Introduction

Among herbivorous insects with a complete metamorphosis the larval and adult stages usually differ significantly in their biology, food requirements, and ecology (Schoonhoven et al. 1998). Often it is the larval stage that is strictly herbivorous, causing damage to a plant, whereas frequently the adult has a different diet, disperses, selects suitable environments (host plants), and reproduces. Studies on herbivore nutritional ecology generally focus on plant feeding by the damaging larval stages. However, the nutritional ecology and foraging behavior of adult stages can also be crucial to our understanding of plant–herbivore interactions. Both as pollinators and as parasites, adult herbivores can impose a strong selective force in the evolution of plant-provided food supplements (Brody 1997). Here we describe the use of plant-provided foods by adult herbivores to provide insight into this often neglected aspect of plant–herbivore interactions.

Adult insects carry over energy reserves and nutrients acquired during larval development. The level of these reserves can vary markedly among species and may be complemented with nutrients obtained through adult feeding (Boggs 1981, 1997a, b; Tsitsipis 1989; May 1992). Some species primarily depend on larval reserves throughout their adult life and require little or no additional feeding (Barbehenn et al. 1999). Such non-feeding adults are relatively common among Lepidoptera (Miller 1996) but have also been reported among Diptera (Drew and Yuval 2000). Females of some species receive nutrients during matings (Wheeler 1996).