Silent assassins: predation of native New Zealand trichopteran eggs by non-native freshwater gastropods

ABSTRACT

Aquatic insects that oviposit on rocks may evolve strategies to mitigate loss of eggs to opportunistic predation by common native grazers, but such strategies may be ineffective against non-native grazers. We tested whether the eggs of common New Zealand caddisfly families (Hydrobiosidae and Hydropsychidae) that oviposit on rocks were more susceptible to predation by native or non-native snails. The native snail Potamopyrgus antipodarum (Grey, 1843) and non-native snails Physa acuta Draparnaud, 1805 and Pseudosuccinea columella (Say, 1817) were presented with caddisfly egg masses and the number of individual eggs consumed was recorded after 24 and 48 hours. The larger Pseudosuccinea readily consumed the eggs, especially spumaline-encapsulated Hydrobiosidae eggs. Physa consumed very few Hydrobiosidae eggs and no Hydropsychidae eggs, whereas Potamopyrgus did not consume eggs of either family. The trichopteran egg masses tested did not succumb to predation by the native Potamopyrgus but are highly vulnerable to predation by a larger non-native snail.

KEYWORDS:

• Trichoptera
• Gastropoda
• Potamopyrgus
• invasive species
• egg predation
• New Zealand

Acknowledgements

The authors would like to thank two anonymous referees for their helpful comments and suggestions. We would also like to thank Richard Storey (NIWA) for many useful comments on an earlier draft, and Elizabeth Graham (NIWA) for her expertise on the statistical package R.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

Financial support for this project was provided by Ministry of Business, Innovation and Employment (MBIE) [contract number C01X0305, Aquatic Restoration].