Perhaps because of the symbiotic requirement for such exploitation, phytophagy is restricted within the animal kingdom as shown in Table 6.1.

Phytophagy and the feeding cycle of Phlebotomus papatasi (Diptera: Psychodidae) under experimental conditions.

Lycaenids are diverse in their food habits and apart from phytophagy, some of them are entomophagous feeding on aphids, scale insects, and ant larvae.

As a consequence it is generally thought that phytophagy was not easily achieved and that only a few insect groups succeeded in overcoming the various difficulties associated with this type of feeding.

Insects play an important role in maintaining community structure and composition; in the case of animals by transmission of diseases, predation and parasitism, and in the case of plants, through phytophagy and by plant propagation through pollination and seed dispersal.

According to Southwood, phytophagy arose from both saprophagy, the consumption of decaying or at least dying plants, and from feeding on fallen propagules including spores and pollen grains, which led to living on the strobili themselves, a route followed by the extinct insect orders, Dictyoneurida and Diaphanopterida.