# Modeling Pine Caterpillar, Dendrolimus spectabilis (Lepidoptera: Lasiocampidae), Population Dynamics with a Stage-Structured Matrix Model Based on Field Observations

## TL;DR

Researchers developed a model to track the population of pine caterpillars in Korea, identifying vulnerable life stages to improve pest control strategies.

## Contribution

A stage-structured matrix model was created using field data to guide targeted pest management for pine caterpillars.

## Key findings

- Newly hatched and overwintered larvae are the most vulnerable stages of the pine caterpillar.
- Matrix models effectively describe population dynamics and support timely pest control decisions.
- Monitoring pest density after overwintering is crucial for effective forest management.

## Abstract

The pine caterpillar (Dendrolimus spectabilis) is a major forest pest that defoliates pine trees in Korea. The moth population was monitored for one year at monthly intervals, excluding winter. The census data obtained was used to construct life tables and a stage-structured matrix model based on the number of eggs, larvae, and pupae per branch area. Sensitivity analysis revealed that newly hatched larvae and overwintered larvae were the most vulnerable stages, primarily influenced by abiotic factors such as rainfall and temperature. This modeling approach suggests that pest management should prioritize monitoring populations immediately after overwintering. Overall, the study demonstrates that matrix models are useful tools for understanding forest insect dynamics and for designing timely, stage-specific control strategies.

Population models offer insights into both theoretical and practical aspects of insect population dynamics. Among the models, stage-structured matrix models are used to describe the population dynamics of insects because the development of insects is by nature stage-structured. Field populations of the pine caterpillar, Dendrolimus spectabilis (Lepidoptera: Lasiocampidae) were monitored in a pine stand located in Dorak-ri, Cheongsan-myeon, Wando-gun, Jeollanam-do, from May 1998 to March 1999, and the pest density was measured as the number of larvae, pupae, or eggs at one-month intervals, excluding the winter season. Life tables and matrix models were constructed based on field observations, and the most vulnerable life stage was identified through sensitivity analysis. The density of the pine caterpillar (number per 1000 cm2 branch) was 7.9 on 8 May 1998, and subsequently decreased to 0.5 on 14 March 1999, showing a decreasing trend of caterpillar density. The population growth rate was 0.74, a decreasing trend. The most vulnerable stages were (1) the larvae immediately after hatching and (2) again during overwintering, probably due to indirect mortality caused by humid conditions and activities of natural enemies during winter. Given the significant damage caused by mature larvae in the spring and that the density of the caterpillar after overwintering typically remains stable, forest management requires that the pest density be monitored soon after overwintering to allow decisions about control measures to be taken. Our results showed that a matrix model is useful to describe the population dynamics of the pine caterpillar and to construct suitable management strategies.