Abstract
The scale insect, Aulacaspic marina Takagi and Williams, has killed a large number of mangroves, Rhizophora mucronata Lamk., planted in abandoned shrimp ponds on Bali Island, Indonesia. In this study, we developed a control method for A. marina using seawater. An examination of the relationship between tree height and leaf damage in an R. mucronata plantation indicated that A. marina did not damage R. mucronata when the saplings were lower than the highest sea level of the spring tide, resulting in the saplings being periodically submerged in seawater by changes in tidal level. To examine how seawater submergence prevents this damage, crawlers of A. marina were artificially transferred to R. mucronata seedlings on which seawater or fresh water were sprayed daily. The crawlers settled on more than 90% of the leaves in fresh-water-sprayed and unsprayed seedlings but only on 37% of the leaves in seawater-sprayed seedlings, indicating that seawater helped prevent crawler settlement. To develop a control method using this seawater effect, seawater was sprayed on damaged saplings in an R. mucronata plantation at weekly intervals using two types of sprayers. In these saplings, leaf damage was lower than that of control saplings after spraying for five or nine weeks for each type of sprayer, respectively. This indicates that periodic spraying of seawater is an effective control measure against A. marina.
