Characteristics of teak trees and stands driving infestations by Xyleutes ceramica (Walker, 1865) (Lepidoptera: Cossidae) in plantations in Thailand

The teak bee-hole borer (Xyleutes ceramica (Walker, 1865)) is widespread in northern Thailand and is considered the most serious pest of teak (Tectona grandis) in the country. The present study investigated the factors affecting the infestation of teak trees by this species in three plantations in northern Thailand at different spatial scales, including the tree, plot and stand levels. At each plantation, 48 plots evenly distributed in three different young stands (1-10 years), three medium-aged stands (11-20 years) and six old stands (exceeding 20 years) were sampled. At the plots, the number of current entrance holes of X. ceramica per teak tree was counted, and the characteristics of the trees and stands were assessed. A total of 1952 teak trees were sampled, 22.7% of which were infested by X. ceramica. According to our results, infestation was much more strongly affected by stand characteristics than by the characteristics of individual trees. Above all, understorey cover exhibited substantial effect with the infestation level being strongly limited in stands with dense understories. Additionally, young and medium-aged stands on better quality sites were found to be the most susceptible to infestation, and well-growing and/or damaged trees were preferred by the pest species. In conclusion, major recommendations for suppressing damage caused by X. ceramica include (a) promoting and maintaining the understorey above 30% cover, (b) planting mixed stands of commercial forest trees and (c) intensively monitoring the pest in young and medium-aged stands, especially those growing at good- and medium-quality sites.