The efficient aquisition of nutrients from leaves by insect herbivores increases their nutrient assimilation rates and overall fitness. Caterpillars of the gypsy moth (Lymantria dispar L.) have high protein assimilation efficiencies (PAE) from the immature leaves of trees such as red oak (Quercus rubra) and sugar maple (Acer saccharum) (71-81%) but significantly lower PAE from their mature leaves (45-52%). By contrast to this pattern, both PAE and carbohydrate assimilation efficiencies (CAE) remain high for L. dispar larvae on the mature leaves of poplar (Populus alba × Populus tremula) grown in greenhouse conditions. The present study tests two alternative hypotheses: (i) outdoor environmental stresses cause decreased nutrient assimilation efficiencies from mature poplar leaves and (ii) nutrients in the mature leaves of trees in the poplar family (Salicaceae) remain readily available for L. dispar larvae. When poplar trees are grown in ambient outdoor conditions, PAE and CAE remain high (approximately 75% and 78%, respectively) in L. dispar larvae, in contrast to the first hypothesis. When larvae feed on the mature leaves of species in the Salicaceae [aspen (Populus tremuloides), cottonwood (Populus deltoides), willow (Salix nigra) and poplar], PAE and CAE also remain high (68-76% and 72-92%, respectively), consistent with the second hypothesis. Larval growth rates are strongly associated with protein assimilation rates, and more strongly associated with protein assimilation rates than with carbohydrate assimilation rates. It is concluded that tree species in the Salicaceae are relatively high-quality host plants for L. dispar larvae, in part, because nutrients in their mature leaves remain readily available.
For capital‐breeding insects, all resources available for adult metabolic needs are accumulated during larval feeding. Therefore, body size at adult eclosion represents the total energetic capacity of the individual. For female capital breeders, body size is strongly correlated with lifetime fecundity, while in males, body size, which correlates with fitness, is less understood. In capital‐breeding species with wingless, flightless, or dispersal‐limited females, flight potential for male Lepidoptera has important implications for mate‐finding and may be correlated with body size. At low population densities, failure to mate has been identified as an important Allee effect and can drive the success or failure of invasive species at range edges and in species of conservation concern. Th capital‐breeding European subspecies of Lymantria dispar (L.), was introduced to North America in 1869 and now ranges across much of eastern North America. In L. dispar, females are flightless and mate‐finding is entirely performed by males. We quantified male L. dispar flight capacity and propensity relative to morphological and physiological characteristics using fixed‐arm flight mills. A range of male body sizes was produced by varying the protein content of standard artificial diets while holding other dietary components constant. Wing length, a proxy for body size, relative thorax mass, and forewing aspect were all important predictors of total flight distance and maximum speed. These results have important implications for mate‐finding and invasion dynamics in L. dispar and may apply broadly to other capital‐breeding insects.
The size of adult gypsy moths, (Lymantria dispar L.), a capitalbreeder, is correlated with environmental conditions experienced as larvae. Proxies for adult size such as wing length may provide information about habitat quality and population density. 2 We used male gypsy moths collected from pheromone traps at intervals through the flight season to assess phenological change in wing length. Consistent with a previous study conducted at our reference site, we found that wing length declines seasonally, likely resulting from phenological reduction in host foliage quality. This pattern was evident at our reference site over 8 years, and at our experimental sites with low-density populations in 3 years. 3 We assessed forest quality using two unique metrics, basal area of red oak (Quercus rubra), a high quality host tree, and a composite value generated from a published ranking of tree species quality for gypsy moth. We did not find a relationship between these metrics and wing length, although we found that the mean size of males was larger in stands with oak. 4 Mean wing length in outbreak populations was significantly smaller reflecting density related processes such as intraspecific competition, although there was no significant seasonal effect on wing length.
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