Phenology-based recommendations for control of the litchi fruit borer ( Conopomorpha sinensis Bradley, Lepidoptera)

Abstract

The litchi fruit borer ( Conopomorpha sinensis Bradley) is a major pest threatening litchi ( Litchi chinensis Sonn.) production by causing substantial fruit infestation and drop. Although pesticides are widely used, optimal application timing is debated due to imprecise descriptions of fruitlet stages and limited knowledge of pest behaviour in orchards. To address this, we aligned fruitlet development with litchi fruit borer behaviour to identify ideal pest-control timing that balances control intensity while maintaining productivity. Oviposition increased sharply during mid-development in both pesticide-treated and pesticide-free trees. Fruit abscission and fruitlet infestation rates were similar during this period, indicating that physiological factors largely determine early abscission despite borer attacks. Subsequently, pesticide-free trees exhibited higher infestation. During late development, 75–100% of shed fruitlets were damaged by the borer, suggesting the pest is the dominant factor in late fruit drop. Further analysis showed that fruit weight is the principal factor correlated with oviposition, while meteorological factors modulate the occurrence of damage. Using a fruit length of approximately 20 mm as a phenology-based indicator optimizes the timing of pesticide application. Furthermore, because insecticides primarily reduce post-oviposition survival rather than deterring oviposition itself, targeting this specific developmental stage is crucial for effectively preventing late-stage fruit loss.