# Different Senses for Different Roles: Sexual Dimorphism in the Sensory System of a Scoliid Wasp

## TL;DR

This study shows that male and female Scoliid wasps have different sensory features linked to their distinct behaviors, with males having better vision and females better smell.

## Contribution

The first quantitative analysis of sensory system dimorphism in Scolia hirta wasps, linking morphology to sex-specific behaviors.

## Key findings

- Males have larger compound eyes and more ommatidia, supporting their visual mating behavior.
- Females have more and larger olfactory sensilla, aiding in host detection underground.
- Females also have physical traits suggesting vibrational sensing for host detection.

## Abstract

The morphological dimorphism in the visual and antennal sensory systems of wasps has not yet been extensively investigated. However, it is interesting to understand whether the marked behavioural differences observed between males and females can also be linked to morphological differences. Therefore, the aim of this study is to provide the first quantitative description of sensory systems for the species Scolia hirta, a parasitic wasp whose females attack beetle larvae in the soil. It is hypothesised that males have better vision because they must chase females to mate, while females have a better sense of smell to find their hosts underground. The results confirm these hypotheses: males have proportionally larger compound eyes than females. Conversely, females have more olfactory sensilla on their antennae. In conclusion, the differences in behaviour are also reflected in the morphology of the sensory systems in this wasp species. Studies of this type are important for increasing our knowledge of the evolutionary connection between form and function in insects.

Mating and feeding behavioural differences have been observed between male and female wasps (Hymenoptera: Aculeata). It is hypothesised that these behavioural differences are supported by morphological dimorphisms in their sensory systems. Here, this hypothesis was tested in the parasitoid aculeate wasp Scolia hirta (Scoliidae), which attacks beetle larvae located in the soil. We have found evidence of a link between the main stimuli used by the sexes to access their target resources and the morphology of the sensory system. Males have a more developed visual system with enlarged eyes, ocelli and a higher number of ommatidia, sinc they have to visually locate and chase females immediately after they emerge. Males possess nine types of sensilla (primarily hygrothermo- and mechanoreceptors), and females possess seven types of sensilla, primarily olfactory. In females, the sensilla placoidea occur in greater numbers and are larger in size, in line with their underground host-seeking behaviour. Furthermore, the females had a blunt tip on their distal flagellomere and wider fore tibiae, which suggests that they may use vibrational sounding to detect concealed hosts, similarly to what has been described for some non-aculeate parasitoid wasps.