Development of Enumerative and Binomial Sequential Sampling Plans for Monitoring Lymantria dispar (L.) (Lepidoptera Erebidae) in Mediterranean Oak Forests

Abstract

Lymantria dispar is the main threat to Mediterranean forests. Sampling methods used for monitoring the pest population density are generally very time-consuming for practical purposes, such as the delimitation of infested areas for control programs. Enumerative and binomial sequential sampling plans were developed using data collected in cork oak forests in Sardinia (Italy). The Taylor’s power law (TPL) was used to evaluate the degree of aggregation of L. dispar egg masses among trees and to develop enumerative sampling plans at precision levels of 0.10 and 0.25 using the Green’s method. Furthermore, binomial plans were computed by Wald’s sequential probability ratio test. Lymantria dispar egg masses on trees were significantly aggregated and the degree of aggregation was similar in all population development phases. Overall, only 31 cork oak trees are to be monitored at the economic damage threshold of 2.5 egg masses/tree with a precision level of 0.25. Binomial sequential sampling plans also required lower sampling sizes (26.9–31.4 trees) than conventional sampling plans. Enumerative and binomial sampling plans could represent suitable methods for sampling L. dispar egg masses in Mediterranean forests, with the practical advantage of lower cost and time consumption than standard sampling plans.

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

“…Thus, our results are based on the analysis of different population development phases, which reinforces the validity of our sampling plans. In fact, developing sampling plans with data from different population development phases allows sampling plans to be considered valid even when the population development phase is unknown (Mannu et al., 2022). However, several factors that can potentially influence the population density of O. trigotephras should be taken into account to improve the reliability of population estimates.…”

“…Among sequential sampling procedures, the enumerative sampling is generally more precise than the binomial sampling but requires more sampling time to count the target pest population. However, as reported for forest pests showing temporal fluctuation in population density, sequential sampling plans based on enumerative sampling have technical limitations as a high number of samples is required during years of low population levels (Mannu et al., 2022). In line with this, a sampling plan for a forest pest such as O. trigotephras should provide accurate estimates of the occurrence of harmful pest densities rather than determining population densities.…”

“…At the same level of precision, we showed that the binomial sampling plan for O. trigotephras based on the KS empirical model required a smaller sample size (i.e., trees) than that estimated for the enumerative sampling plan and for the NB‐based binomial sampling plan. For decision‐making purposes, such as identifying when an economic damage threshold is reached to take decisions for pest control, binomial sampling could be considered more suitable and less labor intensive than enumerative sampling for forest defoliators (Mannu et al., 2022). The binomial samplings performed in our study do not provide information on the population density per unit area.…”

“…In the last decade, severe outbreaks of O. trigotephras occurred in the Mediterranean area, thus causing the defoliation of several hectares of forests (Bella et al, 2011;Ezzine & Ben Jamâa, 2010). As for other defoliators infesting Quercus species in the Mediterranean basin area (Lentini et al, 2020;Mannu et al, 2020Mannu et al, , 2022, the monitoring of O. trigotephras should be of primary interest to estimate its population density and predict the risk of defoliation. The count of egg masses on trees is considered the most suitable sampling method to estimate the O. trigotephras population density in infested forest areas (Ezzine et al, 2015;Ezzine & Ben Jamâa, 2010).…”

Lymantria dispar (L.) (Lepidoptera: Erebidae): Current Status of Biology, Ecology, and Management in Europe with Notes from North America

“…Current control measures include chemical and mechanical methods, natural predators, and silvicultural practices. In addition, the economic damage threshold of 100 egg clusters per 40 trees, which are equivalent to an average number of 2.5 egg clusters/tree, is used to make decisions about the initiation of management tactics [182][183][184].…”