Effects of Light and Water Availability on the Performance of Hemlock Woolly Adelgid (Hemiptera: Adelgidae)

Eastern hemlock (Tsuga canadensis (L.) Carriere) is a dominant shade-tolerant tree in northeastern United States that has been declining since the arrival of the hemlock woolly adelgid (Adelges tsugae Annand). Determining where A. tsugae settles under different abiotic conditions is important in understanding the insect’s expansion. Resource availability such as light and water can affect herbivore selectivity and damage. We examined how A. tsugae settlement and survival were affected by differences in light intensity and water availability, and how adelgid affected tree performance growing in these different abiotic treatments. In a greenhouse at the University of Rhode Island, we conducted an experiment in which the factors light (full-sun, shaded), water (water-stressed, watered), and adelgid (infested, insect-free) were fully crossed for a total of eight treatments (20 two-year-old hemlock saplings per treatment). We measured photosynthesis, transpiration, water potential, relative water content, adelgid density, and survival throughout the experiment. Adelgid settlement was higher on the old-growth foliage of shaded and water-stressed trees, but their survival was not altered by foliage age or either abiotic factor. The trees responded more to the light treatments than the water treatments. Light treatments caused a difference in relative water content, photosynthetic rate, transpiration, and water potential; however, water availability did not alter these variables. Adelgid did not enhance the impact of these abiotic treatments. Further studies are needed to get a better understanding of how these abiotic factors impact adelgid densities and tree health, and to determine why adelgid settlement was higher in the shaded treatments

Dropping behavior in the pea aphid: how does environmental context affect anti-predator responses?

The pea aphid Acyrthosiphon pisumHarris (Hemiptera: Aphididae) is a phloem-feeding insect whose antipredator defenses include kicking, walking away, and dropping from the plant. Aphid dropping, a risky and energetically costly antipredator behavior, can be increased by the release of aphid alarm pheromone; there is also evidence that insect density and plant health can affect the likelihood of aphids engaging in this behavior. We investigated whether interactions between alarm cues, insect density, and plant health can alter the dropping behavior of aphids in response to an artificial disturbance. The presence of the alarm pheromone E-β-farnesene resulted in a nearly 15-fold increase in aphid dropping behavior; the other two factors, however, did not affect dropping and none of the two- or three-way interactions were significant. This was surprising because aphids affected plant health: production of new plant biomass after 5 d of exposure to high aphid densities was 50% lower than in the control treatment. This research adds to our understanding of the factors affecting aphid antipredator behavior; the fact that neither aphid density nor feeding period impacted dropping may reflect the high energetic costs of this activity and an unwillingness to use it in any but the riskiest situations

Can \u3cem\u3eDarapsa myron\u3c/em\u3e (Lepidoptera: Sphingidae) Successfully Use the Invasive Plant \u3cem\u3eAmpelopsis brevipedunculata\u3c/em\u3e as a Food Resource?

Although biological invasions are generally thought to negatively impact native fauna, native herbivores that can utilize invasive plants may benefit. The East Coast of the United States has been invaded by the vitaceous plant Ampelopsis brevipedunculata. The invaded range of A. brevipedunculata overlaps with that of the native Vitis labrusca, a closely-related species that is a host plant for the native moth Darapsa myron (Lepidoptera: Sphingidae). We reared D. myron larvae on either V. labrusca or A. brevipedunculata to assess whether development and survival differed on the two plant species. Larval growth and survival to pupation was only 5% on A. brevipedunculata compared to 30% on V. labrusca, suggesting that the invasive species is an unsuitable hostplant for D. myron

Genome sequencing of the sweetpotato whitefly Bemisia tabaci MED/Q

The sweetpotato whitefly Bemisia tabaci is a highly destructive agricultural and ornamental crop pest. It damages host plants through both phloem feeding and vectoring plant pathogens. Introductions of B. tabaci are difficult to quarantine and eradicate because of its high reproductive rates, broad host plant range, and insecticide resistance. A total of 791 Gb of raw DNA sequence from whole genome shotgun sequencing, and 13 BAC pooling libraries were generated by Illumina sequencing using different combinations of mate-pair and pair-end libraries. Assembly gave a final genome with a scaffold N50 of 437 kb, and a total length of 658 Mb. Annotation of repetitive elements and coding regions resulted in 265.0 Mb TEs (40.3%) and 20 786 protein-coding genes with putative gene family expansions, respectively. Phylogenetic analysis based on orthologs across 14 arthropod taxa suggested that MED/Q is clustered into a hemipteran clade containing A. pisum and is a sister lineage to a clade containing both R. prolixus and N. lugens. Genome completeness, as estimated using the CEGMA and Benchmarking Universal Single-Copy Orthologs pipelines, reached 96% and 79%. These MED/Q genomic resources lay a foundation for future ‘pan-genomic’ comparisons of invasive vs. noninvasive, invasive vs. invasive, and native vs. exotic Bemisia, which, in return, will open up new avenues of investigation into whitefly biology, evolution, and management

False Ring Formation in Eastern Hemlock Branches: Impacts of Hemlock Woolly Adelgid and Elongate Hemlock Scale

Herbivores can alter plant physiology through the induction of abnormal wood formation. Feeding by some insects induces the formation of false rings, a band of thick-walled latewood cells within the earlywood portion of the tree ring that reduces water transport. Hemlock woolly adelgid (Adelges tsugae Annand) and elongate hemlock scale (Fiorinia externa Ferris) are invasive insects that both feed on eastern hemlock [Tsuga canadensis (L.) CarriÈre]. Adelges tsugae has a greater effect on tree health than F. externa, but the mechanism underlying their differential effect is unknown. We explored the effects of these herbivores by assessing growth ring formation in branches of trees that had been experimentally infested for 4 yr with A. tsugae, F. externa, or neither insect. We measured false ring density, ring growth, and earlywood: latewood ratios in the two most recently deposited growth rings. Branches from A. tsugae-infested trees had 30% more false rings than branches from F. externa-infested trees and 50% more than branches from uninfested trees. In contrast, branches from F. externa-infested trees and control trees did not differ in false ring formation. Radial growth and earlywood: latewood ratios did not differ among treatments. Our results show that two invasive herbivores with piercing-sucking mouth parts have differing effects on false ring formation in eastern hemlock. These false rings may be the product of a systemic plant hypersensitive response to feeding by A. tsugae on hemlock stems. If false rings are responsible for or symptomatic of hemlock water stress, this may provide a potential explanation for the relatively large effect of A. tsugae infestations on tree health

Datana drexelii (Lepidoptera: Notododontidae) occurrence and larval survival on highbush blueberry cultivars

Plant genotype influences plant suitability to herbivores; domesticated plants selected for properties such as high fruit yield may be particularly vulnerable to herbivory. Cultivated strains of highbush blueberry, Vaccinium corymbosum L. can be high-quality hosts for larvae of the gregariously-feeding notodontid Datana drexelii (Hy. Edwards). We conducted an experiment assessing D. drexelii larval survival and pupal weight when fed foliage from five blueberry cultivars: ‘Bluecrop’, ‘Bluetta’, ‘Blueray’, ‘Lateblue’, and ‘Jersey’. We complemented this experimental work with repeated bush-level surveys of a managed blueberry patch for naturally occurring D. drexelii larval clusters. Larval survival and pupal weight were significantly higher on ‘Lateblue’ foliage than from the ‘Bluecrop’, ‘Bluetta’, and ‘Jersey’ cultivars. The blueberry patch surveys found more D. drexelii larval clusters on ‘Bluehaven’, ‘Collins’, and ‘Darrow’ bushes than on the cultivars ‘Earliblue’ and ‘Jersey’. The low D. drexelii occurrence and performance on the ‘Jersey’ cultivar suggests that this variety may be appropriate for areas where this pest is common; conversely, their high occurrence on ‘Bluehaven’ ‘Collins’, and ‘Darrow’ suggests that these cultivars may be particularly vulnerable. Cultivar-level variation in herbivore vulnerability highlights how understanding plant-pest interactions can help manage agricultural species

A Comparison of Plants and Animals in Their Responses to Risk of Consumption

Both plants and animals reduce their risk of being eaten by detecting and responding to herbivore and predator cues. Plants tend to be less mobile and rely on more local information perceived with widely dispersed and redundant tissues. As such, plants can more easily multi-task. Plants are more tolerant of damage and use damage to their own tissues as reliable cues of risk; plants have a higher threshold before responding to the threat of herbivory. Plants also use diverse cues that include fragments of plant tissue and molecular patterns from herbivores, herbivore feeding, or microbial associates of herbivores. Instead of fleeing from attackers, plants reallocate valuable resources to organs at less risk. They minimize unnecessary defenses against unrealized risks and costs of failing to defend against actual risk. Plants can remember and learn, although these abilities are poorly understood

\u3cem\u3eTomato Yellow Leaf Curl Virus\u3c/em\u3e Infection Alters \u3cem\u3eBemisia tabaci\u3c/em\u3e MED (Hemiptera: Aleyrodidae) Vulnerability to Flupyradifurone

The whitefly, Bemisia tabaci Gennadius, is a major phloem-feeding pest of agricultural crops that is also an important vector of many plant diseases. The B. tabaci Mediterranean (‘MED’) biotype is a particularly effective vector of Tomato yellow leaf curl virus (TYLCV), a devastating plant pathogen. Although insecticides play an important role in the control of MED and TYLCV, little is known about how TYLCV infection affects MED susceptibility to insecticides. We conducted research addressing how MED susceptibility to flupyradifurone, the first commercially available systemic control agent derived from the butenolide class of insecticides, was affected by TYLCV infection. We first conducted bioassays determining the LC15 and LC50 for control and viruliferous MED feeding on either water- or insecticide-treated plants. We next measured several demographic parameters of control and viruliferous MED exposed to either insecticide- or water-treated plants. TYLCV infection increased MED tolerance of flupyradifurone: the LC15 and LC50 of viruliferous MED were double that of uninfected MED. Viral infection also altered MED demographic responses to flupyradifurone, but in an inconsistent manner. Although the ability of TYLCV and other persistently transmitted viruses to benefit Bemisia via manipulation of host plant defense is well known, this appears to be the first example of virally mediated changes in vector susceptibility to an insecticide

Hemlock Woolly Adelgid in the Eastern United States: What Have We Learned?

Adelges tsugae (Hemlock Woolly Adelgid) is a small piercing-sucking insect that feeds on hemlock trees (Tsuga spp.). Native to Asia and the Pacific Northwest, the Hemlock Woolly Adelgid is invasive in the eastern United States where it attacks Tsuga canadensis (Eastern Hemlock) and T. caroliniana (Carolina Hemlock). It is currently found in 19 eastern states and has caused extensive mortality to hemlock forests. The ecological and economic impacts of this pest are significant, widespread, and often difficult to quantify. As the Hemlock Woolly Adelgid continues to disperse throughout the range of Eastern and Carolina Hemlocks, management techniques aimed at controlling it are being researched, implemented, and assessed. This introductory paper provides an overview of the biology, life cycle, ecology, and history of this pest in the eastern US as a foundation for this special issue