2018 ASHS Annual Conference

Scale-infested cycad leaves were sampled on the island of Guam in a wide range of habitats in 2017 and 2018 to determine the extent of parasitoid control of the scale. The sampling unit was a leaflet selected from five trees per habitat during each sampling date. The number of scales were counted with a hand lens and parasitoids were reared in a growth chamber at 60% relative humidity. Infested leaflets were transferred to new rearing vessels after 48 hour intervals and returned to the growth chamber. Insects were rinsed with 70% EtOH and parasitoids were counted with the aid of a microscope. The abaxial leaflet surfaces harbored greater numbers of scale than the adaxial surfaces. In a Northern Guam site where parasitoids were first fortuitously discovered in 2013, only 20% of the samples yielded parasitoids. For each geographic site, the presence of parasitoids on one sampling date did not always lead to evidence of parasitoids at a later sampling date. The number of parasitized scales was minimal despite the widespread geographic occurrence of the parasitoids. Several native and exotic Cycas cycad species were historically heavily used in the commercial and residential landscapes of Guam, and the recent invasion of the cycad Aulacaspis scale (CAS) Aulacaspis yasumatsui Takagi has devastated these cycad populations. These results provide the first evidence that scale parasitoids are established throughout most of the island, but they are not effectively controlling the scale infestations. This case study is an example of how the horticulture profession can aid in responding to an ecological disaster.