Canadian Forest Service Publications
Adaptive advantages of dietary mixing different-aged foliage within conifers for a generalist defoliator. 2015. Johns, R.C.; Tobita, H.; Hara, H.; Ozaki, K. Ecological Research 30:783-802.
Issued by: Atlantic Forestry Centre
Catalog ID: 36388
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Few herbivores are well adapted to feeding on all foliage age classes available and most have evolved traits that are attuned to the characteristics of either developing or mature foliage; however, recent evidence has shown a number of insect herbivores that may mix different-aged foliage as a means of enhancing fitness. We carried out a series of laboratory and field experiments to investigate whether larvae of Asian gypsy moth (L. umbrosa (Butler) = L. dispar Hokkaidoensis Goldschmidt) (Lepidoptera: Lymantriidae) engage in and benefit from foliage-age dietary mixing in common conifer species that naturally occur in its native range of Hokkaido, Japan. In a laboratory experiment, early instar larvae were observed on both developing and mature foliage when both age classes were available; however, larval survival and weight were highest on hosts with developing foliage available (larch, fir, and pine), whereas all larvae died on spruce where only mature foliage was available. In contrast, larboratory and field experiments indicated that late-instar larvae often consumed both developing and mature foliage on all conifer species studied, although there was general preference bias towards mature foliage. Field biosassays indicated that late-instar larvae provided both foliage age classes (a "mixed" diet) had similar performance to those provided only developing or mature foliage. Results of this study indicate that larvae obtain limited performance benefits from mixing different foliage age classes into their diet, other than perhaps the benefits accrued from having a broader resource pool available on a single host tree.
Plain Language Summary
Asian gypsy moth (AGM) is a major defoliator and may pose a threat to the forests of western North America if it is able to establish. Unlike the European gypsy moth, the Asian species is quite able to feed on evergreen conifers as well as deciduous hosts. Unfortunately, we still know little of how it interacts with conifer hosts in nature, especially in its native habitat. This study was carried out within the native range of Hokkaido Japan to better understand the diet breadth and foraging preferences of young and old AGM larvae on the young vs. mature foliage of various coniferous hosts. Young larvae were restricted to feeding mainly on young foliage, whereas older larvae fed on both age classes with little apparent effect on survival or size. These results underscore the potential threat AGM may pose to conifer stands if they are introduced as herbivores able to feed on multiple age classes of foliage are much more likely to kill their host.