Source and Sink Relations Mediate Depletion of Intrinsic Cycad Seed Carbohydrates by Aulacaspis yasumatsui Infestation

Abstract

<jats:p>Ubiquitous <jats:italic>Aulacaspsis yasumatsui</jats:italic> Takagi infestations of Guam’s <jats:italic>Cycas micronesica</jats:italic> K.D. Hill trees cause direct herbivory of most exposed organ surfaces, including developing naked ovules and seeds. The nonstructural carbohydrates of infested vs. noninfested seeds were quantified to understand more fully the influences on seed quality for propagation purposes. Two studies compared seeds from healthy trees with those of unhealthy trees suffering from whole-tree <jats:italic>A. yasumatsui</jats:italic> infestations. The sugars fructose, glucose, maltose, and sucrose were in greater concentrations and herbivory reduced these free sugars by a greater percentage in sarcotesta tissue than in sclerotesta and gametophyte tissues. Starch concentration was greatest in gametophyte tissue, but herbivory reduced starch by a greater percentage in sarcotesta tissue. A third study was used to manipulate seeds of unhealthy infested trees such that some seeds were uninfested and some seeds were infested and revealed the nonstructural carbohydrates of the uninfested seeds were greater than those of the infested seeds in patterns that were similar to those when the entire tree was protected from herbivory. The combined results indicated that both source and sink relations were involved in the reductions of seed carbohydrates by <jats:italic>A. yasumatsui</jats:italic> herbivory. The reduction in seed resource pool by the herbivore feeding may be one of the mechanisms that results in reduced germination percentage and increased seedling mortality.</jats:p>

Aulacaspis yasumatsui Delivers a Blow to International Cycad Horticulture

“…In Guam, highly disparate germination performance of C. micronesica seeds among numerous habitats was observed, whereby the percentage germination of seeds that were free of A. yasumatsui infestation was six times greater than that of seeds directly infested by the scales [55]. These observations led to manipulative studies which determined that the carbohydrates in gametophyte and sarcotesta tissues were greatly affected by A. yasumatsui herbivory.…”

“…Howard et al [3] were the first to determine the efficacy of imidacloprid for controlling A. yasumatsui, and this systemic insecticide may require the least amount of labor for chemical control of the scale. This systemic insecticide has been used for A. yasumatsui control on C. micronesica to enable in situ research on horticultural and physiological questions [55,56,91,98].…”

Cycas micronesica Stem Carbohydrates Decline Following Leaf and Male Cone Growth Events

“…The plot was positioned at 20-60 m above sea level, aspect was 120-150 • , and mature plant density was 1050 stems per ha. More details for the site are contained elsewhere [7,15,16]. The edaphic substrates at this site were coralline soils formed in slope alluvium, loess, and residuum overlying limestone (clayey-skeletal, gibbsitic, nonacid, isohyperthermic Lithic Ustorthents) [17].…”

Tree conservation can be constrained by agents from conservation permitting and funding agencies

“…Indeed, ecosystem changes can be misunderstood in insular settings if consistent monitoring is not used [50]. This wise approach of a funding agency enabled the accumulation of the only existing long-term C. micronesica survival data set throughout three islands and has resulted in numerous peer-reviewed articles that are available to inform future C. micronesica conservation decisions [51][52][53][54][55][56][57][58][59][60][61][62][63][64][65][66][67][68].…”