Woodpeckers (Picidae) are important natural enemies attacking emerald ash borer (EAB) Agrilus planipennis Fairmaire in North America. There can be considerable variation in predation levels within ...and between sites, and among different times of year; therefore, understanding what causes these differences is necessary for effectively predicting EAB population dynamics. We examined the temporal dynamics of woodpecker predation on EAB in Michigan and Maryland, as well as how they were affected by season, region, resource availability, tree size and crown condition. In Michigan, we quantified predation in association with EAB developmental stages on different trees over 2 years, whereas, in Maryland, we recorded woodpecker attacks on the same trees for 1 year. Season was a significant predictor of woodpecker predation, with most occurring in winter when late‐instar larvae were abundant. Predation also was affected by crown condition and tree size. Additionally, predation levels were similar throughout the year in a region where generations are considered to be less synchronized, representing a more consistent resource for woodpeckers. The present study highlights the various factors affecting woodpecker predation over time. The results demonstrate the importance of multi‐season studies of interactions between invasive species and native natural enemies when aiming to fully understand their dynamics.
1. Predator and alternative food density are important factors influencing herbivore suppression by generalist predators. Herbivore suppression can be reduced if predators forage preferentially on ...alternative foods. Cannibalism can increase at high predator densities, further reducing herbivore suppression. However, complex interactions are possible, as alternative food can increase predator abundance and survival restoring top-down effects on herbivores. 2. In two species of carabid larvae (Poecilus chalcites and Anisodactylus ovularis), we studied how alternative foods (fly pupae and grass seeds) and predator density affect predation of black cutworm larvae and how alternative foods affect cannibalism among carabid larvae. 3. Adding alternative food to microcosms generally reduced total predation of cutworms. However, the strength of this effect was dependent on carabid species, larval density, and food type. 4. Increasing larval density from one to three per microcosm reduced per-capita predation by both species irrespective of alternative food treatment. 5. Alternative food reduced cannibalism in both carabid species and increased survival of carabid larvae in field plots, such that twice as many were captured in plots subsidised with pupae than plots with no alternative food. 6. These results provide new insight into the complex interactions that influence predator survival and herbivore suppression in resource diverse habitats by demonstrating the primacy of intraguild interactions among carabid larvae.
Emerald ash borer (EAB) Agrilus planipennis Fairmaire is an invasive non‐native woodboring beetle that has killed hundreds of millions of ash trees (Fraxinus spp.) in North America. Identifying the ...arthropod community associated with ash trees has been highlighted as an important research requirement in understanding the wider effects of EAB.
We harvested live ash trees infested with EAB at 37 sites in Maryland from 2011 to 2014 and collected a total of 2031 arthropods. All arthropods were identified to order and 94.6% were identified to family or below. The community comprised 13 orders, 60 families and 41 genera, with 28 arthropod species identified. Coleoptera, Diptera, Hymenoptera and Lepidoptera accounted for 98.3% of arthropods collected.
Data on changes in richness and diversity over time were fitted to second‐order polynomial models, corresponding with a transition in the dominant taxa from woodboring beetles (Cerambycidae) to parasitoids (Braconidae and Eulophidae). This resulted in changes to community composition as the EAB infestation intensified.
The findings of the present study provide further evidence of the diversity of arthropods at risk from EAB. Given the number of invasive non‐native insects threatening North American forests, establishing what taxa are present is important for predicting the likely broader impacts of these invasions.
Abstract
Halyomorpha halys (Stål), the brown marmorated stink bug, is a globally invasive stink bug species. Its first major outbreak was in the United States, where it has caused millions of dollars ...in damage, threatened livelihoods of specialty crop growers and impacted row crop growers, and become an extreme nuisance pest in and around dwellings. The BMSB IPM Working Group, funded by the Northeastern IPM Center, was central to providing a mechanism to form a multidisciplinary team and develop initial and subsequent research, Extension, regulatory and consumer priorities. Ultimately, a project team consisting of over 50 scientists from 11 institutions in 10 states obtained the largest ever USDA-NIFA Specialty Crop Research Initiative CAP grant, totaling over $10.7 million, to tackle this crisis over a 5-yr period (2011–2016). Researchers and Extension educators integrated stakeholder feedback throughout the course of the project, and priorities evolved according to needs of affected growers and public stakeholders. Initially, the team focused on identification of H. halys, its damage symptoms and crop-specific risks, and short-term mitigation strategies for crop protection. Subsequently, work focused on its biology, ecology, and behavior leading to the development of potential longer-term IPM tactics and landscape level management solutions, including biological control. This work continues under a second SCRI CAP grant (2016–2021). The information from the initial team reached an estimated 22,000 specialty crop stakeholder contacts via Extension efforts, and over 600 million people via mainstream media. We highlight the main lessons learned from coordinating a national response to the threat posed by H. halys to agriculture in the United States.
Habitat manipulation in the form of beetle banks and flowering insectary strips has been a successful method to increase natural enemy and alternative prey abundance. In this study, beetle banks and ...flowering insectary strips were combined to create conservation strips as refuge for a variety of natural enemies in golf course ecosystems. Conservation strips were installed in the roughs next to golf course fairways. Pitfall traps were used to monitor the abundance of predatory, parasitoid, alternative prey, and pest insects in the roughs and fairways near conservation strips and in roughs and fairways without conservation strips (controls). In addition, Agrotis ipsilon (Hufnagel) larvae were placed in the roughs and fairways to evaluate the effect of conservation strips on the predation of pests. Conservation strips were successful at increasing predator, parasitoid, and alternative prey abundance in golf course fairways and roughs overall. Increases were most evident within 4 m of conservation strips. Moreover, predation of A. ipsilon larvae was greater in fairways adjacent to conservation strips than fairways adjacent to roughs only. Differences in predation did not correspond to differences in predator abundance in the fairways, suggesting “predator abundance” may not be the most reliable estimate of the effect of habitat manipulations. These results suggest conservation strips could be an important new tool in conservation biological control on golf courses and may be applicable in other agro-ecosystems. Other methods of estimating and enhancing the effects of conservation strips are discussed.
Preserving arthropod predator abundance and diversity in agricultural ecosystems may reduce pest populations and subsequent loss in yield. However, since natural enemy species vary in their impact on ...pest populations, it is crucial to identify which predators are effective at reducing pest abundance. Leafrollers spend part of their life on the ground and part in the canopy of vineyards. In this experiment, predation of tethered leafrollers on the ground and in the vine canopy was compared in a New Zealand vineyard. Leafrollers in each stratum were recorded using video equipment to identify predators that were consuming leafrollers. A separate experiment investigated the behavior of
Epiphyas postvittana larvae when encountered by earwigs on vines or concealed within leaf shelters. Predation rates of leafrollers did not differ between the ground and canopy strata. However, predator activity, attack rate, and species richness were higher on the ground. Six predator taxa consumed leafrollers on the ground whereas only earwigs consumed leafrollers in the canopy. Earwigs were more active, and killed significantly more leafrollers in the canopy than on the ground, compensating for the relatively low activity and diversity of other predators in that stratum. This research demonstrates the value of video recording in biological control research, as it permits identification of the predators contributing to pest reduction. In addition, it highlights the need to understand the contributions of individual predator taxa to biological control to better conserve the ‘right diversity’ in agricultural systems and benefit from this ecosystem service.
We tested 10 cm × 10 cm mesh egg-sentinel envelopes (ESEs) containing emerald ash borer eggs on filter paper, and assessed how 2 different mesh sizes (0.5 mm and 1 mm) affected parasitism by Oobius ...agrili in the laboratory, and parasitism and predation in the field. Mesh size significantly affected parasitism in the laboratory, with the 0.5 mm mesh reducing parasitism by approximately 20% relative to the 1 mm mesh. Parasitism was much lower in the field with no significant difference among treatments, but the 0.5 mm mesh did significantly reduce predation by almost 50% in comparison to the 1 mm mesh. To reduce egg predation while enabling detectable levels of parasitism by O. agrili, we therefore recommend using mesh screen 0.5 mm wide to create ESEs for field deployment.
Habitat manipulation is a branch of conservation biological control in which vegetation complexity and diversity are increased in managed landscapes to provide food and other resources for arthropod ...natural enemies. This is often achieved by maintaining noncrop plant material such as flowering strips and beetle banks that provide natural enemies with nectar and pollen, alternative prey, shelter from disturbance, and overwintering sites. In most cases, plant material used in habitat manipulation programs is not native to the area in which it is planted. Using native plant species in conservation biological control could serve a dual function of suppressing pest arthropod outbreaks and promoting other valuable ecosystem services associated with native plant communities. We evaluated 10 plant species native to Maryland for their attractiveness to foliar and ground-dwelling natural enemies. Plants that showed particular promise were Monarda punctata, Pycnanthemum tenuifolium, and Eupatorium hyssopifolium, which generally harbored the greatest abundance of foliar predators and parasitoids, although abundance varied over time. Among ground-dwelling natural enemies, total predator and parasitoid abundance differed between plant species, but carabid and spider abundance did not. Matching certain plant species and their allied natural enemies with specific pest complexes may be enhanced by identifying the composition of natural enemy assemblages at different times of year and in both foliar and ground habitat strata.
•Emerald ash borer (EAB) has recently acquired white fringetree (WF) as a novel host.•Ability of Tetrastichus planipennisi (TP) to parasitize EAB in WF is demonstrated.•TP can parasitize EAB in WF, ...but at lower rates than in its known host green ash.•This indicates that WF may provide enemy free space from this biocontrol agent.
Emerald ash borer (Agrilus planipennis) is one of the most destructive, invasive forest pests in North America and is responsible for the death of hundreds of millions of ash trees (Fraxinus spp.) in its introduced host range. Recently, this invasive beetle was also discovered attacking the white fringetree (Chionanthus virginicus) in North America. In response to emerald ash borer’s lack of evolutionary history with this host plant, we hypothesize that this host range expansion will result in enemy free space from the introduced larval parasitoid Tetrastichus planipennisi. Here we conducted both No Choice and Choice assays to evaluate the parasitism response of T. planipennisi to the emerald ash borer larvae reared or inserted in white fringetree sticks vs sticks of the favored host plant, green ash (F. pennsylvanica). Additionally, we observed the host-finding behavior of T. planipennisi when given a choice with the two host plants infested with emerald ash borer larvae. The No Choice assay demonstrates that T. planipennisi is able to parasitize and successfully develop on emerald ash borer larvae reared in white fringetree sticks. Choice assays further show that T. planipennisi is capable of parasitizing suitable stages of emerald ash borer larvae inserted in white fringetree even with the presence of emerald ash borer infested green ash in the same assay arena. However, rates of the host larval parasitism by T. planipennisi were significantly lower in white fringetree sticks than in green ash sticks and T. planipennisi spent less time on white fringetree sticks than green ash. These findings suggest that emerald ash borer may experience partial enemy free space through the utilization of white fringetree as an alternative host to ash, and thus biological control of emerald ash borer in white fringetrees with T. planipennisi may be less effective than in ash trees.
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•Both Spathius agrili and Tetrastichus planipennisi were recovered in Maryland.•Only T. planipennisi has established and dispersed in Maryland.•Parasitism by T. planipennisi was ...positively associated with number of years post-release.•An exponential decrease model was fitted to the relationship between T. planipennisi parasitism and tree size.
Classical biological control can be an important tool for managing invasive species such as emerald ash borer (EAB), Agrilus planipennis Fairmaire. Emerald ash borer was first detected in Maryland in 2003, and the biological control program to manage this beetle in Maryland was initiated in 2009. Here we examine the establishment and abundance of two introduced parasitoids of EAB larvae (Spathius agrili Yang and Tetrastichus planipennisi Yang). Overall, 56,677 S. agrili and 191,506 T. planipennisi were released at 26 and 32 sites, respectively, from 2009 to 2014. Monitoring parasitoids involved debarking trees, and harvesting trees to place in rearing barrels, and was conducted at 47 sites (23 of which received parasitoids, and 24 of which served as controls) from 2010 to 2015. We recovered 77 S. agrili from 16 EAB larvae at six sites, and 1856 T. planipennisi from 110 EAB larvae at 19 sites. Percentage parasitism by T. planipennisi, and the mean percentage of trees containing T. planipennisi broods, were positively associated with the number of years post-release of the parasitoids (reaching 11.6% and 41.7% four years post-release, respectively). The relationship between T. planipennisi parasitism and tree size was best described by an exponential decrease model, with over 95% of parasitism occurring in trees with a diameter at breast height of <16cm. In conclusion, T. planipennisi has established populations and dispersed in Maryland, while S. agrili releases have been largely unsuccessful. These findings are a step towards optimizing EAB biological control release and recovery strategies, and are particularly pertinent for other states in the Mid-Atlantic region.
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