Role of food quality in the population dynamics of chrysomelid beetles feeding on Eucalyptus

Abstract

Growth rate and development time of Paropsis atomaria (Coleoptera: Chrysomelidae) larvae were not affected by nitrogen (N) concentrations of Eucalyptus blakelyi foliage until N fell below 1.7%. Growth and development of larvae were not affected by fluctuations in tannin or oil concentrations in foliage. Effects of N on larval growth and development were probably intercorrelated with effects of leaf toughness, which increased significantly when N fell below 1.7%. Fecundity of P. atomaria was directly related to foliar N concentrations. Egg viability of adult females was dramatically reduced during the first three weeks of egg laying, regardless of the quality of the adult diet if, as larvae, either males or females fed on poor-quality foliage. Abundance rather than quality of newly expanding foliage, the preferred food of P. atomaria, is probably the important factor for larvae and adults, since N levels and leaf toughness of new foliage are not limiting. If food quality significantly influences P. atomaria population dynamics, then the factors which influence new foliage production, such as rainfall patterns, would play a central role in population fluctuations. The relevance of food-quality x P. atomaria interactions to integrated pest management is discussed.