Sequential sampling plans for Orgyia trigotephras infesting Quercus coccifera forests in North Africa

The tussock moth, Orgyia trigotephras Boisduval (Lepidoptera: Erebidae), is one of the main emerging pests of kermes oak, Quercus coccifera L. (Fagaceae), in the Mediterranean area, where it can cause the defoliation of several hectares of forests during its population outbreaks. Despite this, no specific sampling procedures to properly estimate the population density of this pest have been developed yet. The aims of this research were to develop and compare enumerative and binomial sequential sampling plans to estimate the population density of O. trigotephras in forest environments. Data were collected in four forest stands dominated by Q. coccifera in Tunisia for 7 years (from 2013 to 2019) to take into consideration the potential spatio-temporal variability in pest density. Plant community composition was determined at the beginning of the experimental trials, and enumerative and binomial sampling plans were developed at precision levels of 0.15 and 0.25. Over the entire sampling period, the average O. trigotephras egg batch density differed significantly among sites. Sample sizes of enumerative sampling plans were approximately 39 and 109 trees to estimate an average density of 0.50 O. trigotephras egg batches per tree at the precision levels of 0.25 and 0.15, respectively. Instead, binomial sequential sampling plans required smaller sampling sizes than the enumerative sampling plan. Our findings represent the baseline to develop a program for monitoring O. trigotephras at a large spatial scale.