Panolis flammea (pine beauty moth).
Authors: Hicks Barry 
Published: June 2021

Abstract

Genetics: There was a question in the UK whether the pine beauty moth had formed host races sympatrically on the two hosts (Pinus sylvestris versus Pinus contorta). Wainhouse and Jukes (1997) determined a geographical cline between English and Scottish populations using isozymes. They concluded that P. flammea was not a highly dispersive species, as their overall estimate of population structuring (FST = 0.109) was high for a lepidopteran, but found no direct evidence of host-associated genetic differentiation. Their Scottish specimens were sampled only from lodgepole pine (Pinus contorta) and the English samples were all sampled from Scots pine (P. sylvestris). To further determine any host association in P. flammea, Lowe et al. (2005) used genetic variation within the mitochondrial (sequencing cytochrome c oxidase subunit I locus), nuclear (allozymes) and total (RAPD) genomes of populations of P. flammea sampled from the two host species, and at different scales and locations across Scotland, to examine the dispersive abilities of P. flammea, its origin in Scotland and whether there was any evidence for host-associated races. The RAPD analysis indicated limited long distance dispersal (FST = 0.099), and significant isolation by distance (P < 0.05). When compared with material from Germany, Scottish samples were found to be more diverse and significantly differentiated for all markers. For mtDNA, two highly divergent groups of haplotypes were evident, one group contained both German and Scottish samples and the other was predominantly Scottish. A scenario of two postglacial colonisations was tentatively suggested, one from a continental European source (identified in the German sample) and a second from a cryptic northern refugium in the western British Isles which P. flammea could have shared with its native host. No genetic differentiation was evident between P. flammea populations sampled from different hosts, and no diversity bottleneck was observed in the Lodgepole group. Wang et al. (2014) recently constructed a phylogeny of the genus Panolis based on morphological and molecular evidence. They used sequencing of two mitochondrial genes, cytochrome c oxidase subunit I and 16S ribosomal RNA, and one nuclear gene, Elongation factor-1 alpha. Wang et al. (2014) concluded that P. flammea originated most likely in the Oriental region sometime in the Late Miocene (6.54-10 Mya). Reproductive Biology: The adults are active at night and mating occurs in the upper crown of trees. This is also where the eggs are predominantly deposited (Watt and Leather, 1988; Ballard, 1987). P. flammea females may lay up to 430-460 eggs (Leather, 1984). The eggs are deposited individually or in short rows. Egg development takes 6.3 days at 20°C and 19.7 days at 10°C (Watt and Leather, 1988). Upon hatching the larvae develop through 5 instars. First instar yellow-green larvae are restricted to feeding on developing needles or newly unflushed buds of the current year's foliage (Stoakley, 1979). They often bore a hole at the base of needle pairs and excavate the soft internal tissues but their abdomens remain exposed to the outside (Hicks et al., 2001a). Second instar larvae are also restricted to current year foliage. By the 3rd instar they are capable of consuming entire needles of the current year. The 4th and 5th instar larvae are much larger and feed on the older foliage (Watt, 1987). The mature larvae range in size from 37-40 mm long (Novak, 1976). By mid-July, when the larvae are fully grown, they drop to the litter and pupate at the soil-litter interface (Watt and Leather, 1988). The pupae are 16-18 mm long and shiny brown in colour (Novak, 1976). Deeper litter layers that have good insulating properties are thought to provide optimal microclimates for overwintering pupal survival (Leather, 1984; Evans et al., 1991). Leather (1984) indicated that the pupae have an obligatory diapause that is independent of temperature that lasts 120-130 days. Population Size and Structure: There have been numerous recorded P. flammea outbreaks on Scots pine (Pinus sylvestris) in Continental Europe over a period of almost 200 years (Klimetzek, 1979), whereas it has never reached pest status on Scots pine in Britain. Hicks et al. (2001a) examined P. flammea monitoring data in Scotland and documented the history and control of P. flammea from 1975-2000. Pupal counts and pheromone trap data suggest that the population is cyclic on lodgepole pine (Pinus contorta) in Scotland (Hicks et al., 2001a). The trend resembles a cyclic pattern with a period length of approximately seven years. The periodicity observed in Scotland (seven years) is comparable to the periodicity of P. flammea in Germany (8.1 ± 0.4 years) (Klimetzek, 1979). Biotic factors, namely insect parasitoids and fungal diseases, were shown to cause the collapse of many German populations in the past and to have contributed to the cyclic pattern observed (Barbour, 1987). Watt and Hicks (2000) suggested that natural enemies had been playing a greater role in the population dynamics of P. flammea than had previously been thought. By examining the population levels of P. flammea for several years after spraying, Watt and Hicks (2000) showed that the populations continued to decline or remained low for 2-3 years post-spray without additional spraying. They concluded that a delayed density dependent factor (presumably natural enemies) was the most likely cause of this trend. Nutrition: Scots pine (Pinus sylvestris) was shown to be a better host nutritionally for P. flammea than lodgepole pine (Pinus contorta) having a greater foliar nitrogen concentration and lower concentrations of secondary compounds than lodgepole pine (Watt, 1989, Watt et al., 1991). Vanbergen et al. (2003) performed a series of reciprocal feeding experiments to test whether P. flammea has become adapted to its new host, lodgepole pine. No evidence of host associated trade-offs in larval survival was found but the food plant had significant effects on P. flammea development. Irrespective of the host source (Scot pine or lodgepole pine), larvae subsequently grown on Scots pine developed significantly faster than those on lodgepole pine (Vanbergen et al., 2003)Hicks et al. (2007) found larvae in the field earlier and within a narrower time frame within a Scots pine forest than in a lodgepole pine forest. The larval developmental period is significantly longer on lodgepole pine than on Scots pine. The synchrony/asynchrony of P. flammea to its natural host (Scots pine) and an introduced tree (lodgepole pine) results in the parasitoids having a different impact on the larvae of the two hosts.