Host Plant Associations of an Entomopathogenic Variety of the Fungus, Colletotrichum acutatum, Recovered from the Elongate Hemlock Scale, Fiorinia externa

A fungal epizootic has been detected in populations of the scale Fiorinia externa Ferris (Hemiptera: Diaspididae) in the eastern hemlock, Tsuga canadensis (L.) Carrière (Pinales: Pinaceae), of several northeastern states. Colletotrichum acutatum Simmonds var. fioriniae Marcelino and Gouli var. nov. inedit (Phyllachorales: Phyllachoraceae), a well-known plant pathogen, was the most commonly recovered fungus from these infected scales. This is the second report of a Colletotrichum sp. infecting scale insects. In Brazil C. gloeosporioides f. sp. ortheziidae recovered from Orthezia praelonga is under development as a biopesticide for citrus production. C. acutatum was detected growing endophytically in 28 species of plants within the epizootic areas. DNA sequences of the High Mobility Box at the MAT 1–2, mating type gene indicate that Colletotrichum sp. isolates recovered from scale insects and plants within epizootic areas were identical. Results from plant bioassays showed that this entomopathogenic Colletotrichum variety grew endophytically in all of the plants tested without causing external symptoms or signs of infection, with the exception of strawberry plants where mild symptoms of infection were observed. The implications of these findings with respect to the use of this fungus as a biological control agent are discussed

Contrasting effects of two exotic invasive hemipterans on whole-plant resource allocation in a declining conifer

Invasive herbivores can cause widespread dieback of naïve 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.) Carrière (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 13CO2 and a supply of 15NH415NO3 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, 13C, 15N, total carbon (C), nitrogen (N), protein, and starch pools. Hemlock woolly adelgid feeding decreased new needle biomass by 34%, increased 13C allocation to roots and main stems by 130%, and increased 15N 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 herbivore-induced 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. Entomologia Experimentalis et Applicat