Long-term decline in the parasitism rate of passionvine hopper eggs ( Scolypopa australis )
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Long-term decline in the parasitism rate of passionvine hopper eggs (Scolypopa australis) D. P. Logan . C. A. Rowe . P. G. Connolly
Received: 2 January 2020 / Accepted: 28 May 2020 Ó International Organization for Biological Control (IOBC) 2020
Abstract Passionvine hopper, Scolypopa australis (Walker) (Hemiptera: Ricaniidae), (PVH) is an introduced pest of kiwifruit grown in New Zealand. Two aphelinid egg parasitoids, Centrodora scolypopae Valentine and Ablerus sp., are thought to be its most important natural enemies. Rates of egg parasitism measured during 2010–2015 in the Bay of Plenty region and in a wider survey of the North Island of New Zealand in 2015 were B 10% compared with medians of about 30–50% for historical estimates. PVH eggs laid in bracken, a favored host plant, in 2015 and 2019 were parasitized at about half the rate or less than indicated by measurements made 20, 35–38 and 57 years ago. The apparent decline may have been the result of asynchrony between one or both egg parasitoids and PVH associated with warmer summer and autumn temperatures. Further work is needed to clarify the role of each parasitoid in PVH population dynamics.
Handling Editor: Stefano Colazza D. P. Logan (&) P. G. Connolly The New Zealand Institute for Plant & Food Research Ltd, Private Bag 92169, Auckland 1142, New Zealand e-mail: [email protected] C. A. Rowe The New Zealand Institute for Plant & Food Research Ltd, 412 No. 1 Rd, Te Puke 1142, New Zealand
Keywords Hemiptera Hymenoptera Aphelinidae Ricaniidae Horticulture Climate change
Introduction Passionvine hopper, Scolypopa australis (Walker) (Hemiptera: Ricaniidae), (PVH) is an Australian planthopper that is a production pest of kiwifruit (Actinidia chinensis) crops in New Zealand. Both nymphs and adults feed on phloem sap in the canopy and excrete honeydew leading to the growth of sooty moulds. Any fruit with sooty mould is unsuitable for export. Annual costs of management and lost potential exports are estimated to be NZ$30 m (E. Gould, Zespri Group Ltd, pers. comm.). PVH have an annual life-cycle with eggs the longest-lived and overwintering stage (Steven 1990). These are laid in batches during late summer and autumn in a row of cavities excavated by the female in dead twigs and shoots, in the corners of wooden structures and less often in growing plant stems and leaf midribs. After a single egg is laid in the cavity, it is sealed with a compressed plug of sawdust (Fletcher 1979). Nymphs hatch in the following spring and early summer and aggregate on actively growing shoots and on senescing leaves. Adults are present from midsummer until late autumn.
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Most PVH occur outside of kiwifruit crops on a wide range of plant species (Logan et al. 2002; Martin 2018). Some adults fly into kiwifruit crops from natal areas in the surrounding non-crop vegetation. These immigrant adults make up the majority of PVH in kiwifruit vines as resident populations tend to be small (Steven
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