Oviposition Of Viburnum Leaf Beetle [Pyrrhalta Viburni (Paykull)]: From Ecology To Biological Control Of An Emerging Landscape Pest

Abstract

Pyrrhalta viburni (Coleoptera: Chrysomelidae), an invasive chrysomelid native to Eurasia, is a major pest of viburnums in the northeastern U.S. and southern Canada. P. viburni oviposition behavior was observed under laboratory and field conditions. The time cost of producing an egg mass was 135.3 + 6 min, chewing the egg cavity being the most time consuming part of the process. Choice-tests showed that females laid more eggs in twigs already infested by conspecifics than in non-infested twigs, and positioned their egg masses adjacent to existing ones. P. viburni oviposition behavior is therefore aggregative. An observational study showed that wound response, the main plant defense against P. viburni oviposition, decreased with increasing levels of egg infestation, suggesting a potential benefit of aggregative oviposition. A field study confirmed that there is a realized fitness benefit of aggregative oviposition on three host species: V. dentatum, V. opulus, and V. x bodnantense. Egg survivorship was higher on twigs with high and very high levels of infestation than on lightly or moderately infested twigs and wound response decreased with increasing levels of infestation. Twig mortality was positively correlated with level of infestation, and egg survivorship was higher on dead twigs than on living twigs. P. viburni oviposition on twigs that had died naturally occurred more frequently if the twigs had been infested the previous year, and the probability of new infestation was correlated with the number of old egg masses present in the twig. A study was conducted under quarantine conditions to determine the longevity and host specificity of Aprostocetus sp. (Hymenoptera: Eulophidae), a Eurasian egg parasitoid of P. viburni. Aprostocetus sp. females lived 53.8 days on average, the maximum longevity being 133 days. Aprostocetus sp. successfully parasitized the following non-target species: Galerucella nymphaea, G. pusilla/G. calmariensis, and Plagiometriona clavata (Coleoptera: Chrysomelidae). Due to its lack of host specificity, I think that the egg parasitoid Aprostocetus sp. should not be considered for introduction as a biological control agent against P. viburni in North America. The implications of this research for management of P. viburni in North America are discussed.