14Although sap-feeding insects are known to negatively affect plant growth and physiology, less is 15 known about sap-feeding insects on woody plants. Adelges tsugae (Annand Hemiptera: 16 Adelgidae), the hemlock woolly adelgid, is an invasive sap-feeding insect in eastern North 17America that feeds on and kills Tsuga canadensis (L. Carrière), eastern hemlock. In the summer, 18 newly hatched nymphs crawl to young unattacked tissue, settle and immediately enter diapause 19 (aestivation) while attached to hemlock. We assessed the effect of A. tsugae infestation on T.

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.

No abstract

Invasive herbivores can cause widespread dieback of na€ ıve native hosts in the invaded range. Some consume leaves, some bore through wood, whereas others, such as piercing-sucking insects, alter plant resource allocation through changes to source-sink dynamics and depletion of long-term stores. Invasive sap-sucking herbivores that target cells critical to resource transport and storage may have particularly large effects. Herbivory by two exotic hemipterans, hemlock woolly adelgid (HWA), Adelges tsugae Annand (Adelgidae), and elongate hemlock scale (EHS), Fiorinia externa Ferris (Diaspididae), have very different effects on eastern hemlock, Tsuga canadensis (L.) Carri ere (Pinaceae). Although these insects differ in both timing and feeding site on their hemlock host, the reasons for their differential effects are poorly understood. Here, using potted seedlings in a common garden, we examined the effects of these two herbivores on resource uptake and allocation immediately after an initial attack. We labeled the plants with a single pulse of NO 3 every third day to obtain a whole-plant perspective on resource uptake and allocation. After 10 weeks of controlled infestation, plants were measured and divided into tissue types (needles, branches, main stem, and roots). In each tissue we quantified biomass, 13 C, 15 N, total carbon (C), nitrogen (N), protein, and starch pools. Hemlock woolly adelgid feeding decreased new needle biomass by 34%, increased 13 C allocation to roots and main stems by 130%, and increased 15 N allocation to old foliage by 18%. Hemlock woolly adelgid infestation also resulted in increased starch storage in old branches over new needles, and marginally increased protein content plant-wide. Elongate hemlock scale infestation resulted in a different growth pattern, with a 27% increase in biomass allocation to the main stem. Elongate hemlock scale also caused a 23% increase in N allocation to roots and main stem. Increases in resource allocation to main stem and belowground may indicate herbivoreinduced changes to storage patterns, or compensatory increased fine root growth to facilitate nutrient and water uptake. These resource allocation effects likely underlie the rapid and dramatic decline of hemlock in response to HWA feeding, and the considerably milder effects of EHS feeding.

Prey have evolved a number of defenses against predation, and predators have developed means of countering these protective measures. Although caterpillars of the monarch butterfly, Danaus plexippus L., are defended by cardenolides sequestered from their host plants, the Chinese mantid Tenodera sinensis Saussure guts the caterpillar before consuming the rest of the body. We hypothesized that this gutting behavior might be driven by the heterogeneous quality of prey tissue with respect to toxicity and/or nutrients. We conducted behavioral trials in which mantids were offered cardenolide-containing and cardenolide-free D. plexippus caterpillars and butterflies. In addition, we fed mantids starved and unstarved D. plexippus caterpillars from each cardenolide treatment and nontoxic Ostrinia nubilalis Hübner caterpillars. These trials were coupled with elemental analysis of the gut and body tissues of both D. plexippus caterpillars and corn borers. Cardenolides did not affect mantid behavior: mantids gutted both cardenolide-containing and cardenolide-free caterpillars. In contrast, mantids consumed both O. nubilalis and starved D. plexippus caterpillars entirely. Danaus plexippus body tissue has a lower C:N ratio than their gut contents, while O. nubilalis have similar ratios; gutting may reflect the mantid's ability to regulate nutrient uptake. Our results suggest that post-capture prey processing by mantids is likely driven by a sophisticated assessment of resource quality.