Morphological and biological characteristics of Exolontha castanea Chang (Coleoptera: Melolonthinae)

Exolontha castanea Chang is a significant subterranean pest affecting sugarcane. Clarifying its morphological characteristics and biological characteristics is of great significance for accurate species identification and evidence-based pest management.

The external morphology, postembryonic development, developmental duration, annual life history, and living habits of E. castanea were investigated through indoor rearing observations and systematic field investigations.

Significant differences were found in the number of short setae on the anal sternite between male and female larvae, with females bearing significantly more than males. Distinct sexual dimorphism was observed in the abdomen of both pupae and adults, facilitating sex determination. Sexual size dimorphism was also evident, with females being larger than males in body length, body width, and body weight. The developmental characteristics of eggs, larvae, and pupae changed markedly with age. The growth dynamics of egg length and width conformed to the Logistic model. Larvae underwent three instars, with head width increasing significantly across instars. At 26℃, the developmental durations of egg, larva, female and male pupa were 10.12 d, 309.54 d, 17.54 d and 17.80 d, respectively. The lifespans of female and male adults were 45.27 d and 40.00 d, respectively. E. castanea occurs annually in Guangxi, overwintering as mature larvae in the soil. It began to pupate gradually in mid-March. Adult emergence activity spanned from late April to late June, with peak emergence occurring from mid to late May. Upon emergence, adults can absorb a small amount of water without feeding on plants. Female adults laid an average of 38.43 eggs each. Larvae emerged in early June, and the peak period of damage was from September to November.

This study clarifies the morphological and biological characteristics of E. castanea, providing a foundation for further biological and ecological research and a scientific basis for developing effective control strategies. The larvae are the primary life stage causing damage to sugarcane, and female adults exhibit strong reproductive capacity and phototaxis. Targeted control measures are recommended during the newly hatched larval stage and the adult emergence period.