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First published online May 18, 2006
Journal of Experimental Biology 209, 2076-2084 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02253

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Nutrient regulation in relation to diet breadth: a comparison of Heliothis sister species and a hybrid

Kwang Pum Lee^1,*, Spencer T. Behmer,^1,2 and Stephen J. Simpson,^1,3

¹ Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3PS, UK
² Department of Entomology, Texas A&M University, College Station, TX 77843-2475, USA
³ School of Biological Sciences, University of Sydney, Heydon-Laurence Building, A08, NSW 2006, Australia

^* Author for correspondence (e-mail: kwangpumlee{at}hotmail.com)

Accepted 4 April 2006

We examined the nutritional correlates of diet breadth in insect herbivores by comparing patterns of diet selection, nutrient balancing, post-ingestive utilization and development in two sister species of caterpillar and a hybrid between them. One species, Heliothis virescens (HV) has a broad host range, feeding on plants in at least 14 families. The other, Heliothis subflexa (HS), is a specialist on plants in the genus Physalis (Solanaceae). Experiments using synthetic foods showed that when the caterpillars were allowed to mix their diet, the generalist self-selected a higher-protein diet whereas the specialist ate almost equal amounts of protein and carbohydrate, which accords with differences between the two species in the nutrient content of their natural diets. When confined to nutritionally imbalanced diets, the generalist showed a propensity to over-eat high protein:carbohydrate (P:C) diets to a greater degree than did the specialist and maintained higher rates of development. The generalist did not, however, over-eat low P:C diets to the same degree as the specialist. The hybrid selected a diet composition that was indistinguishable to that of its generalist father (HV), while its response to imbalanced diets was closely similar to that of the specialist mother (HS). The generalist converted ingested nutrient to growth with lower efficiency than did the specialist and the hybrid. Our findings imply that different behavioural and physiological traits linked to nutrient regulation are under genetic control and are explicable in terms of the different life-histories, feeding ecologies and presumed levels of nutritional heterogeneity in the environments of the two insects.

Key words: caterpillar, diet breadth, feeding, generalist, Heliothis, insect herbivore, macronutrient, nutrient regulation, protein:carbohydrate ratio, self-selection, specialist