Parasitoid Populations Research Articles

Insecticidal Activity of Plant Powders against the Parasitoid, Pteromalus venustus, and Its Host, the Alfalfa Leafcutting Bee.

Developing a bee-friendly alternative to traditional insecticides used within commercial environments can contribute to reductions in pesticide exposure experienced by managed bees. We performed acute contact toxicity studies using fifteen plant powders from seven plant families against a parasitoid pest, Pteromalus venustus, and its host, the Alfalfa leafcutting bee (ALB). Ajwain, cinnamon, clove, cumin, fennel, ginger, nutmeg, oregano and turmeric applied at low contact concentrations had sufficient fumigant properties to cause equivalent or higher parasitoid mortality as that obtained with the traditional insecticide. Nutmeg adversely affected adult ALBs at both low and high contact concentrations, thus eliminating it as a candidate. Increasing the contact concentrations did not consistently increase parasitoid control but did increase adverse effects on the ALBs. In addition, the efficacious plant powders significantly reduced the sexual function and fertility of the female parasitoids, a feature not associated with the traditional insecticide. The dual nature of the mechanisms underlying the effects of the plant powders may translate into effective control of the parasitoid populations in the commercial environment. The results reported here support further evaluations of Ajwain, cinnamon, clove, cumin, fennel, ginger, oregano and turmeric as potential botanical insecticides for control of P. venustus.

Within-host competition drives energy allocation trade-offs in an insect parasitoid.

Organismal body size is an important biological trait that has broad impacts across scales of biological organization, from cells to ecosystems. Size is also deeply embedded in life history theory, as the size of an individual is one factor that governs the amount of available resources an individual is able to allocate to different structures and systems. A large body of work examining resource allocation across body sizes (allometry) has demonstrated patterns of allocation to different organismal systems and morphologies, and extrapolated rules governing biological structure and organization. However, the full scope of evolutionary and ecological ramifications of these patterns have yet to be realized. Here, we show that density-dependent larval competition in a natural population of insect parasitoids (Drino rhoeo: Tachinidae) results in a wide range of body sizes (largest flies are more than six times larger (by mass) than the smallest flies). We describe strong patterns of trade-offs between different body structures linked to dispersal and reproduction that point to life history strategies that differ between both males and females and individuals of different sizes. By better understanding the mechanisms that generate natural variation in body size and subsequent effects on the evolution of life history strategies, we gain better insight into the evolutionary and ecological impacts of insect parasitoids in tri-trophic systems.

Effects of exposure time and ratio of irradiated larvae from three medfly strains on progeny yield in Diachasmimorpha longicaudata (Hymenoptera: Braconidae) mass rearing

ABSTRACTAn augmentative biological control strategy against Ceratitis capitata (= medfly) in fruit-producing irrigated-valleys of San Juan, central-western Argentina, has been recently implemented by the San Juan Fruit Fly Control and Eradication Program. The Asian-native parasitoid Diachasmimorpha longicaudata is currently reared at the San Juan Medfly and Parasitoids Mass Rearing Facility for this purpose. In this regard, the objective of this study was to evaluate adult emergence and offspring sex ratio to improve parasitoid production. Three medfly strains at different host larvae densities and exposure times to female parasitoids were assessed. Prevalence of superparasitism was also considered. Three parasitoid population lines were used in the trials: one reared on medfly larvae of the Vienna-8 temperature-sensitive lethal (tsl) genetic sexing strain without inversion, and the other two on larvae of biparental medfly strains native to San Juan (central-western Argentina) and Tucumán (northwestern Argentina). Gamma-irradiated 6 d-old larvae (early third-instars) of each medfly strain were exposed to parasitoids for 30, 60, 90, and 120 min at 3:1, 6:1, and 9:1 host/parasitoid ratios. The Vienna-8 C. capitata strain was as efficient in producing parasitoids as both biparental native strains. Medfly larvae exposed to 10 female parasitoids for a relatively long time (1.30 hrs) at a high ratio (6–9:1) of host to parasitoid were enough to achieve the highest mean adult emergence (50–60%) and a female-biased offspring sex ratio. Superparasitism positively influenced female parasitoid production. These findings may be used to develop a more cost-effective mass rearing method for D. longicaudata.

Compatibility of trap cropping system and insecticides in managing leafminers Liriomyza spp. (Diptera: Agromyzidae) on shallot crop

Trap cropping system has been widely used as a management strategy against various types of pests. However, the efficacy of this strategy varies and need to be increased by combining it with another additional control strategy. This study aimed to evaluate the efficacy of trap cropping system and insecticides against leafminers, an important pest of crops in the world including in shallot crop in Indonesia. The study was arranged in a randomized complete block design with 6 treatments, which were 1) without any treatments (control), 2) trap crops, 3) botanical insecticide (Agonal), 4) synthetic insecticide (Abamectin) 5) trap crops and Agonal, 6) trap crops and abamectin. The results showed that the trap cropping system has a stronger effect on reducing infestation than the population of leafminers. Trap crops reduced leafminer infestation by around 50% when combined with insecticides but only reduced by 32 % without insecticides. Agonal and abamectin insecticides had similar efficacy against leafminers. Trap crop application combined with insecticides had the highest parasitoid population compared with insecticides and control. This study revealed that trap crops were compatible with insecticides in controlling shallot leafminers and supports the integrated pest management of leafminers.

Potato/Maize intercropping reduces infestation of potato tuber moth, Phthorimaea operculella (Zeller) by the enhancement of natural enemies

The potato tuber moth (PTM), Phthorimaea operculella (Zeller), is one of the most economically significant insect pests for potato in both field and storage worldwide. To evaluate the infestation, reduction of potato yield and the control efficacy for PTM, field tests were conducted in two seasons by intercropping of potato as the host plant with maize as a non-host plant of PTM. Three intercropping patterns were tested, which were 2 rows of potatoes with either 2, 3, or 4 rows of maize (abbreviated 2P:2M, 2P:3M, and 2P:4M), and the monocropped potato as the control, 2 rows of potatoes, without maize, (abbreviated 2P:0M). Results showed that the population and infestation of PTM in the 2P:3M intercropping pattern was significantly lower than those in 2P:2M, 2P:4M and the monocropping pattern of 2P:0M, due to the enhancement of natural enemies. Cumulative mines and tunneling in potato leaves in 2P:3M intercropping were significantly lower than those in 2P:2M and 2P:4M patterns. The population of parasitoids and the parasitism rate of PTM in intercropping pattern of 2P:3M were significantly higher than that in intercropping pattern of 2P:2M, 2P:4M and monocropping pattern of 2P:0M. We conclude that the potato intercropped with maize reduced the adult and larva populations, and reduced the damage from PTM by enhancing the number of parasitoids and the level of parasitism. The greatest population density of parasitoids and parasitism rate were in the intercropping pattern of 2 rows of potatoes with 3 rows of maize. These data indicate that the host/non-host intercropping patterns can be used as a biological control tactic against PTM by enhancing the density of natural enemies in the agro-ecosystems.

Bifurcation Analysis of a Discrete-Time Two-Species Model

We study the local dynamics and bifurcation analysis of a discrete-time modified Nicholson–Bailey model in the closed first quadrant R+2. It is proved that model has two boundary equilibria: O0,0,Aζ1−1/ζ2,0, and a unique positive equilibrium Brer/er−1,r under certain parametric conditions. We study the local dynamics along their topological types by imposing method of Linearization. It is proved that fold bifurcation occurs about the boundary equilibria: O0,0,Aζ1−1/ζ2,0. It is also proved that model undergoes a Neimark–Sacker bifurcation in a small neighborhood of the unique positive equilibrium Brer/er−1,r and meanwhile stable invariant closed curve appears. From the viewpoint of biology, the stable closed curve corresponds to the period or quasi-periodic oscillations between host and parasitoid populations. Some simulations are presented to verify theoretical results. Finally, bifurcation diagrams and corresponding maximum Lyapunov exponents are presented for the under consideration model.

Host selection of Dolichogenidea tasmanica: implications for conservation biological control of light brown apple moth

ABSTRACTAn understanding of host selection by parasitoids can help in evaluating alternative host candidates to make conservation biological control of a target pest more reliable. This study investigated the host selection behaviour of Dolichogenidae tasmanica (Hymenoptera: Braconidae) in response to two related tortricid host species (Lepidoptera). The light brown apple moth, Epiphyas postvittana is the biological control target in Australian vineyards, while Merophyas divulsana was selected to evaluate its potential as an alternative host. We quantified the effects of host species, ages and experiences on the landing preferences of the parasitoid in dual choice tests. The effects of these host species on developmental time, sex ratio and body size of adult parasitoids were also examined. During all observations, D. tasmanica exhibited no statistically significant preferences in response to these hosts. Host species did not affect the body size of the wasp, but did influence its developmental time, possibly due to a trade-off between body size and developmental time of the wasp, which took longer in the smaller host, M. divulsana. The sex ratio was similar within host instars and between host species. These results suggest that M. divulsana should be a promising alternative host to support the local parasitoid population in vineyards as part of a conservation biological control programme that targets E. postvittana.

Effects of climatic changes on olive fly, Bactrocera oleae (Rossi) population dynamic with respect to the efficacy of its larval parasitoid in Egyptian olive trees

BackgroundThe potential effects of two parameters of climatic change conditions (temperature and relative humidity) on the population dynamics of the olive fly across the two ecological areas in Egypt were studied. The olive trees in El-Behera Governorate are more affected by the olive fly compared to the olive trees in the orchard of El-Fayoum Governorate. In this study, the character of climate change in influencing the dynamics of insect population and associated parasites was discussed at the regional level.ResultsThe results exhibited that the olive trees in the coast governorate were more susceptible to the olive fly than the inner governorate. The parasitism percentage was recorded 41.7 and 46.4% at the beginning of the seasons 2016 and 2017, respectively in El-Fayoum Governorate. In El-Behera Governorate, the maximum parasitism percentage was recorded 49.5% (2016 season), while the 2017 season, the parasitism percentage was recorded 50.4%. The majority of the ordinary parasite was Psyttalia concolor in the two regions.ConclusionThe study clarifies that there is a positive correlation between B. oleae abundance and the effects of temperature and its parasitoid, Psyttalia concolor. Further, there is no significance found between the olive fly and relative humidity and its parasitoid populations.

The impact of climate on the winter strategies of insects

The impact of climate on the winter strategies of insects

Keanekaragaman parasitoid dan predator kutu lak (Laccifer lacca Kerr) di KPH Probolinggo Perum Perhutani Unit II, Jawa Timur

Kutu lak (Laccifer lacca Kerr) (Homoptera: Kerriidae) merupakan serangga yang hidup secara parasitik pada tanaman inangnya. Serangga tersebut menghasilkan resin alami yang kompak dan tebal, yang menempel pada cabang tanaman tempat hidupnya yang biasa disebut lak. Lak cabang merupakan resin alami dari hasil sekresi serangga L. lacca berupa lapisan tebal lak yang membungkus ranting-ranting tanaman inang. Serangan parasitoid dan predator terhadap kutu lak berdampak langsung pada penurunan produktivitas lak. Penelitian ini bertujuan untuk mengidentifikasi parasitoid dan predator yang menyerang kutu lak, dan menghitung tingkat parasitisasi di BKPH Kabuaran dan Taman, KPH Probolinggo, Perum Perhutani Unit II Jawa Timur. Sampel lak cabang diambil dari BKPH Kabuaran dan Taman masing-masing sebanyak 200 sampel lak cabang. Masing-masing lak cabang dimasukkan ke dalam tabung reaksi. Pengamatan parasitoid yang keluar dari lak cabang dilakukan dalam tabung reaksi. Famili parasitoid yang dominan ditemukan, yaitu Aphelinidae, Encyrtidae, dan Eulophidae. Predator yang ditemukan pada kutu lak terdiri atas Famili Lathridiidae (Coleoptera), Cosmopterigidae, dan Noctuidae (Lepidoptera), Nabidae (Hemiptera), serta Chrysopidae (Neuroptera). Jumlah kumulatif parasitoid di lapangan lebih banyak (5.900 individu) dibandingkan dengan di gudang (5.263 individu). Pertambahan individu parasitoid tertinggi dari lapangan dan gudang terjadi pada pengamatan hari ke-7 sampai hari ke-17. Tingkat parasitisasi kutu lak di lapangan dan gudang tergolong tinggi dengan nilai rata-rata sebesar 93% dan 96%. Dapat disimpulkan bahwa kutu lak yang berasal dari lapangan maupun gudang mengalami serangan parasitoid yang sangat tinggi.

How climate change affects the seasonal ecology of insect parasitoids

1. In the context of global change, modifications in winter conditions may disrupt the seasonal phenology patterns of organisms, modify the synchrony of closely interacting species and lead to unpredictable outcomes at different ecological scales.2. Parasites are present in almost every food web and their interactions with hosts greatly contribute to ecosystem functioning. Among upper trophic levels of terrestrial ecosystems, insect parasitoids are key components in terms of functioning and species richness. Parasitoids respond to climate change in similar ways to other insects, but their close relationship with their hosts and their particular life cycle – alternating between parasitic and free‐living forms – make them special cases.3. This article reviews of the mechanisms likely to undergo plastic or evolutionary adjustments when exposed to climate change that could modify insect seasonal strategies. Different scenarios are then proposed for the evolution of parasitoid insect seasonal ecology by exploring three anticipated outcomes of climate change: (i) decreased severity of winter cold; (ii) decreased winter duration; and (iii) increased extreme seasonal climatic events and environmental stochasticity.4. The capacities of insects to adapt to new environmental conditions, either through plasticity or genetic evolution, are highlighted. They may reduce diapause expression, adapt to changing cues to initiate or terminate diapause, increase voltinism, or develop overwintering bet‐hedging strategies, but parasitoids' responses will be highly constrained by those of their hosts.5. Changes in the seasonal ecology of parasitoids may have consequences on host–parasitoid synchrony and population cycles, food‐web functioning, and ecosystem services such as biological pest control.

Environmental degradation amplifies species' responses to temperature variation in a trophic interaction.

Land‐use and climate change are two of the primary drivers of the current biodiversity crisis. However, we lack understanding of how single‐species and multispecies associations are affected by interactions between multiple environmental stressors.We address this gap by examining how environmental degradation interacts with daily stochastic temperature variation to affect individual life history and population dynamics in a host–parasitoid trophic interaction, using the Indian meal moth, Plodia interpunctella, and its parasitoid wasp Venturia canescens.We carried out a single‐generation individual life‐history experiment and a multigeneration microcosm experiment during which individuals and microcosms were maintained at a mean temperature of 26°C that was either kept constant or varied stochastically, at four levels of host resource degradation, in the presence or absence of parasitoids.At the individual level, resource degradation increased juvenile development time and decreased adult body size in both species. Parasitoids were more sensitive to temperature variation than their hosts, with a shorter juvenile stage duration than in constant temperatures and a longer adult life span in moderately degraded environments. Resource degradation also altered the host's response to temperature variation, leading to a longer juvenile development time at high resource degradation. At the population level, moderate resource degradation amplified the effects of temperature variation on host and parasitoid populations compared with no or high resource degradation and parasitoid overall abundance was lower in fluctuating temperatures. Top‐down regulation by the parasitoid and bottom‐up regulation driven by resource degradation contributed to more than 50% of host and parasitoid population responses to temperature variation.Our results demonstrate that environmental degradation can strongly affect how species in a trophic interaction respond to short‐term temperature fluctuations through direct and indirect trait‐mediated effects. These effects are driven by species differences in sensitivity to environmental conditions and modulate top‐down (parasitism) and bottom‐up (resource) regulation. This study highlights the need to account for differences in the sensitivity of species’ traits to environmental stressors to understand how interacting species will respond to simultaneous anthropogenic changes.

Intraguild predation is independent of landscape context and does not affect the temporal dynamics of aphids in cereal fields

Abundance and diversity of natural enemies increases with higher landscape complexity. However, more species can also increase negative interactions such as intraguild predation (IGP), which could be detrimental to pest control. Direct observations of these trophic interactions are still lacking. In the present study, we employed DNA-based gut content analyses of coccinellid beetles to assess IGP (direct and coincidental) and aphid consumption. Species-specific and group-specific primer pairs were used to unveil the interactions of the most abundant coccinellid species, three cereal aphids and their associated parasitoids. In order to determine whether the landscape complexity promotes these interactions, we used replicated wheat fields in two contrasting landscape contexts over the season in central Chile. With higher abundance of coccinellids, we observed greater aphid consumption in complex contexts. The consumption of parasitized aphids was mostly detected early in complex contexts, suggesting a detrimental effect on the parasitoid population. Following molecular analysis, we can state that the aphids are important feeding resources for the coccinellid assemblage and are actively foraging on this important pest. Finally, this study demonstrates that direct IGP is a common interaction in this system, independently of the landscape context during the complete season. Nevertheless, the native Eriopis chilensis was found to be the most frequently consumed intraguild prey. In contrast with expected predictions, we found little evidence that the landscape context increased negative interactions, such as IGP and IGP-C and in turn that these decrease the control of Sitobion avenae.

Effect of Fluctuating High Temperatures on House Flies (Diptera: Muscidae) and Their Principal Parasitoids (Muscidifurax spp. and Spalangia spp. [Hymenoptera: Pteromalidae]) From the United States.

Colonies of house flies (Musca domestica L. [Diptera: Muscidae]) and four species of parasitoids (Muscidifurax raptor Girault and Sanders, Muscidifurax zaraptor Kogan and Legner, Spalangia cameroni Perkins and Spalangia endius Walker) were established by making collections from dairy farms near Bell, FL, Beatrice, NE, Minneapolis, MN, and San Jacinto, CA. Colonies were assessed for heat tolerance by comparing life history parameters at 25-27°C and fluctuating hot (26.7-41.7°C) temperatures. Muscidifurax raptor, S. cameroni, and S. endius produced 24-28% as many progeny under hot conditions as at 25°C. Colonies of M. zaraptor were more heat-tolerant and produced an average 46.9% as many progeny under the hot regime compared with moderate conditions. There was little evidence for higher heat tolerance in parasitoid populations from historically hot locations (CA desert and FL). Colonies of M. raptor and S. endius that had been in culture for 24 yr were the least heat-tolerant with regard to progeny production. House flies collected from the same locations varied little in longevity, fecundity, or egg-to-adult survival under either hot or moderate regimes. Flies reared under hot conditions laid about half as many eggs (89/female) and had about half the egg-adult survival rate (47.3%) under hot compared with moderate conditions, indicating that heat stress had less effect on flies than on all of the parasitoids except M. zaraptor. An attempt to select for heat tolerance in flies by subjecting them to incremental increases in rearing temperatures for 20 generations resulted in little change in tolerance among the selected flies.

A matrix model describing host-parasitoid population dynamics: The case of Aphelinus certus and soybean aphid.

Integrating elements from life tables into population models within a matrix framework has been an underutilized method of describing host–parasitoid population dynamics. This type of modeling is useful in describing demographically-structured populations and in identifying points in the host developmental timeline susceptible to parasitic attack. We apply this approach to investigate the effect of parasitism by the Asian parasitoid Aphelinus certus on its host, the soybean aphid (Aphis glycines). We present a matrix population model with coupled equations that are analogous to a Nicholson–Bailey model. To parameterize the model, we conducted several bioassays outlining host and parasitoid life history and supplemented these studies with data obtained from the literature. Analysis of the model suggests that, at a parasitism rate of 0.21 d−1, A. certus is capable of maintaining aphid densities below economically damaging levels in 31.0% of simulations. Several parameters—parasitoid lifespan, colonization timeline, host developmental stage, and mean daily temperature—were also shown to markedly influence the overall dynamics of the system. These results suggest that A. certus might provide a valuable service in agroecosystems by suppressing soybean aphid populations at relatively low levels of parasitism. Our results also support the use of A. certus within a dynamic action threshold framework in order to maximize the value of biological control in pest management programs.

Food web structure of parasitoids in greenhouses is affected by surrounding landscape at different spatial scales

Landscape management affects species interactions and can have notable effects on food web structure. Local parasitoid populations in greenhouses usually migrate from outside crops; biological control of greenhouse aphids may be thus highly dependent on the composition of surrounding landscape. However, it is less clear how surrounding landscape composition affects primary-hyperparasitoid food webs and pest control services in greenhouses. We investigated the food web of parasitoids on melon-cotton aphid (Aphis gossypii Glover) in watermelon greenhouses in two suburban Beijing counties over two years. We used the quantitative food web metrics (generality, vulnerability, link density, and interaction evenness) to assess the effects of landscape composition on primary-hyperparasitoid food web structure. We found that landscape with more cropland within 1–3 km tended to have more primary parasitoids per hyperparasitoid species (generality). Higher proportions of woodland at the 0.5 km scale were negatively correlated with the mean numbers of hyperparasitoid per primary parasitoid species (vulnerability), as well as with hyperparasitism rate and hyperparasitoid richness. Link density, interaction evenness and aphid mortality caused by parasitoids (parasitism rate) were not affected by landscape factors. However, active primary parasitism (biocontrol potential) increased with the proportion of woodland. This suggested that the bottom-up effect induced by primary parasitoids might benefit hyperparasitoids, thus exerting little influence of primary parasitoids on pest control. The top-down effect of hyperparasitoids may reduce with increasing woodland proportion. To enhance the effects of primary parasitoids, landscape management programs should also target, and thus limit the impact of hyperparasitoids.

Herbivore-induced plant volatiles enhance field-level parasitism of the mirid bug Apolygus lucorum

In China, the braconid wasp Peristenus spretus Chen & van Achterberg (Hymenoptera: Braconidae) is a native endoparasitoid of the mirid bug Apolygus lucorum (Meyer-Dür) (Hemiptera: Miridae). Castor bean (Ricinus communis L.) is a preferred host plant of A. lucorum, and P. spretus adults are attracted to its herbivore-damaged flowering plants. Here, we used headspace collection to sample the volatiles emitted by A. lucorum-damaged flowering R. communis plants, and employed gas chromatography-electroantennography (GC-EAD) to identify two electrophysiologically-active compounds. Active compounds were identified as m-cymene and 4′-ethyl-acetophenone. Electrophysiological activities were confirmed by EAG, with a gradient of five doses of each compound eliciting significant antennal responses. Next, in Y-tube olfactometer bioassays, female P. spretus were attracted to two synthetic volatile compounds at two different concentrations (10 mg/ml and 100 mg/ml). Under field conditions, A. lucorum parasitism rates – as recorded in volatile-baited barrel traps – for the two compounds were significantly higher than those for mineral oil (control). Our findings emphasize the important role of herbivore-induced plant volatiles in the P. spretus host selection process, and provide a potential way to enhance in-field parasitoid populations and improve biological control of A. lucorum.

Suboptimal oviposition of tephritid flies supports parasitoid wasps

1. Female insects lay eggs on low‐quality plants, resulting in progeny with no or low reproductive potential; this is referred to as ‘suboptimal oviposition’ in this study.2. Here, it is reported that suboptimal oviposition of a tephritid fly species (Tephritis femoralis) supports the populations of parasitoid wasp species in a Tibetan alpine meadow.3. Suboptimal oviposition was confirmed because the adult flies emerging from Asteraceae species Anaphalis flavescens flowerheads did not survive cold winters.4. DNA barcoding of puparia indicated that tephritid larvae developing from suboptimal oviposition hosted populations of at least five parasitoid wasp species. Consequently, suboptimal oviposition has significant effects on parasitoid population dynamics and species diversity.

The Influence of Temperature Variation on Life History Parameters and Thermal Performance Curves of Tamarixia radiata (Hymenoptera: Eulophidae), a Parasitoid of the Asian Citrus Psyllid (Hemiptera: Liviidae).

This study examined the effects of seven constant and fluctuating temperature profiles with corresponding averages of 12 to 38°C on the life history of the Punjab, Pakistan-sourced Tamarixia radiata (Waterston) released in California for biological control of Diaphorina citri Kuwayama. One linear and seven nonlinear regression functions were fit to egg-to-adult development rate data to characterize thermal performance curves. Temperature fluctuations significantly affected both development and longevity of T. radiata. Estimates of degree-days predicted by the linear model were 30% higher for the fluctuating regime than the constant regime. Nonlinear model estimations of theoretical minimum and maximum developmental thresholds were lower for the fluctuating regime when compared to the constant regime. These predictions align with experimental observations. Parasitoids reared under fluctuating profiles at low average temperatures developed faster (15°C) and survived longer (15-20°C) when compared to those reared under constant regimes with corresponding means. In contrast, high average fluctuating temperatures produced parasitoids with an extended developmental period (35°C) and reduced longevity (30-35°C). A meta-analysis of published T. radiata development datasets, together with the results of this study, indicated convergence in degree-days and theoretical minimum developmental thresholds among geographically distinct parasitoid populations. These findings demonstrate the significant effects of temperature on T. radiata life history and have important implications for optimization of mass-rearing and release efforts, improvement of predictions from climate modeling, and comparison of T. radiata population performance across climatic gradients and geographic regions.

Sampling Methods for Adventive Trissolcus japonicus (Hymenoptera: Scelionidae) in a Wild Tree Host of Halyomorpha halys (Hemiptera: Pentatomidae).

Halyomorpha halys (Stål) (Hemiptera: Pentatomidae) is an invasive pest that has established in much of the United States. Adventive populations of an effective Asian egg parasitoid of H. halys, Trissolcus japonicus (Ashmead) (Hymenoptera: Scelionidae), have been detected in several states, including Virginia, and its geographic range is expanding. Documenting changes in its distribution and abundance have thus become key research priorities. For these specific purposes, surveillance of T. japonicus over large geographic areas using sentinel H. halys egg masses may not be optimally efficient, and examination of alternative sampling tactics is warranted. In 2016, sentinel H. halys egg masses were deployed as vertical transects in the canopy of female Ailanthus altissima (Mill.) Swingle (Sapindales: Simaroubaceae) in Virginia. A brief follow-up study in 2016 using yellow sticky traps deployed in the same trees yielded captures of T. japonicus, leading to a comparison of vertical transects of sentinel eggs and yellow sticky traps in 2017. Both methods yielded T. japonicus detections only in the middle and upper tree canopies, whereas other known H. halys parasitoids were detected in the lower, middle, or upper canopies. Based on this information, a method for deploying yellow sticky traps in the middle canopy of H. halys host trees was assessed in 2017, yielding T. japonicus captures. A comparison of estimated time inputs revealed that traps were more efficient than sentinel eggs in this regard. Results are discussed in relation to the utility of each sampling method to address specific questions about the range expansion and ecology of T. japonicus.