Exploring the sensory ecology of mason wasp Pison spinolae Shuckard (Hymenoptera: Crabronidae) in Aotearoa New Zealand

Abstract

Sensory ecology investigates how animals acquire, process and respond to information they receive from their environments, and how this affects their evolution. Spider-hunting parasitoids provide a useful context to investigate sensory ecology as the survival and reproductive fitness of both the wasp and its spider prey are tightly interlinked and may involve various sensory modes. Spider-hunting parasitoids can adopt unique foraging strategies, such as specialisation or generalisation in prey choice, with sensory adaptations that facilitate these interactions. Visual acuity is often important in recognising prey species; spider-hunting parasitoids often hunt by search images. Cuticular hydrocarbons on the surface of prey and airborne volatiles are often used by parasitoids to detect, locate and recognise prey. In many species, this is facilitated by olfactory sensilla on the parasitoid’s antennae. Differences in ecologies may result in varying chemical acuity between sexes. This thesis is a novel investigation of the sensory ecology of the native spider-hunting parasitoid Pison spinolae Shuckard (Hymenoptera: Crabronidae). Some historical observations suggest P. spinolae hunts mostly spiders of the family Araneidae; however, this has not been empirically tested. Furthermore, the sensory ecology of P. spinolae has not been studied, leaving the mode by which P. spinolae detects and recognises spiders as prey unknown. This study aims to investigate P. spinolae’s prey choice and degree of prey specialisation on Aotearoa New Zealand’s spider fauna, and to begin to understand the cues by which P. spinolae detects and recognises prey species. This project also provides antennal morphological information, as a basis for future chemical sensory ecology studies into P. spinolae. In Chapter 2, I determined prey availability and spider diversity using field surveys and museum specimens, and citizen science observations (iNaturalist) of spider species in the environment. Characteristics of prey (taxa, sex, developmental stage) caught by P. spinolae were evaluated using field surveys and museum specimens. In Chapter 3, to investigate the use of visual cues to detect and recognise prey, I conducted spectral analyses of prey spiders collected from P. spinolae nests, prey and non-prey species from the field, museum specimens of prey from nests, and museum specimens of the same prey species that had not been found in P. spinolae nests. I modelled spiders into a Crabronidae (Hymenoptera) visual system and explored how P. spinolae might perceive spiders against a range of natural backgrounds. In Chapter 4, to investigate the ability of P. spinolae to detect and respond to chemical cues, I described and classified the morphology of antennal sensilla of female and male wasps, using scanning electron microscopy. In this thesis, I empirically confirmed that P. spinolae is a specialist hunter of adult female Araneidae and Leucauge dromedaria (Tetragnathidae). Modelling P. spinolae perception of spider spectra indicated that though all spiders were discernible against all natural backgrounds (JND values all > 1), P. spinolae likely cannot discern between caught and not-caught individuals, and prey and non-prey species, suggesting there are no universal similarities in prey species, and that it does not use visual cues to recognise prey type. P. spinolae did, however, show evidence of using chemical cues, with 5 sensilla types classified, 4 of which were olfactory/gustatory sensilla. This study is the first to describe the morphological features of P. spinolae’s antennal sensilla; classifications made in this study can be used to compare and clarify sensilla in other spider-hunting parasitoids. This research also involved the use of citizen science as a proxy for field data during COVID-19 lockdowns. COVID-19 lockdowns positively influenced the number of observations on iNaturalist; spider observations increased since the first reported case of COVID-19 by 37.51% across the 9 regions from which I collected data. A third of total spider observations were recorded under lockdown conditions, with over half (52.80%) post-COVID in Otago alone. Remote methods of data collection, as I have done in this study, may prove very useful for research during a pandemic, thus I provide a methodology for using citizen science to quantify prey diversity. My findings are novel for this species, and add to the sparse literature surrounding the sensory ecology of Crabronidae wasps. Studies of its prey preference and a comparison to spider diversity in Aotearoa New Zealand provide insight into the possible effects of P. spinolae on native spider populations.