Prediction and control of the nun moth Lymantria monacha L. – Lidia Sukovata

Abstract
The aim of this work was to improve the nun moth pest management system in Poland using current knowledge and the results of studies conducted in 2001-2008. The scope of research included:

1. the development of a method for identifying permanent outbreak epicentres (foci),
2. the development of models based on meteorological data for mid-term prediction of nun moth outbreaks,
3. an estimation of the relationship between larval frass drop and the number of larvae in a tree crown,
4. an estimation of the dependence of fecundity on certain characteristics of the female pupa and moth,
5. the development of additional criteria for determining outbreak phases based on the range of values available for fecundity,
6. the development of a nun moth mating disruption technique.

A definition of a permanent outbreak epicentre was introduced, and a simple method for identifying and locating permanent outbreak epicentres (foci) was developed. It was based on two assumptions:

1. the forest is considered a permanent outbreak epicentre if a medium to high forest threat has been observed at lest twice in the same forest over a long-term period (58 years in this case);
2. if the threat remained at a similar level in consecutive years within one outbreak, it should be counted only once. Nine logit and discriminant models were developed on the basis of meteorological data from the period of 1951-2004. They allow the nun moth outbreak to be predicted one or two years prior to its onset.

An indirect method for the estimation of nun moth fecundity was developed using regression functions describing the relationships between fecundity and weight, width or length of a female pupa or the length of the female moth’s forewing. Criteria for determining outbreak phases were also proposed. The direct dependence of frass drop on nun moth larval population density was revealed and the equation was developed to estimate the number of larvae in a crown on the basis of the number of frass pellets per 1 m² of cotton trap per day.

As an alternative to chemical insecticides, mating disruption technique using a new pheromone formulation was developed to control the nun moth populations. It was found that a dose of the 1% formulation should not be lower than 8 g of an active ingredient per ha  when uniformly covering the entire threatened forest. The higher the nun moth population density, the higher the pheromone dosage should be. Effective mating disruption can also be achieved when the pheromone formulation at the dose higher than 16 g a.i./ha is sprayed in swaths with gaps not wider than 80 m. The main principle of the use of the nun moth mating disruption is that it should be applied to epicenters during the increasing phase of an outbreak to prevent the growth and spread of the population.

All the elements mentioned above were used to develop an improved system of the nun moth pest management.