Consumer or Decomposer? Behavioral and Morphological Diagnosis of White Grubs

Determining the ecological role of insect larvae is crucial for pest control and resource utilization, which usually relies on accurate species identification. White grubs, the larvae of Scarabaeoidea, exhibit highly diverse behaviors but share a similar morphology, making identification challenging. In this study, an improved six-armed olfactometer was used to test the feeding preferences of two sympatric white grubs, Anomala mongolica and Protaetia brevitarsis. The correlated morphological traits, including the sensory, feeding, and locomotive organs, were investigated using cross-sections and scanning electron microscopy. Our results show that phytophagous grubs possess well-developed antennal sensilla and digitiform sensilla on maxillary palps, mandibles with incisors for cutting plant roots, and fossorial setae and sharp claws on thoracic legs. In contrast, saprophagous grubs have underdeveloped digitiform sensilla, relatively short and robust antennae and thoracic legs, and mandibles lacking cutting edges suitable for severing roots. This study provides new insights for determining the ecological roles of white grubs.