Hindwing venation is one of the most important morphological features for the functional and evolutionary analysis of beetles, as it is one of the key features used for the analysis of beetle flight performance and the design of beetle-like flapping wing micro aerial vehicles. However, manual landmark annotation for hindwing morphological analysis is a time-consuming process hindering the development of wing morphology research. In this paper, we present a novel approach for the detection of landmarks on the hindwings of leaf beetles (Coleoptera, Chrysomelidae) using a limited number of samples. The proposed method entails the transfer of a pre-existing model, trained on a large natural image dataset, to the specific domain of leaf beetle hindwings. This is achieved by using a deep high-resolution network as the backbone. The low-stage network parameters are frozen, while the high-stage parameters are re-trained to construct a leaf beetle hindwing landmark detection model. A leaf beetle hindwing landmark dataset was constructed, and the network was trained on varying numbers of randomly selected hindwing samples. The results demonstrate that the average detection normalized mean error for specific landmarks of leaf beetle hindwings (100 samples) remains below 0.02 and only reached 0.045 when using a mere three samples for training. Comparative analyses reveal that the proposed approach out-performs a prevalently used method (i.e., a deep residual network). This study showcases the practicability of employing natural images—specifically, those in ImageNet—for the purpose of pre-training leaf beetle hindwing landmark detection models in particular, providing a promising approach for insect wing venation digitization.

Fecal retention is a distinctive reproductive strategy in certain leaf beetles, which enables females to use accumulated fecal material to protect their eggs and enhance offspring survival. The adult flea beetle Asiophrida xanthospilota (Baly, 1881) is a specialist herbivore that feeds on the leaves of Cotinus coggygria Scop. (Anacardiaceae). Using light microscopy, scanning electron microscopy, and micro-computed tomography, we described and illustrated the hindgut anatomy of adult female A. xanthospilota during the pre-mated and post-mated reproductive phases. We further examined the physiological changes in the hindgut associated with fecal retention, and assessed hindgut muscle activity across these two reproductive stages. The hindgut of adult A. xanthospilota consists of three regions: ileum, colon, and rectum. The ileum is a thin, straight or coiled, tube enclosed by malpighian tubules and supported by circular and longitudinal muscles. The colon lies between the ileum and rectum, possesses a chitinized cuticle, and is externally covered with tracheae and tracheoles. A rectal valve separates the colon from the rectum, which forms the posterior end of the alimentary canal and is characterized by intimal spines and robust circular muscles. During the post-mated phase, fecal retention causes pronounced dilation of the hindgut, substantially increasing the volume occupied by food remnants. Electromyographic recordings revealed high hindgut muscle activity in pre-mated females, characterized by short and variable bursts, whereas post-mated females exhibited reduced activity with longer and more sustained bursts. The functional implications of these specialized structural features are discussed. Overall, these morphological and physiological adaptations enhance the fecal retention strategy by increasing fecal capacity, regulating hindgut motility, and enabling the formation of a protective fecal case around the egg mass.