Popualtion Dynamics of Japanese Hemlock Scales: A Comparison of Endemic and Exotic Communities

Abstract

The dynamics of endemic populations of two armored scales, Fiorinia externa and Nuculaspis (=Tsugaspidiotus) tsugae (Homoptera: Diaspididae), were studied in Japan and compared with the dynamics of introduced populations of these scales in the United States. In Japan both scales were distributed widely among the 13 natural and cultivated stands of Tsuga diversifolia and T. sieboldii sampled throughout Honshu, but scale densities were innocuous and low relative to those in North America. Density, survivorship, and fecundity of both scale species were significantly higher on hemlocks planted outside their natural range in Japan than on naturally occurring montane trees, and significantly higher on Tsuga species exotic to Japan than on Japanese hemlocks. I infer from this that trees growing outside their natural habitats are more susceptible to insect herbivores, presumably due to stress from less adequate growing conditions. Experiments conducted in a field plot in Kyoto, Japan, revealed that on each hemlock species scale fecundity was always higher among scales that had been transferred from another individual of that same hemlock species than among scales that had been transferred from an individual of a different hemlock species. These results supported those from a similar experiment involving exotic scale populations in Connecticut, USA, and indicated that scales residing on adjacent trees may be qualitatively different.Data from the field plot study in Kyoto and life table data gathered from 13 sites in Honshu revealed that endemic populations have the potential to attain densities injurious to host hemlocks, especially trees in cultivation. However, this seldom occurs because two hymenopterous parasitoids, Aspidiotiphagus citrinus and Arrhenophagus albitibiae, regularly killed from 90.2 to 94.2% of both scale species. Throughout Honshu the seasonal occurrence of the bivoltine adult parasitoids and vulnerable stages ofbivoltine F. externa and N. tsugae were synchronous, resulting in high parasitism rates and a low range of fluctuation in endemic scale populations. In contrast, Connecticut populations of As. citrinus are asynchronous with their scale host, F. externa, which is univoltine there. The resulting higher populations of the scale in Connecticut injure and kill their new host plant, Tsuga canadensis.

Factors Affecting the Flight Capacity of <I>Tetrastichus planipennisi</I> (Hymenoptera: Eulophidae), a Classical Biological Control Agent of <I>Agrilus planipennis</I> (Coleoptera: Buprestidae)

“…Although the phenology of the native parasitoid Atanycolus cappaerti Marsh & Strazanac (Hymenoptera: Braconidae) attacking emerald ash borer has been described (Cappaert & McCullough 2009), no work to date has described the flight phenology of these parasitoids. Flight phenology of parasitoids and its synchrony with the susceptible stage of the host have important implications for parasitoid effectiveness (McClure 1986;Godfray et al 1994;Van Nouhuys & Lei 2004;Abell & Van Driesche 2012). In this study, we evaluated the flight phenology of egg and larval parasitoids of emerald ash borer at sites in central Michigan using sentinel logs.…”

Biology of the conifer needle scale, Nuculaspis abietis (Hemiptera: Diaspididae), in northern Iran and parasitism by Aspidiotiphagus citrinus (Hymenoptera: Aphelinidae)

“…This results in highly variable parasitism rates from year to year and equilbrium scale densities much higher than observed in Japan. However, because N. tsugae completes two generations per year in Connecticut, its life cycle is more synchronous with that of A. citrinus and parasitism rates around 55% are sustained (McClure, 1986). Despite the fact that N. abietis has one generation in Kelardasht while A. citrinus completes two, the phenology of the scale population is such that adult parasitoids of both generations tend to encounter vulnerable stages of N. abietis, at least in the year of this study.…”

“…that we examined in the infested region of Kelardasht were not. Scale outbreaks are often confined to one host species even when other host species occur in the area (Edmunds, 1973;McClure, 1986). This is thought to occur because nymphal survival is typically highest on the parent tree, lower on other trees of the same species, and very low on host trees of other species.…”

“…Aspidiotiphagus citrinus is known to attack a range of diaspidid scale species (Tao & Chang, 1963;Walker & Deitz, 1979), including other species of Nuculaspis (McClure, 2002), but this is the first report of it attacking N. abietis. Although this species regularly parasitizes more than 90% of Fiorinia externa Ferris and Nuculaspis tsugae (Marlatt) in Japan, it has been less effective in the eastern United States (McClure, 1986). In Kyoto, Japan, A. citrinus and its scale hosts both have two generations per year and the emergence of adult parasitoids is well synchronized with the peak abundance of vulnerable scale stages (McClure, 1986).…”

“…Although this species regularly parasitizes more than 90% of Fiorinia externa Ferris and Nuculaspis tsugae (Marlatt) in Japan, it has been less effective in the eastern United States (McClure, 1986). In Kyoto, Japan, A. citrinus and its scale hosts both have two generations per year and the emergence of adult parasitoids is well synchronized with the peak abundance of vulnerable scale stages (McClure, 1986). However, in Connecticut, USA where F. externa completes only one generation a year (McClure, 1978) the peak emergence of bivoltine A. citrinus occurs almost eight weeks after the peak abundance of F. externa second instar nymphs.…”