Social immunity in eusocial insects involves collective behavioural mechanisms that reduce pathogen transmission within colonies. In ants, necrophoric behaviour plays an important role in colony hygiene; however, the relationship between caste-specific morphology, sensory structures, and hygienic performance remains poorly understood in Oecophylla smaragdina. This study investigated caste differences in necrophoric behaviour, morphometric traits, and antennal sensilla morphology in major and minor workers of O. smaragdina using behavioural assays, morphometric analysis, and scanning electron microscopy (SEM). Linear mixed-effects model analysis revealed significant caste-dependent differences in corpse detection latency, colony included as a random effect. Minor workers detected corpses significantly faster than major workers across all five colonies, exhibiting mean detection latencies of 40.20 ± 13.32 s to 50.60 ± 9.13 s, compared to 122.40 ± 14.03 s to 143.80 ± 17.78 s in major workers. Morphometric analyses showed that major workers possessed significantly larger body dimensions than minor workers across all measured traits. SEM examination revealed distinct caste-specific variation in antennal and mandibular structures. Minor workers exhibited higher total antennal sensillar counts (117) compared to major workers (94), whereas sensilla in majors appeared comparatively larger. These findings suggest that sensory and morphological specialization may contribute to caste-specific hygienic roles and division of labour in O. smaragdina.
Some species of the Anopheles dirus species complex are considered to be highly competent malaria vectors in Southeast Asia. Anopheles dirus is the primary vector of Plasmodium falciparum and P. vivax while An. cracens is the main vector of P. knowlesi. However, these two species are difficult to distinguish and identify based on morphological characters. Hence, the aim of this study was to investigate the potential use of antennal sensilla to distinguish them. Large sensilla coeloconica borne on the antennae of adult females were counted under a compound light microscope and the different types of antennal sensilla were examined in a scanning electron microscope. The antennae of both species bear five types of sensilla: ampullacea, basiconica, chaetica, coeloconica and trichodea. Observations revealed that the mean numbers of large sensilla coeloconica on antennal flagellomeres 2, 3, 7, 10 and 12 on both antennae of both species were significantly different. This study is the first to describe the types of antennal sensilla and to discover the usefulness of the large coeloconic sensilla for distinguishing the two species. The discovery provides a simple, reliable and inexpensive method for distinguishing them.