Testing the effectiveness of pyrazine defences against spiders

Abstract

Insects live in a dangerous world and may fall prey to a wide variety of predators, encompassing multiple taxa. As a result, selection may favour defences that are effective against multiple predator types, or target-specific defences that can reduce predation risk from particular groups of predators. Given the variation in sensory systems and hunting tactics, in particular between vertebrate and invertebrate predators, it is not always clear whether defences, such as chemical defences, that are effective against one group will be so against another. Despite this, the majority of research to date has focused on the role of a single predator species when considering the evolution of defended prey. Here we test the effectiveness of the chemical defences of the wood tiger moth, a species previously shown to have defensive chemicals targeted towards ants, against a common invertebrate predator: spiders. We presented both live moths and artificial prey containing their defensive fluids to female Trichonephila senegalensis and recorded their reactions. We found that neither of the moth’s two defensive fluids were able to repel the spiders, and confirmed that methoxypyrazines, a major component of the defences of both the wood tiger moth and many insect species, are ineffective against web-building spiders. Our results highlight the variability between predator taxa in their susceptibility to chemical defences, which can in part explain the vast variation in these chemicals seen in insects, and the existence of multiple defences in a single species.

Laboratory Evidence of 2-Isobutyl-3-methoxypyrazine as a Male-Released Aggregative Cue in Labidostomis lusitanica (Germar) (Coleoptera: Chrysomelidae)

“…2-Alkyl-methoxypyrazines are common warning cues with a distinctive odor that, along with additional signals (e.g., visual [ 28 , 29 ]), constitute a multimodal defense mechanism to avoid predation. To cite an example, the wood tiger moth Arctia plantaginis (L.) (Lepidoptera: Arctiidae) produces 2-isobutyl-3-methoxypyrazine (IBMP) and 2- sec -butyl-3-methoxypyrazine (SBMP), which deter birds and ants [ 30 ], although they are ineffective against spiders [ 31 ]. In Oncopeltus fasciatus (Dallas) (Hemiptera: Lygaeidae), its chemical defense mechanism relies on the expelling of a fluid that contains IBMP [ 27 ].…”

2-Isobutyl-3-methoxypyrazine as a Putative Male-Specific Aggregation Pheromone in <em>Labidostomis lusitanica</em> (Germar) (Coleoptera: Chrysomelidae)

“…visual [27,28]), constitute a multimodal defense mechanism to avoid predation. To cite an example, the wood tiger moth Arctia plantaginis (L.) (Lepidoptera: Arctiidae) produces 2-isobutyl-3-methoxypyrazine (IBMP), and 2-sec-butyl-3-methoxypyrazine (SBMP), that deter birds and ants [29], although they are ineffective against spiders [30]. In Oncopeltus fasciatus (Dallas) (Hemiptera: Lygaeidae), its chemical defense mechanism relies on the expelling of a fluid that contains IBMP [26].…”

Evolution of multiple prey defences: From predator cognition to community ecology

“…The wood tiger moth is an emerging model system for studying the chemical ecology of antipredator defence (e.g. Burdfield‐Steel et al, 2020; Rojas et al, 2017). The wood tiger moth uses pyrazines to deter avian predators, relying on two different chemicals, the methoxypyrazines SBMP (2‐sec‐butyl‐3‐methoxypyrazine) and IBMP (2‐isobutyl‐3‐methoxypyrazine) (Burdfield‐Steel et al, 2018; Rojas et al, 2017).…”