Stylet Bundle Morphology and Trophically Related Enzymes of the Hemlock Woolly Adelgid (Hemiptera: Adelgidae)

Abstract

The hemlock woolly adelgid, Adelges tsugae Annand (Hemiptera: Adelgidae), is a pest of eastern and Carolina hemlocks (Tsuga canadensis (L.) Carrière and Tsuga caroliniana Engelmann, respectively) in the eastern United States and has already caused catastrophic changes to eastern forests. As one of the significant exotic forest pests, it is imperative that the basic biology of hemlock woolly adelgid be understood for use in novel and improved management techniques. Scanning and transmission electron microscopy and enzyme assays were used to elucidate the feeding biology of hemlock woolly adelgid and are discussed in the context of the pest—plant interactions and the implications for host plant resistance. Morphological characters indicate that hemlock woolly adelgids may use labial sensilla and neural canals within the mandibular stylets to guide their stylets through close-range host acceptance processes. Stylet bundle insertion is likely assisted by external sheath material that secures the stylet bundle to the plant surface and mandibular dentitions that may assist entry into or within plant tissues. In addition, results support the theory that extra-oral digestion is likely used by hemlock woolly adelgid, suggested by both a narrow food canal and the presence of four trophically related enzymes (a trypsin-like enzyme, an amylase-like enzyme, peroxidase, and polyphenol oxidase). The presence of these enzymes also has implications for causing a systemic response in host trees.

Chronic impacts of invasive herbivores on a foundational forest species: a whole‐tree perspective

“…This extra-oral digestion is achieved via deployment of salivary enzymes like a-amylase to local feeding sites. Adelgid, a piercing-sucking herbivore, has been hypothesized to use a similar feeding strategy (Oten et al 2014). Our findings support this hypothesis: adelgid feeding for 4 yr led to a~30% reduction in starch levels in 1-yr needles (Fig.…”

“…Following herbivory, stored carbohydrates are frequently broken down and remobilized to compensate for tissue loss (Appel et al 2014). Adelgid, a piercing-sucking herbivore, has been hypothesized to use a similar feeding strategy (Oten et al 2014). Some herbivores, particularly piercing-sucking insects, exploit hosts and stored resources via extra-oral digestion of stored carbohydrates like starch.…”

Salivary gland structure of Ctenarytaina eucalypti (MASKELL, 1890) (Hemiptera) and phloem exudate in Eucalyptus globulus LABILLARDIÈRE, 1799 (Myrtaceae)

“…Production of quinones in the leaves of E. globulus leaves when infested by C. eucalypti was reported by TRONCOSO et al (2012). Cell-degrading enzymes, such as amylase, lipase and esterase, may enable C. eucalypti to pierce tissues of E. globulus (OTEN et al 2014, SHARMA et al 2013). Amylase and protease have been demonstrated in the saliva of Trioza jambolanae CRAWFORD, 1917 (Hemiptera: Psylloidea: Triozidae), which lives on Syzigium cumini LINNAEUS, 1753 (Myrtaceae) (RAJADURAI et al 1990).…”

Functional principles of steerable multi‐element probes in insects

“…pectinases) that degrade the connection between cells and thus soften the substrate (Boyd, Cohen & Alverson, 2002). Species relying on pectinases generally take intercellular paths (Miles, 1968;Pollard, 1973;Oten, Cohen & Hain, 2014), whereas those mainly relying on mechanical work take predominantly intracellular paths to reach their target tissues (Miles, 1968). Flaring of the mouthparts deep in the target tissue has also been reported, which might occur to enlarge the opening of the food canal (Cohen, 1990).…”

“…The watery saliva contains enzymes which can (i) soften the cell walls (e.g. Michael, 1989;Oten et al, 2014), (ii) help with digesting the food (Miles, 1972(Miles, , 1999, and (iii) inhibit the immune response of the plant (Miles, 1968(Miles, , 1999.…”