Abstract
The invasion of numerous countries by the armored scale Aulacaspis yasumatsui Takagi has caused widespread mortality of host Cycas species. Few studies have looked at reproductive biology responses of host plants to the herbivore. This study was conducted to determine the influence of direct Cycas seed integument infestation of A. yasumatsui on germination and seedling performance. An observational study in a Tinian ex situ Cycas micronesica K.D. Hill garden revealed that germination percentage was reduced two-thirds by heavy pre-harvest integument infestation, and more than half of the seedlings from infested seeds died in the nursery. Multi-year mortality of plants was six times greater for plants from habitats with infested seeds than for plants from minimally infested habitats. Stem height of nine-year-old plants from habitats with infested seeds was 64% of that of plants from habitats with un-infested seeds. A controlled study in a Philippine ex situ C. micronesica and Cycas edentata de Laub. garden corroborated these findings. Germination of infested seeds was about 30% of that for un-infested seeds. Seedling mortality in the nursery following experimental infestation of seed integuments with A. yasumatsui during seed maturation was about 50%, but was minimal for seedlings from un-infested seeds. These results indicate that limitations in regeneration and recruitment of host Cycas plants following A. yasumatsui herbivory may be partly due to the influence of direct seed infestations. Conservationists may use this new knowledge to improve in situ seed selection criteria and use prophylactic treatments to ensure lack of integument infestations for ex situ gardens.
Highlights
The armored scale A. yasumatsui has been invading new territories in recent years to threaten native and cultivated host cycad plants [1]
Cycas micronesica seeds were harvested throughout Guam from 219 female trees beginning January 2006 and segregated among sites defined as 15 areas of occupancy
The armored scale was present in every area of occupancy at the time of seed harvests, the density of infestations was highly heterogeneous among the individual trees and locations
Summary
The armored scale A. yasumatsui has been invading new territories in recent years to threaten native and cultivated host cycad plants [1]. The high-density native C. micronesica population allowed the scale to rapidly spread throughout the island from the initial infestation site. The density of scale infestations exhibited substantial spatiotemporal variations among the areas of occupancy for several years as the non-native herbivore and predator interacted with the native host plant and other organisms [4]. This insular case study illuminated numerous developments about how the host plants responded to A. yasumatsui damage. Regeneration and recruitment of the host species were subsequently terminated by the invasion [7]
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