Sorry about this. Taxonomy is a dynamic field.
 
 
Simple synonymy:

Maladera formosae (Brenske, 1898: 210) SENIOR

= Maladera castanea (Arrow, 1913: 398) JUNIOR
 
 
Fabrizi S, Liu W-G, Bai M, Yang X-K, Ahrens D (2021) A monograph of the genus Maladera Mulsant & Rey, 1871 of China (Coleoptera: Scarabaeidae: Melolonthinae: Sericini), Zootaxa 4922: 1–400. doi:10.11646/zootaxa.4922.1.1.
 
https://www.inaturalist.org/flags/537050