Observed changes in mean temperature and increased frequency of extreme climate events have already impacted the distributions and phenologies of various organisms, including insects. Although some ...research has examined how parasitoids will respond to colder temperatures or experimental warming, we know relatively little about how increased variation in temperature and humidity could affect interactions between parasitoids and their hosts. Using a study system consisting of emerald ash borer (EAB), Agrilus planipennis, and its egg parasitoid Oobius agrili, we conducted environmentally controlled laboratory experiments to investigate how increased seasonal climate variation affected the synchrony of host–parasitoid interactions. We hypothesized that increased climate variation would lead to decreases in host and parasitoid survival, host fecundity, and percent parasitism (independent of host density), while also influencing percent diapause in parasitoids. EAB was reared in environmental chambers under four climate variation treatments (standard deviations in temperature of 1.24, 3.00, 3.60, and 4.79°C), while O. agrili experiments were conducted in the same environmental chambers using a 4 × 3 design (four climate variation treatments × 3 EAB egg densities). We found that EAB fecundity was negatively associated with temperature variation and that temperature variation altered the temporal egg laying distribution of EAB. Additionally, even moderate increases in temperature variation affected parasitoid emergence times, while decreasing percent parasitism and survival. Furthermore, percent diapause in parasitoids was positively associated with humidity variation. Our findings indicate that relatively small changes in the frequency and severity of extreme climate events have the potential to phenologically isolate emerging parasitoids from host eggs, which in the absence of alternative hosts could lead to localized extinctions. More broadly, these results indicate how climate change could affect various life history parameters in insects, and have implications for consumer–resource stability and biological control.
We observed the effect temperature and humidity variation had on a host‐parasite relationship, most notably, how it impacted the fecundity and mortality of both species, and the emergence time, % diapause and % parasitism of the parasatoid. Our findings suggest that significant climate variation, already observed in the newly invaded host range of USA, may decouple the phenological synchrony between host and parasitoid, diminishing the effectiveness of biological control methods. Furthermore, we suspect this decoupling to be a general trend in similar host‐parasitoid relationships.
The brown marmorated stink bug,
Halyomorpha halys
(Stål), is an invasive species native to regions of China, Japan, Korea, and Taiwan. In its native and introduced range,
H. halys
is considered a ...pest of tree fruits, vegetables, legumes, and ornamental trees. The highly polyphagous nature of this insect as well as its vast dispersal capabilities, require an integrated approach to management. Here we focus on the potential impact of indigenous natural enemies on
H. halys
in woody ornamental nurseries in Maryland, USA. We sampled naturally field laid
H. halys
egg masses for mortality and parasitism rates in 2012 and 2013. Overall, egg mortality averaged 54% for both years, and increased within season and between years. The largest source of mortality was from egg parasitoids with mean parasitism rates of 30.73 and 39.63% in 2012 and 2013, respectively. Mortality from predation was much lower and averaged 4.61% by chewing and 2.53% by sucking predators. We found seven species of Hymenopteran egg parasitoids attacking
H. halys
eggs, with
Anastatus reduvii
being the dominant species comprising 61.17 and 79.12% of all parasitoids in 2012 and 2013, respectively. The observed increase in parasitism over time and female biased sex ratio of parasitoids suggests that native parasitoids may be responding to the novel host,
H. halys
. Consequently, the use of these native eupelmid egg parasitoids in augmentative or conservation biological control may be a viable
H
.
halys
management strategy in ornamental nurseries.
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► Seed subsidies increased omnivorous carabid abundance by increasing aggregation and reducing emigration whereas pupae had little effect. ► Seeds and pupae reduced consumption of ...cutworm pests by omnivorous carabids. ► When seeds were present damage to corn seedlings increased compared to when pupae or no alternative food was present.
Conservation biological control tactics, such as beetle banks, that increase habitat complexity generally increase epigeal predator abundance. Habitat complexity also increases alternative food which can attract and sustain predators but may reduce predation of target pests. Our goal was to determine how alternative food from different trophic levels (fly pupae and seeds) affects behavior and biological control efficacy of omnivorous carabid beetles. Seed subsidies increased omnivorous carabid abundance more than pupae by increasing aggregation and reducing emigration. Laboratory experiment demonstrated that both omnivorous carabid species preferred seeds and pupae over cutworms. However, in field cages seeds but not pupae resulted in greater cutworm damage to corn seedlings. Our results indicate that omnivorous carabids have a stronger behavioral response to seeds than prey such that only seeds influence aggregation, emigration, and crop damage. Interestingly, whereas seeds increased omnivorous carabid abundance, pupae had no affect on carnivore abundance. Thus, carabid guild composition is skewed in favor of omnivores when seed density increases. An important finding was that the effect of seeds on behavior, predation, and crop damage was consistent among replicate carabid species suggesting our results pertain to other omnivorous species in resource diverse habitats.
Our results provide insight into the mechanisms underlying the unpredictable benefit of conservation biological control tactics that alter habitat complexity.
This study examined the influence of habitat structural complexity on the collective effects of top-down and bottom-up forces on herbivore abundance in urban landscapes. The persistence and varying ...complexity of urban landscapes set them apart from ephemeral agroecosystems and natural habitats where the majority of studies have been conducted. Using surveys and manipulative experiments. We explicitly tested the effect of natural enemies (enemies hypothesis), host plant quality, and herbivore movement on the abundance of the specialist insect herbivore, Stephanitis pyrioides, in landscapes of varying structural complexity. This herbivore was extremely abundant in simple landscapes and rare in complex ones. Natural enemies were the major force influencing abundance of S. pyrioides across habitat types. Generalist predators, particularly the spider Anyphaena celer, were more abundant in complex landscapes. Predator abundance was related to greater abundance of alternative prey in those landscapes. Stephanitis pyrioides survival was lower in complex habitats when exposed to endemic natural enemy populations. Laboratory feeding trials confirmed the more abundant predators consumed S. pyrioides. Host plant quality was not a strong force influencing patterns of S. pyrioides abundance. When predators were excluded, adult S. pyrioides survival was greater on azaleas grown in complex habitats, in opposition to the observed pattern of abundance. Similarly, complexity did not affect S. pyrioides immigration and emigration rates. The complexity of urban landscapes affects the strength of top-down forces on herbivorous insect populations by influencing alternative prey and generalist predator abundance. It is possible that habitats can be manipulated to promote the suppressive effects of generalist predators.
The invasive brown marmorated stink bug, Halyomorpha halys (Stål), has caused severe economic losses in the United States and is also a major nuisance pest invading homes. In diverse woody plant ...nurseries, favored host plants may be attacked at different times of the season and in different locations in the field. Knowledge of factors influencing H. halys abundance and simple methods to predict where H. halys are found and cause damage are needed to develop effective management strategies. In this study, we examined H. halys abundance on plants in tree nurseries as a function of distance from field edges (edge and core samples) and documented the abundance in tree nurseries adjoining different habitat types (corn, soybean, residential areas, and production sod). We conducted timed counts for H. halys on 2,016 individual trees belonging to 146 unique woody plant cultivars at two commercial tree nurseries in Maryland. Across three years of sampling, we found that H. halys nymphs and adults were more abundant at field edges (0–5mfrom edges) than in the core of fields (15–20mfrom edges). Proximity of soybean fields was associated with high nymph and adult abundance. Results indicate that monitoring efforts and intervention tactics for this invasive pest could be restricted to field edges, especially those close to soybean fields. We show clearly that spatial factors, especially distance from edge, strongly influence H. halys abundance in nurseries. This information may greatly simplify the development of any future management strategies.
With the introduction and establishment of exotic species, most ecosystems now contain both native and exotic plants and herbivores. Recent research identifies several factors that govern how ...specialist herbivores switch host plants upon introduction. Predicting the feeding ecology and impacts of introduced generalist species, however, remains difficult. Here, we examine how plant geographic origin, an indicator of shared co-evolutionary history, influences patterns of host use by a generalist, invasive herbivore, while accounting for variation in plant availability. The brown marmorated stink bug, Halyomorpha halys, is a highly polyphagous Asian herbivore and an economically important invasive pest in North America and Europe. In visual surveys of 220 plant taxa in commercial nurseries in Maryland, USA, H. halys was more abundant on non-Asian plants and selected these over Asian plants. The relationship between the relative use of plants and their availability was strongly positive but depended also on plant origin at two of our three sites, where the higher relative use of non-Asian plants was greatest for highly abundant taxa. These results highlight the importance of considering both plant origin and relative abundance in understanding the selection of host plants by invasive generalist herbivores in diverse, natural and urban forests.
Invasive plant-feeding insects cause billions of dollars in economics losses annually around the world. Understanding how they utilize different host plants directly informs their management. The ...highly invasive brown marmorated stink bug,
Halyomorpha halys
(Stål) (Hemiptera: Pentatomidae), has destroyed crops and invaded homes since its discovery in the U.S. in the mid-1990s. In this study, we test the hypothesis that in diverse resource environments, the presence and maturity of fruits on trees influences the abundance of
H. halys
. Observational surveys of the abundance of
H. halys
life stages (egg masses, nymphs, and adults) on 3884 trees of 223 cultivars in woody plant nurseries revealed that fruit maturity was a strong predictor of the seasonal abundance and within-tree distribution of
H. halys
. We next explicitly tested whether fruits themselves were the key resource for
H. halys
through a manipulative field experiment. Removal of fruits from trees suppressed stink bug abundance throughout the season. Despite being considered a broad feeding generalist, our results highlight that in landscapes with highly heterogeneous and ephemeral resources,
H. halys
specializes on finding mature fruits. Therefore,
H. halys
can be controlled by designing landscapes with fruitless varieties of popular trees, exploiting phenological mismatches between the pest and its host plants, and through targeted management of
H. halys
on fruiting trees in the landscape.
Biological invasions often have devastating impacts on ecosystems and economies, while facilitative interactions between invasive and native species are often overlooked. Here, we demonstrate how the ...invasive brown marmorated stink bug, Halyomotpha halys (Stål) (Hemiptera: Pentatomidae), facilitates native Hymenoptera by opening a novel feeding niche. In the invaded mid-Atlantic region of the United States, several species of native ants and wasps feed on wound exudates from stink bug feeding sites; these exudates have high sugar concentrations and are rapidly used by indigenous Hymenoptera. Positive facilitative interactions between invasive and keystone native species such as ants may have far reaching impacts on invaded ecosystems.
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