larval stage of this pest. D. tasmanica is dominant in vineyards, whereas T. unimaculatus is mainly active in native vegetation. We sought to understand why they differ in their use of habitats. Plants are a major component of habitats of parasitoids, and herbivore-infested plants influence parasitoid foraging efficiency by their architecture and emission of volatile chemicals. We investigated how different plant species infested by E. postvittana could affect the foraging success of the two parasitoid species in both laboratory and field experiments. Four common host-plant species were selected for this study. In paired-choice experiments to determine the innate foraging preferences for plants, both parasitoid species showed differences in innate search preferences among plant species. The plant preference of D. tasmanica was altered by oviposition experience with hosts that were feeding on other plant species. In a behavioral assay, the two parasitoid species allocated their times engaged in various types of behavior differently when foraging on different plant species. For both parasitoids, parasitism on Hardenbergia violacea was the highest of the four plant species. Significantly more larvae dropped from Myoporum insulare when attacked than from the other three host-plant species, which indicates that parasitism is also affected by interactions between plants and host insects. In vineyards, parasitism by D. tasmanica was significantly lower on M. insulare than on the other three host-plant species, but the parasitism rates were similar among the other three plant species. Our results indicate that plants play a role in the habitat preferences of these two parasitoid species by influencing their foraging behavior, and are likely to contribute to their distributions among habitats.     

Coexistence of multiple parasitoids on a single host due to differences in parasitoid phenology

There are many well-documented cases in which multiple parasitoids can coexist on a single host species. We examine a theoretical framework to assess whether parasitoid coexistence can be explained through differences in timing of parasitoid oviposition and parasitoid emergence. This study explicitly includes the phenology of host and parasitoid development and explores how this mechanism affects the population dynamics. Coexistence of the host with two parasitoids requires a balance between parasitoid fecundity and survival and occurs most readily if one parasitoid attacks earlier but emerges later than the other parasitoid. The host density can either be decreased or increased when a second coexisting parasitoid is introduced into the system. However, there always exists a single parasitoid type that is most effective at depressing the host density, although this type may not be successful due to parasitoid competition. The coexistence of multiple parasitoids also affects the population dynamics. For instance, population oscillations can be removed by the introduction of a second parasitoid. In general, subtle differences in parasitoid phenology can give rise to different outcomes in a host–multi-parasitoid system, and this may offer some insight into why establishing criteria for the ‘ideal’ biological control agent has been so challenging.     

Introduction of parasitoids has maintained a stable population of arrowhead scales at extremely low levels

We previously reported the drastic decline of the arrowhead scale, Unaspis yanonensis Kuwana (Hemiptera: Diaspididae) following the introduction of two parasitoid species, Aphytis yanonensis DeBach et Rosen and Coccobius fulvus Compere et Annecke (Hymenoptera: Aphelinidae), which were used as biological control agents in a Japanese grove of Satsuma mandarin oranges, Citrus unshiu Marc. (Rutaceae). In this study, we examined whether the parasitoids regulated the scale population at lower levels after its initial decline. Specifically, we monitored the population dynamics of the scale and the rates of parasitism by the two parasitoids three times per year for 16 years following the introduction of the wasps. The two parasitoid species maintained a U. yanonensis density at 1/200 of the density prior to their introduction. When we excluded the wasps, the scale population grew at a rate that was more than fivefold that of a control (parasitoid‐infested) group. Although the rates of parasitism by C. fulvus fluctuated, they remained at relatively high levels, whereas those of A. yanonensis were 0% over the last 6 years. A repeated‐measures ANOVA indicated that scale density remained stable subsequent to its rapid decline. This showed that the parasitoids stabilized the scale population at a lower level than host plant limitations would have dictated, and strongly suggests that C. fulvus alone regulates the scale population density at an extremely low level. The latter finding contradicts other studies which have suggested that the two parasitoid species complement each other in regulating scale density. We discuss whether a behavioral refuge used by the scale against parasitoids, which we have demonstrated in an earlier study, might contribute to the observed stable host–parasitoid system at low densities.     

Delayed density-dependent parasitism of eggs and pupae as a contributor to the cyclic population dynamics of the autumnal moth

Many populations of forest Lepidoptera exhibit 10-year cycles in densities, with impressive outbreaks across large regions. Delayed density-dependent interactions with natural enemies are recognized as key factors driving these cyclic population dynamics, but emphasis has typically been on the larval stages. Eggs, pupae and adults also suffer mortality from predators, parasitoids and pathogens, but little is known about possible density relationships between mortality factors and these non-feeding life stages. In a long-term field study, we experimentally deployed autumnal moth (Epirrita autumnata) eggs and pupae to their natural enemies yearly throughout the 10-year population cycle in northern Norway. The abundance of another geometrid, the winter moth (Operophtera brumata), increased in the study area, permitting comparisons between the two moth species in predation and parasitism. Survival of autumnal moth eggs and pupae was related to the moth abundance in an inverse and delayed manner. Egg and pupal parasitoids dominated as density-dependent mortality factors and predicted the subsequent growth rate of the host population size. In contrast, effects of egg and pupal predators were weakly density dependent, and generally predation remained low. Parasitism rates did not differ between the autumnal and winter moth pupae, whereas predators preferred winter moth pupae over those of the autumnal moth. We conclude that parasitism of the autumnal moth by egg and pupal parasitoids can be related to the changes of the moth density in a delayed density-dependent manner. Furthermore, egg and pupal parasitoids cannot be overlooked as causal factors for the population cycles of forest Lepidoptera in general.     

Density-dependent parasitism of cowpea aphid,Aphis craccivora by Lysiphlebus fabarum,Binodoxys acalephae,and Aphidius matricariae (Hymenoptera: Braconidae: Aphidiinae)

Biological control, as a major component of pest management strategies, uses natural biological agents to reduce pest populations. Studying the interaction among Aphis craccivora and its parasitoids including, Lysiphlebus fabarum, Binodoxys acalephae, and Aphidius matricariae in 2016 and 2017 in Tehran Parke-Shahr, showed positive, significant correlations in all cases between the densities of three parasitoid species and that of aphid nymphs and adults. The density of the parasitoids increased by increasing the density of the aphids. The parasitoids showed aggregative behavior in response to different densities of the host. There was a positive density-dependent correlation between the density of A. craccivora and rate of parasitism. Parasitism rates of nymphs and adult aphids by L. fabarum, B. acalephae, and A. matricariae increased or decreased along with decline or increase in the population of the aphid host. In 2016 spring, the highest rates of parasitism on aphid nymphs by L. fabarum, B. acalephae, and A. matricariae were 46.82, 23.09, and 17.16%, respectively. In 2017 spring, the highest rates of parasitism on aphid nymphs by L. fabarum, B. acalephae, and A. matricariae were 48.97, 21.77, and 15.06%, respectively. So, given the accordance between changes in aphid population and that of parasitoids, and parasitoids’ efficacy in Tehran’s polluted air, they can be used as biological agents in the management of A. craccivora population.     

The relationship between variable host grouping and functional responses among parasitoids of Antispila nysaefoliella (Lepidoptera: Heliozelidae)

Our study investigated the importance of variability in the parasitoid community as a source of selection on host group size using a field population of the tupelo leafminer, Antispila nysaefoliella Clemens, which specializes on tupelo, Nyssa sylvatica Marsh. Larvae were collected from leaves with variable numbers of larvae and screened for parasitism using polymerase chain reaction of mitochondrial cytochrome oxidase I using markers designed specifically for amplifying parasitoid DNA while excluding host DNA. This method of selective PCR was effective for detecting the presence and identifying species of immature stages of three hymenopteran superfamilies: Chalcidoidea, Ichneumonoidea and Platygastroidea, which represented 83.4%, 16.0% and 0.6% of the total detectable parasitism, respectively. Our resulting sequences were then calibrated with sequences from identified adult parasitoids that had been either reared or field‐captured. A cluster analysis revealed 10 distinct clades that showed differences in attack patterns with respect to host traits and season. Total parasitism followed an inverse density‐dependent or density‐independent pattern with respect to host density (number per leaf). However, when parasitoid taxa were considered separately, one clade, which could be a cryptic species of Pnigalio maculipes Crawford (Chalcidoidea: Eulophidae), was found to increase its per leaf attack rate with host density. Our results suggest that parasitoid community composition and differences among species in their attack strategies can play a large role in determining the adaptive advantage of host grouping.