Winter moth (Operophtera brumata(Lepidoptera: Geometridae)) outbreaks on Scottish heather moorlands: effects of host plant and parasitoids on larval survival and development

Abstract

Outbreaks of the winter moth, Operophtera brumata Linnaeus (Lepidoptera: Geometridae), have recently become widespread on heather moorlands in northeast Scotland. These outbreaks represent remarkable phenomena given the poor nutritional quality of the dominant moorland host plant Calluna vulgaris (Linnaeus) Hull (Ericaceae). Winter moth performance on C. vulgaris was compared with that on the other available moorland host plant, Vaccinium myrtillus (Linnaeus) (Ericaceae), and parasitism levels were measured in two moorland outbreak populations. Larval densities in the field were generally higher on Calluna than on Vaccinium. However, larvae showed better survival, more rapid development and greater pupal weights on Vaccinium than on Calluna. Feeding trials indicated that Vaccinium was more digestible than Calluna. No evidence of parasitism was found in a high-altitude moorland winter moth outbreak population from mainland Scotland, but the parasitoid Phobocampe neglecta (Holmgren) (Hymenoptera: Ichneumonidae) was present in 27% of larvae from a lower-altitude moorland outbreak on Orkney. The results indicate that the presence of Vaccinium and the opportunity to escape from parasitism may facilitate O. brumata outbreak formation in high-altitude moorland sites. However, neither factor can provide a full explanation for the present phenomenon.

Using diet to assess the sensitivity of northern and upland birds to climate change

“…For example, Lymantria dispar abundance is negatively correlated with winter and spring temperature (Miller et al 1989, Williams & Liebhold 1995, but milder winters increase the survival of Epirrita autumnata (Tenow & Nilssen 1990, Virtanen & Neuvonen 1999 and, similarly, the survival of sawfly (Hymenoptera: Symphata) pupae (Aebischer 1990, Barker & Reynolds 2004. Increasing temperatures may improve caterpillar development (Williams et al 2000), but risk phenological mismatch between bud-burst and caterpillar emergence (Visser & Holleman 2001, Forkner et al 2008, and increase parasitoid infection rates (Kerslake et al 1996, Virtanen & Neuvonen 1999. Warming may therefore increase the abundance of some Lepidoptera and Coleoptera species, but decrease the abundance of others (Butterfield 1996, Frampton et al 2000, Morecroft et al 2002, Wilson et al 2005, Franco et al 2006, which is likely to result in species replacements northward and upward.…”

Habitat selection and diet of the Capercaillie Tetrao urogallus in Abernethy Forest, Strathspey, Scotland

“…and these areas contained larger numbers of groundliving Coleoptera, Formicidae and Lepidoptera larvae than other vegetation types (Table 7). Bilberry leaves have a higher nitrogen content than Heather (Kerslake et al 1996) and therefore provide a better food for Lepidoptera larvae, which in turn are food for predatory Coleoptera and Formicidae. All these invertebrates are food sources for Capercaillie chicks (Kastdalen & Wegge 1985, Spidsø & Stuen 1988, Picozzi et al 1999.…”

“…The time of pupation may be related to the decline in nitrogen and increase in toughness of Vaccinium sp. leaves as the summer progresses (Kerslake et al 1996).…”

Variation in Captures of Adult Winter Moths (Operophtera brumata) in Coastal Maine Over Two Years

“…Outbreaks of winter moth have occurred on Sitka spruce (Picea sitchensis [Bongard] Carr.) in Europe (Stoakley 1985, Watt andMcFarlane 1991), on heather (Calluna vulgaris L.) in Scotland (Kerslake et al 1996), and on mountain birch (B. p. subsp. czereapanovii) in Fenno-Scandinavia (Jepsen et al 2008).…”