Introduction

Interspecific interactions between insect herbivores can be either negative (competitive) or positive (facilitative) (Damman 1993, Denno et al. 1995). In the context of traditional community ecology, however, negative interactions have received the most attention (e.g., Lawton and Strong 1981, Schoener 1982, Strong et al. 1984, Denno et al. 1995) until quite recently (e.g., Lill and Marquis 2003, Nakamura et al. 2003). Nonetheless, the importance of interspecific competition as a factor structuring communities of insect herbivores has experienced a controversial history to say the least (Strong et al. 1984, Damman 1993, Denno et al. 1995). During the 1960s and 1970s, competition was revered as a central organizing force structuring communities of phytophagous insects (Denno et al. 1995). During these decades, field investigations into interspecific competition were heavily dominated by observational studies of resource partitioning as evidence for reduced competition and thus coexistence (e.g., McClure and Price 1976, Rathcke 1976, Waloff 1979). Notably, experimental field studies documenting the occurrence of interspecific competition between insect herbivores were scarce (but see McClure and Price 1975).

In the 1980s, the role of competition in structuring phytophagous insect communities was challenged severely, and within a few years it fell from a position of prominence to the status of a weak and infrequent process (Lawton and Strong 1981, Lawton 1982, Lawton and Hassell 1984, Strong et al. 1984).