Effects of nitrogen and Douglas-fir allelochemicals on development of the gypsy moth,Lymantria dispar

Abstract

Two experiments were conducted to examine the influence of foliar nitrogen, terpenes, and phenolics of Douglas-fir on the development of gypsy moth larvae. In the first experiment, foliar concentrations of nitrogen and allelochemicals were manipulated by fertilizing 3-year-old potted seedlings with 0 or 200 ppm nitrogen. Concentrations of foliar nitrogen (0.33-2.38%) were negatively correlated with the phenolics (15.8-24.4 mg/g). Sixth-instar larvae previously reared on current-year Douglas-fir needles were allowed to feed on these seedlings. Pupal weights (312.8-995.6 mg) were positively correlated with levels of foliar nitrogen, negatively correlated with amounts of foliar phenolics, and uncorrelated with terpene concentrations. In the second experiment, terpene and phenolic extracts from Douglas-fir foliage were incorporated at natural levels into artificial diets with high and low levels of protein nitrogen. Neonate larvae grew faster and were larger on the high nitrogen control diet (4.1-4.5%), however, fourth instars performed better on the control diet with low nitrogen levels (2.5-2.7%). Foliar terpenes incorporated into diet had little effect on neonate fitness, but may induce subtle physiological changes in later instar larvae. Phenolics, alone or in combination with terpenes, excessively suppressed growth and survival, with no individuals living through the fourth instar, regardless of the nitrogen level. Incorporating foliar phenolic extracts into artificial diet caused unnatural levels of toxicity and failed to clarify the effects of Douglas-fir phenolics on gypsy moth fitness. Foliar nitrogen is a key factor influencing gypsy moth development on Douglas fir, but may be mitigated to some degree by phenolics.

Effects of Phenolic Glycosides and Protein on Gypsy Moth (Lepidoptera: Lymantriidae) and Forest Tent Caterpillar (Lepidoptera: Lasiocampidae) Performance and Detoxication Activities

“…In the current study, forest tent caterpillars also decreased consumption rates on high protein diets, and efÞciency of conversion of digested foods were strongly reduced on protein-supplemented leaves. The reduced efÞciency of conversion of digested foods may indicate a higher metabolic cost associated with nitrogen excretion on diets with excessive protein (Schroeder 1986, Joseph et al 1993. Gypsy moths were from a lab strain reared for many generations on casein-enriched artiÞcial diets.…”

A conceptual model for the development of Phytophthora disease in Quercus robur

“…This is an essential enzyme in the shikimic acid pathway, which, together with the pentose phosphate pathway, is used to produce phenolic compounds in plants (Taiz & Zeiger, 2002). Phenolic compounds have been shown to limit the infection of Phytophthora and other pathogens (Afek & Sztejnberg, 1988; Cahill & McComb, 1992; Cahill et al ., 1993), as well as impairing the performance of phyllophagous insects (Joseph et al ., 1993; Schafellner et al ., 1994; Hättenschwiler & Schafellner, 1999). However, it has been suggested that the allocation of C to production of phenols diverts resources from the growth of plants (see the section ‘The C assimilation and allocation of forest trees’), and a large investment in defence against Phytophthora attack may thus result in retardation of growth.…”

Herbivore Resistance in Betula pendula: Effect of Fertilization, Defoliation, and Plant Genotype

“…The quality of leaves as food for herbivores may be determined by their concentration of secondary chemicals as well as by their nutrient content. Fertilization increases nutritional quality of the host plant and thus benefits herbivores (Ohmart et al 1985, Bjö rkman et al 1991, Joseph et al 1992, Mopper and Whitham 1992, Potter 1992. Thus the relative contributions of nutrients and secondary chemicals may be difficult to distinguish.…”